A new study by an international team of astronomers reveals that four Earth-size planets orbit a very close Sun-like star, tau Ceti, which is about 12 light-years away, very close to us; so much so that it is visible to the naked eye. These planets are of ‘small’ mass, 1.7 times the mass of Earth, making them among the smallest planets that have been detected around Sun-like stars. Two of them are super-earths located in the habitable zone of the Earth. star, which means they could contain liquid surface water.
The planets were detected by observing the oscillations in the motion of tau Ceti. This required techniques sensitive enough to detect variations in the star’s motion as small, at 30 centimeters per second.
“We are now crossing a threshold where, through very sophisticated modeling of large combined data sets from multiple independent observers, we can unravel the noise of stellar surface activity from the tiny signals, generated by the gravitational tugs of the planets. in Earth orbit, ”according to one of the study’s authors, Steven Vogt, a professor of astronomy and astrophysics at Santa Cruz.
Lead author Fabo Feng, from the University of Hertfordshire, UK, notes that researchers are getting tantalizingly close to the 10-centimeter-per-second limit required to detect Earth analogs . “Our detection of such faint wobbles is a milestone in the search for Earth-like planets and the understanding of Earth’s habitability by comparing these analogs,” says Feng. “We have introduced new methods to remove noise in the data in order to reveal the faint planetary signals.”
This illustration compares the four planets detected around the nearby star tau Ceti (top) and the inner planets of our solar system (bottom). / Credits: Fabo Feng
If habitable, the two outer planets around tau Ceti are much more likely to be habitable, although a massive disk of debris from the surrounding star reduces their likelihood of sustaining life , due to intensive bombardment by asteroids and comets.
The same team also investigated tau Ceti in 2013, when co-author Mikko Tuomi from the University of Hertfordshire carried out an effort in developing data analysis techniques and using the star as a reference. “We have discovered an ingenious way to distinguish the signals caused by planets and those caused by the activity of stars. We realized that the activity of stars differed at different wavelengths and used that information to separate this activity from signals. of planets, ”he explains.
The researchers improved the sensitivity of their techniques and were able to rule out two of the signals the team had identified in 2013 as planets . “But no matter how we look at the star, there appear to be at least four rocky planets orbiting it,” says Tuomi. “Little by little, we are learning to distinguish between the oscillations caused by the planets and those caused by the active stellar surface, which allows us to essentially verify the existence of two potentially habitable outer planets in the system, ” he concludes.
