Exoplanet’s atmosphere is directly detected

The observations were the first to look at light reflected off the planet

Since 51 Pegasus b was discovered in 1995 thousands of other exoplanets have been discovered.
Credit: ESO/M. Kornmesser/Nick Risinger (skysurvey.org)

By Elizabeth Pearson

The first ever direct spectra of an exoplanet has been observed using the High Accuracy Radial Velocity Planet Searcher (HARPS) on ESO’s La Silla Observatory in Chile.

This is the first time that a light reflecting off a planet has been captured directly, rather than by interpreting the light from the host star. The new technique will allow even more of the thousands of currently known exoplanets to be studied.

The planet, 51 Pegasus b, was discovered in 1995, and was the first exoplanet confirmed to be in orbit around a star similar to our Sun. It is a hot Jupiter, meaning that it is a gas giant but orbiting very close to its star.

The method of looking at the atmospheres of distant planets most commonly used at the moment studies exoplanets by looking at the change in the host star's light as a planet passes in front of it. By working out what wavelengths of light have been absorbed to interpret what elements are in the planet’s atmosphere. However, this only works for planets that pass directly in front of the star from the perspective of Earth.

Direct detection does not have this draw back, opening up hundreds more exoplanets for study. However, the signal from the planet is tiny. It was previously thought that it would be swamped by noise, so this observation with HARPS is important to proving the method will work.

“This type of detection technique is of great scientific importance, as it allows us to measure the planet’s real mass and orbital inclination, which is essential to more fully understand the system,” says Jorge Martins, from the Instituto de Astrofísica e Ciências do Espaço. “It also allows us to estimate the planet’s reflectivity, or albedo, which can be used to infer the composition of both the planet’s surface and atmosphere.”


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