What is a medium exoplanet? ESA’s next ARIEL mission should provide answers

Five thousand extrasolar planets detected and counting, we still don’t have a standard model of the full range of planets circling other sun-like stars. Or so says Giovanna Tinetti, an astrophysicist at University College London (UCL), principal investigator for a consortium of dozens of institutions that are part of the Agency’s next €500 million ARIEL mission. European space (ESA).

Using infrared and visible spectroscopy, the ARIEL (Atmospheric Remote-sensing Infrared Exoplanet Large-survey) mission is expected to classify at least 1,000 known exoplanets based on the chemical composition of their atmosphere. These days, most exoplanet characterization efforts, both from the ground and from space, focus on finding an Earth-like twin, an Earth 2.0.

But ARIEL is designed to offer the planetary science community a study of all kinds of extrasolar planets – from Earth-mass to gas giants.

Due to a 2029 launch to the gravitationally stable Earth-Sun L2 (Lagrange point), ARIEL will perform spectroscopic observations of a target planet as it transits around its parent star. Such transits make it possible to characterize an exoplanetary atmosphere since it is backlit by its parent star. Thus, ARIEL will help planetary scientists determine whether a planet’s chemistry is related to its forming environment, or whether the type of host star determines the physics and chemistry of the planet’s birth and evolution.

“I’m interested in the big picture; how planets form and evolve in our galaxy,” Tinetti told me recently in his office at University College London (UCL). “All of these planets are going to tell us a different story.”

Observations of these worlds will provide insight into the early stages of planetary and atmospheric formation, and their subsequent evolution, in turn contributing to the understanding of our own solar system, according to ESA.

Using its one-meter-class elliptical telescope, ARIEL will observe transiting gas giants, Neptunes, super-Earths and Earth-sized planets around a range of host star types. .

We’ll focus primarily on planets around very bright stars that are typically tens or, in some cases, hundreds of light-years away, Tinetti says. This is because the brighter the star, the easier it is to make these measurements, she says. And so will be able to better measures even faster, says Tinetti.

Potentially, most of these planets will be warm and hot, Tinetti says.

Surprisingly, planetary theorists have made relatively little progress over the past twenty years in understanding how a planet’s host star may have influenced its formation and evolution.

“We don’t know if a planet’s chemistry is related to its forming environment, or if the type of host star determines the physics and chemistry of planet birth and evolution,” Tinetti wrote. and his co-authors in a 2018 article published in the journal Experimental astronomy.

As for ARIEL’s planetary targets?

We want to make sure we have a good statistical survey that includes different kinds of planets around different kinds of stars, Tinetti says. We want to understand how atmospheric composition and characteristics change based on a wide variety of parameters, she says.

Depending on where the planets formed; whether they were close to the star or much further away, they could have captured different materials in the protoplanetary disks, says Tinetti. And if we look at the atmospheric composition, we should be able to see the difference in terms of elemental abundances, she says.

ARIEL will provide us with the knowledge of the kind of exoplanetary atmospheric chemistry that we can say with certainty cannot support life, says Tinetti. But most importantly, she says, they’ll tell us what normalcy is there and give us a sort of standard model of non-habitable worlds.

Does Tinetti think the Earth is rare?

“I don’t think we’re rare,” she says. “But I’m interested not only in finding an Earth 2.0, but also in the Earth’s cousins.”

As for finding life elsewhere?

I don’t want to be Earth-centric and I think the only way to host life is to have an Earth-like planet, says Tinetti. I want to keep my options open because I don’t think we have the complete picture, she said.