Planetary Variations Interactive (83.0K)
This Interactive helps explain why Earth can retain a life-sustaining atmosphere with oxygen, but Mars cannot. Some of the same principles that apply to the Escape Velocity Interactive also apply here, like the impact of the planet’s mass. But there’s more to it with atmospheres, as surface temperature and the heaviness of the molecules also come into play. Try out some combinations of the key variables, and watch as the atmospheres evolve. You can plot multiple trials on the graph to understand what’s happening.

1			What critical component of the Earth's atmopshere can be a liquid, solid, or gas at our temperature and pressure, but only a gas at Venus, and chiefly a solid at Mars. Need a Hint?
			A)	Carbon Dioxide
			B)	Nitrogen
			C)	Hydrogen
			D)	Water Vapor

Three main factors determine the atmospheric composition of a body; its own mass, the masses of its constituent gases, and its temperature. Let's look at that last factor on two worlds of almost the same sizes.

2			Mercury and Saturn's large moon Titan are almost the same exact size, and Mercury is denser, with a huge iron core and thus larger mass and surface gravity. Yet its atmosphere is almost nonexistent, and the Huygen's probe to Titan's surface reports a nitrogen atmosphere about 1.6X desner than our own. Why? Need a Hint?
			A)	Formed farther from the Sun, Titan started with a much heavier set of molecules than Mercury did.
			B)	Mercury's greater gravity prevented as much of its mass from outgassing from its volcanoes as happened on Titan.
			C)	At Mercury's distance, the temperature is so high that even heavy gases like carbon dioxide can escape; even with lower gravity, Titan is so cold that it can retain nitrogen.
			D)	The mass of a planet has no bearing on its atmosphere.

There is a marked difference in the atmospheric compositions of the terrestrial and jovian planets. Basically, the jovians are almost nothing but atmosphere. Why?

3			What very common gas is rare in the inner solar system, but dominates the outer planets, and why? Need a Hint?
			A)	Hydrogen, because only beyond 5 A.U. are the temperatures cold enough to let the larger planets retain it for long.
			B)	Helium
			C)	Nitrogen
			D)	Oxygen

We are now discussing "planetary variations" not just for planets orbiting the sun, but for those around other stars as well.

4			The jovian planet orbiting the star HD 209458 is 63% as massive as Jupiter, orbits its home star every 3.5 days, and when it transits in front of its star, blocks 1.7% of the star's light, letting us find that it is 1.6 times larger in diameter than Jupiter. Explain why it is larger. Need a Hint?
			A)	It must be made of even less dense elements than hydrogen and helium.
			B)	It much contain more material than Jupiter.
			C)	It is so hot that its jovian type atmosphere is pushed higher above its core.
			D)	It is so hot it has lost its atmosphere, and we are seeing only a solid body.

Three main factors determine the surface conditions on a planet; its size, mass, and distance from the Sun. Here we study how they could create a living planet elsewhere.

5			The ecosphere of a star is defined as the region around another sun where an Earth sized world could have liquid water on its surface. Which of these four possible worlds might therefore be the most promising? Need a Hint?
			A)	A Mercury at .7 A.U from a star like the sun.
			B)	A Mars at 1 A.U. from a star twice as hot as the Sun.
			C)	A Europa orbiting a Jupiter at 1.2 A.U. from a star like ours.
			D)	A Uranus orbiting at 3 A.U. from a star like ours.