Webb lifts veil on a type of common but mysterious exoplanet

Although they do not organize around our sun, the sub-neptunes are the most common type of exoplanet, or planet outside our solar system, which have been observed in our galaxy. These little gaseous planets are wrapped in mystery … and often, a lot of mist. Now, by observing Exoplanet TOU-421 B, the James Webb space telescope of NASA helps scientists understand the sub-nevings in a way that was not possible before the launch of the telescope.

“I expected my entire career for webb so that we can significantly characterize the atmospheres of these small planets,” said the main investigator Eliza Kempton from the University of Maryland, College Park. “By studying their atmospheres, we have a better understanding of how the sub-nevings have formed and evolved, and this understands why they do not exist in our solar system.”

The results are published in Astrophysical newspaper letters.

Small, fresh, wrapped in mist

The existence of sub-neptunes was unexpected before being discovered by the Kepler space telescope to NASA retirement in the last decade. Now astronomers are trying to understand where these planets come from and why they are so common.

Before webb, scientists had very little information about them. Although the sub-neptuans are several times larger than the earth, they are still much smaller than the giant gas planets and generally fresher than hot jupiters, which makes them much more difficult to observe than their giant gas counterparts.

A key front discovery webb was that most of the under-nursing atmospheres had flat or stroke transmission spectra. This means that when scientists observed the spectrum of the planet when he passed his host star, instead of seeing spectral characteristics – chemical fingerprints that would reveal the composition of the atmosphere – they only saw a flat spectrum. Astronomers have concluded from all these flat-line spectra that at least some sub-nevings were probably very very obscured by clouds or dangers.

Another type of sub-neptune?

“Why did we observe this planet, you-421 B? It is because we thought it might not have dangers,” said Kempton. “And the reason is that there were previous data which implied that perhaps the planets on a certain temperature range were less enriched with mist or clouds than others.”

This temperature threshold is approximately 1,070 degrees Fahrenheit. Below, scientists have hypothesized that a complex set of photochemical reactions would occur between sunlight and methane gas, and this would trigger the mist. But the warmer planets should not have methane and should therefore not have mist.

The temperature of TOU-421 B is approximately 1,340 degrees Fahrenheit, well above the alleged threshold. Without mist or clouds, the researchers expected to see a clear atmosphere – and they did it!

A surprising discovery

“We have seen spectral characteristics that we attribute to various gases, and this allowed us to determine the composition of the atmosphere,” said Brian Davenport of the University of Maryland, a third -year doctorate. Student who analyzed primary data.

“While with many other sub-neptuss that had been observed before, we know that their atmospheres are made of something, but they are blocked by the mist.”

The team found a water vapor in the planet’s atmosphere, as well as provisional signatures of carbon monoxide and sulfur dioxide. Then there are molecules that they have not detected, such as methane and carbon dioxide. From the data, they can also deduce that a large amount of hydrogen is in the atmosphere of Tou-421 B.

The light hydrogen atmosphere was the big surprise for researchers. “We had recently wrapped our minds around the idea that these first sub-neptuans observed by Webb had heavy molecule atmospheres, so that it had become our expectations, then we found the opposite,” said Kempton. This suggests that TOI-421 B may have been formed and evolved differently from the colder sub-nevings observed above.

You-421 B is unique?

The atmosphere dominated by hydrogen is also interesting because it imitates the composition of the Hosito star of Toi-421 B. “If you have just taken the same gas which has made the star star, to have plunged it on the atmosphere of a planet and to put it at the much fresher temperature of this planet, you will get the same combination of gas. This process is more in line with the giant planets, And it is different from the other sub-representatives that have been observed with webb so far, “said Kempton.

In addition to being warmer than the other sub-neptuss previously observed with webb, to-421 b orbit a star similar to a sun. Most of the other sub-neptuss that have been observed so far in smaller orbit, cooler stars called red dwarfs.

Is you-421b emblematic of hot sub-neptus in orbit of sun stars, or is it simply that exoplanets are very diverse? To find out, researchers wish to observe more hot sub-nevings to determine whether it is a unique case or a wider trend. They hope to better understand the training and evolution of these common exoplanets.

“We have released a new way to look at these sub-neptus,” said Davenport. “These high-temperature planets lend themselves to characterization. So, examining the sub-nevings of this temperature, we may be more likely to accelerate our ability to learn more about these planets.”