What is the average exoplanet? The European Space Agency’s next ARIEL mission should provide answers

Five thousand extrasolar planets have been discovered, and we still don’t have a standard model for the full range of planets orbiting other Sun-like stars. Or so says University College London (UCL) astrophysicist Giovanna Tinetti, principal investigator for a group of dozens of institutions that are part of the European Space Agency’s (ESA) upcoming €500 million ARIEL mission.

Using visible and infrared spectroscopy, the ARIEL (Large Extrasolar Infrared Survey) mission must classify at least 1,000 known exoplanets by the chemical composition of their atmospheres. These days, most efforts to characterize exoplanets, both from Earth and from space, focus on the search for its Earth-like twin, Earth 2.0.

But ARIEL is designed to provide the planetary science community with surveys of all kinds of exoplanets – from Earth mass to gas giants.

Launched in 2029 to gravitationally stable Earth-Sun L2 (Lagrangian point), ARIEL will take spectroscopic observations of a target planet as it passes around its parent star. These transits allow the exoplanets’ atmospheres to be distinguished due to the background illumination of their parent star. Thus, ARIEL will help planetary scientists determine whether a planet’s chemistry is related to its formation environment, or whether the type of host star drives the physics and chemistry of planet birth and evolution.

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

Observations of these worlds will give insight into the early stages of formation of planets and atmospheres, and their subsequent evolution, in turn, contributing to understanding of our solar system, says the European Space Agency.

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

We will focus mainly on planets around very bright stars that are usually dozens or in some cases hundreds of light-years away, says Tinetti. That’s because the brighter the star, the easier it is to make these measurements, she says. Thus you’ll be able to make better measurements faster, says Tinetti.

Most of these planets are likely to be warm and hot, Tinetti says.

Surprisingly, planetary theorists have made relatively little progress in the past 20 years in understanding how a planet’s host star influences its formation and evolution.

“We have little idea whether a planet’s chemistry is related to its formation environment, or whether the type of host star drives the physics and chemistry of planet birth and evolution,” Tinetti and co-authors wrote in a 2018 paper. in the journal experimental astronomy.

As for ARIEL’s planetary goals?

We want to make sure we have a good statistical survey that includes different types of planets around different types of stars,” says Tinetti. We want to understand how the composition and properties of the atmosphere change as a function of a variety of parameters, she says.

Depending on where the planets are; Either near or far from the star, Tinetti says, they may have picked up different materials in the protoplanetary disks. She adds that if we look at the composition of the atmosphere, we will be able to see the difference in terms of the abundance of the elements.

ARIEL will provide us with knowledge of the kind of atmospheric chemistry of exoplanets that we will be able to say for sure cannot harbor life, Tinetti says. But more importantly, she says, they will tell us what normal life is out there and give us a kind of standard model of uninhabitable worlds.

Does Tinetti think the Earth is rare?

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

As for finding life elsewhere?

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

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