The Evaporating Atmosphere of the TOI-1759b Sub-Neptune Exoplanet Could Tell Us How Habitable Planets Form

Astronomers sifting through data from a NASA planet-hunting satellite have hit the jackpot: a common type of planet 131 light-years away known as TOI-1759b, with a polar story rare to tell. Thanks to its close proximity to its host star, the planet’s atmosphere appears to be evaporating into dead space – extremely fast, by astronomical standards.

See the “optical variation” caused by this radiation, reported in one new research led by Eder Martioli at the Laboratório Nacional de Astrofísica in Brazil, could help us understand one of the strangest mysteries in modern astronomy. As we continue to discover more extrasolar planets – what we call exoplanets – the inexplicable absence of planets the size of Neptune or slightly smaller (“Neptune”) in orbits close to their host stars.

By sheer probability alone, we must further discover these mid-sized planets capable of completing full orbits around their host stars in just a few days. Instead, we are left with a planetary dead zone for average planets that astronomers call the “desert under Neptune”. All of this begs the question: How can there be so many medium-sized planets out there, yet so some medium-sized planets in orbits close to their stars?

This is not simply an intriguing question for astronomers interested in learning about planet formation. Measuring the amount of evaporation in the atmosphere could also help us narrow the search for alien life in the universe — something a lot of More people can get behind.

An artist’s conception of HD 209458b, another alien planet known to be escaping its atmosphere thanks to how close its orbit is to its sun.

NASA, European Space Agency, Alfred Vidal-Madjar (Institut d’Astrophysique de Paris, CNRS)

One theory is that the sub-Neptunes are of such size, density, and composition that when they are exposed to the hot light of a really close star, they simply cannot cling to the atmosphere. of them. All that powered hydrogen would fly up and disappear.

On less gaseous and less dense planets with weaker gravity, stellar radiation can kick-start a process astronomers call “hydrogen draining,” which eventually removes all the gas that makes up the planet. so much of the atmosphere, leaving behind grains of inert rock that are only a fraction of the original size of the planet.

In contrast, larger planets tend to cling more tightly to their atmospheres, preventing the escape of hydrogen. Smaller planet with higher gravity, Earth among them, also enjoy this protection. A small amount of hydrogen leaked from our planet’s upper atmosphere, but the leak wasn’t fast enough to really matter, so we’re all still warm and fuzzy down here.

This seems to be the only fate of Neptunes orbiting close to lose their atmosphere and turn into smaller, naked rocks. The whole process can take hundreds of millions, even billions of years.

Everywhere we look in space, we see these small, rocky, orbiting planets — the remains of sub-Neptunes that have undergone a likely stellar wash. millions or billions of years ago. “Fossils,” Martioli called them.

Hydrogen escape could turn TOI-1759b into one of these fossils, robbing our galaxy of yet another of its many average planets and expanding the desert under Neptune.

“If we catch this process in action by detecting hydrogen escape in TOI-1759b, we should be able to quantify the contribution of this process” to the formation, Martioli told The Daily Beast. into a desert.

Martioli and his team found TOI-1759b in the piles of data collected by NASA Switch to exoplanet survey satellite (TESS), launched in 2018. They published their discovery in a new paper, a preprint appeared online this month (although not yet peer-reviewed).

TESS’s high-tech camera cluster can examine distant stars and look for the shadows of planets passing in front. In the last few decades, this “transit” survey method has found nearly 5,000 distant exoplanets in star systems other than our own. Their light signature, registered with UV filters, can indicate the movement of gases in their atmosphere.

At least half of all known exoplanets are the size of Earth and Neptune, the sub-Neptune range. But only a handful of Neptunes are in close orbits with their stars. One lucky sub-Neptune with a narrow orbit, NGTS-4b, appears to be stable — perhaps because it has an unusually large core more strongly attached to its atmosphere. There is no observable hydrogen escape.

According to George McDonald, an astronomer with Rutgers, TOI-1759b is further away from its star than NGTS-4b — in fact, TOI-1759b lies just outside the normal boundary of the sub-Neptune desert. But more seriously, the ultraviolet snapshots show it is losing its atmosphere. This may be the best place to see the evaporating atmosphere in real time because it is so close to us (131 light-years is just a stone thrown into space).

An artist’s illustration of TESS.


Ideally, someone could point out what’s new James Webb . Space Telescope at TOI-1759b, said Martioli. But he doesn’t count on it, believing the new space telescope’s 21-foot-wide mirror is overkill for this kind of research. “The planet’s evaporating atmosphere is easily detectable even with ground-based facilities,” he said.

But detecting hydrogen escaping on a distant planet is one thing. Just calculate how a lot of hydrogen is escaping, and at what rate, is another matter. Étienne Artigau, an astrophysicist from the University of Montréal and a member of Martioli’s team, told The Daily Beast: “Escape from hydrogen is generally difficult to measure.

Mathematical models of hydrogen escape, based in part on data from the Earth’s atmosphere and the atmospheres of the planets and moons in our solar system, still include many assumptions and may not always apply to distant alien planets.

Validating and measuring optical variability on TOI-1759b can help us refine our models for hydrogen escape and, by extension, our models for planetary evolution. That not only can help us detect planets but We lose their atmospheres and make Neptune a little less mysterious, it could also tell us where to look for planets Not lose their atmosphere.

That has obvious implications for Our ever-expanding search for extraterrestrial life. As far as we know, a stable atmosphere is a prerequisite for biological evolution.

TOI-1759b’s star is a red dwarf, making it smaller and cooler than our sun, a yellow dwarf. There are many red dwarf star systems around us in the Milky Way galaxy. Many of these systems have planets that are slightly smaller than the sub-Neptunes but slightly bigger than the Earth, called “Super Earth. ”

“The very different properties of red dwarfs compared to sun-like stars mean that there are still many unknowns about how habitable these planets really are,” said McDonald.

If astronomers can calculate the rate of hydrogen escape on TOI-1759b, they can begin to guess what red dwarf orbit super-Earths might have. short rate of escape — and possibly a stable atmosphere where life could thrive.

Those could be the first clues that will eventually confirm whether we are alone in the universe. And it could all start with an ill-fated sub-Neptune that is sending a lot of gas into space.

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