Douglas Nelson, age 9, of Spokane, Washington, for his question:

How heavy is Mars?

Mars is a little more than half as wide as our big, round world. The bulk of the little planet weighs four times more than an equal amount of water. This means it is made of lighter materials than our earth, which equals 5 1/2 times the weight of water. If the earth were hollow, it could swallow seven little Mars sized Planets. And on a pair of gigantic scales, our solid earth would equal the weight of nine little Mars planets.

Scientists do not talk about the weight of a planet. They say, instead, that it has mass. The mass of the planet is the amount of material stuffed into its size – the amount of matter in its volume. Let's say that the earth has a mass figure of 1. In that case, the mass of Mars would be 0.11. This is an expert's way of saying that Mars weighs just a little less than one ninth as much as the earth.  Mars Statistics

Planetary Symbol: Name in Roman/Greek Mythology: Mars/Ares

Diameter: 6,785 km (4,217 miles)

Rotation Period about Axis: 24.6 hrs

Mass: 0.64x10^24 kilograms (0.11 x Earth's)

Revolution Period about the Sun: 1.88 years

Density: 3,933 kg/m^3   Tilt of Axis: 25o 12"

Minimum Distance from Sun: 205 million km (128 million miles)

Surface Gravity: 3.7 m/s^2 (0.37 x Earth's)

Maximum Distance from Sun: 249 million km (155 million miles)

Temperature: -129o C to 0o C ( -200o F to 32o F)

Orbital Semi-major Axis: 1.52 AU (Earth=1 AU)

Average Surface Temperature (K): 218K

Minimum Distance from Earth: 35 million miles

Satellites: 2