Exoplanet Odyssey

When I was a young astronomy enthusiast as a teenager in the early 90's, one of the biggest mysteries of the universe at the time was whether or not there were planets outside our solar system orbiting other stars. While everyone thought it was overwhelmingly likely, we had yet to see one. In the intervening years, that has all dramatically changed and just a few days ago NASA made history by announcing the discovery of over 1200 new exoplanets in one shot bringing the total number known to over 4000. More, they now believe that most stars in our universe probably host at least one planet.

Out of all these newly discovered worlds a few dozen of these are known to be earthlike. These are the most interesting ones as far as finding life in the universe is concerned because, well, Earth itself stands as a testament that life can arise on a planet like this. Current estimates place the number of earthlike planets orbiting stable stars in the Milky Way galaxy as high as 40 billion. Of those, about 11 billion are estimated to orbit sun-like stars within their zones of habitability like earth. That's a lot of chances for life to develop within the Milky Way alone, and it gets incomprehensibly higher if you start looking at the multitudes of other galaxies in the universe. Chances are, the Milky Way is teeming with life. But how much of it is intelligent other than us is still a big unknown.

The most interesting earth-like planet we've found so far is Kepler 438b. Located in the constellation Lyra, this planet orbits within the habitable zone of a red dwarf star at a distance of about 475 light years from us. It's nearly the same size as earth, it could have liquid water on its surface, and if it does it very likely looks like earth with clouds and rain and maybe even oceans. It is as close to a twin of earth as we've found so far. Unfortunately, Kepler 438b is very likely uninhabited due to it being subject to periodic  superflare activity from its star that would sterilize the surface of the planet never allowing life to gain a foothold. Even still, it shows us that there are twins of Earth out there.

Another possible twin of earth is a planet 490 light years away known as Kepler 186f. Located in a true solar system with multiple other planets, this planet exists within the habitable zone of its red dwarf star. Red dwarves are frequently cited as being capable of sustaining a living planet due to the extreme longevity of this class of star. We don't know as much about Kepler 186f, only that it occupies roughly the same position in its star system that Mars does in our own. Unlike Mars, which is simply too small to hold onto a dense earth-like atmosphere, Kepler 186f could. Unlike earth, however, it does not seem to be tilted on its axis, so thusly does not have seasons. Unfortunately, we don't really know that much more about this world, but it was earth-like enough to warrant a search by SETI using the Allen Telescope array to see if they picked anything up. Unfortunately, they did not.

But, as it turns out, not just the earthlike planets we're finding are interesting. In fact, some of the wildest exoplanets we've found are interesting specifically because they are so different from earth. As a science fiction writer, I have always enjoyed trying to imagine what strange alien worlds might look like, but I never really knew if what I was thinking was really possible. To my delight, scientists are now finally able to tell us a little bit about these strange exoplanets that exist out in deep space. And some of them are very strange indeed, and often quite different than what the old school science fiction writers I grew up reading had imagined.

One such planet is known as Gliese 436 b. This world is about the size of the planet Neptune, but it's much hotter. Like 570 degrees Fahrenheit hot. But even at that temperature, this planet happens to be covered in water ice. That's right, burning hot 570 degree water ice, kept in solid form by the intense pressure present on this world. And if that wasn't strange enough, the planet is also slowly losing its hydrogen and helium atmosphere, forming a huge comet-like tail that follows it around as it orbits its star.

Then there are worlds that don't like to be seen. A planet in Draco located about 750 light years away known as TrES-2b is so dark that it only reflects about 1 percent of the light that hits it. It's a gas giant that's too hot for clouds, so if you were looking at it, it would look like a giant black ball with weak tinges of red light. The exact reason for why this planet is so dark isn't settled, but it's most likely due to the planet being composed of materials such as potassium that absorb light efficiently.

Another planetary oddity is the so-called "Hell Planet" or Kepler 78b. This planet is only a little larger than earth, but all similarity ends there. It's a world of lava and extreme temperatures. So much so that we have no idea how this planet exists. It's so close to its star that at the time of its formation it would have had to form inside the star, something that surely must be impossible. It isn't clear whether it was a wandering unlucky planet captured into that orbit by the star or where exactly it came from, but its surface temperature is thought to be a whopping 4300 degrees Fahrenheit. While we may not know how "Hell Planet" formed, we do know how it will be destroyed. It will fall into its own sun in about 3 billion years.

My own personal favorite is HD 189773b. This planet is a true delight for a science fiction writer because it has one totally crazy attribute to it: it rains glass on this world.

Unlike many exoplanets, this one is fairly close at just 63 light years away. It's also one of the few worlds that we know the color of it, which is blue like Neptune. It's a hot gas giant, boiling at about 1800 degrees Fahrenheit. This creates some very weird weather. Suspended within the atmosphere are silicate particles. The heat and pressure melts those particles into glass which then rains into the planet's atmosphere. Given that the wind on this world gusts to 4000 miles per hour, HD 189773b is one huge planetary-sized sand blaster.