A monster week for extrasolar planets
It’s been a busy week for extrasolar planets. At the summer meeting of the American Astronomical Society in Boston, Harvard astronomers have been wowing the attendees with a host of exciting new results. The first is the so-called ‘Godzilla’ planet (or Mega-Earth), Kepler-10c which was first discovered back in 2011. An analysis of its composition by Xavier Dumusque and collaborators shows it to be rocky, like the Earth, but about 17 times more massive than our little planet. This is a pretty amazing find, because normally, planets as beasty as this are not made of rock, but are more similar to the gas giants in our solar system, like Neptune, Jupiter and Saturn. This is because they are so massive, they can easily suck up any surrounding gas, forming a gas-dominated planet. Kepler-10c is thus something of a mystery, and will doubtless attract much attention from observers and theorists alike over the next few years.
Harvard astronomers led by Gongjie Li have also predicted the time of death for two planets orbiting Kepler-56.The planets, Kepler-56b and and -56c, have orbits of only 10-20 days around their host star, and are so close, that the expanding star will soon boil off their atmospheres before swallowing them whole. The digestion process will take about 130-150 million years in total. All is not lost for the system though, as its 3rd planet, Kepler-56d, is located further out and will live on for many years yet.
Hot on the heels of stars digesting planets, Lars A. Buchhave (also at Harvard) likened exoplanets to Neopolitan ice cream. In our solar system, we have only two types of planets: Rocky - like the Earth, and gas giants - like Saturn, Jupiter and Neptune. Buchhave has used data from the Kepler telescope to show that there is a 3rd type of planet: the gas dwarf. These objects have sizes somewhere between 2 and 4 times the mass of the Earth, and have rocky cores, but thick, soupy atmospheres of Hydrogen and Helium. The team also showed that the number of metals in the host star correlates with the type of planet formed in their system. Stars with similar metal contents to our Sun tend to make rocky planets. Those with gas dwarfs tend to have a few more metals than our sun, and those with gas giants tend to be the most rich in metals.
Finally, the guys at Harvard put a dampener on our search for life in the Universe. The most common star-type in our galaxy is the red dwarf star, and if we can find planets around them within the habitable zone (i.e., the right distance from a star to have right conditions for Earth-like life), then this would indicate that life in our Galaxy may be very common. But, from computer models run by Ofer Cohen and collaborators, such planets would be so close to their host star that they would experience extreme space weather making it very difficult, if not impossible, for life to evolve. The planet would be bombarded by the stellar winds from its host stars, causing spectacular aurorae, but also: death by radiation. In addition, the planet would probably be tidally locked (like our moon is to us), so one side would be permanently in darkness, the other in sun. This would cause a huge temperature difference between the night and day sides, generating hurricane strength winds at the surface. All in all, not hospitable for soft, wimpy humans like us.