欧博官网Natural History Museum
What is Mars's atmosphere made of?
Mars's atmosphere is made up of around 96% carbon dioxide. It also contains small quantities of argon, nitrogen, oxygen and water vapour.
The atmosphere is very thin, but it is thought that in the past it was much thicker. The loss has been attributed to the solar winds, although there are other processes that can thin an atmosphere (such as the impacts of astronomical bodies).
Is there water on Mars?Mars almost certainly had surface water in the past, interpreted from the evidence of canyons, dry lakebeds and river networks.
Although these features could only have been formed by liquid water, there is none left on the surface now due to the cold, thin atmosphere. But the planet has polar ice caps. If these melted, the planet would be covered by 20- to 30-metre-deep water.
How many moons does Mars have?Mars has two moons: an inner moon called Phobos and a much smaller outer moon, Deimos. They are unevenly shaped, rocky satellites and may be asteroids caught in the planet's gravity.
Phobos is slowly moving towards Mars and is likely to crash into the surface in about 50 million years. Deimos appears smoother than Phobos as loose dirt, known as regolith, fills its craters.