Signs and symptoms are both signals of injury, illness, disease â signals that something is not right in the body. A sign is a signal that can be seen by someone else â maybe a loved one, or a doctor, nurse, or other health care professional.
Besides silicon and oxygen, the most abundant elements in the Martian crust are iron, magnesium, aluminum, calcium, and potassium. Oxidation of the iron dust is what gives the surface its reddish hue. Composite image showing the size difference between Earth and Mars. Credit: NASA/Mars Exploration.
Mars also has an atmosphere that is primarily carbon-dioxide, but on Mars, the atmosphere is extremely thin, and prone to high winds. The giant outer planets Jupiter, Saturn, Uranus, and Neptune have extremely thick atmospheres of hydrogen, helium, methane, and ammonia. Titan, the moon of Saturn also has a methane-ammonia atmosphere. For reference, Titan has roughly the mass as the planet Mercury (which doesn't have an atmosphere at all).