(ORDO NEWS) — The exoplanet, about 1,360 light-years away, is so close to its star that its clouds are made of evaporated rock.
Named WASP-178b, it orbits WASP-178, a young white star with twice the mass of the Sun, in an insanely short orbit of just 3.3 days. At this proximity, the temperature on the gaseous world increases dramatically – so much so that it is classified as an “ultra-hot Jupiter”, perhaps the most extreme type of exoplanet that we know of.
A new weather study on this wild world has revealed silicon monoxide (SiO) in an exoplanet’s atmosphere for the first time, giving us new insights into these truly alien worlds.
“We still don’t have a good understanding of the weather in different planetary environments,” says astrophysicist David Sing of Johns Hopkins University.
“When you look at Earth, all of our weather forecasts are still exactly what we can measure. But when you go to a distant exoplanet, you have limited ability to predict because you haven’t created a general theory about how everything in atmosphere combines and responds to extreme conditions.”
Hot Jupiters, in particular, are downright adorable and ripe for exploration. As the name suggests, these worlds are gas giants like Jupiter, but they are also very hot because they are in very close orbits to their stars – some of them revolve around them in less than a day.
They present an interesting mystery: they could not have formed in their current orbit because gravity, radiation, and intense stellar winds must have kept the gas from merging. However, over 300 hot Jupiters have been discovered to date; astronomers believe they form further away from their stars and migrate inward.
The mass of WASP-178b is about 1.4 times the mass of Jupiter and about 1.9 times its size. Swelling from the heat of its star, the exoplanet reaches a temperature of 2,450 Kelvin (2,177 degrees Celsius, or 3,950 degrees Fahrenheit). This temperature is optimal for the detection of evaporated silicate: theoretical studies have shown that above 2,000 Kelvin silicon monoxide can be detected.
Here’s how it goes. An exoplanet passes between us and its host star. With each passage, some of the light from the star is absorbed by the atoms in the exoplanet’s atmosphere; each element absorbs or emits at a different wavelength, which means it can be identified as a signal in the spectrum of light received from the star.
As you can imagine, the signal is absolutely negligible, but by adding up the transits, astronomers can amplify the spectrum to get a readable signal. Using this method, evaporated metals such as titanium, iron and magnesium were found in the atmospheres of hot Jupiters.
A team of researchers led by Sing and his colleague Josh Lothringer at the University of Utah Valley used the Hubble Space Telescope to acquire the spectrum of WASP-178b and found a signal unlike anything seen before. According to their analysis, it turned out to be silicon and magnesium.
“SiO in particular has not previously been detected on exoplanets to our knowledge,” they write in their paper, “but the presence of SiO on WASP-178b is consistent with theoretical expectations as the dominant Si-bearing species at high temperatures.”
WASP-178b, like all known hot Jupiters, is tidally attached to its star. This means that one side is constantly facing the star, in constant day mode, and the other side is in constant night mode. This creates a significant difference in temperature between the exoplanet’s two hemispheres, with a rotating atmosphere spinning between them.
It can be cool enough on the exoplanet’s night side for vapors to condense into clouds that rain down into the atmosphere before being blown back to the day side, where the minerals evaporate again.
At the WASP-178b terminator, the line that separates day from night, the researchers saw no sign of such condensation. However, the results suggest that silicon monoxide may be present on other exoplanets for which detailed terminator observations are more visible, namely WASP-76b. If rain of rocks is present on an exoplanet, then this could be the exact place to find it.
The results of the team’s work also show that we are increasingly able to peer into the mysterious atmospheres of distant worlds. This portends that we will be able to study smaller exoplanets more distant from their stars.
“If we can’t understand what’s happening on superhot Jupiters, where we have reliable observational data, then we won’t have a chance to understand what’s happening in the fainter spectra when observing terrestrial exoplanets,” Lothringer said.
“This is a test of our methods that allows us to build a common understanding of physical properties such as cloud formation and atmospheric structure.”
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