Venus may be the hottest terrestrial world in our solar system, super-volcanic Io might most resemble Dante’s Inferno, but we have a new candidate for most hellish earth-like world and it’s not even a close call:
Red Orbit — According to the Harvard scientists involved with the discovery, Kepler 78b is the first known Earth-sized planet that also shares an Earth-like density. While the exoplanet is only about 20 percent larger than Earth in terms of size and volume, it weighs almost twice as much – suggesting an Earth-like composition of iron and rock.
“It’s Earth-like in the sense that it’s about the same size and mass, but of course it’s extremely unlike the Earth in that it’s at least 2,000 degrees hotter,” said team member Josh Winn, an associate professor of physics at MIT. “It’s a step along the way of studying truly Earth-like planets.”
The determination of the planet’s orbit and size was made by analyzing the light given off by its host star as the planet passes in front of it in a phenomenon known as a transit. The researchers recorded a transit each time the star’s light dipped, and calculated the amount of dimming to determine the planet’s size.
It may seem strange that the very first rocky-iron earth-sized exoplanet we find is so close to its star. Until you stop and think about how it was detected. NASA’s Kepler is basically a horrendously accurate photometer connected to special telescope. It’s so accurate it can detect minute changes in brightness as a tiny planet passes in front of its sun. If a planet is only a million miles away from a star a million miles wide, the odds of it passing in front of that star’s disk as seen from our perspective many light-years away is much higher than it would be for a planet orbiting at a more familiar distance.
How in the hell 78b ended up a million miles away, with an eight-and-a-half hour year, is a much bigger mystery. We have only the most rudimentary understanding of early solar nebula dynamics. We’re only just now starting to piece together clues from important events like Late Heavy Bombardment or the Giant Impact theory that shaped our own solar system and planets, and those clues are right next door by comparison to exo-systems. Odds are it has to do with chaotic proto-planetary formation in the early accretion disk around a new star. Some objects gang up on others and kick them into higher orbits or clear out of the system, to roam the galaxy as rogue planets until the last stars wink out. Others get kicked in, Kepler 78b is probably one of those.
But it won’t last long, the planet is on a death spiral. It will become part of it’s star in a relatively short time by astronomical standards, leaving virtually no direct trace behind. If something similar happened in the early history of our own solar system, it would be extremely difficult and perhaps impossible to reliably infer such a planet ever existed.