The European Space Agency's exoplanet-hunting satellite CHEOPS, in which the Instituto de Astrofsica de Canarias is part, unexpectedly discovered a third planet passing right in front of its star as it was studying two other planets around the same star. Researchers claim that this transit will reveal fascinating details about a mysterious planet "without any known equivalent."This discovery is among the first results from CHEOPS (Characterising ExOPlanet Satellite). It is also the first time an exoplanet with a transit period of more than 100 days has been observed. Nature Astronomy published the discovery today.The bright star Nu2 Lupi is similar to the sun and lies approximately 50 light years away from Earth in the constellation Lupus. HARPS (High Accuracy Radial velocity planet Searcher) from the European Southern Observatory in Chile found three exoplanets within this system. They were called b, c and d and had masses similar to those of Neptune and orbital periods of 11.6, 27.6, and 107.6 respectively. NASA's TESS satellite was used to detect transiting stars. It found that the two inner planets, Nu2 Lupi and b, transited Nu2 Lupi. This makes it one of three naked-eye star systems with more than one transiting world."Transiting systems like Nu2 Lupi are of great significance in our understanding of planet formation and evolution, because we can compare multiple planets around the bright star in detail," says Laetitia Delrez (Belgium), a researcher at University of Liege (Belgium), and the first author of this article.She adds that her idea was to continue previous studies of Nu2 Lupi.Transits of planets offer valuable opportunities to study their atmospheres and orbits, as well as their sizes, compositions, and provide valuable information. Researchers discovered that a transiting planet blocks out a small but discernible amount of the star's light when it passes by it. This tiny drop of light was what led to the discovery. The possibility of detecting a transiting planet while it is orbiting far from its stars makes exoplanets that have long periods orbit far from their stars very unlikely. This makes the discovery with CHEOPS a great surprise.AdvertisementUsing high precision techniques from CHEOPS planet d, it was discovered to have a radius 2.5 times that of Earth and a period of orbit around its star of just over 107 days. Its mass was also estimated using archive observations made by terrestrial telescopes."The amount radiation that falls from the star onto planet d, compared to other exoplanets, is very small." Mahmoudreza Ozhagh, senior postdoctoral researcher at IAC and co-author of this paper, says that if it was in our solar system, Nu2 Lupi, planet d would orbit between Mercury, Venus, and Venus. This, combined with the bright parent star, long orbital period, and ideal conditions for follow-up, makes planet d very exciting. It will be an extraordinary object with no known counterpart, and will undoubtedly be a key object in future research.Most long-period transiting exoplanets that have been discovered so far orbit stars too faint to permit detailed follow up observations. This means we don't know much about their properties. However, Nu2 Lupi's brightness is sufficient to make it attractive for other powerful space telescopes, such as the NASA/ESA Hubble Space Telescope and the James Webb Space Telescope. Laetitia Derez adds that planet d, due to its general properties and orbit, will be an extremely favorable objective for studying an exoplanet having a moderate atmosphere around a star like the Sun.The researchers combined the new data from CHEOPS and archive data from other observatories to find that planet b was primarily rocky. Planets c, d and e had large amounts of water surrounded with hydrogen and helium. The planets c, and d actually contain more water than Earth. A quarter of their mass is water, while Earth has less than 0.1%. This water isn't liquid. It is either high-pressure ice or high-temperature water vapour.Enric Pall, an IAC researcher, and co-author of this article, says that although none of these planets could be habitable, their variety makes the system exciting. We can also search for rings and moons in the Nu2 Lupi system because of the stability and extreme accuracy of CHEOPS. This could enable us to find bodies similar to Mars.CHEOPS was designed to collect high-precision data on individual stars that are known to harbor planets. It is not intended to survey all possible exoplanets surrounding many stars. This method and its accuracy have been extremely useful in understanding the planetary systems surrounding the stars.Enric Pall says, "These amazing results again show, yet again the major potential of that satellite." CHEOPS will give us a better understanding about exoplanets we know, but it will also allow us to discover new ones and reveal their secrets, as demonstrated by this and other results in the initial phase.
