Kapteyn’s star and its planets likely come from a dwarf galaxy now merged with the Milky Way. These streams of stars are characteristic of a galactic merging event. Image: University of California – Irvine : Victor Robles, James Bullock and Miguel Rocha University of California – Santa Cruz : Joel Primack

An international team of scientists have found two new planets, one in the right position to allow liquid water on its surface, around the ancient red dwarf star Kapteyn.

Discovered at the end of the 19th century and named after the Dutch astronomer who discovered it (Jacobus Kapteyn), Kapteyn’s star is the second fastest moving star in the sky and belongs to the galactic halo, an extended cloud of stars orbiting our galaxy.

With a third of the mass of the sun, this red-dwarf can be seen in the southern constellation of Pictor with an amateur telescope.

The astronomers used new data from HARPS[1]spectrometer at the ESO’s La Silla observatory in Chile to measure tiny periodic changes in the motion of the star.

Using the Doppler Effect, which shifts the star’s light spectrum depending on its velocity, the scientists can work out some properties of these planets, such as their masses and periods of orbit.

“We were surprised to find planets orbiting Kapteyn’s star,” says lead author Guillem Anglada-Escude from Queen Mary University of London’s School of Physics and Astronomy.

“Previous data showed some moderate excess of variability, so we were looking for very short period planets when the new signals showed up loud and clear.”

Based on the data collected, the planet Kapetyn b is at least five times as massive as the Earth and it orbits the star every 48 days.

This means the planet is warm enough for liquid water to be present on its surface.

The second planet, Kapteyn c is a more massive super-Earth and quite different. Its year lasts for 121 days and astronomers think it’s too cold to support liquid water.

Typical planetary systems detected by NASA’s Kepler mission are hundreds of light-years away. Kapteyn’s star is the 25th nearest star to the sun and it is only 13 light years away from Earth.

Kapteyn’s star was born in a dwarf galaxy absorbed and disrupted by the early Milky Way.

The likely remnant core of the original dwarf galaxy is omega Centauri, an enigmatic globular cluster 16,000 light years from earth which contains hundreds of thousands of similarly old suns.

This sets the most likely age of the planets at 11.5 billion years; which is 2.5 times older than Earth and ‘only’ 2 billion years younger than the universe itself (around 13.7 billion years).

Dr Anglada-Escude says:

“It does make you wonder what kind of life could have evolved on those planets over such a long time.”

The discovery has prompted renowned science fiction writer Alistair Reynolds to write a short story.

Sad Kapteyn describes the arrival of a robotic interstellar probe reaching Kapteyn’s planetary system, and a first exploratory survey of its planets in the far future.

Alastair Reynolds worked as an astronomer at the European Space Agency and later he became a full time science fiction writer.

Copyright remains with Alastair Reynolds 2014. Read the full story here.

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