For the first time, an astronomer using a ground-based telescope has succeeding in observing and measuring at least part of the atmosphere on an exoplanet, or planet lying outside our solar system. In this particular case, a planet that lies a good 63 light years away, a distance which might help underscore the scale of the achievement.
University of Texas at Austin professor Seth Redfield observed the planet, 20 times more massive than Jupiter, as it was passing in front of its local star, a point known as the "transit" which gives the ability to observe otherwise invisible properties. A French astronomer discovered the same planet in 1994, during a similar transit period.
Exoplanet atmospheres have been observed before using the same method by an instrument on the Hubble Telescope. Unfortunately, this tool, called the Space Telescope Imaging Spectrograph (STIS), has broken, without an easy option for repair. So for now, scientists are stuck with what they have on the ground.
Luckily, Redfield has now proved that this isn't such a terrible thing, from a strictly exoplanet-atmosphere detection perspective.
He studied the planet over the course of 11 different transits over the course of a year, using a theoretically simple (although in practice quite complicated) idea:
Easier said than done. The planet's passage blocks just 2.5 percent of the star's total light. Add in the atmosphere and you subtract maybe another .3 percentage points.
Redfield and others had guessed that the planet's atmosphere held sodium, so he looked at the specturm of light emitted by the star that would be absorbed by sodium atoms. And indeed, the planet appeared about 6 percent larger when looking at the "shadow" cast by the planet in the range of light absorbed by this element.
Thus, Redfield determined, the atmosphere does indeed have a substantial sodium component. Not bad for a measurement at 63 light years. Next up? Studying whether potassium and hydrogen cast similar atmospheric shadows.
While interesting, the real goal is to find Earth-like planets, with atmospheres potentially conducive to supporting life. This technique can be used for that as well, astronomers say.
Texas Astronomer Makes First Ground-Based Detection of Extra-Solar Planet Atmosphere with HET [McDonald Observatory]
(Image: The Hobby-Eberly Telescope at McDonald Observatory, used for
Redfield's observations. Credit: Marty Harris/McDonald Observatory.)
