A “hot Neptune” exoplanet was found to contain sulfur dioxide in its atmosphere – an atmosphere that also bursts into space as the planet orbits above its star’s poles in a highly inclined orbit every three and a third days.
The existence of sulfur dioxide in the atmosphere of the exoplanet, called GJ 3470b and located 96 Light years Since Earthwas a shock when he was spotted by 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 understand how these planets came to be. trained.” Thomas Beatty of the University of Wisconsin, Madison said in a statement. “And small planets are particularly interesting, because their composition really depends on how the planet formation process happened.”
Everything about the GJ 3470b tells us that it has a fascinating and colorful history.
Planets form in a disk of gas and dust that swirls around a plane aligned with the axis of rotation of a star. In our solar systemwe can see evidence for the existence of this disk in the fact that all the planets of Mercury has Neptune orbit in the ecliptic plane. GJ 3470b, for its part, follows a trajectory inclined by 89 degrees relative to the axis of rotation of its cold body. red dwarf star. In other words, it is in a steep orbit that loops above the star’s poles. Planets generally do not form in such orbits.
Related: Why are there so few “hot Neptune” exoplanets?
With a mass 13.9 times greater than The mass of the Earthand a diameter of approximately 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). Fahrenheit).
Current models of planet formation describe how gas giants generally form further from their star than rocky planets, in cold depths where gas is more abundant. Yet GJ 3470b orbits just 5.3 million kilometers (3.3 million miles) from its star. For comparison, Mercury, the closest planet to our sunorbits at an average distance of 58 million kilometers (36 million miles) from our star, although red dwarf systems are generally smaller than our solar system.
Normally, we would expect GJ 3470b to have formed further out and then migrated inward as a result of interactions with its star’s planet-forming disk. Meanwhile, scientists would normally suspect that the world would have been pushed out of the orbital plane via a gravitational interaction with another planet, or perhaps even an upheaval caused by a star passing nearby.
However, the planet’s atmospheric mixing suggests otherwise.
Despite JWST detecting molecules inside it, such as sulfur dioxide, GJ 3470b’s atmosphere remains predominantly hydrogen and helium, even more so than the gaseous planets in our solar system – a fact discerned by the JWST. The Hubble Space Telescope in 2019. Thus, the advanced explanation is that GJ 3470b actually formed near its star as a rocky planet before forming a thick atmosphere of almost pure hydrogen and helium – but, at the moment, that’s only a hypothesis. This is why JWST’s detection of sulfur dioxide is so important, because its presence could help differentiate between different theories of planet formation.
The detection of sulfur dioxide was revealed by GJ 3470b passing through its star, allowing astronomers to perform what is called “transmission spectroscopy.” As light from its parent star shines through GJ 3470b’s atmosphere, molecules in the global atmosphere absorb some of the star’s light, leaving dark absorption lines in the star’s spectrum .
It is difficult to determine these absorption lines, however, especially for a hot Neptune which is likely covered in a featureless haze.
“The thing is, everyone looks at these planets and often everyone sees flat lines,” Beatty said. “But when we looked at this planet, we didn’t really get a flat line.”
Instead, JWST was able to confirm the absorption lines of carbon dioxide, methane and water vapor, and actually detect sulfur dioxide in the region for the first time. time. This actually makes GJ 3470b the lightest and coldest exoplanet ever known to have sulfur dioxide in its atmosphere. Previous detections involved the atmospheres of hot Jupiters with temperatures above a thousand degrees Celsius (1,830 degrees Fahrenheit).
“The discovery of sulfur dioxide on a planet as small as GJ 3470b gives us one more important element in the list of ingredients for planetary formation,” Beatty said.
Sulfur likely began as a component of hydrogen sulfide, the team believes. However, because GJ 3470b orbits so close to its star, ultraviolet light from the stellar body is powerful enough to easily break apart atmospheric molecules, leading to a sort of chemical churn formed of broken molecular components recombining with others. atoms and molecules. One sulfur atom combined with two oxygen atoms forms sulfur dioxide.
However, the planet’s parent star doesn’t just break apart atmospheric molecules; the hydrogen released by these molecules can eliminate them entirely from the planet. GJ 3470b is therefore literally evaporate before our eyes, the stellar wind gradually blows its atmosphere into space, leaving behind a stream of hydrogen gas. The planet has already lost around 40% of its initial mass.
The presence of sulfur dioxide in its atmosphere, the tilted orbit that remains unexplained, and the loss of mass that radically changes GJ 3470b forever are significant clues to the origin of this strange 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 this are made,” he said.
Beatty presented the results at the 244th meeting of the American Astronomical Society on June 10, and they were accepted for publication in Astrophysical Journal Letters.