634 light years away, a gas giant exoplanet has a quirk in its atmosphere that suggests it may have swallowed a smaller world.
The planet is called WASP-76b and is already famous for being one of the hottest exoplanets in the galaxy. Revolving around its host star every 1.8 days, WASP-76b reaches temperatures above 2,000 degrees Celsius (3,632 degrees Fahrenheit), and previous analyses of its atmosphere suggest that it rains liquid iron.

Now, an international team of astronomers led by astronomer Stefan Pelletier from the University of Montreal in Canada has taken another look at this wild world. They detected at least 11 separate elements in the atmosphere of the gas giant - with some abundances indicating planet-destroying tendencies.
"Pelletier said: "It's rare indeed when an exoplanet hundreds of light-years away can teach us something we couldn't possibly know about our own Solar System. "That's the case in this study."
WASP-76b is not the hottest known exoplanet in the galaxy, but it falls into that category. These worlds are known as hot Jupiters, gas giants so close to their stars that they reach mind-boggling temperatures. Hot Jupiters are usually gas giants with masses similar to Jupiter, but they have much larger radii because the heat causes their atmospheres to expand.

This is the case for WASP-76b: It has about 90 per cent of Jupiter's mass and a radius about 185 per cent that of Jupiter. And it orbits its star in such a way that it passes between us and its star, meaning that starlight shines through the exoplanet's atmosphere during the transits. By analysing the light from the star, astronomers can see how it changes at these times and study the spectrum to find out which elements cause these changes.
Pelletier and colleagues used an instrument called MAROON-X on the Gemini North telescope to obtain these s. They took them apart to identify and measure the elements swirling in the scorching atmosphere of WASP-76b.

In addition to the previously observed iron in the exoplanet's atmosphere, the team found sodium, calcium, chromium, lithium, hydrogen, vanadium, magnesium, nitrogen, manganese, potassium and barium.
They also found vanadium oxide, which is particularly interesting: this is the first time this molecule has been definitively detected on an exoplanet.
"This molecule is of great interest to astronomers because it could have a major impact on the atmospheric structure of hot giant planets," explains Pelletier. "This molecule plays a role similar to ozone, which is extremely effective in warming the Earth's upper atmosphere."

Some elements seemed to be relatively absent. The team found no trace of metals such as titanium and aluminium, which have high melting points compared to those present in their observations. The team thinks this could mean that the upper atmospheres of hot Jupiters are very sensitive to temperature and can vary quite widely, even when their temperatures appear close.
Interestingly, the abundances of some of the elements they found were very similar to those seen in WASP-76b's host star - and on the Sun too. But they are very different from the abundances seen on rocky worlds like Earth, Venus, Mars and Mercury. This could be a clue to how gas giant planets form.
Rocky planets form gradually from the bottom up, in clusters of rocks that stick together like a Katamari ball. Stars, on the other hand, form from top to bottom as a dense mass of matter in a gas cloud that collapses under gravity and absorbs gas to grow. The composition of WASP-76b could mean that gas giants, or some gas giants, form in a similar way to stars.
But the elements that don't exactly match these abundances are also interesting, the researchers say. They suggest that at some point there was a planet-to-planet crime.

"This is the first study to measure with high precision the abundance of chemical elements such as nickel, magnesium and chromium on any giant planet," says astrophysicist Mohamad Ali-Dib of New York University Abu Dhabi in the United Arab Emirates.
"The deviation of their values from what was expected led us to hypothesise that WASP-76b may have swallowed another, much smaller planet with the same chemical composition as Mercury."
The results show that we have only scratched the surface of what these strange, extreme worlds can tell us about the different ways planets can form and exist in our galaxy.
"Generations of researchers have used the measured abundances of Jupiter, Saturn, Uranus and Neptune for hydrogen and helium to compare theories of the formation of gas planets," says Benneke. "Likewise, measurements of heavier elements such as calcium or magnesium in WASP-76 b will help to better understand the formation of gaseous planets."

 

Source: https://www.sciencealert.com/