Thirty-five light-years is next door by galactic standards, and the small red star L 98-59 has turned out to be an unusually crowded neighbour. Astronomers at the Trottier Institute for Research on Exoplanets at the Université de Montréal have confirmed a fifth planet in the system, L 98-59 f, and it sits in the region around the star where liquid water can exist on a planet’s surface.
How it was found
The system has been assembled one planet at a time. NASA’s TESS space telescope spotted three small planets in 2019 by watching them pass in front of the star and dim it slightly. A fourth turned up in data from the European Southern Observatory’s ESPRESSO spectrograph, which detects the tiny wobble a planet’s gravity gives its star. The fifth does not cross the star from our viewpoint, so it was found the second way — combining years of high-precision wobble measurements with the space-telescope data until the signal of another body became unmistakable. “Combining data from space telescopes and high-precision instruments, we found this planet in a region where conditions could allow water,” the team said.
What kind of planet
L 98-59 f has a mass at least 2.8 times Earth’s, which makes it a super-Earth — larger than our planet, smaller than Neptune, a type that does not exist in our solar system and is the most common kind in the galaxy. Its orbit is almost perfectly circular, and because the star is small and cool, the planet receives roughly the same energy from it that Earth gets from the Sun despite orbiting far closer. That places it in the habitable zone. It does not mean the planet is habitable: that depends on whether it has an atmosphere, what the atmosphere is made of, and how the star’s flares have treated it over billions of years.
Why Webb is next
Those are questions the James Webb Space Telescope can start to answer. If L 98-59 f has an atmosphere, Webb’s instruments can look for the signatures of water vapour and carbon dioxide in the starlight filtering through it. René Doyon, who leads the institute, says the system offers a rare chance to study how rocky planets form and vary around small stars, what super-Earths and sub-Neptunes are made of, and whether rocky worlds around red dwarfs can hold on to atmospheres at all — the single biggest open question about where life might be common. For anyone who has stood on a rooftop in Bangladesh and wondered whether the nearest stars have planets: the nearest ones we can study closely do, five of them here, and one of them is in the right place.
Source: NDTV, via Prothom Alo.
