I’ve come down to listen to a General Interest seminar about climate change given by retired physics professor, but I’ve discovered it’s next week. I’ll have to wait to find out if it satisfies the stereotype. Since there is no point in going back up to my office before my next meeting, I thought I would mention a paper of ours that has got quite a lot of press coverage.
The paper is about Kepler-107, an exoplanetary system already known to host 4 planets. We collected a lot of high-precision spectra which allowed us to determine the radial velocity of the host star and, consequently, estimate the masses of the planets. The observations were made using an instrument on the Telescopio Nazionale Galileo, a telescope operated by the Italian National Institute for Astrophysics (INAF), researchers from which led the paper. I did an extra radial velocity analysis and carried out some dynamical simulations to test the stability of the planetary system.The reason that this is an interesting system is that the two inner planets (Kepler-107b and Kepler-107c) have very similar radii, but very different masses. Kepler-107c is more than twice the mass of Kepler-107b. If Kepler-107c were the innermost planet, then you could explain this through it being born in an environment that is heavily bathed in radiation from the central star. Since it orbits beyond Kepler-107b, this explanation seems implausible. What is most likely is that Kepler-107c underwent some kind of giant impact that stripped part of the mantle, leaving behind a dense (probably iron) core that now makes up 70% of its mass. Kepler-107b, on the other hand, has a composition more like that of the Earth, with the core making up around 30% of its mass.
There is evidence for giant impacts in our Solar System; we think that the Moon formed through a collision between the Earth and a Mars-sized body. However, we think this is the first convincing evidence for a giant planetary impact occuring outside our Solar System.