About 80 percent of all exoplanets known today were discovered using the transit method. The latter is based on the fact that some of the distant worlds in their orbits regularly pass directly in front of their parent stars when viewed from Earth. During each of these transits, the planet shadows part of the starlight. Then the star appears a little fainter than usual, which suggests the planetary companion.
For the definitive confirmation of an exoplanet through the transit method, it takes at least three rounds; the protocol being to exclude a random event. Of course, the method also has its drawbacks: To verify that exoplanets with long periods of orbit, it may take years – too long for a quick statement as to whether the potential planet actually exists. But now Swiss astronomers have developed a method that could solve this problem.
“To discover a planet like Jupiter, which takes eleven years to complete an orbit, we would have to wait more than 30 years,” says Helen Giles of the Department of Astronomy at the University of Geneva. Under Giles’ direction, a research team has now found a method based on analyzing data from the Kepler satellite.
Giles looked more closely at a star called Epic248847494. Based on data from the Gaia satellite, she was able to deduce its diameter and its distance to Earth. Epic is located 1,500 light-years from Earth. Knowing that the first observed transit took 53 hours, Giles was able to situate the planet: the distance to its central star is about 4.5 times the distance between Earth and Sun; it takes about ten years to complete its orbit.
However, the question was still open, whether it was actually a planet or a star, as the researchers in the journal “Astronomy & Astrophysics” report. Using the Euler telescope of the University of Geneva in Chile Giles was able to determine the radial velocity of the star and the mass of the planet. The latter was indeed was well below the minimum mass for a star. So it was clear that it was indeed an exoplanet.
According to the astronomer, this method could also be used to discover earth-like, life-friendly planets. In the future, it will not take more years to know if a transit was due to a planet. “We could even see if the planet has one or more moons like our Jupiter,” Giles said.