Using the light of that orbiting star, astronomers have plunged into the atmosphere of an exoplanet 850 light-years away. Not just an exoplanet, but one of the hottest we’ve ever met – and at least seven metals are now known to float around its atmosphere as gas.
Exoplanet is WASP-121B, a type of planet we call the hot Jupiter. It is because it is a gas giant so close to its star that its temperature is the same as that of the stars; Nice stars, for sure, but the stars nonetheless.
The WASP-121B is very popular as far as Explanet goes. It was first found in 2015, in an orbit close to just 1.27 days, an exoplanet about 1.18 times the mass and 1.81 times the size of Jupiter. Two years later, it became the first exoplanet to find water in the source area – although, given the planet’s extreme heat, it is unlikely to be habitable.
Now astronomers have taken a closer look at the atmosphere of the exoplanet, and what they have found is astonishing to them.
At temperatures between 2,500 and 3,000 degrees Celsius (approximately 4,500 and 5,500 degrees Fahrenheit), it is not the hottest of these exoplanets we have seen.
But it is so hot that its atmosphere must be much simpler than what astronomers have observed in previous studies – complex molecules should not be able to form at such high temperatures.
These previous studies suggested that molecules lacking the rare metal vanadium and titanium could explain the spectrum of WASP-121B in previous observations of the atmosphere.
“Previous studies have tried to explain these complex observations with theories that do not seem plausible to me,” said Jens Hoijmaker, an astronomer at the University of Bern in Switzerland and Geneva.
“But it turned out that they are true. My surprise is that we found strong signatures of vanadium in the observations.”
Going to the pier in an exoplanet environment is not an easy thing to do. First, you need an exoplanet to pass between us and the stars. This is a great way to find an exoplanet in the first place – you’ll see a regular dip in a really obscure, starlight to say something big around the star.
To study the atmosphere, you also need vague signals.
As the exoplanet passes in front of the star, some of the star’s light passes through the atmosphere. Depending on the elements present in the atmosphere, some wavelengths of light will be absorbed and amplified. If you can take the full spectrum of the wavelength, these will appear as absorption and emission lines.
As you can imagine, the signal is not very strong, and there is a lot of noise. So, for starters, you need good noise reduction tools that won’t destroy the data you need.
Signals can also be amplified and clarified by taking multiple transit spectra and stacking them – so it would be much easier to analyze an explanate with a shorter orbital period that allows us to take more transit spectra. For example, an exoplanet would not be an ideal candidate on a 12-year orbit like Jupiter. But the tight orbit of the WASP-121B works well.
To obtain strong spectrum for the WASP-121B, Hoisemakers and his team used three previously seen transitions using the HRPS spectrograph instrument on the European Southern Observatory’s La Sila 6.6M telescope, and reproduced the data.
And they found an interesting metallic cocktail in the atmosphere of the exoplanet. Of course the above was vanadium. In addition, the team identified spectral signatures of iron, chromium, calcium, sodium, magnesium and nickel. Significantly, there is no titanium – consistent with previous findings.
“All metals evaporate as a result of the high temperatures prevailing at WASP-121B, thus ensuring that the air on the exoplanet contains evaporative metals, among other things.”
Hot Guptas are very mysterious planets and such an analysis of their atmosphere can help us understand that. We don’t know why or why they are so close to their stars, and knowing what is in their atmosphere can help us find out if they form there, or if they move inward from the next orbit.
But the study is also helping to develop a toolkit to examine planets in search of alien life. What we use today to identify iron and sodium, with the help of more sensitive devices, could one day help to find molecules produced and used by living organisms, such as oxygen and methane.
“After years of being listed there, we’re no longer just measuring,” Hoisemakers said.
“We are really beginning to understand what the data from the instruments show us. How the planets meet and separate from each other. In the same way, perhaps, Charles Darwin began to develop the theory of evolution after characterizing numerous species of animals. We are beginning to understand more about how these exoplanets were formed and how they work. “
Research has been published in Astronomy and Astrophysics.
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