→ Widely unknown Exoplanet Astronomer

Credit: NASA

The Exoplanet group lead by Dr. David Sing at the University of Exeter has been awarded nearly 200 hours of telescope time at the Hubble Space Telescope. As a PhD student of his this means a busy time ahead of me.  The awarded telescope time will be used to study the atmospheres of Exoplanets.

Dr. David Sing:

“This is one of the biggest exoplanet research programmes ever using the Hubble Space Telescope. It is a major coup for the University of Exeter to have secured such a significant amount of time on the world’s best telescope”.

“Astronomers have now detected hundreds of exoplanets and we now know that some of these planets have extreme environments, unlike anything in our own solar system. Everything we have discovered so far about these planets has been puzzling so I am expecting the unexpected.”

Further reading: BBC News, University of Exeter and University of Arizona

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