This Jupiter-like planet may have eaten its neighbour at some point: Canadian study

The ultra-hot giant exoplanet WASP-76 b, studied here, is an extremely hot world orbiting very close to its giant star. (NOIRLab)

Scientists have long been able to measure the chemicals in our own atmosphere with a huge amount of detail — but now, with the power of a very good telescope, astronomers are able to obtain those same details for planets hundreds of lightyears away.

A new study from Canadian and international scientists has laid out in detail what the chemical composition is for the atmosphere of an enormous planet hurtling through space more than 634 light years away from us.

The planet in question, called WASP-76 b, is a gas giant closely orbiting a massive star in the constellation of Pisces. According to the new study, published Wednesday in the peer-reviewed journal Nature, it orbits its star so closely that the planet itself can get up to 2000 degrees Celsius.

“This is the first study to measure the abundances of chemical elements such as nickel, magnesium, and chromium at high precision in any giant planet,” Mohamad Ali-Dib, NYU Abu Dhabi Research Scientist from the Centre for Astro, Particle, and Planetary Physics and one of the authors of the study, said in a press release.

WASP-76 b isn’t a newly discovered exoplanet — meaning a planet which orbits outside of our solar system. It was first observed in 2013. However, this study provides a more in-depth look at just what makes up this interstellar curiosity.

It’s not just a fun fact to know the chemicals that make up a planets’ atmosphere — they tell a story about the planet’s formation and major events in its past.

In this case, researchers found chemicals in WASP-76 b’s atmosphere that are known to be rock-forming elements, and are not usually found in this quantity in gas giants like Jupiter and Saturn. The abundance of these rock-forming elements led researchers to hypothesize that WASP-76 b, which orbits its star on its lonesome, may once have had a rockier neighbour which orbited with it.

“The deviations of (the chemical) values from what is expected led us to postulate that WASP-76 b might have swallowed another much smaller planet, one with the same chemical composition of Mercury,” Ali-Dib said.

The study details the abundances of 11 chemical elements in the atmosphere in total.

Researchers also observed that the chemicals were constantly shifting in WASP-76 b’s upper atmosphere as the temperature changed.

As the planet revolves and moves around its star, different elements experience the temperature shifts that come with night and day — being turned away from the star and facing it. They heat or cool depending on whether or not they’re facing the star, meaning a constant shift through the cycle of condensation: elements forming into a gas and moving to the top layer of the atmosphere, then turning liquid and sinking deeper into the planet’s layers as they cooled.

This shift from gas to liquid can be very abrupt for some elements depending on their condensation temperature, researchers noted.

One of the exciting things about this research, which was done by an international team led by the Université de Montréal, is that ultra-hot gas giants such as WASP-76 b allow scientists to study elements within gas giants that aren’t close enough to the surface in the gas giants in our solar system to study.

WASP-76 b is around 12 times closer to its star than Mercury is to our sun. It’s so hot on WASP-76 b that elements which could form into rocks are present only in gaseous form, but they’re in the upper atmosphere, where we can study them. The same compounds may be found in a colder gas giant like Jupiter, but if they are, they’re in the lower atmosphere, closer to the centre of the planet, where astronomers aren’t yet able to detect them.

Researchers used data recorded by the MAROON-X instrument on the Gemini-North Telescope, which was designed to discover exoplanets and collect detailed information on their composition by analyzing light.