“hot neptune” exoplanet it was found to contain sulfur dioxide in its atmosphere—an atmosphere that also jets out into space as the planet loops over the poles of its star every three and a half days in a steeply inclined orbit.
The existence of sulfur dioxide in the atmosphere of the exoplanet, dubbed GJ 3470b and located 96 light years of Earthit came as a shock when he noticed him The James Webb Space Telescope (JWST).
“We didn’t think we’d see sulfur dioxide on such small planets, and it’s exciting to see this new molecule in a place we didn’t expect because it gives us a new way to find out how these planets formed.” Thomas Beatty of the University of Wisconsin, Madison said va declaration. “And minor planets are particularly interesting because their composition really depends on how the planet formation process played out.”
Everything about GJ 3470b tells us that it has a fascinating and eventful history.
Planets are formed in a disk of gas and dust that swirls around a plane aligned with the star’s rotation axis. In ours Solar Systemwe can see evidence of this disk in that all the planets from Quicksilver on Neptune orbit in the plane of the ecliptic. GJ 3470b, in contrast, follows an orbit inclined 89 degrees to the axis of rotation of its cool Red dwarf star. In other words, it is on a steep orbit that curves across the poles of the star. Planets do not usually form in such orbits.
Related: Why are there so few “hot Neptune” exoplanets?
With a mass 13.9 times greater than Earth’s massand average about 40% that of Jupiter, GJ 3470b is an inflated gas bag. When such worlds are close to their star, astronomers call them ‘hot Neptunes.'” GJ 3470b has an atmospheric temperature of 325 degrees Celsius (617 degrees Fahrenheit); Neptune’s temperature in our solar system is -200 degrees Celsius (-330 degrees Fahrenheit).
Current models of planet formation describe how gas giants usually form further from their star than stone planetsin cold depths where there is more gas. Yet GJ 3470b orbits just 5.3 million kilometers (3.3 million miles) from its star. For comparison, Mercury, the closest planet to ours sunit orbits at an average distance of 58 million kilometers (36 million miles) from our star, although red dwarf systems are typically diminutive compared to our solar system.
Under normal circumstances, we would expect GJ 3470b to have formed further and then migrated inwards due to interactions with the planet-forming disk of its star. Meanwhile, scientists would normally think that the world would have been pushed out of its orbital plane by a gravitational interaction with another planet, or perhaps even a jolt from a close-by star.
However, the planet’s atmospheric mix suggests otherwise.
Despite the detection of molecules inside JWST, such as sulfur dioxide, GJ 3470b’s atmosphere remains overwhelmingly hydrogen and helium, even more so than gaseous planets in our solar system—a fact they discerned Hubble Space Telescope in 2019. So presented interpretation is that GJ 3470b actually formed close to its star as a rocky planet before a dense atmosphere of near-pure hydrogen and helium accumulated—but that’s just a hypothesis at this point. This is why the detection of sulfur dioxide on the JWST is so important, as its presence could help distinguish different theories about how the planet formed.
The detection of sulfur dioxide came to light thanks to the fact that GJ 3470b is transiting its star, allowing astronomers to perform what is called “transmission spectroscopy.” As light from the parent star shines through GJ 3470b’s atmosphere, molecules in the world’s atmosphere absorb some of the starlight, leaving dark absorption lines in the star’s spectrum.
However, disentangling these absorption lines is difficult, especially for hot Neptune, which is likely covered in a featureless haze.
“The thing is, everybody looks at these planets and often everybody sees flat lines,” Beatty said. “But when we looked at this planet, we didn’t really get a straight line.
Instead, JWST was able to confirm absorption lines from carbon dioxide, methane and water vapor and indeed detect sulfur dioxide in the region for the first time. time. This makes GJ 3470b the lightest and coolest exoplanet known to have sulfur dioxide in its atmosphere. Previous detections involved hot Jupiter atmospheres with temperatures above a thousand degrees Celsius (1,830 degrees Fahrenheit).
“The discovery of sulfur dioxide in a planet as small as GJ 3470b gives us another important entry on the list of planet-forming ingredients,” Beatty said.
Sulfur likely started as a component of hydrogen sulfide, the team believes. However, because GJ 3470b orbits so close to its star, the ultraviolet light from the star’s body has a strong enough punch to easily break the molecules of the atmosphere into pieces, leading to a kind of chemical wave of broken molecular components recombining with others. atoms and molecules. A sulfur atom combines with two oxygen atoms to form sulfur dioxide.
But the planet’s parent star doesn’t just break down atmospheric molecules; the hydrogen released from these molecules can completely remove them from the planet. So GJ 3470b is literally evaporation before our eyes the stellar wind gradually blows away its atmosphere space, leaving behind a stream of hydrogen gas. The planet has already lost an estimated 40% of its original mass.
The presence of sulfur dioxide in its atmosphere, the tilted orbit that remains unexplained, and the mass loss that dramatically changes GJ 3470b forever are important clues to the origin of this weird and wonderful planet, according to Beatty.
“These are important steps in the recipe that created this particular planet and can help us understand how planets like it are made,” he said.
Beatty presented the results at the 244th meeting of the American Astronomical Society on June 10, and they have been accepted for publication in the Astrophysical Journal Letters.