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 has two small moons, called Phobos and Deimos. The planet Mars is made of rock. The ground there is red because of iron oxide (rust) in the rocks and dust. The planet's atmosphere is very thin and contains a lot of carbon dioxide and a very tiny amount of oxygen.