First exoplanet seen with reflected visible light

A "hot Jupiter" planet has been spotted using visible light from 50 light-years away.
By Kathy Fey | Apr 22, 2015
An exoplanet known as 51 Pegasi b has been detected with visible light a first in the history of space observation beyond our solar system. This achievement of capturing a visible-light spectrum image from 50 light-years out may hail a new era of similar observations of faraway planets.

According to Discovery News, astronomers used the HARPS component on the European Southern Observatory's 3.6-meter telescope, located at the La Silla Observatory in Chile, to capture the image.

The planet that scientists observed is a type known as a "hot Jupiter" a gas giant that orbits relatively close to its parent star. 51 Pegasi b was first spotted in 1995, gaining the distinction of being the first planet discovered beyond our solar system that orbited a Sun-like star. The most recent data collected by scientists suggests that the exoplanet is slightly larger than Jupiter but about half as massive, and it has a highly reflective surface.

Since the initial discovery of 51 Pegasi b, over 1900 exoplanets have been found, but until now, astronomers could not observe the features of those planets in the visible light spectrum. Scientists most commonly gather data regarding an exoplanet's atmosphere by waiting until the planet passes in front of its parents star and then observing how the star's light spectrum is filtered as it passes through the planet's atmosphere a technique called transmission spectroscopy.

As outlined in a EurekAlert report, another method of detecting just the temperature of an exoplanet is to view it when on the far side of its star. The new method of observation employed with the HARPS instrument, however, does not rely on planetary transit, and it reveals planetary characteristics not detectable by other methods.

Scientists are impressed with the ability of the HARPS instrument to pick up the planet's reflected light despite the planet's dimness relative to the nearby star and despite other sources of interstellar interference.

"This type of detection technique is of great scientific importance, as it allows us to measure the planet's realmass 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." Jorge Martins of the European Southern Observatory said.

The HARPS instrument has a limited range of use for this planet-spotting technique, and the fact that it performed so well is highly promising. Larger telescopes such as ESO's Very Large Telescope and the European Extremely Large Telescope could reveal much more about the many exoplanets scattered throughout the galaxy.

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