Webb Space Telescope reveals case of puffy exoplanet ‘Marshmallow Microwave’.

The sudden lack of methane suggests that tidal heating has inflated the atmosphere of the warm gas giant WASP-107 b.

Why is warm gas considered a giant? Exoplanet WASP-107b too puffy? With a moderate temperature and extremely low density on par with a microwaved marshmallow, it appears to defy standard theories of planetary formation and evolution.

Two independent teams of researchers think they’ve figured it out. Data from Webb, combined with previous observations from Hubble, show that the interior of WASP-107 b should be much hotter than previously estimated. The unexpectedly high temperatures, thought to be caused by tidal forces stretching the planet like silly putty, could explain how planets like WASP-107 b can be so buoyant, and perhaps solve a long-standing mystery in exoplanet science.

This artist’s concept shows what the exoplanet WASP-107 b could look like based on recent data collected by NASA’s James Webb Space Telescope, along with previous observations from Hubble and other space-based and ground-based telescopes. WASP-107 b is a “warm Neptune” exoplanet orbiting a small, relatively cool star about 210 light-years from Earth, in the constellation Virgo. The planet is about 80% the size of Jupiter by volume, but its mass is less than 10% that of Jupiter, making it one of the least massive exoplanets known. Image credit: NASA, ESA, CSA, Ralph Crawford (STScI)

Webb Space Telescope reveals case of a bloated exoplanet

Why is the warm gas giant exoplanet WASP-107 b so bloated? Two independent research teams now have an answer.

Data collected using NASA’s James Webb Space Telescope, as well as previous observations from NASA’s Hubble Space Telescope, show a trace amount of methane (CH).₄) in the planet’s atmosphere. This suggests that the interior of WASP-107 b must be significantly hotter and the core much larger than previously estimated.

The unexpectedly high temperature is thought to be the result of tidal heating caused by the planet’s slightly irregular orbit, and could explain how WASP-107 b could have inflated without resorting to extreme theories about how it formed.

The results, made possible by Webb’s exceptional sensitivity and accompanying ability to measure light passing through exoplanetary atmospheres, may explain the bloating of dozens of low-density exoplanets, helping to solve a long-standing mystery in exoplanet science.

The problem with WASP-107b

More than three-quarters of the size Jupiter But less than a tenth of the mass is “warm.” NeptuneThe exoplanet WASP-107 b is one of the least dense planets known. While bulge planets are not uncommon, most are hotter and more massive, and thus easier to explain.

“Based on its radius, mass, age and assumed internal temperature, we thought WASP-107 b had a very small rocky core surrounded by a huge mass of hydrogen and helium,” explained Louis Wilbanks of Arizona State University (ASU). The lead author of a paper published May 20 in the journal nature. “But it was difficult to understand how such a small core could sweep up so much gas and then stop growing entirely into a Jupiter-mass planet.”

This transmission spectrum, taken with NASA’s Hubble and James Webb Space Telescopes, shows the amounts of different wavelengths (colors) of starlight blocked by the atmosphere of the gas giant exoplanet WASP-107 b.
The spectrum includes light collected by five separate observations using a total of three different instruments: Hubble’s WFC3 (0.8–1.6 microns), Webb’s NIRCam (2.4–4.0 microns and 3.9–5.0 microns), and Webb’s MIRI (5–12 microns ). Each set of measurements was made by observing the planet-star system for approximately 10 hours before, during and after the transit as the planet moved across the face of the star.
By comparing the brightness of light filtered through a planet’s atmosphere (transmitted light) with unfiltered starlight, it is possible to calculate how much of each wavelength is blocked by the atmosphere. Since each molecule absorbs a unique combination of wavelengths, the transmission spectrum can be used to constrain the abundances of different gases.
This spectrum shows clear evidence of the presence of water (H2O), carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), sulfur dioxide (SO2), and ammonia (NH3) in the planet’s atmosphere, allowing researchers Estimating the planet’s interior atmosphere. Temperature and mass of the nucleus.
The wavelength coverage from optical to mid-infrared is the broadest of any exoplanet transmission spectrum to date, and includes the first detection by a space telescope of ammonia in the atmosphere of an exoplanet.
Image credit: NASA, ESA, CSA, Ralf Crawford (STScI), Luis Welbanks (ASU), JWST MANATEE Team

If WASP-107 b had more mass than its core, the atmosphere should have shrunk as the planet cooled over time since its formation. 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 5 million miles (one-seventh of the distance between Mercury and the Sun), it does not receive enough energy from its star to inflate that much.

“WASP-107 b is an interesting target for the Webb because it is significantly cooler and more similar to Neptune in mass than many of the other low-density planets, such as hot Jupiters, that we have been studying,” said David Singh of Jones University. Hopkins University (JHU), lead author on A Parallel study Also published today in nature. “As a result, we should be able to detect methane and other molecules that can give us information about its chemistry and internal dynamics that we cannot get from a hotter planet.”

A wealth of previously undetectable molecules

WASP-107 b’s giant radius, extended atmosphere, and edge-on orbit make it ideal for transmission spectroscopy, a method used to identify different gases in exoplanet atmospheres based on how they affect starlight.

By combining observations from Webb’s NIRCam (near-infrared camera), Webb’s MIRI (mid-infrared instrument), and Hubble’s WFC3 (Wide Field Camera 3), the Webbanks team was able to construct a wide range of absorbed light from 0.8 to 12.2 microns. By the atmosphere of WASP-107 b. Using Webb’s NIRSpec (near-infrared spectrometer), Sing’s team built an independent spectrum covering 2.7 to 5.2 microns.

The accuracy of the data makes it possible to not only detect but actually measure the abundance of a wealth of molecules, including water vapor (H₂O) and methane (CH₄), carbon dioxide (CO₂), carbon monoxide (CO), sulfur dioxide (SO₂) and ammonia (NH₃).

This transmission spectrum, taken with Webb’s near-infrared spectrograph, shows the amounts of different wavelengths (colors) of near-infrared starlight blocked by the atmosphere of the gas giant exoplanet WASP-107 b.
The spectrum was created by observing the planet-star system for about 8.5 hours before, during, and after the transit as the planet moves across the face of the star.
By comparing the brightness of light filtered through a planet’s atmosphere (transmitted light) with unfiltered starlight, it is possible to calculate how much of each wavelength is blocked by the atmosphere. Since each molecule absorbs a unique combination of wavelengths, the transmission spectrum can be used to constrain the abundances of different gases.
This spectrum shows clear evidence of the presence of water (H2O), carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), and sulfur dioxide (SO2) in the planet’s atmosphere, allowing researchers to estimate the internal temperature and mass of Planet. essence.
Image credit: NASA, ESA, CSA, Ralf Crawford (STScI), David Sing (JHU), NIRSpec GTO Transiting Exoplanet Team

Boiling gas, hot interior, massive core

Both spectra show a surprising lack of methane in the atmosphere of planet WASP-107 b: one thousandth of the amount expected based on its assumed temperature.

“This is evidence that hot gas coming from deep within the planet must mix strongly with the cooler layers above,” Singh explained. “Methane is unstable at high temperatures. The fact that we have detected so little, even though we have detected other carbon-bearing molecules, tells us that the interior of the planet must be much hotter than we thought.”

The likely source of WASP-107 b’s additional internal energy is tidal heating generated by its slightly elliptical orbit. As the distance between the star and the planet changes continuously over the course of 5.7 days, the force of gravity also changes, causing the planet to expand and heat up.

Researchers had previously suggested that tidal heating could be a cause of the swelling of WASP-107 b, but until Webb’s results, there was no evidence.

Once it was confirmed that the planet had enough internal heat to fully animate the atmosphere, the team realized that the spectra could also provide a new way to estimate the size of the core.

“If we know how much energy is in the planet, and we know what proportion of the heavier elements like carbon, nitrogen, oxygen and sulfur are in the planet, versus the amount of hydrogen and helium, we can calculate how much mass the planet should have.” JHU’s Daniel Thorngren explained.

The core mass turns out to be at least twice what was originally estimated, which makes more sense in terms of how planets form.

Overall, WASP-107 b is not as mysterious as it previously appeared.

“Webb’s data tell us that planets like WASP-107 b didn’t have to form in a strange way with a very small core and a massive gaseous envelope,” explained Mike Lane of Arizona State University. “Instead, we could take something that looks like Neptune, with a lot of rock and not a lot of gas, just increase the temperature, and adjust it to look the same.”

Reference: “High internal heat flux and a large core in the warm exoplanet Neptune” by Lewis Wilbanks, Taylor J. Bell, Thomas J. Beatty, Michael R. Lane, Kazumasa Ono, Jonathan J. Fortney, Everett Schlewein, Thomas P. Green, Emily Rauscher, Peter McGill, Matthew Murphy, Vivien Parmentier, Yao Tang, Isaac Edelman, Sajnik Mukherjee, Lindsay S. Weiser, Pierre-Olivier Lagage, Akren Derek and Kenneth E. Arnold, May 20, 2024, nature.
doi: 10.1038/s41586-024-07514-s

the James Webb Space Telescope It is the first space science observatory in the world. Webb solves the mysteries of our solar system, looks beyond the distant worlds around other stars, and explores the mysterious structures and origins of our universe and our place in it. WEB is an international led programme NASA With its partners the European Space Agency (ESA)European Space Agency) and CSA (Canadian Space Agency).