Astronomers Spot First Ever Hot Jupiter Exoplanet in the Visible Light Spectrum

First Posted: Apr 22, 2015 07:38 AM EDT

Astronomers have spotted the first ever exoplanet in the visible light spectrum. The exoplanet, called 51 Pegasi b, is located just 50 light-years from Earth in the constellation of Pegasus.

The exoplanet was first discovered in 1995. In fact, it was the first ever confirmed exoplanet to be found orbiting an ordinary star like the sun. It's a hot Jupiter, which is a class of planets that are similar in size and mass to Jupiter, but orbit much closer to their parent stars.

Since this exoplanet was first discovered, more than 1,900 exoplanets in 1,200 planetary systems have been confirmed. Now, astronomers have taken another look at 51 Pegasi b and have seen it for the first time ever in visible light.

The most widely used method to examine an exoplanet's atmosphere is to observe the host star's spectrum as it's filtered through the planet's atmosphere during transit, a technique known as transmission spectroscopy. Another technique is to watch the system when the star passes in front of the planet, which primarily provides information about the exoplanet's temperature.

This new method actually doesn't depend on finding a planetary transit, and so can potentially be used to study many more exoplanets. In fact, it allows the planetary spectrum to be directly detected in visible light. The host star's spectrum is used as a template to guide a search for a similar signature of light that is expected to be reflected off the planet as it describes its orbit.

"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," said Jorge Martins, one of the researchers, in a news release. "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."

The exoplanet, in this case, has a mass about half that of Jupiter's and an orbit with an inclination of about nine degrees to the direction of Earth. The planet also seems to be larger than Jupiter in diameter and highly reflective.

The findings are published in the journal Astronomy & Astrophysics.

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