For the first time, astronomers have detected a visible-light spectrum directly from an exoplanet.
The researchers used the HARPS planet-hunting machine at the European Southern Observatory’s La Silla Observatory in Chile. They have made the first-ever direct detection of the spectrum of visible light reflected off an exoplanet. The spectrum of visible light was reflected off exoplanet 51 Pegasi b, which lies some 50 light-years from Earth in the constellation of Pegasus.
The exoplanet was discovered in 1995, and will forever be remembered as the first confirmed exoplanet to be found orbiting an ordinary star like the Sun. It is also regarded as the archetypal hot Jupiter — a class of planets now known to be relatively commonplace, which are similar in size and mass to Jupiter, but orbit much closer to their parent stars.
Jorge Martins from the Instituto de Astrofísica e Ciências do Espaço (IA) and the Universidade do Porto, Portugal, led the team who made this discovery. Martins currently is a PhD student at ESO in Chile.
The most-widely used method to examine an exoplanet’s atmosphere is to observe the host star’s spectrum as it is filtered through the planet’s atmosphere during transit — a technique known as transmission spectroscopy. However, the technique sed with 51 Pegasi b does not depend on finding a planetary transit, and so can potentially be used to study many more exoplanets.
51 Pegasi b has a mass about half that of Jupiter’s and an orbit with an inclination of about nine degrees to the direction to the Earth. The planet also seems to be larger than Jupiter in diameter and to be highly reflective. These are typical properties for a hot Jupiter that is very close to its parent star and exposed to intense starlight.
“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. 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,” Martins said in a statement.
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