Mercury & Venus: Understanding hot rocks & Greenhouse gases

The latest episode of The Universe focused on our solar system’s hottest two planets: Mercury and Venus. In looking at each of these worlds, scientists are faced with Sun related issues no other planet has: we can never study these planets when they are high in the sky well after sunset (the ideal time to study any celestial object), and any space probe we send to them must be heat shielded in the extreme. While a quick look at the lists of latest space missions shows that NASA and ESA do throw things at these planets now and then, it is clear that easier outer solar system targets are much more popular planetary proves. One has to ask, all because Mars is hansom and popular, why should he get all the attention? While one might say (tongue throughly planted in check) that this is another case of sexism in science, it is more honest to say that while getting to Mars is hard, getting to Venus is harder, and Mercury just makes things want to melt.

Mercury is a sun-baked world, with surface temperatures typically sufficient to cook a turkey and humidity levels that make the sub-Saharan desert look excessively humid. This little world is locked in a strange gravitational dance with the Sun, which causes it to rotate on its axis only 1.5 times during its brief 88 Earth-day year. This means 1 day on Mercury stretches across 58.7 Earth days. During its languid rotation, it very precisely keeps its poles pointed straight up and down – there is none of the tilt that on Earth provides us out seasons. This means that its poles never face the Sun and within the depths of it’s polar craters there are places that only know darkness. In those shadows, Mercury actually has ice. But… Where the Sun hits their is nothing but baked metallic dirt.

Its small orbit keeps Mercury always within 28 degrees of the Sun. In a perfect world, Telescopes never get within 30 degrees of the Sun and objects are measured when they are within 45 degrees of straight overhead. Mercury forces us to either observe it during the day when it is high in the sky (which can be done, but gets the telescope hot and makes it useless to night time observers), or in twilight when it stands out against the coming darkness but twinkles violently in the atmosphere. From Earth, it is impossible to take detailed images of this little world. It just doesn’t know how to line up for a picture in a proper location. So… we send out probes, and maybe in January we’ll finally at least know what all the sides of Mercury look like. Today, all we have is a crescent image from Mariner 10.

Venus too, is over heated, but while the Sun definitely provides the energy to necessary to keep the planetary inferno roaring, it is actually Venus’ atmosphere that is too blame. Composed primarily of carbon dioxide, sulfur dioxide, sulfuric acid, and other green house gases, the planet’s clouds prevent Venus from cooling to temperatures that allow liquid water to collect. Average surface temperatures are over 450C (a temperature my sad old stove can’t achieve). Exactly what caused this world to self-destruct is a hard to understand.

It is thought this world may once have had water oceans not too different from our own, but when they evaporated for reasons that are being argued, a run away green house effect began. It is possible that Venus had life that was destroyed (I’m talking about microbes or bacteria). It is possible that we could trigger on our planet the same catastrophic green house effect. Once out oceans start to noticeably evaporate, really, we’re dead. (And like with Venus, the heat, storms, and potential acid will eradicate any possible surface signs that life one existed).

Part of me has always felt that understanding Venus is one of the most important things we could do. People often talk about terraforming Mars, but Mars is a little world with out enough gravity to hold on to any atmosphere we manage to put there. Venus is a little bigger than the Earth, and clearly likes to be cloudy. If we could somehow figure out how to end its greenhouse effect, we could learn how to save our planet, and we could have a neat, acid etched planet to explore. Admittedly, the Sun is just waiting to irradiate both the worlds in a few tens of millions of years, and at that point Mars is really the better world to hide on, but… that’s tens of millions of years away.

So, (I’m not saying this is a good idea, I’m just saying it’s an idea), I vote for thinking about figuring out how to end Venus’ green house effect. If we can stop green house gases there, we can stop them anywhere. Go Venus Express, go.

One Comment

  1. ioresult July 24, 2007 at 1:37 pm #

    Venus is a little smaller than Earth, not bigger.

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