In the world of exoplanets, Earth-like planets are what everyone’s most excited over. And for good reason. It sure would be great if we could get a close look at one, don’t you think?
I mean, we all grew up watching things like Star Trek which, obviously, is full of Earth like planets. Many of which look suspiciously like Southern California. Unfortunately, the chances of an actual exoplanet being like that are really quite unlikely (albeit impossible to predict), no matter how much you might want to battle a giant lizard. The thing is, going by the definitions the exoplanet hunters use, there’s an awfully convenient Earth-like planet right nearby. In fact, it’s actually the closest planet to Earth. Its name is Venus.
It feels a bit like we, as a species, haven’t quite forgiven Venus for not being the idyllic paradise planet that the sci-fi writers used to love telling us about. Or at least for not being a swampy dinosaurland.
No, sadly everything that we’ve discovered about Venus seems to be given by people as reasons not to go there. Just imagine if everything about you was considered a good reason not to visit? Besides, while exploring Venus is admittedly not as easy as exploring Mars, there aren’t any difficulties which are insurmountable.
Human technology has progressed greatly since the old Soviet Venera landers. Moreover, we now know what kind of conditions we’ll need our technology to stand up to, if we try sending robots to Venus.
Sulfuric acid? No problem. We can use high grade ceramics and fluorinated polymers which are resistant to acid attack.
High pressure? Venus has a surface pressure of about 9.1 megapascals, and we have deep sea submersibles which can comfortably survive ten times that much.
Furnace-like temperatures? Sure, most human made electronics use semiconductors which can’t function above 250°C, but we know how to construct electronics that can.
Hah! Your move, Venus!
Seriously though, Venus is tragically underexplored. It’s actually the most visited other planet in the Solar System, but sadly, that’s purely because it’s a convenient way to get a gravitational slingshot before continuing to go somewhere else. NASA doesn’t seem to want to touch Venus with a proverbial barge pole, having not sent any spacecraft there since Magellan in 1989. Since then, there have only been two craft sent specifically to study Venus – ESA’s Venus Express, and JAXA’s Akatsuki. Though ISRO are considering sending a craft that way.
It’s a pity, really. Because while exoplanet astronomers are busily finding Earth-like planets, our only real criteria defining them as “Earth-like” are that they are of a similar mass and equilibrium temperature★ to Earth. By that definition, Venus is most definitely an Earth-like planet. Which means we have two Earth-like planets which we can study up close, characterise, try to understand, and ultimately use in making predictions about exoplanets. And right now, we have no way of knowing if the planets we find elsewhere are going to be more like Earth, more like Venus, or altogether different. For all we know, the planets we’re discovering may actually be Venus-like, with genuinely Earth-like planets being an oddity.
With all this in mind, you’d think it might be a good idea to spend some time studying the only other Earth-like planet we’ll be able to actually visit in the near future.
I’m just saying!
★ It’s worth pointing out that by equilibrium temperature, I mean the temperature predicted for an object without an atmosphere. Equilibrium temperatures of Venus and Earth are roughly 260 K (-13°C) and 255 K (-18°C) respectively, which really does go to show what a huge difference a planet’s atmosphere can make.