Mars is a little over half the size of the Earth. Its diameter is 4,222 miles, which is 53 percent of Earth's diameter. The planet's mass is also small, at about 10 percent of Earth's total. More » Science Astronomy Planets

Mars has two moons: Phobos and Deimos. Both moons are irregularly shaped and very small in size compared to the Earth’s moon. Phobos is the larger of the two, with an average radius of 6.9 miles; Deimos has an average ra... More » Science Astronomy Planets

The force of gravity on the planet Mars is only about 38 percent as strong as that on Earth. Surface gravity on Mars is much weaker than that of Earth due to the planet's small size and relatively low mass. More » Science Astronomy Planets
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A person weighing 50kg (110lbs) on Earth would weigh 19kg (42 lbs) on Mars. This is because the gravitational force on Mars is only 38 percent that of the gravitational force on Earth. More » Science Astronomy Planets

Mars is similar to Earth in the fact that both planets have about the same amount of dry land surface. Both planets also have volcanoes and impact basins. More » Science Astronomy Planets

Because Venus has an axial tilt of only 2.7 degrees, it lacks the seasons found on both Earth and Mars. Venus also has a very thick atmosphere and suffers from a runaway greenhouse effect, meaning that the surface of the... More » Science Astronomy Planets

Depending on the time of year and its position in the sky, Mars can be seen from Earth with the naked eye or in more detail with a small telescope. To the naked eye, Mars appears as a bright red star. With a telescope, o... More » Science Astronomy Planets