Astronomers led Dr Guillem Anglada-Escude from Queen Mary University of London, UK, have announced the discovery of two exoplanets circling a very old nearby star known as Kapteyn’s star.
This artistic representation shows the potentially habitable exoplanet Kapteyn b and the globular cluster Omega Centauri in the background. It is believed that this cluster is the remaining core of a dwarf galaxy that merged with our own Milky Way Galaxy billions of years ago bringing Kapteyn’s star along. Image credit: PHL / UPR Arecibo / Aladin Sky Atlas.
Discovered in 1897 and named after the Dutch astronomer Jacobus Kapteyn who discovered it, Kapteyn’s star is the second fastest moving star in the sky.
It came within 7 light-years of the Sun about 11,000 years ago and has been moving away since that time.
Right now, this red dwarf star is 13 light-years away and is the 25th nearest star to the Sun. It has a magnitude of 9 and can be seen in the southern constellation of Pictor with an amateur telescope or binoculars.
This image shows Kapteyn’s star (center). Image credit: Digital Sky Survey / Centre de Données astronomiques de Strasbourg.
Scientists say Kapteyn’s star belongs to the Galactic halo – an extended cloud of stars orbiting our Milky Way Galaxy, and likely came from a dwarf galaxy now merged with our Galaxy.
In order to measure tiny periodic changes in the motion of the star, Dr Anglada-Escude and his colleagues used data from the HARPS spectrometer at the ESO La Silla observatory in Chile.
They also analyzed data from two other spectrometers – HIRES at Keck Observatory and PFS at Magellan/Las Campanas Observatory – to secure the results.
The Habitable Exoplanets Catalog now has 22 planets including Kapteyn b, the oldest and second closest to Earth potentially habitable exoplanet. Image credit: PHL / UPR Arecibo / Aladin Sky Atlas.
“When we initially analyzed the data for Kapteyn’s star a few years ago we found a moderate excess of variability which we did not expect to find in such an old star, so we were on the lookout for planets. Once we had collected enough data the new signals showed up loud and clear,” explained Dr Anglada-Escude, who is the first author of a paper published in the Monthly Notices of the Royal Astronomical Society Letters (arXiv.org version).
“We were surprised to find planets orbiting Kapteyn’s star,” he said.
The newly found exoplanets have been dubbed Kapteyn b and Kapteyn c.
Kapetyn b is a so-called super-Earth. It orbits the star every 48 days and has a mass of about 5 times that of Earth.
Kapteyn’s star and its planets likely come from a dwarf galaxy now merged with our Milky Way Galaxy. Image credit: Victor H. Robles / James S. Bullocks / Miguel Rocha.
The planet is probably colder than Earth given a similar atmosphere. However a denser atmosphere could easily provide for equal or even higher temperatures.
Based on its stellar flux and mass, the Earth similarity index of Kapteyn b is comparable to Kepler-62f and Kepler-186f.
Kapteyn b is about 11.5 billion years old, over twice as old as Earth. Given its age, the planet has had plenty of time to develop life, as we know it.
It is now the oldest potentially habitable exoplanet discovered to date.
Kapteyn c is a massive super-Earth in comparison. Its year lasts for 121 days and astronomers think it’s too cold to support liquid water.
“At the moment, only a few properties are known for these planets, but by measuring their atmospheres with next-generation instruments which are under construction, we will try to establish whether these planets are water-bearing worlds,” concluded Dr Mikko Tuomi, an astronomer with from the University of Hertfordshire’s Center for Astrophysics Research and a co-author of the discovery.
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G. Anglada-Escude et al. Two planets around Kapteyn’s star: a cold and a temperate super-Earth orbiting the nearest halo red-dwarf. Monthly Notices of the Royal Astronomical Society Letters, published online June 03, 2014; doi: 10.1093/mnrasl/slu076
