The search for exoplanets (planets located outside our Solar System) has increased in recent years. With more than 5500 new worlds Discovered orbiting other stars, scientists look for signs of possible life in them.
One of these potential habitable worlds is WASP-107b which has intrigued astronomers since its discovery. Why is the gas giant exoplanet WASP-107 b so bloated?
According to data collected using the James Webb Space Telescope from NASA, combined with previous observations of the Hubble Space Telescope From NASA, the planet shows surprisingly little methane (CH4) in its atmosphere, indicating that the interior of WASP-107 b must be significantly hotter and the core much more massive than previously estimated.
It is believed that the unexpectedly high temperature is the result of tidal heating caused by the planet’s slightly non-circular orbit, and may explain how WASP-107 b can become so inflated without resorting to extreme theories about how it formed.
“The results, which were made possible by the extraordinary sensitivity of James Webb and his ability to measure light passing through the atmospheres of exoplanets, can explain the swelling of dozens of low-density exoplanets, helping to solve a long-standing mystery in exoplanet science,” they explain from NASA.
Puffy planets are not uncommon, and most are hotter and more massive and therefore easier to explain.
“Based on its radius, mass and age, we think that WASP-107 b had a very small rocky core surrounded by a huge mass of hydrogen and helium,” he explained in a statement. Luis Welbanks from Arizona State University (ASU), lead author of a study published in Nature.
“But it was difficult to understand how such a small nucleus could absorb so much gas and then not grow until it became a planet with the mass of Jupiter,” he said.
For the researcher, If WASP-107 b instead had more mass in the core, the atmosphere should have shrunk as the planet cooled over time elapsed since it was formed. Without a heat source to re-expand the gas, the planet would have to be much smaller. Although WASP-107 b has an orbital distance of only 7.5 million kilometers (one-seventh the distance between Mercury and the Sun), it does not receive enough energy from its star to be so inflated.
“WASP-107 b is a very interesting target for Webb because it is significantly colder and more Neptune-like in mass than many of the other low-density planets, the hot Jupiters, which we have been studying”said the doctor in astronomy David Sing from Johns Hopkins University (JHU), lead author of a parallel study also published in Nature.
He added: “As a result, we should be able to detect methane and other molecules that can give us information about their chemistry and internal dynamics that we cannot get from a hotter planet.”
The radius giant, extended atmosphere, and edge orbit of WASP-107 b They make it ideal for transmission spectroscopy, a method used to identify the various gases in an exoplanet’s atmosphere based on how they affect starlight.
The exoplanet observational work was achieved by combining observations from NIRCam (near-infrared camera) and MIRI (mid-infrared instrument) from Webb, and WFC3 (Wide Field Camera 3) from Hubble. Thus, Welbanks’ team was able to construct a broad spectrum of light from 0.8 to 12.2 microns absorbed by WASP-107 b’s atmosphere. Using Webb’s NIRSpec (near-infrared spectrograph), Sing’s team constructed an independent spectrum spanning 2.7 to 5.2 microns.
The precise data collected by the supertelescope makes it possible not only to detect, but also to measure the abundance of a large number of molecules, including water vapor (H2O), methane (CH4), carbon dioxide (CO2), carbon monoxide (CO), sulfur dioxide (SO2) and ammonia (NH3). “With Webb’s NIRSpec spectroscopy we obtain direct information on the chemistry of WASP-107 b,” said Stephan Birkmann of the European Space Agency (ESA) and principal investigator of the study’s NIRSpec observations.
“NIRSpec spectroscopy allows us to probe the planet’s atmospheric composition and perfectly complements MIRI and NIRCam observations. “Both spectra show a surprising lack of methane in the atmosphere of WASP-107 b: one thousandth of the amount expected based on the assumed temperature,” he added.
“This is evidence that Hot gas from deep inside the planet must be mixing vigorously with the colder layers above. Methane is unstable at high temperatures. “The fact that we have detected so little, although we did detect other carbon-containing molecules, tells us that the planet’s interior must be significantly hotter than we thought,” Sing added.
One reason for WASP-107 b’s likely source of additional internal energy is tidal heating caused by its slightly elliptical orbit. Since the distance between the star and the planet changes continuously during the 5.7-day orbit, the gravitational pull is also changing, stretching the planet and warming it.
The researchers had previously proposed that the Tidal warming could be the cause of the swelling of WASP-107 b, but until Webb’s results came in, there was no evidence. Once they established that the planet has enough internal heat to completely churn up the atmosphere, the teams realized that the spectra could also provide a new way to estimate the size of the core.
“If we know how much energy there is on the planet, and we know what proportion of the planet is heavier elements like carbon, nitrogen, oxygen and sulfur, versus how much is hydrogen and helium, we can calculate how much mass there must be in the core of the planet,” he explained. JHU’s Daniel Thorngren.
It turns out that the core is at least twice as massive as originally estimated, which makes more sense in terms of how planets form.
Ultimately, it turns out that WASP-107 b is not as mysterious as it seemed. “Webb’s data tells us that planets like WASP-107 b didn’t have to form in some strange way with a super small core and a huge gas envelope,” explained ASU’s Mike Line.
“Instead, we can take something more like Neptune, with a lot of rock and not so much gas, simply increase the temperature and raise it so that it looks like it does,” the expert concluded.
