An exoplanet is so close to its star that its clouds are made of rock.
WASP-178b is a young, white star twice the mass of the Sun, which is why it is called WASP-178b. The hottest planet we know of is at that proximity, so hot that it is classified as an "ultra-hot Jupiter".
For the first time, a study of the weather on this wild world has identified a substance in the atmosphere of an exoplanet.
David Sing, an astronomer at the University of Baltimore, said that they still don't have a good understanding of weather in different planetary environments.
When you look at Earth, all of our weather predictions are still in tune with what we can measure. You don't have a general theory about how everything in an atmosphere goes together and responds to extreme conditions when you go to a distant exoplanet.
Hot Jupiters are fascinating and are ripe for study. These worlds are gas giants, like Jupiter, but they are also very hot because they are very close to their stars.
They pose a dilemma, because they can't have formed at their current location because of gravity, radiation, and stellar winds. Astronomers believe that hot Jupiters form farther from their stars and migrate inwards.
WASP-178b is 1.9 times larger than Jupiter. The exoplanet has a temperature of 2,450 degrees Celsius or 3,950 degrees Fahrenheit. It's important to detect vaporized silicate at that temperature, because theoretical studies show that it's possible to detect Silicon monoxide above 2,000Kelvin.
Here is how. The exoplanet passes between us. The light from the star is absorbed by atoms in the exoplanet's atmosphere, meaning it can be identified as a signal in the spectrum of light received from the star.
Astronomers can amplify the spectrum to get a readable signal by stacking transits. Titanium, iron, and magnesium have been detected in the atmospheres of hot Jupiters using this method.
The spectrum of WASP-178b was obtained by the Hubble Space Telescope and found to be unlike anything seen before. It turned out to be magnesium and Silicon, according to their analysis.
The presence of SiO in WASP-178b is consistent with theoretical expectations as the dominant Si-bearing species.
All hot Jupiters are locked to their star. One side is facing the star in permanent day and the other side is facing away in night. A rotating atmosphere that whirls around between the two hemispheres of the exoplanet produces a significant difference in temperature.
It may be cool enough on the night side to allow the vapors to condense into clouds that rain down deeper into the atmosphere, before being blown back to the day side where the minerals are once again vaporized.
There was no sign of condensation on the terminator, the line that separates day from night. The results show that Silicon monoxide may be present on other exoplanets, like WASP-76b. If there is rain of rocks on an exoplanet, this is the place to look for it.
The results show that we are getting better at peering into the mysterious atmospheres of distant worlds. This will bode well for looking at exoplanets that are smaller and farther away from their stars.
If we can't figure out what's happening on Jupiters where we have reliable observational data, we won't have a chance to see what's happening on exoplanets.
This is a test of our techniques that allows us to build a general understanding of physical properties such as cloud formation and atmospheric structure.
The research has been published.
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