![]() ![]() New research suggests K2-18b could hover in a third zone: planets that looks like a gaseous mini-Neptune but are actually rocky planets covered in superheated, super-compressed seas, where the water exists somewhere on the threshold between liquid and gas, and is topped by a steamy water vapour atmosphere. For the first time, we’d found a rocky planet orbiting in the habitable zone of its star, in which liquid water could potentially pool on the surface.īefore we could dream of luxuriating in exotic oceans, though, came the view that K2-18b may be more like the far less friendly mini-Neptunes – planets with a thick hydrogen atmosphere, a watery layer and a rocky iron core, where temperatures and pressures are far too high to support life. K2-18b, twice the radius and eight times the mass of Earth, has been a top contender for an Earth-like planet for years, so there was huge excitement when it was announced in 2019 that water had been discovered in K2-18b's atmosphere. Likely smaller than Earth, it’s one of the lowest-mass objects ever found using microlensing techniques.ĩ K2-18b – where a swim may vaporise you Credit: ESA/Hubble, M. The recently identified OGLE-201 is another. This cosmic wanderer is eleven times more massive than Jupiter and thought to have a circumstellar disc of dust, rock and ice. One such planet is OT44, located 550 lightyears away in the constellation Chamaeleon. With no parent star to light and warm them, life is dark and cold on these nomads adrift in the vastness of space.Ĭatching sight of these hard-to-detect ‘rogue planets’ will be one of the tasks for NASA’s Nancy Grace Roman Space Telescope, coming online around 2025. Or do they? While most planets are locked in orbit around their sun, some worlds are actually roaming the galaxy untethered. Many exoplanets may be scary and inhospitable, and they may come in different sizes, colours and densities, but at least they all reliably do one thing: orbit a star. ![]() 4 Rogue worlds: exoplanets on the loose Credit: NASA/JPL-Caltech/R. ![]()
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