What is the temperature of Venus' atmosphere?
Atmosphere of Venus
The large amount of CO in the atmosphere together with water vapour and sulfur dioxide create a strong greenhouse effect, trapping solar energy and raising the surface temperature to around 740 K (467 °C), hotter than any other planet in the Solar System, even that of Mercury despite being located farther out from the Sun and receiving only 25% of the solar energy (per unit area) Mercury does. The average temperature on the surface is above the melting points of lead (600 K, 327 °C), tin (505 K, 232 °C), and zinc (693 K, 420 °C). The thick troposphere also makes the difference in temperature between the day and night side small, even though the slow retrograde rotation of the planet causes a single solar day to last 116.5 Earth days. The surface of Venus spends 58.3 days in darkness before the sun rises again behind the clouds.
The troposphere on Venus contains 99% of the atmosphere by mass. Ninety percent of the atmosphere of Venus is within 28 km of the surface; by comparison, 90% of the atmosphere of Earth is within 10 km of the surface. At a height of 50 km the atmospheric pressure is approximately equal to that at the surface of Earth. On the night side of Venus clouds can still be found at 80 km above the surface.
Gliese 1132 b
The planet receives 19 times more stellar radiation than Earth. The temperature of the top of its atmosphere is estimated at . The planet is estimated to be hotter than Venus, as higher temperatures may prevail near the surface. "(cf. Atmosphere of Venus, Colonization of Venus)" It is possible that one side of the planet is cooler, because it is presumed to be tidally locked due to its proximity to its star; however, under most circumstances where an atmosphere is thick, it would be able to transfer heat to the far side.
Vega program
The balloons were dropped onto the planet's darkside and deployed at an altitude of about . They then floated upward a few kilometres to their equilibrium altitude. At this altitude, pressure and temperature conditions of Venus are similar to those of Earth, though the planet's winds moved at hurricane velocity and the carbon dioxide atmosphere is laced with sulfuric acid, along with smaller concentrations of hydrochloric and hydrofluoric acid.
Venus
Venus is one of the four terrestrial planets in the Solar System, meaning that it is a rocky body like Earth. It is similar to Earth in size and mass, and is often described as Earth's "sister" or "twin". The diameter of Venus is —only less than Earth's—and its mass is 81.5% of Earth's. Conditions on the Venusian surface differ radically from those on Earth because its dense atmosphere is 96.5% carbon dioxide, with most of the remaining 3.5% being nitrogen.
Atmosphere of Venus
The cloud cover is such that typical surface light levels are similar to a partly cloudy day on Earth, around 5000–10000 lux. The equivalent visibility is about three kilometers, but this will likely vary with the wind conditions. Little to no solar energy could conceivably be collected by solar panels on a surface probe. In fact, due to the thick, highly reflective cloud cover, the total solar energy received by the surface of the planet is less than that of the Earth.
Ozone layer
Venus also has a thin ozone layer at an altitude of 100 kilometers from the planet's surface.
Life on Venus
Solar radiation constrains the atmospheric habitable zone to between 51 km (65 °C) and 62 km (−20 °C) altitude, within the acidic clouds. It has been speculated that clouds in the atmosphere of Venus could contain chemicals that can initiate forms of biological activity. It has been speculated that any hypothetical microorganisms inhabiting the atmosphere, if present, could employ ultraviolet light (UV) emitted by the Sun as an energy source, which could be an explanation for the dark lines observed in the UV photographs of Venus.
Gliese 581c
Using the measured stellar luminosity of Gliese 581 is of 0.013 times that of our Sun, it is possible to calculate Gliese 581c's effective temperature a.k.a. black body temperature. (note: this probably differs from its surface temperature). According to Udry's team, the effective temperature for Gliese 581c, assuming an albedo (reflectivity) such as Venus' (0.64), would be , and assuming an Earth-like albedo (0.296), then it would be , a range of temperatures which overlaps with the range that water would be liquid at a pressure of 1 atmosphere. However, the effective temperature and actual surface temperature can be very different due to the greenhouse properties of the planetary atmosphere: for example, Venus has an effective temperature of , but a surface temperature of (mainly due to a 96.5% carbon dioxide atmosphere), a difference of about .
Terraforming of Venus
Difficulties include the fact that the production of organic molecules from carbon dioxide requires hydrogen, which is very rare on Venus. Because Venus lacks a protective magnetosphere, the upper atmosphere is exposed to direct erosion by the solar wind and has lost most of its original hydrogen to space. And, as Sagan noted, any carbon that was bound up in organic molecules would quickly be converted to carbon dioxide again by the hot surface environment. Venus would not begin to cool down until after most of the carbon dioxide has already been removed.
Terraforming of Venus
It has until recently been assumed that the rotation rate or day-night cycle of Venus would have to be increased for successful terraformation to be achieved. More recent research has, however, shown that the current slow rotation rate of Venus is not at all detrimental to the planet's capability to support an Earth-like climate. Rather, the slow rotation rate would, given an Earth-like atmosphere, enable the formation of thick cloud layers on the side of the planet facing the sun. This in turn would raise planetary albedo and act to cool the global temperature to Earth-like levels, despite the greater proximity to the Sun. According to calculations, maximum temperatures would be just around 35 °C, given an Earth-like atmosphere. Speeding up the rotation rate would therefore be both impractical and detrimental to the terraforming effort. A terraformed Venus with the current slow rotation would result in a global climate with "day" and "night" periods each about 58 days long, resembling the seasons at higher latitudes on Earth. The "day" would resemble a short summer with a warm, humid climate, a heavy overcast sky and ample rainfall. The "night" would resemble a short, very dark winter with quite cold temperature and snowfall. There would be periods with more temperate climate and clear weather at sunrise and sunset resembling a "spring" and "autumn".
Pioneer Venus Multiprobe
Below the altitude of 50 km the temperatures measured by the four probes are identical to within a few degrees. They are between 448 °C and 459 °C (838 °F and 858 °F) on the surface. The ground pressure is between 86.2 bar and 94.5 bar. Nephelometers identified three cloud layers with different characteristics. The most remarkable discovery was that the ratio of argon / argon isotopes much higher than in the atmosphere which seems to indicate that the genesis of the Venusian atmosphere is very different from that of Earth. The reconstituted trajectory of atmospheric probes was determined that the wind averaged a speed of 200 m/s in the middle cloud layer at 50 m/s at the base of these clouds and just 1 m/s at the ground. Overall data from airborne sensors confirmed, while specifying the data obtained by the Soviet space probe Venera program that preceded this mission.
Climate of Titan
Titan receives just about 1% of the amount of sunlight Earth does. The average surface temperature is about 98.29 K (−179 °C, or −290 °F). At this temperature water ice has an extremely low vapor pressure, so the atmosphere is nearly free of water vapor. However the methane in the atmosphere causes a substantial greenhouse effect which keeps the surface of Titan at a much higher temperature than what would otherwise be the thermal equilibrium.
Terraforming of Venus
Birch proposed that solar shades could be used to not merely cool the planet but that this could be used to reduce atmospheric pressure as well, by the process of freezing of the carbon dioxide. This requires Venus's temperature to be reduced, first to the liquefaction point, requiring a temperature less than and partial pressures of CO to bring the atmospheric pressure down to 73.8 bar (carbon dioxide's critical point); and from there reducing the temperature below (carbon dioxide's triple point). Below that temperature, freezing of atmospheric carbon dioxide into dry ice will cause it to deposit onto the surface. He then proposed that the frozen CO could be buried and maintained in that condition by pressure, or even shipped off-world (perhaps to provide greenhouse gas needed for terraforming of Mars or the moons of Jupiter). After this process was complete, the shades could be removed or solettas added, allowing the planet to partially warm again to temperatures comfortable for Earth life. A source of hydrogen or water would still be needed, and some of the remaining 3.5 bar of atmospheric nitrogen would need to be fixed into the soil. Birch suggests disrupting an icy moon of Saturn, for example Hyperion (moon) and bombarding Venus with its fragments.
Atmosphere of Venus
On January 29, 2013, ESA scientists reported that the ionosphere of the planet Venus streams outwards in a manner similar to "the ion tail seen streaming from a comet under similar conditions."
Venera 7
The probe transmitted information to Earth for 53 minutes, which included 20 minutes from the surface. It was found that the temperature at the surface of Venus was ± 20 °C Using the temperature and models of the atmosphere a pressure of 9 Megapascal ± 1.5 MPa was calculated. From the spacecraft's rapid halt (from falling to stationary inside 0.2 seconds) it was possible to conclude that the craft had hit a solid surface with low levels of dust.
Maat Mons
Intriguingly for planetary geologists, atmospheric studies carried out by the Pioneer Venus probes in the early 1980s revealed a considerable variation in the concentrations of sulfur dioxide (SO) and methane (CH) in Venus' middle and upper atmosphere. One possible explanation for this was the injection of volcanic gases into the atmosphere by plinian eruptions at Maat Mons.
Atmosphere of Venus
The atmosphere contains a range of compounds in small quantities, including some based on hydrogen, such as hydrogen chloride (HCl) and hydrogen fluoride (HF). There is carbon monoxide, water vapour and atomic oxygen as well. Hydrogen is in relatively short supply in the Venusian atmosphere. A large amount of the planet's hydrogen is theorised to have been lost to space, with the remainder being mostly bound up in sulfuric acid (HSO) and hydrogen sulfide (HS). The loss of significant amounts of hydrogen is proven by a very high D–H ratio measured in the Venusian atmosphere. The ratio is about 0.015–0.025, which is 100–150 times higher than the terrestrial value of 1.6. According to some measurements, in the upper atmosphere of Venus D/H ratio is 1.5 higher than in the bulk atmosphere.
Venus
The surface of Venus is effectively isothermal; it retains a constant temperature not only between day and night sides but between the equator and the poles. Venus's minute axial tilt—less than 3°, compared to 23° on Earth—also minimises seasonal temperature variation. The only appreciable variation in temperature occurs with altitude. The highest point on Venus, Maxwell Montes, is therefore the coolest point on Venus, with a temperature of about and an atmospheric pressure of about . In 1995, the "Magellan" spacecraft imaged a highly reflective substance at the tops of the highest mountain peaks that bore a strong resemblance to terrestrial snow. This substance likely formed from a similar process to snow, albeit at a far higher temperature. Too volatile to condense on the surface, it rose in gaseous form to higher elevations, where it is cooler and could precipitate. The identity of this substance is not known with certainty, but speculation has ranged from elemental tellurium to lead sulfide (galena).
Automaton Rover for Extreme Environments
Automaton Rover for Extreme Environments (AREE) is a project to create a rover that uses Venus' harsh conditions to its advantage, controlled by a wind-powered mechanical computer. Venus' atmosphere is about 90 times denser than Earth's and heats to about , conditions which would prevent a standard electronic computer from operating for any significant period of time. While AREE was designed for operation on Venus, the rover's design could be re-purposed for use on Mercury, which has a comparably high surface temperature, on Jovian moons Europa or Io, where high radiation makes use of traditional electronics difficult, or on lava flows or highly radioactive areas on Earth.
Atmosphere of Uranus
The atmosphere of Uranus is composed primarily of hydrogen and helium. At depth it is significantly enriched in volatiles (dubbed "ices") such as water, ammonia and methane. The opposite is true for the upper atmosphere, which contains very few gases heavier than hydrogen and helium due to its low temperature. Uranus's atmosphere is the coldest of all the planets, with its temperature reaching as low as 49 K.
Mariner 5
Radio occultation data from Mariner 5 helped to understand the temperature and pressure data returned by the Venera 4 lander, which arrived at Venus shortly before it. After these missions, it was clear that Venus had a very hot surface and an atmosphere even denser than expected.
Terraforming of Venus
Modelling by astrobiologists Mark Bullock and David Grinspoon of Venus' atmospheric evolution suggests that the equilibrium between the current 92 bar atmosphere and existing surface minerals, particularly calcium and magnesium oxides is quite unstable, and that the latter could serve as a sink of carbon dioxide and sulfur dioxide through conversion to carbonates. If these surface minerals were fully converted and saturated, then the atmospheric pressure would decline and the planet would cool somewhat. One of the possible end states modelled by Bullock and Grinspoon was a atmosphere and surface temperature. To convert the rest of the carbon dioxide in the atmosphere, a larger portion of the crust would have to be artificially exposed to the atmosphere to allow more extensive carbonate conversion. In 1989, Alexander G. Smith proposed that Venus could be terraformed by lithosphere overturn, allowing crust to be converted into carbonates. Landis 2011 calculated that it would require the involvement of the entire surface crust down to a depth of over 1 km to produce enough rock surface area to convert enough of the atmosphere.
Venus in fiction
Before "Mariner 2" explored Venus, scientists expected that Venus would be ocean, swamp, or desert. Space probes that found that the planet's surface temperature was , and ground atmospheric pressure was many times that of Earth's, obsoleted earlier fiction that depicted the planet with exotic but habitable settings.
Atmosphere of Venus
Mikhail Lomonosov was the first person to hypothesize the existence of an atmosphere on Venus based on his observation of the transit of Venus of 1761 in a small observatory near his house in Saint Petersburg, Russia.
Carl Sagan
Sagan's contributions were central to the discovery of the high surface temperatures of the planet Venus. In the early 1960s no one knew for certain the basic conditions of Venus' surface, and Sagan listed the possibilities in a report later depicted for popularization in a Time Life book "Planets". His own view was that Venus was dry and very hot as opposed to the balmy paradise others had imagined. He had investigated radio waves from Venus and concluded that there was a surface temperature of . As a visiting scientist to NASA's Jet Propulsion Laboratory, he contributed to the first Mariner missions to Venus, working on the design and management of the project. Mariner 2 confirmed his conclusions on the surface conditions of Venus in 1962.
Atmosphere of Venus
The atmosphere of Venus is the layer of gases surrounding Venus. It is composed primarily of carbon dioxide and is much denser and hotter than that of Earth. The temperature at the surface is 740 K (467 °C, 872 °F), and the pressure is 93 bar (9.3 MPa), roughly the pressure found underwater on Earth. The Venusian atmosphere supports opaque clouds made of sulfuric acid, making optical Earth-based and orbital observation of the surface impossible. Information about the topography has been obtained exclusively by radar imaging. Aside from carbon dioxide, the other main component is nitrogen. Other chemical compounds are present only in trace amounts.
Symphony No. 3 &quot;Universe&quot;
Venus is a planet that represents femininity and beauty throughout astrology and the history of humankind. According to astronomers, however, Venus is a much different place. It has a volcanic structure, is earth-like in size, and its temperature is almost 800 degrees even though it is very close to the Earth. There is also speculation in the world of science that billions of years ago Venus and Earth crashed, and it’s out of this idea that Fazıl Say created a fantasy with his work.
According to Say’s fantasy, there was life on Venus that ended with a meteor shower, and the composition tells a story about those last minutes of life. The Bass flute, Theremin, and English horn symbolize the people of Venus while the Waterphone is the voice of their fear. Venus is represented by tritone intervals and strong hits of trumpets to represent a meteor shower.
Planetary equilibrium temperature
The equilibrium temperature is neither an upper nor lower bound on actual temperatures on a planet. Because of the greenhouse effect, planets with atmospheres will have temperatures higher than the equilibrium temperature. For example, Venus has an equilibrium temperature of approximately 227 K, but a surface temperature of 740 K. The Moon has a black body temperature of 271 K, but can have temperatures of 373 K in the daytime and 100 K at night. This is due to the relatively slow rotation of the Moon compared to its size, so that the entire surface doesn't heat evenly. Orbiting bodies can also be heated by tidal heating, geothermal energy which is driven by radioactive decay in the core of the planet, or accretional heating.
Vacuum airship
where formula_28 formula_29 and formula_30 formula_31 are pressure and density of standard Earth atmosphere at sea level, formula_32 and formula_33 are molar mass (kg/kmol) and temperature (K) of atmosphere at floating area.
Of all known planets and moons of the Sun system only the Venusian atmosphere has formula_21 big enough to surpass formula_20 for such materials as some composites (below altitude of ca. 15 km) and graphene (below altitude of ca. 40 km). Both materials may survive in the Venusian atmosphere. The equation for formula_21 shows that exoplanets with dense, cold and high-molecular (formula_37, formula_38, formula_39 type) atmospheres may be suitable for vacuum airships, but it is a rare type of atmosphere.
Venus Express
"Venus Express" studied the Venusian atmosphere and clouds in detail, the plasma environment and the surface characteristics of Venus from orbit. It is also made global maps of the Venusian surface temperatures. Its nominal mission was originally planned to last for 500 Earth days (approximately two Venusian sidereal days), but the mission was extended five times: first on 28 February 2007 until early May 2009; then on 4 February 2009 until 31 December 2009; and then on 7 October 2009 until 31 December 2012. On 22 November 2010, the mission was extended to 2014. On 20 June 2013, the mission was extended a final time until 2015.
Uranus
Although there is no well-defined solid surface within Uranus's interior, the outermost part of Uranus's gaseous envelope that is accessible to remote sensing is called its atmosphere. Remote-sensing capability extends down to roughly 300 km below the level, with a corresponding pressure around and temperature of . The tenuous thermosphere extends over two planetary radii from the nominal surface, which is defined to lie at a pressure of 1 bar. The Uranian atmosphere can be divided into three layers: the troposphere, between altitudes of and pressures from 100 to 0.1 bar (10 MPa to 10 kPa); the stratosphere, spanning altitudes between and pressures of between (10 kPa to 10 µPa); and the thermosphere extending from 4,000 km to as high as 50,000 km from the surface. There is no mesosphere.
Greenhouse gas
A greenhouse gas is a gas that absorbs and emits radiant energy within the thermal infrared range. Greenhouse gases cause the greenhouse effect. The primary greenhouse gases in Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide and ozone. Without greenhouse gases, the average temperature of Earth's surface would be about , rather than the present average of . The atmospheres of Venus, Mars and Titan also contain greenhouse gases.
Life on Venus
Although there is little possibility of existing life near the surface of Venus, the altitudes about 50 km above the surface have a mild temperature, and hence there are still some opinions in favor of such a possibility in the atmosphere of Venus.
Venus
Studies have suggested that billions of years ago Venus's atmosphere was much more like Earth's than it is now, and that there may have been substantial quantities of liquid water on the surface, but after a period of 600 million to several billion years, a runaway greenhouse effect was caused by the evaporation of that original water, which generated a critical level of greenhouse gases in its atmosphere. Although the surface conditions on Venus are no longer hospitable to any Earthlike life that may have formed before this event, there is speculation on the possibility that life exists in the upper cloud layers of Venus, up from the surface, where the temperature ranges between but the environment is acidic.
Atmosphere of Uranus
The outermost layer of the Uranian atmosphere, extending for thousands of kilometres, is the thermosphere/exosphere, which has a uniform temperature of around 800 to 850 K. This is much higher than, for instance, the 420 K observed in the thermosphere of Saturn. The heat sources necessary to sustain such high temperatures are not understood, since neither solar FUV/EUV radiation nor auroral activity can provide the necessary energy. The weak cooling efficiency due to the depletion of hydrocarbons in the stratosphere may contribute to this phenomenon. In addition to molecular hydrogen, the thermosphere contains a large proportion of free hydrogen atoms, while helium is thought to be absent here, because it separates diffusively at lower altitudes.
Observations and explorations of Venus
To overcome the high pressure and temperature at the surface, a team led by Geoffrey Landis of NASA's Glenn Research Center produced a concept in 2007 of a solar-powered aircraft that would to control a resistant surface rover on the ground. The aircraft would carry the mission's sensitive electronics in the relatively mild temperatures of Venus' upper atmosphere. Another concept from 2007 suggests to equip a rover with a Stirling cooler powered by a nuclear power source to keep an electronics package at an operational temperature of about 200 °C (392 °F).
Venus snow
Venus snow is a brightening of the radar reflection from the surface of Venus at high elevations. The "snow" appears to be a mineral condensate of lead sulfide and bismuth sulfide precipitated from the atmosphere at altitudes above 2600 metres.
Atmosphere of Venus
Images from the "Akatsuki" orbiter revealed something similar to jet stream winds in the low and middle cloud region, which extends from 45 to 60 kilometers in altitude. The wind speed maximized near the equator. In September 2017 JAXA scientists named this phenomenon 'Venusian equatorial jet'.
Geology of Venus
Eolian landforms are not widespread on the planet's surface, but there is considerable evidence the planet's atmosphere causes the chemical weathering of rock, especially at high elevations. The planet is remarkably dry, with only a chemical trace of water vapor (20 ppm) in the Venusian atmosphere. No landforms indicative of past water or ice are visible in radar images of the surface. The atmosphere shows isotopic evidence of having been stripped of volatile elements by offgassing and solar wind erosion over time, implying the possibility that Venus may have had liquid water at some point in the distant past; no direct evidence for this has been found. Much speculation about the geological history of Venus continues today.
High Altitude Venus Operational Concept
Venus has an induced magnetosphere from the interaction of its thick atmosphere with the solar wind, and its nearer proximity to the Sun brings it further within the Sun's magnetic field, which decreases the interstellar radiation levels. With the addition of the reduced deep space exposure time, the radiation levels anticipated by astronauts are potentially much less than an equivalent Mars mission.
Atmosphere of Venus
In 1761, Russian polymath Mikhail Lomonosov observed an arc of light surrounding the part of Venus off the Sun's disc at the beginning of the egress phase of the transit and concluded that Venus has an atmosphere. In 1940, Rupert Wildt calculated that the amount of CO in the Venusian atmosphere would raise surface temperature above the boiling point for water. This was confirmed when Mariner 2 made radiometer measurements of the temperature in 1962. In 1967, Venera 4 confirmed that the atmosphere consisted primarily of carbon dioxide.
Observations and explorations of Venus
"Venus Express" was a mission by the European Space Agency to study the atmosphere and surface characteristics of Venus from orbit. The design was based on ESA's "Mars Express" and "Rosetta" missions. The probe's main objective was the long-term observation of the Venusian atmosphere, which it is hoped will also contribute to an understanding of Earth's atmosphere and climate. It also made global maps of Venerean surface temperatures, and attempted to observe signs of life on Earth from a distance.
Terraforming of Venus
The main problem with Venus today, from a terraformation standpoint, is the very thick carbon dioxide atmosphere. The ground level pressure of Venus is . This also, through the greenhouse effect, causes the temperature on the surface to be several hundred degrees too warm for any known lifeforms. Basically, all approaches to the terraforming of Venus include somehow getting rid of practically all the carbon dioxide in the atmosphere.
Atmosphere of Venus
After missions discovered the reality of the harsh nature of the planet's surface, attention shifted towards other targets such as Mars. There have been a number of proposed missions afterwards however, and many of these involve the little-known upper atmosphere. The Soviet Vega program in 1985 dropped two balloons into the atmosphere, but these were battery-powered and lasted for only about two Earth days each before running out of power. Since then, there has been no exploration of the upper atmosphere. In 2002, the NASA contractor Global Aerospace proposed a balloon that would be capable of staying in the upper atmosphere for hundreds of Earth days as opposed to two.
Life on Venus
Venus's location closer to the Sun than Earth and the extreme greenhouse effect raising temperatures on the surface to nearly , and the atmospheric pressure 90 times that of Earth, make water-based life as we know it unlikely on the surface of the planet. However, a few scientists have speculated that thermoacidophilic extremophile microorganisms might exist in the lower-temperature, acidic upper layers of the Venusian atmosphere.
Atmosphere of Venus
Through studies of the present cloud structure and geology of the surface, combined with the fact that the luminosity of the Sun has increased by 25% since around 3.8 billion years ago, it is thought that the early environment of Venus was more like that of Earth with liquid water on the surface. At some point in the evolution of Venus, a runaway greenhouse effect occurred, leading to the current greenhouse-dominated atmosphere. The timing of this transition from Earthlike to Venuslike is not known, but is estimated to have occurred around 4 billion years ago. The runaway greenhouse effect may have been caused by the evaporation of the surface water and the rise of the levels of greenhouse gases that followed. Venus's atmosphere has therefore received a great deal of attention from those studying climate change on Earth.
Atmosphere of Venus
Sulfuric acid is produced in the upper atmosphere by the Sun's photochemical action on carbon dioxide, sulfur dioxide, and water vapour. Ultraviolet photons of wavelengths less than 169 nm can photodissociate carbon dioxide into carbon monoxide and atomic oxygen. Atomic oxygen is highly reactive; when it reacts with sulfur dioxide, a trace component of the Venusian atmosphere, the result is sulfur trioxide, which can combine with water vapour, another trace component of Venus's atmosphere, to yield sulfuric acid.
Extraterrestrial atmosphere
The Martian atmosphere is very thin and composed mainly of carbon dioxide, with some nitrogen and argon. The average surface pressure on Mars is 0.6-0.9 kPa, compared to about 101 kPa for Earth. This results in a much lower atmospheric thermal inertia, and as a consequence Mars is subject to strong thermal tides that can change total atmospheric pressure by up to 10%. The thin atmosphere also increases the variability of the planet's temperature. Martian surface temperatures vary from lows of approximately −140 °C (−220 °F) during the polar winters to highs of up to 20 °C (70 °F) in summers.
Between the Viking and Mars Global Surveyor missions, Mars saw "Much colder (10-20 K) global atmospheric temperatures were observed during the 1997 versus 1977 perihelion periods" and "that the global aphelion atmosphere of Mars is colder, less dusty, and cloudier than indicated by the established Viking climatology," with "generally colder atmospheric temperatures and lower dust loading in recent decades on Mars than during the Viking Mission." The Mars Reconnaissance Orbiter, though spanning a much shorter dataset, shows no warming of planetary average temperature, and a possible cooling. "MCS MY 28 temperatures are an average of 0.9 (daytime) and 1.7 K (night- time) cooler than TES MY 24 measurements." Locally and regionally, however, changes in pits in the layer of frozen carbon dioxide at the Martian south pole observed between 1999 and 2001 suggest the south polar ice cap is shrinking. More recent observations indicate that Mars' south pole is continuing to melt. "It's evaporating right now at a prodigious rate," says Michael Malin, principal investigator for the Mars Orbiter Camera. The pits in the ice are growing by about 3 meters (9.8 ft) per year. Malin states that conditions on Mars are not currently conductive to the formation of new ice. A web site has suggested that this indicates a "climate change in progress" on Mars. Multiple studies suggests this may be a local phenomenon rather than a global one.
Venus Atmospheric Maneuverable Platform
The habitability of Venus' clouds has been a subject of discussion since scientists Harold Morowitz and Carl Sagan speculated it in 1967. Since then, subsequent studies have highlighted the potential for microbial habitability in Venus' cloud layers due to favorable chemical and physical conditions, including the presence of sulfur compounds, carbon dioxide (CO), water, and moderate temperatures (0–60 °C) and pressures (∼0.4–2 atm). The surface conditions on the planet, however, are known to be inhospitable, with temperatures above 450 °C (860 °F).
Venera 4
During entry into the Venusian atmosphere, the heat shield temperature rose to and at one point the cabin deceleration reached 300 G. The descent lasted 93 minutes. The capsule deployed its parachute at an altitude of about , and started sending data on pressure, temperature and gas composition back to Earth. The temperature control kept the inside of the capsule at . The temperature at 52 km was recorded as , and the pressure as less than . At the end of the 26-km descent, the temperature reached and pressure increased to , and the signal transmission terminated. The atmospheric composition was measured as 90–93% carbon dioxide, 0.4–0.8% oxygen, 7% nitrogen and 0.1–1.6% water vapor.
Pioneer Venus project
The Pioneer Venus bus also carried two experiments, a neutral mass spectrometer and an ion mass spectrometer to study the composition of the atmosphere. With no heat shield or parachute, the bus made measurements only to about 110 km altitude before burning up.
Observations and explorations of Venus
On February 12, 1961, the Soviet spacecraft "Venera 1" was the first probe launched to another planet. An overheated orientation sensor caused it to malfunction, losing contact with Earth before its closest approach to Venus of 100,000 km. However, the probe was first to combine all the necessary features of an interplanetary spacecraft: solar panels, parabolic telemetry antenna, 3-axis stabilization, course-correction engine, and the first launch from parking orbit.
The first successful Venus probe was the American "Mariner 2" spacecraft, which flew past Venus in 1962, coming within 35,000 km. A modified "Ranger" Moon probe, it established that Venus has practically no intrinsic magnetic field and measured the planet's temperature range as 490 to 590 K.
James Hansen
In the late 1960s and early 1970s, following his Ph.D. dissertation, Hansen published several papers on the planet Venus. Venus has a high brightness temperature in the radio frequencies compared to the infrared. He proposed that the hot surface was the result of aerosols trapping the internal energy of the planet. More recent studies have suggested that several billion years ago, Venus's atmosphere was much more like Earth's than it is now and that there were probably substantial quantities of liquid water on the surface, but a runaway greenhouse effect was caused by the evaporation of that original water, which generated a critical level of greenhouse gases in its atmosphere.
Atmosphere of Titan
On October 24, 2014, methane was found in polar clouds on Titan.
The persistence of a dense atmosphere on Titan has been enigmatic as the atmospheres of the structurally similar satellites of Jupiter, Ganymede and Callisto, are negligible. Although the disparity is still poorly understood, data from recent missions have provided basic constraints on the evolution of Titan's atmosphere.
Roughly speaking, at the distance of Saturn, solar insolation and solar wind flux are sufficiently low that elements and compounds that are volatile on the terrestrial planets tend to accumulate in all three phases. Titan's surface temperature is also quite low, about 94 K. Consequently, the mass fractions of substances that can become atmospheric constituents are much larger on Titan than on Earth. In fact, current interpretations suggest that only about 50% of Titan's mass is silicates, with the rest consisting primarily of various HO (water) ices and NH·HO (ammonia hydrates). NH, which may be the original source of Titan's atmospheric N (dinitrogen), may constitute as much as 8% of the NH·HO mass. Titan is most likely differentiated into layers, where the liquid water layer beneath ice I may be rich in NH.
Tentative constraints are available, with the current loss mostly due to low gravity and solar wind aided by photolysis. The loss of Titan's early atmosphere can be estimated with the N–N isotopic ratio, because the lighter N is preferentially lost from the upper atmosphere under photolysis and heating. Because Titan's original N–N ratio is poorly constrained, the early atmosphere may have had more N by factors ranging from 1.5 to 100 with certainty only in the lower factor. Because N is the primary component (98%) of Titan's atmosphere, the isotopic ratio suggests that much of the atmosphere has been lost over geologic time. Nevertheless, atmospheric pressure on its surface remains nearly 1.5 times that of Earth as it began with a proportionally greater volatile budget than Earth or Mars. It is possible that most of the atmospheric loss was within 50 million years of accretion, from a highly energetic escape of light atoms carrying away a large portion of the atmosphere (hydrodynamic blow off event). Such an event could be driven by heating and photolysis effects of the early Sun's higher output of X-ray and ultraviolet (XUV) photons.
Atmosphere of Venus
Unlike Earth, Venus lacks a magnetic field. Its ionosphere separates the atmosphere from outer space and the solar wind. This ionised layer excludes the solar magnetic field, giving Venus a distinct magnetic environment. This is considered Venus's "induced magnetosphere". Lighter gases, including water vapour, are continuously blown away by the solar wind through the induced magnetotail. It is speculated that the atmosphere of Venus up to around 4 billion years ago was more like that of the Earth with liquid water on the surface. A runaway greenhouse effect may have been caused by the evaporation of the surface water and subsequent rise of the levels of other greenhouse gases.
Surface features of Venus
Impact craters are roughly circular shaped depressions in the surface of a planet due to high velocity impacts with extraterrestrial bodies. The surface of Venus contains almost 1000 impact craters. However, unlike some planets in our system, Venus' thick atmosphere creates a strong shield that decelerates, flattens, and can fracture incoming projectiles. The Venusian surface is devoid of small craters (≤30–50 km in size) because of the effect the atmosphere has on small bodies. Depending on the angle of impact, velocity, size, and strength of the approaching body, the atmosphere may tear and crush the projectile, essentially melting it in the air. This is an important observation for studies of the surface of Venus, as crater are used to determine relative ages and to approximate absolute ages of surface features.
Kepler-69c
Kepler-69c is a super-Earth, an exoplanet that has a radius and mass larger than Earth, but smaller than that of the ice giants Uranus and Neptune. It has a surface temperature of . It has an estimated mass of around 6 , and a radius of 1.71 . These characteristics make it an analog to Venus, but more massive, so it is called a "super-Venus".
Venera-D
The "D" in Venera-D stands for "dolgozhivushaya," which means "long lasting" in Russian. Venera-D will be the first Venus probe launched by the Russian Federation (the earlier Venera probes were launched by the former Soviet Union). Venera-D will serve as the flagship for a new generation of Russian-built Venus probes, culminating with a lander capable of withstanding the harsh Venerian environment for more than the 1½ hours logged by the Soviet probes. The surface of Venus experiences average temperatures of 462° Celsius (864 Fahrenheit), crushing 90-bar pressures, and corroding clouds of carbon dioxide laced with sulfuric acid. Venera-D would be launched with either a Proton or Angara A5 rocket.
Extraterrestrial atmosphere
The atmosphere of Neptune is similar to that of Uranus. It is about 80% hydrogen, 19% helium, and 1.5% methane. However the weather activity on Neptune is much more active, and its atmosphere is much bluer than that of Uranus. The upper levels of the atmosphere reach temperatures of about 55 K, giving rise to methane clouds in its troposphere, which gives the planet its ultramarine color. Temperatures rise steadily deeper inside the atmosphere.
Neptune has extremely dynamic weather systems, including the highest wind speeds in the Solar System, thought to be powered by the flow of internal heat. Typical winds in the banded equatorial region can possess speeds of around 350 m/s, while storm systems can have winds reaching up to around 900 m/s, nearly the speed of sound in Neptune's atmosphere. Several large storm systems have been identified, including the Great Dark Spot, a cyclonic storm system the size of Eurasia, the Scooter, a white cloud group further south than the Great Dark Spot, and the Wizard's eye/Dark Spot 2, a southern cyclonic storm.
Mariner 2
The microwave radiometer made three scans of Venus in 35 minutes on December 14, 1962 starting at 18:59 UTC. The first scan was made on the dark side, the second was near the terminator, and the third was located on the light side. The scans with the 19 mm band revealed peak temperatures of on the dark side, 595 ± 12 K near the terminator, and 511 ± 14 K on the light side. It was concluded that there is no significant difference in temperature across Venus. However, the results suggest a limb darkening, an effect which presents cooler temperatures near the edge of the planetary disk and higher temperatures near the center. This also supported the theory that the Venusian surface was extremely hot or the atmosphere optically thick.
Ushas Mons
Ushas Mons is a 2-kilometer-high (1.25 mile) volcano in the southern hemisphere of Venus at 25 degrees south latitude, 323 degrees east longitude. Its name is derived from vedic goddess of dawn Ushas The volcano is marked by numerous bright lava flows and a set of north-south trending fractures, many of which appear to have formed after the lavas were erupted onto the surface. In the central summit area, however, younger flows remain unfractured. An impact crater can be seen among the fractures in the upper center of the image. The association of faulting and volcanism is common on this type of volcano on Venus, and is believed to result from a large zone of hot material upwelling from the Venusian mantle, a phenomenon known on Earth as a "hotspot."
Observations and explorations of Venus
Before radio observations in the 1960s, many believed that Venus contained a lush, Earth-like environment. This was due to the planet's size and orbital radius, which suggested a fairly Earth-like situation as well as to the thick layer of clouds which prevented the surface from being seen. Among the speculations on Venus were that it had a jungle-like environment or that it had oceans of either petroleum or carbonated water. However, microwave observations by C. Mayer "et al.", indicated a high-temperature source (600 K). Strangely, millimetre-band observations made by A. D. Kuzmin indicated much lower temperatures. Two competing theories explained the unusual radio spectrum, one suggesting the high temperatures originated in the ionosphere, and another suggesting a hot planetary surface.
Atmosphere of Venus
The Venus Express probe has shown through stellar occultation that the atmospheric haze extends much further up on the night side than the day side. On the day side the cloud deck has a thickness of 20 km and extends up to about 65 km, whereas on the night side the cloud deck in the form of a thick haze reaches up to 90 km in altitude—well into mesosphere, continuing even further to 105 km as a more transparent haze. In 2011, the spacecraft discovered that Venus has a thin ozone layer at an altitude of 100 km.
Terraforming
The renowned astronomer Carl Sagan proposed the planetary engineering of Venus in an article published in the journal "Science" in 1961. Sagan imagined seeding the atmosphere of Venus with algae, which would convert water, nitrogen and carbon dioxide into organic compounds. As this process removed carbon dioxide from the atmosphere, the greenhouse effect would be reduced until surface temperatures dropped to "comfortable" levels. The resulting carbon, Sagan supposed, would be incinerated by the high surface temperatures of Venus, and thus be sequestered in the form of "graphite or some involatile form of carbon" on the planet's surface. However, later discoveries about the conditions on Venus made this particular approach impossible. One problem is that the clouds of Venus are composed of a highly concentrated sulfuric acid solution. Even if atmospheric algae could thrive in the hostile environment of Venus's upper atmosphere, an even more insurmountable problem is that its atmosphere is simply far too thick—the high atmospheric pressure would result in an "atmosphere of nearly pure molecular oxygen" and cause the planet's surface to be thickly covered in fine graphite powder. This volatile combination could not be sustained through time. Any carbon that was fixed in organic form would be liberated as carbon dioxide again through combustion, "short-circuiting" the terraforming process.
High Altitude Venus Operational Concept
Venus is a planet with a runaway greenhouse effect, with surface temperatures and pressure of and respectively. Conventional rocket engines will not work at those pressures. Hence, human missions to Venus have historically been thought impractical, if not impossible. However, Venus has advantages for crewed travel, such as Earth-like gravity (.90 Earth gravity), an atmosphere that provides a level of protection from solar and interstellar radiation, and a much greater proximity compared to Mars.
Surface features of Venus
The surface of Venus is dominated by geologic features that include volcanoes, large impact craters, and aeolian erosion and sedimentation landforms. Venus has a topography reflecting its single, strong crustal plate, with a unimodal elevation distribution (over 90% of the surface lies within an elevation of -1.0 and 2.5 km) that preserves geologic structures for long periods of time. Studies of the Venusian surface are based on imaging, radar, and altimetry data collected from several exploratory space probes, particularly "Magellan", since 1961 (see Venus Exploration). Despite its similarities to Earth in size, mass, density, and possibly composition, Venus has a unique geology that is unlike Earth's. Although much older than Earth's, the surface of Venus is relatively young compared to other terrestrial planets (<500 million years old), possibly due to a global-scale resurfacing event that buried much of the previous rock record. Venus is believed to have approximately the same bulk elemental composition as Earth, due to the physical similarities, but the exact composition is unknown. The surface conditions on Venus are more extreme than on Earth, with temperatures ranging from 453 to 473 °C and pressures of 95 bar. Venus lacks water, which makes crustal rock stronger and helps preserve surface features. The features observed provide evidence for the geological processes at work. Twenty feature types have been categorized thus far. These classes include local features, such as craters, coronae, and undae, as well as regional-scale features, such as planitiae, plana, and tesserae.
Atmosphere of Venus
The upper atmosphere of Venus can be measured from Earth when the planet crosses the sun in a rare event known as a solar transit. The last solar transit of Venus occurred in 2012. Using quantitative astronomical spectroscopy, scientists were able to analyse sunlight that passed through the planet's atmosphere to reveal chemicals within it. As the technique to analyse light to discover information about a planet's atmosphere only first showed results in 2001, this was the first opportunity to gain conclusive results in this way on the atmosphere of Venus since observation of solar transits began. This solar transit was a rare opportunity considering the lack of information on the atmosphere between 65 and 85 km. The solar transit in 2004 enabled astronomers to gather a large amount of data useful not only in determining the composition of the upper atmosphere of Venus, but also in refining techniques used in searching for extrasolar planets. The atmosphere of mostly CO, absorbs near-infrared radiation, making it easy to observe. During the 2004 transit, the absorption in the atmosphere as a function of wavelength revealed the properties of the gases at that altitude. The Doppler shift of the gases also enabled wind patterns to be measured.
Atmosphere of Venus
The circulation patterns in the upper mesosphere and thermosphere of Venus are completely different from those in the lower atmosphere. At altitudes 90–150 km the Venusian air moves from the dayside to nightside of the planet, with upwelling over sunlit hemisphere and downwelling over dark hemisphere. The downwelling over the nightside causes adiabatic heating of the air, which forms a warm layer in the nightside mesosphere at the altitudes 90–120 km. The temperature of this layer—230 K (−43 °C) is far higher than the typical temperature found in the nightside thermosphere—100 K (−173 °C). The air circulated from the dayside also carries oxygen atoms, which after recombination form excited molecules of oxygen in the long-lived singlet state (Δ), which then relax and emit infrared radiation at the wavelength 1.27 μm. This radiation from the altitude range 90–100 km is often observed from the ground and spacecraft. The nightside upper mesosphere and thermosphere of Venus is also the source of non-local thermodynamic equilibrium emissions of CO and nitric oxide molecules, which are responsible for the low temperature of the nightside thermosphere.
Atmospheric escape
Depending on planet size and atmospheric composition, however, a lack of magnetic field does not fully determine the fate of a planet's atmosphere. Venus, for instance, has no powerful magnetic field. Its close proximity to the Sun also increases the speed and number of particles, and would presumably cause the atmosphere to be stripped almost entirely, much like that of Mars. Despite this, the atmosphere of Venus is two orders of magnitude denser than Earth's. Recent models indicate that stripping by solar wind accounts for less than 1/3 of total non-thermal loss processes.
Dry ice
In 2012, the European Space Agency's Venus Express probe detected a cold layer in the atmosphere of Venus where temperatures are close to the triple point of carbon dioxide and it is possible that flakes of dry ice precipitate.
Terraforming of Venus
The terraforming of Venus is the hypothetical process of engineering the global environment of the planet Venus in such a way as to make it suitable for human habitation. Terraforming Venus was first scholarly proposed by the astronomer Carl Sagan in 1961, although fictional treatments, such as "The Big Rain" of The Psychotechnic League by novelist Poul Anderson, preceded it. Adjustments to the existing environment of Venus to support human life would require at least three major changes to the planet's atmosphere:
These three changes are closely interrelated, because Venus' extreme temperature is due to the high pressure of its dense atmosphere, and the greenhouse effect.
Supercritical fluid
The atmosphere of Venus is 96.5% carbon dioxide and 3.5% nitrogen. The surface pressure is 9.3 MPa (93 bar) and the surface temperature is 735 K, above the critical points of both major constituents and making the surface atmosphere a supercritical fluid.
Atmosphere of Venus
It has been proposed that microbes at this level could be soaking up ultraviolet light from the Sun as a source of energy, which could be a possible explanation for dark patches seen on UV images of the planet. Large, non-spherical cloud particles have also been detected in the cloud decks. In 2012, the abundance and vertical distribution of these unknown ultraviolet absorbers in the Venusian atmosphere have been investigated from analysis of Venus Monitoring Camera images, but their composition is still unknown. In 2016, disulfur dioxide was identified as a possible candidate for causing the so far unknown UV absorption of the Venusian atmosphere.
Life on Venus
Since the 1960s, increasingly clear evidence from various space probes showed Venus has an extreme climate, with a greenhouse effect generating a constant temperature of about 500 °C on the surface. The atmosphere contains sulfuric acid clouds and the atmospheric pressure at the surface is 90 bar, almost 100 times that of Earth and similar to that of more than deep in Earth's oceans. In such environment, and given the increasingly hostile characteristics of the Venusian weather, the chances of life as we know it are excluded from the surface of Venus.
Neptune
In contrast to the hazy, relatively featureless atmosphere of Uranus, Neptune's atmosphere has active and visible weather patterns. For example, at the time of the "Voyager 2" flyby in 1989, the planet's southern hemisphere had a Great Dark Spot comparable to the Great Red Spot on Jupiter. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, with recorded wind speeds as high as . Because of its great distance from the Sun, Neptune's outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching . Temperatures at the planet's centre are approximately . Neptune has a faint and fragmented ring system (labelled "arcs"), which was discovered in 1984, then later confirmed by "Voyager 2".
Gliese 581g
An atmosphere that is dense will circulate heat, potentially allowing a wide area on the surface to be habitable. For example, Venus has a solar rotation rate approximately 117 times slower than Earth's, producing prolonged days and nights. Despite the uneven distribution of sunlight over time intervals shorter than several months, unilluminated areas of Venus are kept almost as hot as the day side by globally circulating winds. Simulations have shown that an atmosphere containing appropriate levels of CO and HO need only be a tenth the pressure of Earth's atmosphere (100 mbar) to effectively distribute heat to the night side. Current technology cannot determine the atmospheric or surface composition of the planet due to the overpowering light of its parent star.
Atmosphere of Venus
The circulation in Venus's troposphere follows the so-called cyclostrophic flow. Its windspeeds are roughly determined by the balance of the pressure gradient and centrifugal forces in almost purely zonal flow. In contrast, the circulation in the Earth's atmosphere is governed by the geostrophic balance. Venus's windspeeds can be directly measured only in the upper troposphere (tropopause), between 60–70 km, altitude, which corresponds to the upper cloud deck. The cloud motion is usually observed in the ultraviolet part of the spectrum, where the contrast between clouds is the highest. The linear wind speeds at this level are about 100 ± 10 m/s at lower than 50° latitude. They are retrograde in the sense that they blow in the direction of the retrograde rotation of the planet. The winds quickly decrease towards the higher latitudes, eventually reaching zero at the poles. Such strong cloud-top winds cause a phenomenon known as the super-rotation of the atmosphere. In other words, these high-speed winds circle the whole planet faster than the planet itself rotates. The super-rotation on Venus is differential, which means that the equatorial troposphere super-rotates more slowly than the troposphere at the midlatitudes. The winds also have a strong vertical gradient. They decline deep in the troposphere with the rate of 3 m/s per km. The winds near the surface of Venus are much slower than that on Earth. They actually move at only a few kilometres per hour (generally less than 2 m/s and with an average of 0.3 to 1.0 m/s), but due to the high density of the atmosphere at the surface, this is still enough to transport dust and small stones across the surface, much like a slow-moving current of water.
All winds on Venus are ultimately driven by convection. Hot air rises in the equatorial zone, where solar heating is concentrated, and flows to the poles. Such an almost-planetwide overturning of the troposphere is called Hadley circulation. However, the meridional air motions are much slower than zonal winds. The poleward limit of the planet wide Hadley cell on Venus is near ±60° latitudes. Here air starts to descend and returns to the equator below the clouds. This interpretation is supported by the distribution of the carbon monoxide, which is also concentrated in the vicinity of ±60° latitudes. Poleward of the Hadley cell a different pattern of circulation is observed. In the latitude range 60°–70° cold polar collars exist. They are characterised by temperatures about 30–40 K lower than in the upper troposphere at nearby latitudes. The lower temperature is probably caused by the upwelling of the air in them and by the resulting adiabatic cooling. Such an interpretation is supported by the denser and higher clouds in the collars. The clouds lie at 70–72 km altitude in the collars—about 5 km higher than at the poles and low latitudes. A connection may exist between the cold collars and high speed midlatitude jets in which winds blow as fast as 140 m/s. Such jets are a natural consequence of the Hadley–type circulation and should exist on Venus between 55–60° latitude.
Worlds in Collision
Carl Sagan wrote that the high surface temperature of Venus was known prior to Velikovsky, and that Velikovsky misunderstood the mechanism for this heat. Velikovsky believed that Venus was heated by its close encounter with the Earth and Mars. He also did not understand the greenhouse effect on Venus, which had earlier been elucidated by astronomer Rupert Wildt. Ultimately, Venus is hot due to its proximity to the sun; it does not emit more heat than it receives from the sun, and any heat produced by its celestial movements would have long dissipated. Sagan concludes: "(1) the temperature in question was never specified [by Velikovsky]; (2) the mechanism proposed for providing this temperature is grossly inadequate; (3) the surface of the planet does not cool off with time as advertised; and (4) the idea of a high surface temperature on Venus was published in the dominant astronomical journal of its time and with an essentially correct argument ten years before the publication of "Worlds in Collision"" (p. 118).
Atmospheric temperature
In the Earth's atmosphere, temperature varies greatly at different heights relative to the Earth's surface. The coldest temperatures lie near the mesopause, an area approximately 80 km above the surface. In contrast, some of the warmest temperatures can be found in the thermosphere, which receives strong ionizing radiation at the level of the Van Allen radiation belt.
Microwave Radiometer (Juno)
At the time of its use in the 2010s, it was one of only four microwave radiometers to have been flown on interplanetary spacecraft. The first was Mariner 2, which used a microwave instrument to determine the high surface temperature of Venus was coming from the surface not higher up in the atmosphere. There is also radiometer type instruments on "Rosetta" comet probe, and "Cassini-Huygens". Previously, the "Galileo" probe directly measured Jupiter's atmosphere "in situ" as it descended into the atmosphere, but only down to 22 bars of pressure. However, MWR is designed to look down as deep as 1000 bar of pressure. (1000 bar is about 14,500 psi, or 100000 kpa)
Colonization of Venus
Venus also presents several significant challenges to human colonization. Surface conditions on Venus are difficult to deal with: the temperature at the equator averages around , higher than the melting point of lead, which is 327 °C. The atmospheric pressure on the surface is also at least ninety times greater than on Earth, which is equivalent to the pressure experienced under a kilometer of water. These conditions have caused missions to the surface to be extremely brief: the Soviet Venera 5 and Venera 6 probes were crushed by high pressure while still 18 km above the surface. Following landers such as Venera 7 and Venera 8 succeeded in transmitting data after reaching the surface, but these missions were brief as well, surviving no more than a single hour on the surface.
Colonization of Venus
Venus's atmosphere is made mostly out of carbon dioxide, which, after filtering from sulfuric acid, can be used to grow food. Because nitrogen and oxygen are lighter than the carbon-dioxide that makes the atmosphere, breathable-air-filled balloons will float at a height of about . At this height, the temperature is a manageable ; or if we could get higher (see ).
David Catling
In the field of planetary atmospheres, David Catling and Tyler Robinson have proposed a general explanation for a curious observation: the minimum air temperature between the troposphere (the lowest atmospheric layer where temperature declines with altitude) and stratosphere (where temperature increases with altitude in an 'inversion') occurs a pressure of about 0.1 bar on Earth, Titan, Jupiter, Saturn, Uranus and Neptune. This level is the tropopause. Robinson and Catling used the physics of radiation to explain why the tropopause temperature minimum in these extremely different atmospheres occurs at a common pressure. They propose that a pressure around 0.1 bar could be a fairly general rule for planets with stratospheric temperature inversions. This rule could constrain the atmospheric structure on exoplanets and hence their surface temperature and habitability.
Observations and explorations of Venus
In October 1983, "Venera 15" and "Venera 16" entered polar orbits around Venus. The images had a 1–2 kilometre (0.6–1.2 mile) resolution, comparable to those obtained by the best Earth radars. "Venera 15" analyzed and mapped the upper atmosphere with an infrared Fourier spectrometer. From November 11, 1983 to July 10, 1984, both satellites mapped the northern third of the planet with synthetic aperture radar. These results provided the first detailed understanding of the surface geology of Venus, including the discovery of unusual massive shield volcanoes such as coronae and arachnoids. Venus had no evidence of plate tectonics, unless the northern third of the planet happened to be a single plate. The altimetry data obtained by the Venera missions had a resolution four times better than "Pioneer"'s.
Atmosphere of Venus
Surface level humidity is less than 0.1%. Venus's sulfuric acid rain never reaches the ground, but is evaporated by the heat before reaching the surface in a phenomenon known as virga. It is theorized that early volcanic activity released sulfur into the atmosphere and the high temperatures prevented it from being trapped into solid compounds on the surface as it was on the Earth.
Atmosphere of Venus
The atmosphere is divided into a number of sections depending on altitude. The densest part of the atmosphere, the troposphere, begins at the surface and extends upwards to 65 km. At the furnace-like surface the winds are slow, but at the top of the troposphere the temperature and pressure reaches Earth-like levels and clouds pick up speed to 100 m/s (360 km/h).
TRAPPIST-1b
In 2018, the planet's atmosphere was better examined with the Spitzer Space Telescope and found to be quite large and hot. The planet's transmission spectrum suggested two main possibilities for the atmosphere: one rich in carbon dioxide, and one with water vapor. The more likely CO atmosphere would have a scale height of approximately 52 km (with Earth's being at 8 km, and Venus's at 15.9 km) and an average temperature in excess of , far higher than its equilibrium temperature. A water vapor atmosphere would need to have a scale height of >100 km and a temperature of > to produce the variations seen in the planet's transit depths and its transmission spectrum. Other sources for the effects seen, such as hazes and thick clouds, would require an even larger atmosphere. TRAPPIST-1b will have to be studied further to confirm its potential large atmosphere.
Venera 7
Venera 7 entered the atmosphere of Venus on 15 December 1970. The lander remained attached to the interplanetary bus during the initial stages of atmospheric entry to allow the bus to cool the lander to −8 °C for as long as possible. The lander was ejected once atmospheric buffeting broke the interplanetary bus's lock-on with Earth. The parachute opened at a height of 60 km and atmospheric testing began with results showing the atmosphere to be 97% carbon dioxide. The parachute appeared to fail during the descent, resulting in a descent more rapid than planned. As a result, the lander struck the surface of Venus at about 16.5 m/s (37 mph) at 05:37:10 UTC. The landing coordinates are .
Uranus
The troposphere is the lowest and densest part of the atmosphere and is characterised by a decrease in temperature with altitude. The temperature falls from about at the base of the nominal troposphere at −300 km to at 50 km. The temperatures in the coldest upper region of the troposphere (the tropopause) actually vary in the range between depending on planetary latitude. The tropopause region is responsible for the vast majority of Uranus's thermal far infrared emissions, thus determining its effective temperature of .
Atmosphere of Venus
The atmosphere of Venus is composed of 96.5% carbon dioxide, 3.5% nitrogen, and traces of other gases, most notably sulfur dioxide. The amount of nitrogen in the atmosphere is relatively small compared to the amount of carbon dioxide, but because the atmosphere is so much thicker than that on Earth, its total nitrogen content is roughly four times higher than Earth's, even though on Earth nitrogen makes up about 78% of the atmosphere.
Solar activity and climate
Solar forcing should warm Earth's atmosphere roughly evenly by altitude, with some variation by wavelength/energy regime. However, the atmosphere is warming at lower altitudes while cooling higher up. This is the expected pattern if greenhouse gases drive temperature, as on Venus.
Uranus
The outermost layer of the Uranian atmosphere is the thermosphere and corona, which has a uniform temperature around 800 to 850 K. The heat sources necessary to sustain such a high level are not understood, as neither the solar UV nor the auroral activity can provide the necessary energy to maintain these temperatures. The weak cooling efficiency due to the lack of hydrocarbons in the stratosphere above 0.1 mBar pressure level may contribute too. In addition to molecular hydrogen, the thermosphere-corona contains many free hydrogen atoms. Their small mass and high temperatures explain why the corona extends as far as , or two Uranian radii, from its surface. This extended corona is a unique feature of Uranus. Its effects include a drag on small particles orbiting Uranus, causing a general depletion of dust in the Uranian rings. The Uranian thermosphere, together with the upper part of the stratosphere, corresponds to the ionosphere of Uranus. Observations show that the ionosphere occupies altitudes from . The Uranian ionosphere is denser than that of either Saturn or Neptune, which may arise from the low concentration of hydrocarbons in the stratosphere. The ionosphere is mainly sustained by solar UV radiation and its density depends on the solar activity. Auroral activity is insignificant as compared to Jupiter and Saturn.
DEN 0255-4700
The photospheric temperature of DENIS 0255-4700 is estimated at about 1300 K. Its atmosphere in addition to hydrogen and helium contains water vapor, methane and possibly ammonia. The mass of DENIS 0255-4700 lies in the range from 25 to 65 Jupiter masses corresponding to the age range from 0.3 to 10 billion years.
Atmosphere of Venus
The Venus In-Situ Explorer, proposed by NASA's New Frontiers program is a proposed probe which would aid in understanding the processes on the planet that led to climate change, as well as paving the way towards a later sample return mission.
Atmosphere of Venus
Odd structures known as polar vortices lie within the cold polar collars. They are giant hurricane-like storms four times larger than their terrestrial analogs. Each vortex has two "eyes"—the centres of rotation, which are connected by distinct S-shaped cloud structures. Such double eyed structures are also called polar dipoles. Vortices rotate with the period of about 3 days in the direction of general super-rotation of the atmosphere. The linear wind speeds are 35–50 m/s near their outer edges and zero at the poles. The temperature at the cloud-tops in the each polar vortex is much higher than in the nearby polar collars reaching 250 K (−23 °C). The conventional interpretation of the polar vortices is that they are anticyclones with downwelling in the centre and upwelling in the cold polar collars. This type of circulation resembles a winter polar anticyclonic vortex on Earth, especially the one found over Antarctica. The observations in the various infrared atmospheric windows indicate that the anticyclonic circulation observed near the poles penetrates as deep as to 50 km altitude, i.e. to the base of the clouds. The polar upper troposphere and mesosphere are extremely dynamic; large bright clouds may appear and disappear over the space of a few hours. One such event was observed by Venus Express between 9 and 13 January 2007, when the south polar region became brighter by 30%. This event was probably caused by an injection of sulfur dioxide into the mesosphere, which then condensed forming a bright haze. The two eyes in the vortices have yet to be explained.
The first vortex on Venus was discovered at the north pole by the Pioneer Venus mission in 1978. A discovery of the second large 'double-eyed' vortex at the south pole of Venus was made in the summer of 2006 by Venus Express, which came with no surprise.
Extraterrestrial atmosphere
The air pressure at Venus' surface is about 92 times that of the Earth. The enormous amount of CO in the atmosphere creates a strong greenhouse effect, raising the surface temperature to around 470 °C, hotter than that of any other planet in the Solar System.
Volcanology of Venus
The surface of Venus is dominated by volcanic features and has more volcanoes than any other planet in the Solar System. It has a surface that is 90% basalt, and about 65% of the planet consists of a mosaic of volcanic lava plains, indicating that volcanism played a major role in shaping its surface. There are more than 1,000 volcanic structures and possible periodic resurfacing of Venus by floods of lava. The planet may have had a major global resurfacing event about 500 million years ago, from what scientists can tell from the density of impact craters on the surface. Venus has an atmosphere rich in carbon dioxide, with a density that is 90 times greater than Earth's atmosphere.
Planets in science fiction
Venus was never quite so popular as Mars, probably because it obdurately refused to display any surface features (it is covered with sulfuric acid clouds only dimly translucent to visible light), making any statement about its nature disturbingly speculative. In 1918, chemist Svante Arrhenius, deciding that Venus' cloud cover was necessarily water, decreed in "The Destinies of the Stars" that "A very great part of the surface of Venus is no doubt covered with swamps" and compared Venus' humidity to the tropical rain forests of the Congo. Venus thus became, until the early 1960s, a place for science fiction writers to place all manner of unusual life forms, from quasi-dinosaurs to intelligent carnivorous plants, and where hostile interactions with Venusian natives were reminiscent of European colonial projects in Africa and Asia (see Venus in fiction). In fact Venus's surface is hot enough to melt lead, and it is extremely hostile to life.
Venus
The atmosphere of Venus was discovered in 1761 by Russian polymath Mikhail Lomonosov. Venus's atmosphere was observed in 1790 by German astronomer Johann Schröter. Schröter found when the planet was a thin crescent, the cusps extended through more than 180°. He correctly surmised this was due to scattering of sunlight in a dense atmosphere. Later, American astronomer Chester Smith Lyman observed a complete ring around the dark side of the planet when it was at inferior conjunction, providing further evidence for an atmosphere. The atmosphere complicated efforts to determine a rotation period for the planet, and observers such as Italian-born astronomer Giovanni Cassini and Schröter incorrectly estimated periods of about from the motions of markings on the planet's apparent surface.
Colonization of Venus
Furthermore, water, in any form, is almost entirely absent from Venus. The atmosphere is devoid of molecular oxygen and is primarily carbon dioxide. In addition, the visible clouds are composed of corrosive sulfuric acid and sulfur dioxide vapor.
Terraforming of Venus
Research projects in Iceland and Washington (state) have recently shown that potentially large amounts of carbon dioxide could be removed from the atmosphere by high-pressure injection into subsurface porous basalt formations, where carbon dioxide is rapidly transformed into solid inert minerals.
Other recent studies
predict that one cubic meter of porous basalt has the potential to sequester 47 kilograms of injected carbon dioxide. According to these estimates a volume of about 9.86 × 10 km of basalt rock would be needed to sequester all the carbon dioxide in the Venusian atmosphere. This is equal to the entire crust of Venus down to a depth of about 21.4 kilometers. Another study concluded that under optimal conditions, on average, 1 cubic meter of basalt rock can sequester 260 kg of carbon dioxide. Venus's crust appears to be thick and the planet is dominated by volcanic features. The surface is about 90% basalt, and about 65% consists of a mosaic of volcanic lava plains. There should therefore be ample volumes of basalt rock strata on the planet with very promising potential for carbon dioxide sequestration.