In the search for life beyond Earth, science has taken astronomers to mysterious giant gas planets that race around their host stars in extremely tight orbits. A new study is now shedding more light on the formation of these objects, known as hot Jupiters, as astronomers combine observations from the Hubble space telescope with theoretical modelling.

Astronomers found chemical signatures of water molecules and carbon monoxide on gas giants. Published in the journal ‘Nature Astronomy’, the study provides astronomers with an unprecedented “field guide” to hot Jupiters and offers insight into planet formation in general.

Ranging in size from about one-third the size of Jupiter to 10 Jupiter masses, all hot Jupiters orbit their host stars at an extremely close range, usually much closer than Mercury (the innermost planet in our solar system) is to the sun.

Although astronomers think that only about 1 in 10 stars host an exoplanet (a planet that orbits a star outside the solar system) in the hot Jupiter class, the peculiar planets make up a sizeable portion of exoplanets discovered to date. The study is the first to look at a broader population of strange worlds.

Led by Megan Mansfield, a Nasa Sagan Fellow at the University of Arizona, astronomers used observations made with the Hubble Space Telescope and measured emission spectra from hot Jupiters. “These systems, these stars and their hot Jupiters are too far away to resolve the individual star and its planet. All we can see is a point the combined light source of the two,” Mansfield said in a statement.

In a bid to look deeper into the formation of these gas giants, the team used a method known as secondary eclipsing. It involves measuring the combined light coming from the star and its planet and comparing that measurement with when the planet is hidden behind its star. “This allows us to subtract the star’s contribution and isolate the light emitted by the planet, even though we can’t see it directly,” Mansfield explained.

The University of Arizona, in a release, said the eclipse data provided the researchers insight into the thermal structure of the atmospheres of hot Jupiters and allowed them to construct individual profiles of temperatures and pressures for each one.

“In a way, we use molecules to scan through the atmospheres on these hot Jupiters. We can use the spectrum we observe to get information on what the atmosphere is made of, and we can also get information on what the structure of the atmosphere looks like,” Mansfield said.

They found that “all hot Jupiters are likely to contain similar sets of molecules, like water and carbon monoxide, along with smaller amounts of other molecules”. The findings also revealed that the observed water absorption features varied slightly from one hot Jupiter to the next.

“Taken together, our results tell us there is a good chance we have the big picture items figured out that are happening in the chemistry of these planets. At the same time, each planet has its own chemical makeup, and that also influences what we see in our observations,” the researcher said.