<p>We actually have a very good idea of this because the <a href="https://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiter" rel="noreferrer">Mars Reconnaissance Orbiter</a> has been orbiting Mars for over a decade. The MRO is, basically, a spy satellite around Mars and is continually taking high-resolution photos of the surface. It has revisted much of the surface, taking pictures multiple times over the years.</p>

<p>As a consequence, we have a very good idea of the rate of formation of craters on Mars. We have seen numerous craters that have formed between visits to a spot, but none are very large. The key thing is that we now have a very solid measurement of the flux of smaller objects onto Mars and can say with certainty, that that sort of impact is way down on the list of perils. (It's probably less than the odds of being killed by a tornado in the Midwest.)</p>

<p>Larger impacts are a bit harder since we haven't seen any, but we have two lines of evidence. First, space debris follows a distribution in size vs. frequency that we've measured, and it's not much different around Mars' orbit than it is around Earth's.</p>

<p>Second, the <em>extensive</em> photography we have of Mars' surface (which we now have mapped better than Earth's!) allows us to count craters and to make estimates of their age. We know that small craters a few yards to tens of yards across are much more common and we know the rate at which they hit, so astronomers count the number of small craters on the floors of larger craters and can make a very good estimate of the age of the larger crater. </p>

<p>From this we have developed measurements of the rate of cratering at all sizes, and, again, the hazard isn't that great.</p>

<p>I'd note that the risk of what on Earth would be civilization-killers is actually <em>lower</em> on Mars because of its lack of an atmosphere. The <a href="https://en.wikipedia.org/wiki/Chicxulub_impactor" rel="noreferrer">Chicxulub</a> impact that killed the dinosaurs killed most of them through the superheated steam and air shockwave that went around the Earth followed by the years of Asteroid Winter that followed.  Mars' atmosphere isn't heavy enough to support either, so "all" you'd have to do is hunker down and wait out the fall of rock fragments... (Still, it's an event better watched from orbit than from the ground.)</p>

CC BY-SA 4.0
2018-07-06T15:37:42.190Z
This was really surprising "Second, the extensive photography we have of Mars' surface (which we now have mapped better than Earth's!)" How come?
csiz
CC BY-SA 4.0
2018-07-06T16:10:28.183Z
@csiz: just speculating, but probably less weather issues to deal with, and no political aspects either.
whatsisname
CC BY-SA 4.0
2018-07-06T16:12:31.720Z
Definitely having no weather helps.  Also no forests obscuring the land, nor any glaciers, and also no lakes and oceans!
Mark Olson
CC BY-SA 4.0
2018-07-06T16:57:29.843Z
and one more reason:  Mars has 28% of the surface area of the Earth.  (55.91 million square miles vs 196.9 million square miles)
Reginald Blue
CC BY-SA 4.0
2018-07-06T18:26:42.073Z
Where would the energy from a Mars impact event go, if not into the atmosphere? Would it mostly be radiated into space?
DylanSp
CC BY-SA 4.0
2018-07-06T18:46:50.367Z
We have not mapped Mars' surface better than Earth's.  1. There are far more reconnaissance satellites orbiting Earth than Mars, so there are just more photos getting taken overall.  2.  Bandwidth: getting data from a satellite around Earth is much easier than getting is from MRO, and if I remember right this is actually the limiting factor in the data return from MRO.  3.  Private business are interested in Earth imagery but not really Mars imagery, so for that reason along there is a lot more money heading towards Earth imaging.
NeutronStar
CC BY-SA 4.0
2018-07-06T18:58:59.260Z
None of which do much to map the ice-, tree-, or water-covered portions of the Earth.
Mark Olson
CC BY-SA 4.0
2018-07-06T21:05:42.287Z
Depending on interpretation, the (solid) surface of Mars is better mapped than the (solid) surface of Earth, just because 75% of Earth surface is covered by water and satellites can't photograph it. With a more straightforward interpretation, that statement is likely to be false.
Pere
CC BY-SA 4.0
2018-07-06T12:03:58.287Z
2018-07-06T12:03:58.287Z
Mark Olson
<p>Further to Mark Olson's answer, while an asteroid impact is popularly thought of as the reason for <a href="https://en.wikipedia.org/wiki/Extinction_event" rel="nofollow noreferrer">extinction events on Earth</a>, the reality is more prosaic, with volcanism and glaciation being the most common causes. In all cases, including impact events, the loss of species is primarily the result of a dramatic change to the global <em>environment</em>. </p>

<p>The K–Pg extinctions were mostly plants (from loss of photosynthesis), pure herbivores (from loss of plant food) and pure carnivores (from loss of prey animals especially herbivores). A Mars base would have to find solutions to a temporary reduction in solar energy, e.g. to sustain its hydroponics, maintain indoor warmth, etc - but hopefully it would have alternative energy sources (generation or storage) anyway.</p>

<p>Excluding an impact in the local vicinity, a Mars base is less at risk from the immediate aftermath than if a similar impact occurred on Earth. There won't be a giant tidal wave or fire front to contend with. There won't the same global infrared atmospheric firestorm as that of the <a href="https://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_extinction_event#Effects_of_impact" rel="nofollow noreferrer">Chicxulub impact</a>, since the Mars atmosphere is much thinner and has little free oxygen. There will be no burnt forests and no vaporisation of combustible hydrocarbons and sulphur in undersea carbonate rock, each of which contributed to the "impact winter".</p>

<p>Debris impacts might be an issue, but remember the lower Mars gravity will affect the ejecta differently. Now <em>that</em> would make an interesting question in its own right.</p>

CC BY-SA 4.0
2018-07-07T05:31:06.027Z
The impact on humans of any atmospheric effects that do happen would also be lower: Cities on Mars already need to be sealed pressure vessels with their own air supply.
Peter Cordes
CC BY-SA 4.0
2018-07-07T06:58:54.353Z
Yes indeed, but it depends on how evolved the colony is. For self-sufficient sealed cities à la Total Recall, the atmospheric risks would be lower but there would be greater risk from fractured seals due to atmospheric shock waves, seismic events, impact ejecta etc. For small colonies of a few sealed buildings, the impact on energy and food production might be the biggest risk, either from direct damage or from reduced sunlight due to atmospheric particles and gases. Significant battery and food storage would mitigate this.
Chappo Hasn't Forgotten
CC BY-SA 4.0
2018-07-07T12:31:38.887Z
@Chappo *"reduced sunlight due to atmospheric particles and gases"* Well, there's already dust storms, which would need to be dealt with even in the absence of impact.
user
CC BY-SA 4.0
2018-07-07T02:03:47.373Z
2018-07-07T02:03:47.373Z
Chappo Hasn't Forgotten
<p>Yesterday my sister and I have discussed the recent efforts of SpaceX to create a permanent colony on mars.</p>

<p>When coming to the several dangers of creating a habitat on a different planet, we got stuck on the probability of mars getting hit by an astronomical object thats large enough to wipe out life anywhere on the planet.
I assume the probability is higher than on Earth, due to Mars being closer to the Asteroid Belt, its size and thinner atmosphere. There are more potential objects to enter martian atmosphere and can be smaller than on Earth to create the same hazardous impact for life. </p>

<p>I have tried to research the numbers, but the only calculations I found were for specific asteroids and their probability to hit Mars.</p>

<p>On this StackExchange there are some questions concerningthe probability of an <a href="https://astronomy.stackexchange.com/questions/11418/what-is-the-probability-of-an-astronomical-body-hitting-you">individual  (on earth)</a> or a <a href="https://astronomy.stackexchange.com/questions/21372/is-there-any-mathematical-formula-paper-or-anything-that-shows-the-probability">specific spot (on the moon)</a> getting hit, but I found none for the hit of an object with a certain amount of impact (I hope thats the right word here). </p>

<p>So my question is: </p>

<p><strong>What is the probability of an astronomical object hitting mars anywhere on its surface and kill all people currently living there?</strong> </p>

<p>Any impact destroying life-support systems and thus wiping out life on mars indirectly can also be included.</p>

<p>Assume that there is only one habitat, it is built directly on the surface and the first humans have arrived with the latest flight. </p>

<p>If there are any questions about the scope of this question, don't hesitate to ask.</p>

CC BY-SA 4.0
2018-07-06T15:02:31.273Z
Other than the extremely rare case of an object hitting Mars that would otherwise have continued on to Earth, I don't think the proximity to the Belt makes much difference.
Carl Witthoft
CC BY-SA 4.0
2018-07-07T15:29:55.283Z
An impactor probably has to be *larger* on Mars to have the same effect - Mars is smaller, so the impactor will probably hit slower.
Martin Bonner supports Monica
CC BY-SA 4.0
2018-07-09T12:50:12.403Z
@MartinBonner you're forgetting terminal velocity in Earth's atmosphere
Carl Witthoft
<asteroids><mars><life><impact-probability>
Whats the probability of a hazardous impact for human life on Mars?
Starguin
# Whats the probability of a hazardous impact for human life on Mars?

(Asked by: username_0 on 2018-07-06)

Yesterday my sister and I have discussed the recent efforts of SpaceX to create a permanent colony on mars.

When coming to the several dangers of creating a habitat on a different planet, we got stuck on the probability of mars getting hit by an astronomical object thats large enough to wipe out life anywhere on the planet.
I assume the probability is higher than on Earth, due to Mars being closer to the Asteroid Belt, its size and thinner atmosphere. There are more potential objects to enter martian atmosphere and can be smaller than on Earth to create the same hazardous impact for life.

I have tried to research the numbers, but the only calculations I found were for specific asteroids and their probability to hit Mars.

On this StackExchange there are some questions concerningthe probability of an [individual (on earth)](https://astronomy.stackexchange.com/questions/11418/what-is-the-probability-of-an-astronomical-body-hitting-you) or a [specific spot (on the moon)](https://astronomy.stackexchange.com/questions/21372/is-there-any-mathematical-formula-paper-or-anything-that-shows-the-probability) getting hit, but I found none for the hit of an object with a certain amount of impact (I hope thats the right word here).

So my question is:

**What is the probability of an astronomical object hitting mars anywhere on its surface and kill all people currently living there?**

Any impact destroying life-support systems and thus wiping out life on mars indirectly can also be included.

Assume that there is only one habitat, it is built directly on the surface and the first humans have arrived with the latest flight.

If there are any questions about the scope of this question, don't hesitate to ask.

**Tags:** asteroids, mars, life, impact-probability
> **Comments:**
> **username_1**: Other than the extremely rare case of an object hitting Mars that would otherwise have continued on to Earth, I don't think the proximity to the Belt makes much difference.  
> **username_2**: An impactor probably has to be *larger* on Mars to have the same effect - Mars is smaller, so the impactor will probably hit slower.  
> **username_1**: @MartinBonner you're forgetting terminal velocity in Earth's atmosphere  

---

## 2 answers

### Answer by username_3 on 2018-07-06. Score: 16

We actually have a very good idea of this because the [Mars Reconnaissance Orbiter](https://en.wikipedia.org/wiki/Mars_Reconnaissance_Orbiter) has been orbiting Mars for over a decade. The MRO is, basically, a spy satellite around Mars and is continually taking high-resolution photos of the surface. It has revisted much of the surface, taking pictures multiple times over the years.

As a consequence, we have a very good idea of the rate of formation of craters on Mars. We have seen numerous craters that have formed between visits to a spot, but none are very large. The key thing is that we now have a very solid measurement of the flux of smaller objects onto Mars and can say with certainty, that that sort of impact is way down on the list of perils. (It's probably less than the odds of being killed by a tornado in the Midwest.)

Larger impacts are a bit harder since we haven't seen any, but we have two lines of evidence. First, space debris follows a distribution in size vs. frequency that we've measured, and it's not much different around Mars' orbit than it is around Earth's.

Second, the *extensive* photography we have of Mars' surface (which we now have mapped better than Earth's!) allows us to count craters and to make estimates of their age. We know that small craters a few yards to tens of yards across are much more common and we know the rate at which they hit, so astronomers count the number of small craters on the floors of larger craters and can make a very good estimate of the age of the larger crater.

From this we have developed measurements of the rate of cratering at all sizes, and, again, the hazard isn't that great.

I'd note that the risk of what on Earth would be civilization-killers is actually *lower* on Mars because of its lack of an atmosphere. The [Chicxulub](https://en.wikipedia.org/wiki/Chicxulub_impactor) impact that killed the dinosaurs killed most of them through the superheated steam and air shockwave that went around the Earth followed by the years of Asteroid Winter that followed. Mars' atmosphere isn't heavy enough to support either, so "all" you'd have to do is hunker down and wait out the fall of rock fragments... (Still, it's an event better watched from orbit than from the ground.)

> **Comments:**
> **username_4**: This was really surprising "Second, the extensive photography we have of Mars' surface (which we now have mapped better than Earth's!)" How come?  
> **username_5**: @csiz: just speculating, but probably less weather issues to deal with, and no political aspects either.  
> **username_3**: Definitely having no weather helps.  Also no forests obscuring the land, nor any glaciers, and also no lakes and oceans!  
> **username_6**: and one more reason:  Mars has 28% of the surface area of the Earth.  (55.91 million square miles vs 196.9 million square miles)  
> **username_7**: Where would the energy from a Mars impact event go, if not into the atmosphere? Would it mostly be radiated into space?  
> **username_8**: We have not mapped Mars' surface better than Earth's.  1. There are far more reconnaissance satellites orbiting Earth than Mars, so there are just more photos getting taken overall.  2.  Bandwidth: getting data from a satellite around Earth is much easier than getting is from MRO, and if I remember right this is actually the limiting factor in the data return from MRO.  3.  Private business are interested in Earth imagery but not really Mars imagery, so for that reason along there is a lot more money heading towards Earth imaging.  
> **username_3**: None of which do much to map the ice-, tree-, or water-covered portions of the Earth.  
> **username_9**: Depending on interpretation, the (solid) surface of Mars is better mapped than the (solid) surface of Earth, just because 75% of Earth surface is covered by water and satellites can't photograph it. With a more straightforward interpretation, that statement is likely to be false.  

---

### Answer by username_10 on 2018-07-07. Score: 3

Further to Mark Olson's answer, while an asteroid impact is popularly thought of as the reason for [extinction events on Earth](https://en.wikipedia.org/wiki/Extinction_event), the reality is more prosaic, with volcanism and glaciation being the most common causes. In all cases, including impact events, the loss of species is primarily the result of a dramatic change to the global *environment*.

The K–Pg extinctions were mostly plants (from loss of photosynthesis), pure herbivores (from loss of plant food) and pure carnivores (from loss of prey animals especially herbivores). A Mars base would have to find solutions to a temporary reduction in solar energy, e.g. to sustain its hydroponics, maintain indoor warmth, etc - but hopefully it would have alternative energy sources (generation or storage) anyway.

Excluding an impact in the local vicinity, a Mars base is less at risk from the immediate aftermath than if a similar impact occurred on Earth. There won't be a giant tidal wave or fire front to contend with. There won't the same global infrared atmospheric firestorm as that of the [Chicxulub impact](https://en.wikipedia.org/wiki/Cretaceous%E2%80%93Paleogene_extinction_event#Effects_of_impact), since the Mars atmosphere is much thinner and has little free oxygen. There will be no burnt forests and no vaporisation of combustible hydrocarbons and sulphur in undersea carbonate rock, each of which contributed to the "impact winter".

Debris impacts might be an issue, but remember the lower Mars gravity will affect the ejecta differently. Now *that* would make an interesting question in its own right.

> **Comments:**
> **username_11**: The impact on humans of any atmospheric effects that do happen would also be lower: Cities on Mars already need to be sealed pressure vessels with their own air supply.  
> **username_10**: Yes indeed, but it depends on how evolved the colony is. For self-sufficient sealed cities à la Total Recall, the atmospheric risks would be lower but there would be greater risk from fractured seals due to atmospheric shock waves, seismic events, impact ejecta etc. For small colonies of a few sealed buildings, the impact on energy and food production might be the biggest risk, either from direct damage or from reduced sunlight due to atmospheric particles and gases. Significant battery and food storage would mitigate this.  
> **username_12**: @Chappo *"reduced sunlight due to atmospheric particles and gases"* Well, there's already dust storms, which would need to be dealt with even in the absence of impact.  

---

