Recently, the web has been abuzz in a small way with news of the discovery of a “possible super-Earth.” This assessment is accurate: in the planet Kepler 22-b, we have confirmation of the second planet known to man to be near Earth’s size and in a similar orbit around a similar parent star.
Theoretically, Kepler 22-b is in exactly the right place to have plentiful liquid water, plentiful sunlight, and mild temperatures. It’s the perfect recipe for life, including those precious photosynthetic organisms that created Earth’s own oxygen atmosphere. Kepler 22-b is far more likely than any world we’ve yet discovered to be completely habitable to human colonists; it’s entirely possible that settlers on Kepler-22b could touch down on this larger-than-Earth planet and find that they could take a stroll through balmy, breathable air under an orange-tinted sun. Kepler 22-b could look like home.
That’s possible, and this is hugely exciting. This has never happened before. Even if it’s not quite so idyllic, Kepler 22-b may still prove far more hospitable than any of our neighbors; any atmosphere or liquid water might be better than Mars’ none-at-all, let alone the sulfuric acid pressure cooker that Venus calls a surface. So why aren’t we talking about colonizing Kepler-22b yet?
There are many reasons this mightn’t have caught the popular imagination the way that prospects of life on Mars, Venus, and even the Moon were everywhere in the early 20th century. Maybe we’re jaded by too many exciting-sounding discoveries that turned out to be less awesome than advertised. Maybe we’re thinking practically about the challenges of mounting a mission to a planet 600 light years away. But there’s one big reason that scientists aren’t shouting this discovery from the rooftops: New Earth is only one of a great many possibilities for what Kepler 22-b might turn out to be.
We don’t yet know if it’s a gas, liquid, or solid planet. At that size and orbit, it’s probably solid, like Earth, but we can’t be sure. And if it is solid, that doesn’t clarify much; in our own solar system alone we have three drastically different solid, terrestrial planets in similar orbits. And that’s just what’s possible with our own solar system’s chemistry.
Mega-Mars is perhaps the least likely among our Sol System models for Kepler 22-b, because Mars’ cold, dry surface is accounted for at least in part by its small size. But Mega-Venus may be much more likely; and the unnerving thing about the Venus scenario is that we have no idea how likely it is, because we have no idea why our “planetary twin” is so different from our home.
Venus is weird. Profoundly weird. It mystifies scientists and makes at least some of them very uncomfortable, because we like to think that most variables about a planet are determined by predictable factors like its size or proximity to its parent star. Earth, Mars, and Venus all have atmospheres largely based on carbon dioxide (well, Earth doesn’t anymore because of those pesky photosynthesizers). Earth is larger than Mars, and as a result has more gravity, retains more heat, and can sustain more gas-releasing geologic activity; as a result, we have much more atmosphere than Mars. Venus is between Earth and Mars in size, and fairly similar to us in orbit. So it should be between the two in geologic activity and also in atmosphere. Right?
Turns out, no. Most people hear a few basic facts about Venus in elementary school: it’s very hot. It has acid. But that doesn’t quite get across the magnitude of hella strange that Venus is. Hot? Try an average surface temperature of over 800 degrees Fahrenheit as a result of a rampant greenhouse effect. High pressure to the tune of 92 times Earth’s surface air pressure; this air pressure crushed the first five probes we sent there before they could reach the surface.
Also…you know how Venus is all bright and shiny? That’s the sulfuric acid in the atmosphere. On Venus, instead of water it rains the same acid we’re not allowed to dump down our drains for fear of accidentally killing things. And there’s so much of it that the entire planet has a perpetual, thick cloud cover that reflects fully 60% of the light Venus gets from the Sun. So, it’s pretty dark down there too. If you somehow survived the 800 degree sulphuric acid rains at nearly 100 times Earth’s air pressure. Also, thanks to the heat and the convection currents it creates, Venus is so windy that its entire atmosphere moves circles the planet’s surface faster than the planet rotates.
The heat, pressure, and repletion of skin-eating acid is only the beginning. It turns out Venus’ geology also makes no sense. Instead of experiencing geological change gradually, in the form of occasional earthquakes and volcanoes, Venus appears to undergo a single “resurfacing” once every several hundred million years. That’s right: for reasons we don’t understand, every billion years or so the entire surface of the planet breaks up and is replaced by lava from the planet’s molten core, erasing all previous geologic history and releasing ungodly amounts of greenhouse gases into the atmosphere in the process. Scientists figured this out when they realized that there were no intact craters or geologic forms older than 600 million years on the planet’s surface. Anywhere.
And nobody has any idea why this is the case. There are lots of theories; the leading one right now is that a lack of water is responsible for all of Venus’ eccentricities. This may well be the case, as water may play a role in easing Earth’s routine plate tectonics, and it reacts with corrosive chemicals to keep them from completely taking over the atmosphere. But then…why didn’t Venus get any water? Did it somehow form without it, even though its near neighbors Mars and Earth both got plenty and they formed out of neighboring parts of the same accretion disk? Did it boil away as a result of Venus’ slightly smaller size and slightly closer orbit than Earth’s? Are we really that close to not existing? That’s an unnerving thought. Or did Venus just get the hell battered out of it by massive impact events? We have evidence of Venus undergoing at least two catastrophic impacts, but then Earth has had at least one (which created our Moon), and we still have plenty of water.
Whatever the reason, the uncertainty is unsettling when it comes to the question of Kepler-22b. If Kepler 22-b’s geologic activity (probably more of it than Earth, for the same reason Earth has more than Mars) outweighs the amount of water on its surface, it could very well be a super-Venus. Kepler 22-b could look like the sulfuric acid pressure cooker at left.
…if, that is, the rules for determining planetary climate in our solar system even apply to Kepler-22b’s. It’s also possible that Kepler’s whole star system has a different composition than ours, which could result in weird wonders as “carbon planets” with crusts composed of graphite and mountain ranges made of diamond. Some theories suggest that even a slight difference from our own solar system’s composition could “push” planetary chemistry this way. So, on the bright side, Kepler-22b could be a type of planet entirely new to science that we’ve never discovered before!
When will we know what Kepler 22-b is? Unfortunately, it’s probably going to be at least a decade. Presently, our only knowledge of Kepler 22-b comes from distortions in its star’s light so small that we had to spend months confirming that there actually was a planet there. Our best near-future hope for getting a good enough view to analyze its atmosphere will be the James Webb Telescope.
This truly impressive in-the-works NASA project is currently slated for launch in 2018. But with recent budget cuts, the James Webb Telescope’s future is in very real danger–so, if you feel the urge, please don’t hesitate to write to your congressman and tell him to continue NASA’s funding for the James Webb! Because who doesn’t want to know whether we have a second chance at Earth staring us in the face?
Get to know the James Web Telescope here: http://www.jwst.nasa.gov/about.html