The hot gas giant WASP-107 b, known for its unusually low density and moderate temperature, may have its bloated atmosphere due to tidal heat heating its interior much hotter than previously thought. (Artist’s concept.) Credit: SciTechDaily.com
A surprising omission of methane suggests that tidal heating has boosted the atmosphere of the hot gas giant WASP-107 b.
Why is it a hot gas-giant? extraterrestrial WASP-107 b, too bloated? With a moderate temperature and extremely low density comparable to a microwave marshmallow, it seems to defy standard theories of planet formation and evolution.
Two independent groups of researchers think they’ve figured it out. Webb’s data, combined with Hubble’s previous observations, show that WASP-107 b’s interior must be much hotter than previously estimated. The unexpectedly high temperature, thought to be caused by tidal forces stretching the planet like goofy putty, could explain how planets like WASP-107 b can be so buoyant, solving a long-standing mystery in exoplanet science.
This artist’s concept shows what exoplanet WASP-107 b might look like based on recent data collected by NASA’s James Webb Space Telescope, along with previous observations from Hubble and other space and ground-based telescopes. WASP-107 b is a “hot Neptune” exoplanet orbiting a small and cool star about 210 light-years from Earth in the constellation Virgo. The planet is about 80% the size of Jupiter by volume, but has less than 10% the mass of Jupiter, making it one of the least dense exoplanets known. Credit: NASA, ESA, CSA, Ralf Crawford (STScI)
Web Space Telescope Cracks Case of Inflated Exoplanet
Why is the hot gas-giant exoplanet WASP-107 b so bloated? Two independent research teams now have the answer.
Data collected using NASA’s James Webb Space Telescope, combined with earlier observations from NASA’s Hubble Space Telescope, show surprisingly little methane (CH).4) in the planet’s atmosphere. This indicates that the interior of WASP-107 b must be considerably 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 circular orbit, and could explain how WASP-107 b is elevated without resorting to radical theories of how it formed.
The results, made possible by the web’s extraordinary sensitivity and ability to measure light passing through exoplanet atmospheres, could explain the bulges of dozens of low-density exoplanets, helping to solve a long-standing mystery in exoplanet science.
Problem with WASP-107 b
More than three-quarters of the volume Thursday But less than one-tenth the mass, “hot Neptune“Exoplanet WASP-107 b is one of the least dense planets known. While bulge planets are not uncommon, most are hotter and more massive, so it’s easier to explain.
“Based on its radius, mass, age, and internal temperature, we thought that WASP-107 b has a very small, rocky core surrounded by hydrogen and helium,” explained Louise Wellbanks of Arizona State University (ASU). lead author on an article published May 20 in the journal Nature. “But it was hard to understand how such a small core could sweep up so much gas and then stop growing completely into a Jupiter-mass planet.”
Captured using NASA’s Hubble and James Webb Space Telescopes, this transmission spectrum shows the amount of different wavelengths (colors) of starlight blocked by the atmosphere of the gas-giant exoplanet WASP-107 b.
The spectrum includes a total of light collected over five separate observations using three different instruments: Hubble’s WFC3 (0.8–1.6 μm), Webb’s NIRCam (2.4–4.0 μm and 3.9–5.0 μm), and Webb’s MIRI (5–12 μm). Each measurement was made by observing the planet-star system 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 the planet’s atmosphere (transmitted light) to unfiltered starlight, the amount of each wavelength blocked by the atmosphere can be calculated. Because each molecule absorbs a unique combination of wavelengths, the transmission spectrum can be used to control the abundance of various gases.
The spectrum shows clear evidence of water (H2O), carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), sulfur dioxide (SO2) and ammonia (NH3) in the planet’s atmosphere, allowing researchers to estimate the interior. Temperature and mass of core.
The optical to mid-infrared wavelength coverage is the widest of any exoplanet transmission spectrum so far, and includes the first space telescope detection of ammonia in an exoplanet’s atmosphere.
Credit: NASA, ESA, CSA, Ralf Crawford (STScI), Luis Welbanks (ASU), JWST MANATEE Team
If WASP-107 b instead has more mass at the core, the atmosphere must have contracted as the planet cooled over time since its formation. Without a source of heat for the gas to re-expand, the planet would have to be very small. Although WASP-107 b has an orbital distance of just 5 million miles (one-seventh the distance between Mercury and the Sun), it does not receive enough energy from its star.
“WASP-107 b is a particularly interesting target for Webb because it is significantly cooler and more Neptune-like in mass than many low-density planets, such as hot Jupiters. Hopkins University (JHU), lead author A A parallel study Also published today Nature. “As a result, we can detect methane and other molecules that can give us information about its chemistry and internal dynamics that we can’t get from a hot 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, which can be used to identify various gases in an exoplanet’s atmosphere based on how it affects starlight.
Combining observations from Webb’s NIRCam (Near-Infrared Camera), Webb’s MIRI (Mid-Infrared Instrument), and Hubble’s WFC3 (Wide Field Camera 3), Welbanks’ team was able to create a broad spectrum of absorbed light from 0.8- to 12.2-micron. by the atmosphere of WASP-107 b. Using Webb’s NIRSpec (Near-Infrared Spectrograph), Singh’s team produced an independent spectrum covering 2.7 to 5.2 microns.
The accuracy of the data allows not only to detect but actually measure a wealth of molecules, including water vapor (H).2O), methane (CH4), carbon dioxide (CO2), carbon monoxide (CO), sulfur dioxide (SO2), and ammonia (NH3)
This transmission spectrum, captured using Webb’s NIRSpec (near infrared spectrometer), shows the amount 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 about 8.5 hours before, during, and after the planet moves across the face of the star.
By comparing the brightness of light filtered through the planet’s atmosphere (transmitted light) to unfiltered starlight, the amount of each wavelength blocked by the atmosphere can be calculated. Because each molecule absorbs a unique combination of wavelengths, the transmission spectrum can be used to control the abundance of various gases.
The spectrum shows clear evidence for water (H2O), carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), and sulfur dioxide (SO2) in the planet’s atmosphere. Cor.
Credit: NASA, ESA, CSA, Ralf Crawford (STScI), David Singh (JHU), NIRSpec GTO Transiting Exoplanet Team
Rolling case, hot interior and massive core
Both spectra show the absence of methane in WASP-107 b’s atmosphere: one-thousandth of the amount expected given its temperature.
“This is evidence that hot gas from deep within the planet must mix vigorously with the cold layers above,” Singh explained. “Methane is unstable at high temperatures. The fact that we found so few other carbon-bearing molecules, though, suggests that the planet’s interior must be significantly hotter than we thought.
WASP-107 b’s source of additional internal energy is tidal heating caused by its slightly elliptical orbit. As the distance between the star and the planet continues to change over its 5.7-day orbit, the gravitational force also changes, stretching and heating the planet.
Researchers had previously proposed that tidal heating might be responsible for WASP-107 b’s swelling, but until Webb’s results came in, there was no proof.
Once they established that the planet had enough internal heat to completely replace the atmosphere, the teams realized that the spectra could provide a new way to estimate the size of the core.
“If we know how much energy the planet has, and if we know what proportion of heavy elements like carbon, nitrogen, oxygen and sulfur the planet has, and how much hydrogen and helium there is, we can calculate how much mass there must be in the core,” explained Daniel Thorngren from JHU.
It turns out that the core is at least twice as large as first estimated, which makes more sense for how planets form.
All together, WASP-107 b is not as mysterious as it once seemed.
“The Webb data tells us that planets like WASP-107 b don’t have to form in some weird way with a super-small core and a large gaseous envelope,” explained Mike Line from ASU. “Instead, we could take something like Neptune, with lots of rocks and not much gas, dial up the temperature and turn it down to see what it’s like.”
Reference: Louise Wellbanks, Taylor J. Bell, Thomas G. Beatty, Michael R. Line, Kazumasa Ono, Jonathan J. Fortney, Everett Sclavin, Thomas B. Greene, Emily Rauscher, Peter McGill, Matthew Murphy, Vivian Parmentier, Yao Tang, Isaac Edelman, Saknik Mukherjee, Lindsay S. Weiser, Pierre-Olivier Luggage, Acreen Direk, and Kenneth E. Arnold, May 2020, 2020 Nature.
DOI: 10.1038/s41586-024-07514-w
The The James Webb Space Telescope It is the world’s premier space science laboratory. Webb solves the mysteries of our solar system, looks beyond to distant worlds around other stars, and explores the mysterious structures and origins of our universe and our place in it. The Web is an international project NASA With its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).
