Deeper into Jeopardy! XLVII: The Solar System – Final Jeopardy!

No oxygenated Final Jeopardy!’s in the J!Archive, so this one deals instead with its “opposite” (as far as aerobic life goes), carbon dioxide.

Final Jeopardy! category: THE SOLAR SYSTEM (22-2-2006)

Final Jeopardy! clue: The 2 planets in our solar system that have atmospheres made up mostly of carbon dioxide

Correct response

The gist: Sure, they’re both mostly carbon dioxide, but the similarities in their atmospheres basically end there. While hot, sticky Venus‘ thick carbon dioxide atmosphere swirls around it in fierce winds moving up to 60 times the planet’s rotational speed, Mars‘ atmosphere is thin and attenuated after being stripped away by billions of years of solar bombardment. In fact, to demonstrate just how different experiencing Venus’ CO2 would be from Mars’, consider that Earth’s atmospheric pressure is just about 1% that of Venus, and Mars’ is just about 1% of Earth’s, or 0.01% of Venus’. Our solar system’s planets are wild, crazy places.

Even though Venus is the second-closest planet to the Sun, all that carbon dioxide actually gives it a hotter surface temperature than Mercury, the closest. In a highly-exaggerated version of the same greenhouse gas process that is warming the Earth, the extremely thick carbon dioxide atmosphere of Venus traps heat within the planet, and the very fast winds spread around the planet from the daylit half to the dark half, since a Venusian day last 243 Earth days. Astronomers believe that about four billion years ago, Venus had a surface ocean of liquid water, but the runaway greenhouse effect literally caused them to boil away.

On Mars, where there is barely any atmosphere, the carbon dioxide in the atmosphere does little besides blowing bits of dust around the planet’s surface. Much of the planet’s carbon dioxide spends its time frozen at its north and south poles. Because Mars’ axial tilt is quite similar to Earth’s, it experiences summer and winter, and the caps – which are actually mostly water, but carbon dioxide makes up significant portions of it – grow and shrink depending on their hemisphere’s season. The planet’s carbon dioxide may also be responsible for its methane contents, although vulcanism, comets, and even microbial life are also possible candidates as the methane’s source.

A comparison of the greenhouse effect on Earth (left) and Venus. Mars doesn’t have much of one at all.

The clue: This isn’t easy, and I’m tempted to say you might just need to know the answer to this one. You might be able to figure that it’s not going to be the gas giants, both because those are mostly hydrogen and because people (maybe?) tend to know less about them than they do about the rocky planets. Next, you should know that Earth’s atmosphere is almost 80% nitrogen, so scratch that one off. I suppose if it comes down to Mercury, Venus, or Mars, you might as well pick the closest ones to us, but I’m not really sure why. Feel free to let me know if you do.

In Jeopardy!: Venus and Mars, of course, have a storied history together, and they appear in 30 regular clues and this FJ! in the J!Archive. John Gray’s Men are from Mars, Women are from Venus, about the differences between the sexes, gets 14 of those. Their astronomical symbols ♂ and ♀ also signify men (Mars) and women (Venus), which also shows up in a few clues. Astronomically, they’re often mentioned as being the two brightest planets in the night sky, ahead of Jupiter. And there are lots of clues where a contestant guessed Mars when the correct response was Venus or vice versa; I recommend against it unless you’re fairly sure you’ve got the right one.

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