A group of Japanese astronomers have recently identified what they consider to be a super-Earth, possessing a water-rich atmosphere, orbiting its host star. The train of thought seems to be, if scientists can determine the atmospheric composition of these exoplanets, their mysterious origins and evolution might be deduced within the future.
Super-Earth’s are considered a relatively new type of exoplanet (a planet that orbits a star outside of this Solar System). The term super-Earth actually refers to the mass of the planet, which is typically much greater than that of Earth, but bears little reflection of the atmospheric conditions of the planet.
A super-Earth’s mass and radius is typically bigger than Earth, but no larger than that of our Solar System’s sizable ice planets, Neptune and Uranus. The actual atmosphere of this exoplanet has, until now, has remained shrouded in mystery.
The very first super-Earths were discovered during 1992 around a rotating neutron star, situated a thousand light years from our Sun, by Aleksander Wolszczan and Dale Frail.
During the latest study, researchers attempted to use two cameras of the Subaru Telescope of the National Astronomical Observatory of Japan, situated in Hawaii. The cameras include the Faint Object Camera and Spectrometer (FOCAS), constituting a spectrograph and visible-light camera, and the Subaru Prime Focus Camera (Suprime-Cam), housing an 80-megapixel visible-light camera device. A blue filter was utilized to demonstrate the transit of the exoplanet, classified as super-Earth GJ 1214 b, as it passed in front of its host star.
To establish whether some of these super-Earths had their own hydrogen or water-rich atmospheres, the group decided to turn their attention towards an exoplanet that is 40 million light years away from Earth situated within Ophiuchus, a constellation that is northwest of the Milky Way.
During GJ 1214 b’s transit, the degree of Rayleigh scattering was measured. Rayleigh scattering occurs when wavelengths of light or electromagnetic radiation interface with particles, most typically observed when travelling through particles of either gaseous or liquid form. When the light moves through this medium, whether it be solid, liquid or gas, it does not experience any change in wavelength.
When the planet makes this transit, the host star’s transit depth can be measured to determine the exoplanet’s atmospheric constituents, a phenomenon that appears greater in the blue wavelength, as opposed to the red wavelength.
According to a press release from the National Astronomical Observatory of Japan, one of the greatest complications involved trying to measure this Rayleigh scattering, as the host star was very faint in blue light. The Subaru Telescope’s sheer power helped the group to overcome these technical difficulties, however, and they were able to measure the scattering at very high sensitivity.
The above image aptly demonstrates the different forms of scattering that occurs between planets with different atmospheric compositions. Firstly, the top image reveals the typical scenario in a hydrogen-rich atmosphere; blue light scatters, whilst red light remains relatively unaffected.
Next, the middle image shows almost the same transit depths for red and blue wavelengths, as the reach of the water-rich atmosphere is small, and relatively close to the planet’s surface; on this basis, Rayleigh scattering is far weaker.
Finally, in an extensive, cloudy atmosphere the same transit depths are seen across the board, with the majority of the light not making it through the afore-said clouds.
The Water-Rich Atmosphere
The authors substantiate their hypothesis with previous research, conducted by a pair of astronomers (Howe and Burrows), who looked at the theoretical spectra for the exoplanet, alongside a number of additional super-Earths, during 2012.
Based upon these datasets, and the lack of Rayleigh scattering, the Japanese astronomers have decided that GJ 1214 b is likely to have a water-rich atmosphere; however, the group remain somewhat on the fence, maintaining that they haven’t ruled out the slight possibility that it could still be a hydrogen-rich exoplanet, instead.
They also plan to continue their research endeavors to cement their existing knowledge. Meanwhile, the team await the arrival of the Transiting Exoplanet Survey Satellite (TESS), which is due for deployment in 2017 by NASA, and is also being partially funded by Google. TESS will carry out a two year mission to explore the transit of various exoplanets across their host stars, using a series of wide-angle telescopes and has the potential to provide much more research data in the field. Who knows, maybe there are many more super-Earth exoplanets, with water-rich atmospheres, just waiting to be identified.
By: James Fenner