Hertfordshire scientists discover two potentially habitable planets

The discovery was made by an international group of astronomers

A new study by an worldwide team of astronomers, led by the University of Hertfordshire, reveals that tau Ceti, the nearest Sun-like star (about 12 light years away from the Sun), has four Earth-sized planets orbiting it - two of which could be habitable.

Stars the size of the Sun are the best targets for finding habitable Earth-seized planets.

But as phys.org explains, smaller stars like Proxima Centauri - the closest star to the sun at only 4.2 light-years away - tend to have habitable zones so close to their surface that any planet orbiting sufficiently close to it will be tidally-locked, meaning that the same side of the planet always faces the star, rendering it an uninhabitable world of temperature extremes.

The two "super-Earths" are located in the habitable zone of the star - the area that is not too hot and not too cold - which scientists believe could mean they support liquid surface water.

These planets are detected by observing the wobbles in the movement of tau Ceti.

Spectroscopy is a technique that, according to NASA's website "measures light that is emitted, absorbed, or scattered by materials".

The researchers say that if this method can be refined further to the point where we can detect variations as minor as 10 cm/s, we'll pass a threshold where we can definitely tell the gravitational pull of exoplanets from noise in the signal generated by stellar fluctuations.

A study published in 2013, with research by the same team, lay the groundwork for the breakthrough. It also revealed that two of the planets, Tau Ceti e and Tau Ceti f, lay inside the star's habitable zone.

But keen space tourists shouldn't pack their bags just yet.

Neither of Tau Ceti's "super-Earths" lie in the center of its habitable zone. But even if none of tau Ceti's planets are remotely habitable, the existence of such nearby cosmic neighbors would be a boon to search for life beyond Earth. "Our detection of such weak wobbles is a milestone in the search for Earth analogs and the understanding of the Earth's habitability through comparison with these analogs", Feng said. Since then we've painstakingly improved the sensitivity of our techniques and could rule out two of the signals our team identified in 2013 as planets.

"But no matter how we look at the star, there seems to be at least four rocky planets orbiting it", Dr Tuomi said. Little is know about the conditions within Tau Ceti and while both planets have potential there is still every chance that they're inhospitable for external reasons such as constant bombardment from asteroids. While they couldn't support water on their surfaces, they're among the smallest, Earth-sized planets ever detected around a nearby Sun-like star, with masses as low as 1.7 times the amount of Earth's mass.

The astronomers analyzed data on the wavelength of star light received from the European southern Observatory in Chile and the Keck Observatory on Mauna Kea, Hawaii.

Tuomi is one of the co-authors on a paper detailing the discovery, which has been accepted for upcoming publication in the Astrophysical Journal.

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