'Life-friendly' planets traced...or possibly, say Spanish astronomers

Both planets orbit the star known as Teegarden, a red dwarf  around 12.5 light years from the Solar System, and both have a mass similar to Earth, according to co-researcher of the CARMENES Consortium, Pedro J. Amado.

“If there's water in liquid form, this greatly improves the probabilities of a planet's housing life as we know it on Earth,” says Amado.

“We already know that for life to develop on our own planet, oceans and liquid water have played a really important role.”

Teegarden is much smaller and less bright than the sun which the Earth goes around, and is only about half as hot – 2,600ºC compared with the 5,500ºC of the sun at the centre of the Solar System – and is 1,500 times weaker with 10 times less mass.

Because of these factors, the two exo-planets found orbit their sun at a much closer distance than that between the Earth and the brightest star in the Solar System.

Teegarden B, the closest planet to the Teegarden star, completes its orbit every 4.9 Earth days, whilst the more distant planet, Teegarden C, orbits the star in 11.4 days – meaning each planet's year is less than a week and less than a fortnight respectively.

Both orbit the Teegarden star within what is known as the 'habitable zone', or at a distance where the climate is least hostile and more likely to be suitable for life to form.

“Until now, no exo-planet has ever been found with liquid water on it,” Amado explains, “although water in steam form has been found in the atmospheres of some, and other exo-planets detected have a density which would be conducive to possibly holding liquid water.

“We have not ruled out, either, that the system orbiting the Teegarden star may be made up of more planets besides the two we have found.”

But it will not be until the 2020s when investigations can finally be refined, when the giant telescopes needed for the team's observations are completely built.

They include an E-ELT (Extremely Large Telescope) and a TMT (Thirty-Metre Telescope), which will be able to show clearly whether Teegarden B and Teegarden C have water on their surface.

The CARMENES Consortium, which has traced the two planets, is a unique instrument in the world, and one of its main telescopes is based in the province of Almería.

As a project, it suffered major funding cuts a few years ago which threatened its future, but the CARMENES' discovery has suddenly made it considerably more viable.

Although the CARMENES system has already contributed to other discoveries, such as that of a planet orbiting the star Barnard, its latest findings are a complete first, says Amado.

“This is the first time we've managed to detect such small planets using this radial velocity technique – they're the two planets with the smallest mass and with the most Earth-like mass orbiting ultra-cold stars found to date employing these techniques.”

The 'radial velocity' technique involves studying the light emitted from a star.

“We always have to observe, watch and take data about the star, because that's what we see – planets, using these indirect techniques, are not visible,” Amado reveals.

The speed with which the star 'pulsates' or 'shimmers' when a planet orbits it is measured and, if this speed changes periodically and there are no other elements that could explain these variations, it is inferred that the alteration in speed is produced by the presence of a planet.

CARMENES was co-developed by the Andalucía Astronomy Institute (IAA) which produced the above artist's impression of the layout of Teegarden and its two known exo-planets.