At least four Earth-sized planets are detected recently, orbiting a sun-like star, located about 12 light years away from the Earth. A new study conducted by a team of international astronomers revealed that these planets have a low mass similar to that of the Earth, making them one of the smallest planets ever detected around a sun-like star. These planets were detected by observing minute vibrations in the movement of their host star, Tau Ceti.
“We are now crossing a threshold”, said co investigator and author Steven Vogt, currently a professor of astrophysics at the UC Santa Cruz, “where, with the advanced modeling of the large combined data sets retrieved from various independent observers, we can now discard the resultant noise caused due to stellar surface activity from the very weak signals generated by the Earth-sized planets.”
Moreover, Fabo Fang from the University of Hertfordshire, UK explained that “detection of such weak vibrations is extremely difficult and not less than any milestone in the search for planets comparable to the Earth also known as the Earth analogs”. “Here, we have introduced several new methods to remove such noise and impurities in the data in order to catch planetary signals which are extremely weak.” he added.
The study revealed that the two outer planets around tau Ceti are the most likely candidate to sustain life. Although, a massive disc of debris around the host star might reduce their habitability due to continuous asteroid strikes.
Image credit: Phys.org
The group of astronomers who discovered these planets were also involved in the investigation of Tau Ceti four years ago in 2013. ‘We have been able to develop an ingenious way of determining the difference between the signals coming from planets and those coming from a star’. Said, lead author Mikko Tuomi of the University of Hertfordshire. ‘After realizing that how star’s activity differed at various wavelengths, we can use that information to isolate stellar signals from that of planets’, he added.
Search For Habitable Planets
In search for habitable planets, sun-like stars are thought to be the best shots for the humanity due to their striking similarities to the sun. Unlike common smaller stars, such as Proxima Centauri, a red dwarf 4.25 light years from the sun, and Trappist-1, ultra-cool dwarf star located 39.5 light years, where all planets are most likely to be tidally locked, (one side permanently facing a star), Tau Ceti appears to be very similar to the sun in its size and brightness. The only striking difference between Tau Ceti and Sun is that the former has only 78% of the later’s mass.
One of the major challenges for using the radial velocity method to detect Earth like planets are the careful removal of noise which is typically correlated in time and wavelength. After analyzing the radial velocity of the newly found host star Tau Ceti, the team found strong evidences of wavelength dependent noise. They also find this noise can be cancelled out by combining “differential radial velocities” and moving average. “After applying the noise model to Tau Ceti, we find four periodic signals at 20.0, 49.3, 160 and 642 d which we interpret as planets.
Journal Reference: 4 planet candidates around tau Ceti
All the data were acquired by the HARPS spectrograph installed at the European Southern Observatory (La Silla), Chile and Keck-HIRES (W. M. Keck Observatory, Mauna Kea, Hawaii).