Two Exoplanets Discovered Orbiting Star 13 Light-years From Earth

Posted on June 4, 2014

Two exoplanets have been discovered orbiting a very old star by an international team of astronomers. The planets are orbiting Kapteyn's Star, which is located about 13 light-years from Earth. It is the 25th nearest star to our sun. The star and its planets are estimated to be about 11.5 billion years old, which is 2.5 times older than Earth and 2.2 billion years younger than the Universe.

One of the planets, Kapteyn b, is potentially habitable. The astronomers say it is at the right distance to allow liquid water to exit on its surface. An artist's conception of the planets orbiting Kapteyn's Star is pictured above and an artistic representation of Kapteyn b from the Planetary Habitability Laboratory (PHL) is pictured below. The PHL reports that Kapteyn b is the oldest known potentially habitable exoplanet.

The team of astronomers used data from the HARPS spectrometer at the European Southern Observatory's La Silla observatory, the Planet Finding Spectrometer at the Magellan/Las Campanas Observatory in Chile, and the HIRES spectrometer at Keck Observatory in Hawaii to measure tiny periodic changes in the motion of the star. The Doppler Effect enabled the astronomers to calculate properties of the planets, include their masses and orbits.

Dr. Guillem Anglada-Escude, a former Carnegie postdoc, now at the Queen Mary University of London, and lead author of the study, says in a statement, "We were surprised to find planets orbiting Kapteyn's star. Previous data showed some irregular motoin so we were looking for very short period planets when the new signals showed up loud and clear."

Kapteyn b, the planet that might support water, has an orbit of 48 days and a mass at least five times that of the Earth. The second planet, Kapteyn c, is a massive super-Earth with an orbit of 121 days. Astronomers think it is too cold to support liquid water.

Pamela Arriagada, the second author of the study, and a Carnegie postdoctoral researcher, says, "Finding a stable planetary system with a potentially habitable planet orbiting one of the very nearest stars in the sky is mind blowing. This is one more piece of evidence that nearly all stars have planets, and that potentially habitable planets in our Galaxy are as common as grains of sand on a beach."

Anglada-Escude also says, "It does make you wonder what kind of life could have evolved on those planets over such a long time."

The research team's finding have been accepted for publication in the Monthly Notices of the Royal Astronomical Society.

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