When studying a unique class of extremely hot exoplanets, astronomers aboard NASA’s Hubble Space Telescope may be looking to dance to the Calypso party song “Hot, Hot, Hot.” That’s because these bulging Jupiter-sized worlds are so close to their parent star that they’re heating to a boiling point above 3,000 degrees Fahrenheit. It’s hot enough to vaporize most of the stars. metals, including titanium. They have the hottest planetary atmospheres ever seen.
In two new papers, teams of Hubble astronomers are reporting on strange weather conditions on these hot worlds. It’s raining evaporating hail over one planet, and another planet whose upper atmosphere is getting hotter instead of cooler because it’s being “sunburned” by intense ultraviolet (UV) radiation. high from its star.
This research is not simply about finding out the atmosphere of the strange and odd planet. Studying extreme weather gives astronomers deeper insights into the variety, complexity, and strange chemistry taking place in distant worlds across our galaxy.
“We still don’t fully understand weather in different planetary environments,” said David Sing of Johns Hopkins University in Baltimore, Maryland, co-author of the two reported studies. “When you look at Earth, all of our weather predictions are still fine-tuned to match what we can measure. But when you go to a distant exoplanet, you have limited predictability because you haven’t built up a general theory of how everything in the atmosphere comes together and reacts to extreme conditions. . Even though you know basic chemistry and physics, you don’t know how it will manifest in complex ways.”
In one paper in the April 7 magazine Nature, astronomers describe Hubble observations of WASP-178b, located about 1,300 light-years away. During the day, the atmosphere is cloudless and enriched with silicon monoxide. Because one side of the planet is permanently facing its star, the atmosphere swirls around the night side at superstorm speeds in excess of 2,000 miles per hour. On the dark side, silicon monoxide may cool enough to condense into rock to create clouds, but even at dawn and dusk, the planet is hot enough for the rock to evaporate. “We knew we were seeing something really interesting with this silicon monoxide feature,” said Josh Lothringer of Utah Valley University in Orem, Utah.
In one paper published in the January 24 issue of Astrophysical Journal Letters, Guangwei Fu of the University of Maryland, College Park, reports on a super-hot Jupiter, KELT-20b, located about 400 light-years away. On this planet, a burst of ultraviolet light from its parent star is creating a layer of heat in the atmosphere, much like Earth’s stratosphere. “Until now, we never knew how the host star directly affected a planet’s atmosphere. There have been a lot of theories, but now we have the first observational data,” said Fu.
For comparison, on Earth, ozone in the atmosphere absorbs ultraviolet light and raises the temperature in a layer 7 to 31 miles above the Earth’s surface. On KELT-20b, UV radiation from the star is heating up metals in the atmosphere, creating a very strong inversion layer.
Evidence comes from Hubble’s detection of water in near-infrared observations and from the detection of carbon monoxide by NASA’s Spitzer Space Telescope. They radiate through the hot, transparent atmosphere above created by the inversion layer. This signature is unique compared to what astronomers see in the atmospheres of hot Jupiters orbiting cooler stars, like our Sun. “The emission spectrum of KELT-20b is quite different from other hot workpieces,” says Fu. “This is compelling evidence that planets do not live in isolation but are influenced by their host stars.”
Although super-hot Jupiters are uninhabitable, this type of research helps pave the way to better understand the atmospheres of potentially habitable terrestrial planets. “If we can’t figure out what’s happening on super-hot Jupiters, where we have solid, reliable observational data, then we won’t stand a chance to find out what’s going on,” Lothringer said. what is happening in the weaker spectra from observations of extraterrestrial planets. “This is a test of our techniques that allows us to build a common understanding of physical properties such as cloud formation and atmospheric structure.”
The Hubble Space Telescope is an international cooperation project between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts science operations on Hubble. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, DC
Illustration of KELT-20b Image supplier: NASA, ESA, Leah Hustak (STScI)
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