An global team of astronomers, led by the University of Hertfordshire, has discovered two potentially habitable planets.
Past year we learned the nearest star beyond our sun has a planet about the size of Earth, but it's very different than our solar system and not an ideal candidate for finding alien life. Two of them are super-Earths located in the habitable zone* of the star and thus could support liquid surface water. This "wobble" method of planet finding measures the influence of gravitational interaction on a star.
Dr Fabo Feng, research fellow at the University of Hertfordshire and lead researcher on the study, said: 'We're getting tantalisingly close to observing the correct limits required for detecting Earth-like planets.
"Our detection of such weak oscillations is an important milestone in the search for analogues of the Earth and understanding the viability of the Land by comparison with them".
Earth-sized planets, due to their similarity to the Sun.
Download the News Nation Mobile App and stay connected with top stories from India and around the world. A massive disc of debris around the star means that the planets are likely being bombarded by asteroids and comets, making it hard for life to emerge. Much larger stars than the sun tend to be more unstable, releasing radiation and pulsing novae of heat that would make the development of life on a planet over millions of years impossible.
The two other, smaller planets fall outside this temperate space, orbiting the star significantly closer. And, as before, the claim that tau Ceti e and f might reside in the habitable zone is already being contested.
The researchers painstakingly improved the sensitivity of their techniques and were able to rule out two of the signals the team had identified in 2013 as planets.
Sun-like stars represent the best opportunity to find planets suitable for life outside the Solar system. Numerous other "potentially habitable" exoplanets discovered to date orbit dim red dwarf stars, which, for a variety of reasons, could prove hostile to life.
Meanwhile astronomers from Nasa using a telescope operated by Liverpool John Moores University discovered seven planets which are similar in size to Earth, rocky and probably have oceans.
"Despite how we look on the star, it seems that she has at least four rocky planets", said Dr. Tuomi.
"We're slowly learning to tell the difference between wobbles caused by planets and those caused by stellar active surface. This enabled us to essentially verify the existence of the two outer, potentially habitable planets in the system", said Mikko Tuomi from the University of Hertfordshire. Unlike more common smaller stars, such as the red dwarf stars Proxima Centauri and Trappist-1, they are not so faint that planets would be tidally locked, showing the same side to the star at all times.
This work is funded by grants from STFC and Leverhulme and the data were obtained by using the HARPS spectrograph (European Southern Observatory, Chile) and Keck-HIRES (Mauna Kea, Hawaii, USA).