Astronomers should focus on understanding exoplanets we’ve already discovered, says researcher

This summer marks nearly three decades since the discovery of 51 Pegasi b, the first known extrasolar planet to circle a sun-like star. Today there are more than 5000 known planetary systems surrounding sun-like stars and half of all sun-like stars are now believed to harbor planets.

The discoveries of exoplanets in the last decade alone – largely thanks to the work of NASA’s defunct Kepler space telescope – are enough to blow your mind. But astronomers are only just beginning to seriously characterize most of these planets. And this is arguably where this burgeoning field of exoplanetary science should now be focused.

So, two years after Covid-19 blocked in-person meetings, one of the world’s leading exoplanetary science conferences – Extrasolar Planets IV (Exo4) – has just ended in Las Vegas. Last week I was able to catch up with Exo4 Host President Jason Steffen to discuss some of the major issues in the field.

At the top of my list was simply why after decades of searching with ground-based and space-based telescopes, we have yet to find a true exo-earth.

We know Earth-sized planets close to the habitable zone, Steffen, an astrophysicist at the University of Nevada in Las Vegas, told me. But he says that in terms of understanding the properties of their atmospheres; the nature of any liquid water in the atmosphere or on their surface, we are still a generation away from telescopes that can give us these kinds of measurements.

When will we actually start getting ghosts from an exo-earth?

2050 is a guess, says Steffen.

What does our study of exoplanets tell us about our own solar system?

“That you can have very different solar systems than ours,” Steffen said.

We have a pretty good idea of ​​how our solar system formed and evolved, but exoplanetary science says here’s all the other stuff that didn’t happen in our solar system that produces different types of planets, he says .

As for the synergy between solar system science and exoplanetary science?

Planetary scientists who focus on bodies in our own solar system have an abundance of riches, Steffen says. Mars researchers have had the luxury of taking samples from the surface there and performing in situ analyzes that can indicate the abundance of dozens of chemical compounds. Solar system scientists also have access to the world’s best ground-based spectrometers, capable of identifying dozens of chemical species on bodies in our solar system, from Mercury to Pluto.

But at this point, extrasolar planet researchers are lucky if they can detect hydrogen in an exoplanet’s atmosphere, Steffen says. However, he notes that there is one area where the competition is fairer. That is to say in the extrasolar dynamic measurements of the movements of a given planet. And how the movements of one planet affect the movements and movements of other planets within the same system.

We can understand the orbital properties of exoplanetary systems and compare them to the orbital properties of planets in our solar system, Steffen says.

One of the most interesting presentations from the Exo4 conference was identifying putative planetary material accreted onto dying stellar remnants known as white dwarfs.

White dwarf stars are super dense, and if you dumped something on a white dwarf, it would only stay visible on the surface for a few thousand years before it all sinks in, Steffen says.

So if you observe something that only has a lifespan of a thousand years on a star that has been there for a billion years, that tells you that it must be a recent influx at the surface of a white dwarf, says Steffen. It must be planetary remnants, he said. This is the only method I know of to measure the composition of the material forming the planet; that is, the abundance of nickel, iron and sodium, says Steffen.

Would this material come from planets that were destroyed by the stellar endgame of the system itself?

The origin of this material is unclear; whether from planets that were destroyed in the star’s red giant phase, or before the planet was engulfed by the dying red giant, Steffen says.

The other big discussion at Exo4 was evidence for the existence of a third Earth-mass planet circling our nearest stellar neighbor, Proxima Centauri. Just 4.2 light years away, Proxima Centauri is a pale red dwarf that is literally the next star.

The evidence that there is a third ley planet seems compelling, says Steffen. That it’s habitable seems a bit of a stretch, but the fact that we’re observing it around the nearest star just tells us how common planet formation is, he says.

Is it a numbers game? Should we try to find the most planets or study them in detail?

We haven’t done detailed studies of even 10% of the planets that were discovered by Kepler, says Steffen. While it’s helpful to find more planets, it’s also helpful to understand the planets we’ve discovered, he says.

Steffen says the Webb Space Telescope and the next generation of extremely large ground-based telescopes are a way to characterize the atmospheres of many of the planets we’ve found. Observations that span a longer period also add information about the systems where those planets reside, he says.

But exoplanetary science still lacks the kind of funding it needs to enable more high-risk, high-reward initiatives, Steffen says.

“Everything is competitive to the point where the overwhelming majority of proposals are rejected,” Steffen said. “The current financial situation [makes] the discipline is too risk averse.

A 30% success rate for grant proposals would be much healthier than the less than 10% success rate we currently experience, he says.

“Science would move faster if there was enough room for more studies that aren’t happening,” Steffen said.

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