→ Widely unknown Exoplanet Astronomer

There has recently been a lot of talk in the media about the discovery of new Super-Earths (ESO, BBC). The Kepler team has also announced that they will be revealing new discoveries tomorrow. In this post I thought I might write about the Super-Earths Kepler has found so far.

Super-Earths are a class of exoplanets with masses between 1-10 times the mass of Earth. The study of Super-Earths are of great interest as there is no planet in this mass and size regime in our solar system.

Kepler-10 b – The smallest Super-Earth

Kepler-10 b is the smallest Super-Earth discovered to date with a Radius of 1.4 Earth radii. It is also the first rocky planet found by the Kepler spacecraft and also the first terrestrial planet found outside our solar system. Here is a video by NASA about this exoplanet:

Kepler-11 – A planetary system with multiple Super-Earths

The Kepler-11 planetary system has 4 Super-Earths (so far) and is the most compact exoplanet system discovered to date. Kepler-11 is a remarkable planetary system whose architecture and dynamics provide clues to its formation. More information on this in the discovery paper.

Kepler-9 d – Thought to be a Super-Earth

Kepler-9 d is thought to be a Super-Earth. I say “thought to be” as current spectroscopic observations are still insufficient to establish its mass. The discoverers of the planet led by Torres, G say:

Based on several realistic estimates of this frequency, we conclude with very high confidence that this small signal is due to a super-Earth-size planet (Kepler-9 d) in a multiple system, rather than a false positive.

Secret companion found via Transit Timing Variations

Worth mentioning here is last weeks news of the discovery of Kepler-19 b. What made this discovery so special wasn’t so much the exoplanet Kepler-19 b but that a companion of this planet, Kepler-19 c was found using transit timing variations (mentioned in my post here). In short, transit timing variations deals with inferring the presence of one or more planets due to timing variations in the expected transit time. For this to be possible, very high quality data is needed, something Kepler provides.  Although Kepler-19 is not a Super-Earth it is likely that the transit timing variations technique will discover more Super-Earths in the future.

The exoplanet GJ1214b is a transiting super-Earth which orbits a relatively bright M-star (I=11.52). It’s observed transit depth is 1.37 % [Kempton et al.].

We have no super-Earths in our Solar System thus the bulk composition of the planets and the type of atmospheres they have is still largely unknown. GJ1214 b has a rather low average density which lead astronomers to believe that it has a significant atmosphere. It is thought that either the planet has a thick hydrogen atmosphere or that it is a water-rich planet with a thick steam atmosphere. A combination of these two scenarios are also possible. More accurate measurements of the mass and radius of GJ1214b (thus a more accurate average density) will not settle the dispute of what the atmosphere is made up of as there are significant degeneracies. The only way to break this degeneracy is to conduct observations of the planet’s atmosphere. The most effective way to do this is through transmission spectroscopy where the idea is to compare the amplitude of spectral features and the mean molecular weight of the planet’s atmosphere [Miller-Ricci]. This results from the fact that

The depth of the transmission spectral features atmospheric scale height  1/ mean molecular weight

GJ1214 b is the first super-Earth to have its atmosphere analysed. GJ1214 is about 6 times more massive than Earth. Credit: ESO/L. Calçada

A hydrogen-rich atmosphere would show spectral features in transmission with amplitudes of 0.1 -0.3% relative to light from the host star whereas a water atmosphere would only show spectral features in transmission at the 0.01% level (about 100 times less) which is undetectable with the most current instruments.

Artist impression of GJ1214b transiting infront of GJ1214. Credit: ESO/L. Calçada

Further reading:

• The Atmospheres of Extrasolar Super-Earths
• The Atmospheric Signatures of Super-Earths: How to Distinguish Between Hydrogen-Rich and Hydrogen-Poor Atmospheres
• The Nature of the Atmosphere of the Transiting Super-Earth GJ 1214b