Free Astronomy Magazine November-December 2023

46 NOVEMBER-DECEMBER 2023 ASTRO PUBLISHING four times bigger than expected for this size (73 times the mass of the Earth) which makes it the densest Neptunian exoplanet observed, with nearly twice the density of the Earth. TOI-1853b lies at a distance of 545 light years, towards the constella- tion Bootes, and is very close to its star, in a region normally classified as a “Neptune desert” in which there ought not to be any planets the size of Neptune, because of the intense radiation from the star. “If we rely on the theories of the for- mation and evolution of planets, we would not expect a planet to exist so close to its star,” comments Luca Naponiello, a doctoral student at the University of Rome, Tor Vergta, who is the first author of the paper. Its exact composition is not known. “It is a planet with a density too high to be a classical Neptunian type of planet, and we infer that it must be very rich in heavy ele- ments” adds Naponiello. The re- search team are looking at two possibilities. One of them is that TOI-1853b may be mainly rocky, sur- rounded by a thin gassy atmos- phere of hydrogen and helium. The other is that it might be composed partly of rock and partly of ice, so that given its high temperature, around 1200 degrees Celsius, this exoplanet might have an atmos- phere of water vapour. But the most challenging aspect for The densest “Neptune” ever observed by IAC Outreach Team A n international team of re- searchers, with participation from the Instituto de As- trofísica de Canarias, has discovered an extremely dense Neptune-sized planet, which challenges the con- ventional theories about the forma- tion and evolution of planets. It was first identified with NASA’s TESS satellite, and the present studies were made with the HARPS-N spec- trograph on the Telescopio Na- zionale Galileo (TNG), at the Roque de los Muchachos Observatory (Garafía, La Palma, Canary Islands). It is called TOI-1853b and is really peculiar: it orbits its star in only 30 hours, and although its radius is similar to that of Neptune (3.5 times that of the Earth) its mass is some