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What is an average exoplanet? The upcoming ESA air mission should provide answers

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

Using infrared and visible spectroscopy, the Atmospheric Remote-Sensing Infrared Exoplanet Large-Survey (ARIEL) mission is to classify at least 1,000 known exoplanets based on the chemical composition in their atmospheres. Most attempts to characterize exoplanets, both from the ground and from space, today focus on the search for an Earth-like twin, an Earth 2.0.

But ARIEL is designed to provide the planetary science community with an overview of all types of exoplanets – from terrestrial masses to gas giants.

Due to launch in 2029 at a gravitationally stable Earth-Sun L2 (Lagrangian point), ARIEL will make spectroscopic observations of the target planet as it orbits its parent star. Such transits allow the characterization of an exoplanetary environment as it is illuminated by its 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 a planet’s birth and evolution.

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

ESA says observations of these worlds will provide information about the early stages of planetary and atmospheric formation and their subsequent evolution, contributing to understanding our own solar system.

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

We will primarily focus on planets around very bright stars that are typically tens 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. And so we can take better measurements even faster, says Tinetti.

Possibly most of these planets will get hotter and hotter, says Tinetti.

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

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

As for Ariel’s planetary goals?

We want to make sure we have a good statistical study that includes all the different kinds of planets around different kinds of stars, says Tinetti. She says we want to understand how the composition and characteristics of the atmosphere change as a function of various parameters.

Depending on where the planets formed; Whether they’re close to the star or very far away, they could have trapped other material in the protoplanetary disk, Tinetti says. And if we look at the composition of the atmosphere, we should be able to see differences in terms of elemental abundance, she says.

Tinetti says ARIEL will provide us with the kind of knowledge of exoplanetary atmospheric chemistry that we can say with certainty that life cannot exist. But most importantly, she says, they tell us what’s normal out there and provide us with a normative model of non-habitable worlds.

Does Tinetti think the Earths are rare?

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

Find life elsewhere?

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

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