University of Warwick: Scientists measure the atmosphere of a planet 340 light years away with unprecedented precision

The first direct measurements of the amount of both water and carbon monoxide in the atmosphere of a planet in another solar system roughly 340 light years away have been made by an international team of scientists that includes University of Warwick astronomers, using the ground-based Gemini Observatory telescope in Chile.

The team led by Arizona State University have published their results in the journal Nature. The University of Warwick scientists led independent data analysis and modelling / interpretation to validate the result due to the unprecedented precision required for the conclusions.

There are thousands of known planets outside of our own solar system (called exoplanets). Scientists use both space telescopes and ground-based telescopes to examine how these exoplanets form and how they are different from the planets in our own solar system.

This study focused on planet “WASP-77Ab,” a type of exoplanet called a “hot Jupiter” because they are like our solar system’s Jupiter, but with a temperature in excess of 1500C.

They then focused on measuring the composition of its atmosphere to determine what elements are present, and compared them to the star it orbits.

While we cannot yet send spacecraft to planets beyond our solar system, scientists can study the light from exoplanets with telescopes. The telescopes they use to observe this light can be either in space, like the Hubble Space Telescope (HST), or from the ground, like the Gemini Observatory telescopes.

The team had been extensively involved in measuring the atmospheric compositions of exoplanets using HST, but obtaining these measurements was challenging. Not only is there a steep competition for telescope time, HST instruments only measure water (or oxygen) and the team needed to also gather measurements of carbon-monoxide (or carbon) as well.

This is where the team turned to the Gemini South telescope.

Gemini South is an 8.1 m diameter telescope located on a mountain in the Chilean Andes called Cerro Pachón, where very dry air and negligible cloud cover make this a prime telescope location. It is operated by the National Science Foundation’s NOIRLab (National Optical-Infrared Astronomy Research Laboratory).

Using the Gemini South telescope, with an instrument called the Immersion GRating INfrared Spectrometer (IGRINS), the team observed the thermal glow of the exoplanet as it orbited its host star. From this instrument, they gathered information on the presence and relative amounts of different gases in its atmosphere.

And with clear measurements of both water and carbon monoxide in the atmosphere of WASP-77Ab, the team was then able to extract the relative amounts of oxygen and carbon in the exoplanet’s atmosphere.

Co-author Dr Matteo Brogi of the University of Warwick Department of Physics, who led on validating the results, said: “While these were observations from the ground, we obtained a level of precision in our measurements that we only thought possible with the upcoming James Webb Space Telescope. This means that we now have a complementary method to study exoplanets at a similar level of detail.

“If we can do this with today’s technology, think about what we will be able to do with the up-and-coming telescopes like the Extremely Large Telescope at the European Southern Observatory. It is a real possibility that we can use this same method by the end of this decade to sniff out potential signatures of life, which also contain carbon and oxygen, on rocky Earth-like planets beyond our own solar system.”

Co-author Professor Vivien Parmentier of the University of Oxford said: “What I find incredible is that our measurement of the amount of carbon in a planet that is more than 300 light-years away is almost as precise as the measurements that we get for solar-system planets, that are comparatively next door. Jupiter is roughly 6 million times closer to us than WASP-77Ab so if Jupiter was your neighbour’s house, a few metres away from you, WASP-77Ab would be a house in Sydney, Australia!”

Obtaining ultra-precise gas abundances in exoplanet atmospheres is not only an important technical achievement, especially with a ground-based telescope, it may also help scientists look for life on other planets.

“This work represents a pathfinder demonstration for how we will ultimately measure biosignature gases like oxygen and methane in potentially habitable worlds in the not too distant future,” says lead author Assistant Professor Michael Line of Arizona State University.

What Line and the team expect to do next is repeat this analysis for many more planets and build up a “sample” of atmospheric measurements on at least 15 more planets.

“We are now at the point where we can obtain comparable gas abundance precisions to those planets in our own solar system. Measuring the abundances of carbon and oxygen (and other elements) in the atmospheres of a larger sample of exoplanets provides much needed context for understanding the origins and evolution of our own gas giants like Jupiter and Saturn,” says Line.

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