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 by Brooks Hays Washington (UPI) Aug 1, 2019
Astronomers have detected heavy metal gases streaming away from an extremely hot, football-shaped exoplanet located 900 light-years from Earth. It's the first time scientists have identified heavy metal gases emanating from a so-called hot Jupiter. WASP-121b is a planet of firsts. During an earlier survey, the hot Jupiter became the first exoplanet found with water in its stratosphere. The latest investigation, which revealed the presence of hot metal gases, was made possible by NASA's Hubble Space Telescope. Researchers described their latest discovery Thursday in the Astronomical Journal. "This planet is a prototype for ultra-hot Jupiters. These planets are so heavily irradiated by their host stars, they're almost like stars themselves," Drake Deming, professor of astronomy at the University of Maryland, said in a news release. "The planet is being evaporated by its host star to the point that we can see metal atoms escaping the upper atmosphere where they can interact with the planet's magnetic field. This presents an opportunity to observe and understand some very interesting physics." Typically, hot Jupiters are cool enough to condense heavier elements, which keeps them stabilized in their atmosphere. But WASP-121b isn't your average hot Jupiter. It's extremely hot, with an upper atmosphere boasting temperatures of 4,600 degrees Fahrenheit. What's not being quickly evaporated by the heat of the exoplanet's host star is being pulled apart by the WASP-121's gravity. The gravitational tug of its host star explains WASP-121b's football-like shape. "Heavy metals have been seen in other hot Jupiters before, but only in the lower atmosphere," said lead researcher David Sing, an astronomer at Johns Hopkins University. "With WASP-121b, we see magnesium and iron gas so far away from the planet that they're not gravitationally bound. The heavy metals are escaping partly because the planet is so big and puffy that its gravity is relatively weak. This is a planet being actively stripped of its atmosphere." Scientists used Hubble's Space Telescope Imaging Spectrograph to analyze the light from WASP-121 as it passed through the atmosphere of WASP-121b. The data showed the system's ultra-hot Jupiter is rapidly shedding its atmosphere. "The hot Jupiters are mostly made of hydrogen, and Hubble is very sensitive to hydrogen, so we know these planets can lose the gas relatively easily," Sing said. "But in the case of WASP-121b, the hydrogen and helium gas is out-flowing, almost like a river, and is dragging these metals with them. It's a very efficient mechanism for mass loss." As new, more powerful telescopes are put into orbit, scientists hope to compile a more complete picture of WASP-121b's chemical composition.
Potentially habitable planet found in new solar system Three new planets were discovered orbiting GJ 357, a red dwarf -- a small and cooling star -- 31 light years away, relatively close in space terms, said Rafael Luque of Spain's Institute of Astrophysics in the Canary Islands. The discovery was also reported by NASA, whose TESS planet-hunting satellite made it possible. The planet known as GJ 257d -- the furthest away from the star -- was particularly intriguing as researchers estimate it could be habitable. The other two are deemed too hot. Signs of habitability in any planet include a rocky terrain, a size similar to Earth and a distance from their sun -- the temperate "Goldilocks" zone neither too close nor too far -- that allows the right temperature for liquid water, a key requirement for life. Given its distance from its star, similar to that of Mars to our Sun, researchers estimate the planet has temperatures of -53 degrees Celsius (-63.4 Fahrenheit), Luque told AFP. "That seems a little cold at first," he said. But "if this planet had an atmosphere (unlike Mars), it could retain the heat it receives from its star, and water could be liquid." Researchers also estimate GJ 257d could be roughly the same size as Earth or up to twice the size. It is not the first potentially habitable planet to have been discovered close to us. In 2016, the discovery of Proxima b at a mere four light years from the Solar System made waves. But there is a hitch. Proxima b and GJ 257d were discovered via so-called radial velocity, which involves looking for signs of a wobble in a star from the gravitational tug of an orbiting planet. But Luque says the method is not precise enough to ascertain whether it actually is habitable. As things stand, in order to measure its size, density and composition, the planet has to pass directly between its star and an observer, the so-called "transit" method, he says. That has not been possible for Proxima b and other nearer potentially habitable planets, Luque says. In the coming months, Luque and his team will be working to try and catch GJ 257d in "transit" to try and confirm it as a habitable planet. "The probability that a planet passes in front of a star from our line of vision on Earth is pretty small," he adds.
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