Astronomers have identified two more planets orbiting Tau Ceti, a star about 12 light years away.
The planets are among the smallest ever detected around the nearest sun-like stars, with masses 1.7 times that of Earth, according to W.M. Keck Observatory.
An international team of researchers made the discovery using Keck atop Mauna Kea and the European Southern Observatory in Chile. Their research also revised the sizes of two larger planets believed to be in that system’s habitable zone, reducing their estimated minimum mass to 3.9 Earths.
“Tau Ceti is very similar to the sun in its size and brightness, and they both host multi-planets,” a Keck press release said. “If the outer two planets are found to be habitable, Tau Ceti could be an optimal target for interstellar colonization, as seen in science fiction.” The star, close enough to be visible to the naked eye, has been referenced in movies, video games and TV shows, including “Star Trek.”
According to Keck, the team found the two smaller planets, both too close to the star to be habitable, by detecting variations in the movement of Tau Ceti as small as 30 centimeters per second. That brings researchers closer to the limit of 10 centimeters per second required for detection of Earth analogs.
These variations or wobbles are a result of the gravitational pull of planets that orbit the star. The smaller the planet, the harder that is to detect.
“The planets we have found have masses as low as 1.7 Earths, making them the smallest planets ever detected around sun-like stars at such wide orbits,” Keck spokeswoman Mari-Ela Chock said in an email.
Chock indicated the research is significant since it shows that astronomers are getting better at detecting smaller planets closer to Earth’s size.
Astronomer Mikko Tuomi said in the Keck press release: “We are 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.”
There’s at least one major drawback to this system. A massive debris disc around the star would reduce the planets’ habitability due to bombardment from asteroids and comets.
The study did not confirm three other candidate planets in the system, known as b, c and d.
