Moons: Mars has two little moons: Phobos and Deimos. They are irregular in shape. Phobos is about 21 kilometers across, and Deimos is about 12 kilometers across. Their small sizes and their irregular shapes resemble those of asteroids that orbit the Sun between Mars and Jupiter. So, one theory, for the origin of these two moons, is that these two moons are asteroids which were captured by Mars.

Atmosphere: Mars has a very thin atmosphere consisting of carbon dioxide (95%), nitrogen (2.7%), argon (1.6%) and other gases in small quantities. The atmospheric pressure on the surface of Mars is just 7 millibar which is 1/150th of Earth‘s atmospheric pressure at the sea level.

Size: Mars is only half the size of Earth, and its mass is one-tenth of the Earth’s mass. Mean radius of Mars is about 3390 kilometers. The picture below is a comparison of sizes of the first 4 planets. 

Orbit: Mars’ orbit is more elliptical. Its mean distance from the Sun is about 228 million kilometers. Its rotational period and tilt are identical to earth. It rotates once on its axis in every 24.62 hours, and its tilt is 25.2 degrees. Because of the tilt, Mars too has four seasons like Earth.

Day and Year:  The word ‘Sol’ refers to Martian day which is 24.62 hours. Martian year is 669.6 sols or 687 earth days.

Surface temperature: The temperature on the surface can vary from 70° Fahrenheit to minus 225° Fahrenheit. As it has very thin atmosphere it loses sun’s heat fast.

Life on Mars: Scientists think that life, at least in primitive form, might have existed on Mars when it had liquid water, billions of years ago. Living things may not exist now as the conditions are very harsh due to the thin atmosphere and the lack of magnetic field. However, what scientists are looking for is any sign that could prove that life existed on Mars in the past.