Since its discovery in 2009, astronomers have been studying something 400 light-years away that is so enticing. One circle for WASP-18 b around the star is marginally bigger than our sun, which requires only 23 hours. There is nothing similar to it in our planetary group.
Based on new data from the Canadian NIRISS instrument on the James Webb Space Telescope (JWST), a new study led by Ph.D. student Louis-Philippe Coulombe about this exoplanet, an ultra-hot gas giant 10 times larger than Jupiter, contains numerous surprises.
Mapping an exoplanet An international team of astronomers has identified water vapor in the atmosphere of the exoplanet WASP-18 b and produced a temperature map of the planet as it slipped behind its star and reappeared. The term for this occurrence is “secondary eclipse. The combined light from the star and the planet can be read by scientists, who can then refine the measurements taken from the star alone as the planet moves behind it.
The dayside of WASP-18 b always faces its star, just like the earth-facing side of the moon always faces the sun. Tidal locking is the term for this. From the hottest point facing the star to the terminator, the point at which the day and night sides of the tidally-locked planet meet in permanent twilight, the temperature map of the exoplanet—also known as its brightness—shows a significant temperature change of up to 1,000 degrees.
“JWST provides us with the sensitivity to make much more detailed maps of hot giant planets like WASP-18 b than we have ever had before. This is the first time JWST has mapped a planet, and it’s incredibly exciting to see that some of what our models anticipated, such as a rapid reduction in temperature away from the point on the planet directly facing the star, is actually shown in the data.”
Megan Mansfield, a Sagan Fellow at the University of Arizona,
“JWST gives us the sensitivity to make maps of hot giant planets like WASP-18 b that are much more detailed than ever before.” Megan Mansfield, a Sagan Fellow at the University of Arizona and one of the authors of the paper describing the results, stated, “It’s really exciting to see that some of what our models predicted, such as a sharp drop in temperature away from the point on the planet directly facing the star, is actually seen in the data.” This is the first time a planet has been mapped using JWST.
The group mapped temperature gradients on the planet’s dayside. Considering how much cooler the planet is at the eliminator, there is probably something impeding breezes from productively reallocating intensity to the night side. However, it is still unknown what is influencing the winds.
“Models with atmospheric drag best match the absence of east-west winds on the brightness map of WASP-18 b.” Co-author Ryan Challener of the University of Michigan stated, “One possible explanation is that this planet has a strong magnetic field, which would be an exciting discovery.”
This infographic shows how exoplanet transits and eclipses are used by astronomers to learn more about these far-off worlds. Credit: NASA/JPL-Caltech/R.
Hurt One interpretation of the eclipse map is that magnetic effects cause the winds to blow east-west rather than east-west from the planet’s equator over the north pole and south pole.
Specialists recorded temperature changes at various levels of the gas monster planet’s layers of environment. They saw temperatures increase with each rise, fluctuating by many degrees.
Signs of water vapor
The planet’s atmospheric spectrum clearly reveals a number of tiny, precisely measured water features, even at nearly 2,700 degrees Celsius. It is hot to the point that it would destroy most water particles, so as yet, seeing its presence addresses Webb’s exceptional aversion to distinguishing remaining water. According to Louis-Philippe Coulombe, a Ph.D. student at the Université de Montréal who is also a member of the Trottier Institute for Research on Exoplanets (iREx) and the lead author of the WASP-18 b paper, “It was a great feeling to look at WASP-18 b’s JWST spectrum for the first time and see the subtle but precisely measured signature of water.” The amounts that were recorded in the atmosphere of WASP-18
“Utilizing this sort of estimation, we will actually want to distinguish such particles for a great many planets in the years to come,” added Björn Benneke, UdeM teacher, iREx participant, and co-writer of this paper. Since 2016, Benneke has been leading international efforts to study WASP-18 b. He is also Coulombe’s advisor for his Ph.D.
An artistic illustration depicts WASP-18 b, a gas giant exoplanet that orbits its star in just 23 hours and is 10 times larger than Jupiter. The planet’s movement behind its star was studied with the help of the James Webb Space Telescope’s NIRISS instrument. There, the temperature rises to 2,700 degrees Celsius. Credit: NASA/JPL-Caltech/K. Miller/IPAC
Crafted by the NIRISS instrument and early-profession researchers
The group of cosmologists observed WASP-18 b for around six hours utilizing one of Webb’s instruments, the Close Infrared Imager and Slitless Spectrograph (NIRISS), contributed by the Canadian Space Organization and a few accomplices, including the Université de Montréal and iREx.
“It was difficult to identify the water features in this spectrum in previous observations because they are so subtle.” “That made it really exciting to finally see water features with these JWST observations,” said one of the new research’s authors, postdoctoral fellow Anjali Piette, of the Carnegie Institution for Science.
The WASP-18 b observations were taken as part of the Transiting Exoplanet Community Early Release Science Program, which was led by Natalie Batalha, an astronomer at the University of California, Santa Cruz. Batalha helped coordinate the new research as well as the work of the team’s more than 100 researchers. Young scientists like Coulombe, Challener, Piette, and Mansfield are doing a lot of this groundbreaking work.
WASP-18 b’s large mass and proximity to both its star and us made it such an intriguing target for these researchers. One of the most massive worlds whose atmospheres we can study is WASP-18 b. Scientists are trying to figure out how these planets get formed and where they are in their systems. Webb provided some initial responses to this as well.
“We learn not only about the various molecules that can be found in its atmosphere but also about how it formed by analyzing the spectrum of WASP-18 b. We find from our perceptions that WASP-18 b’s structure is basically the same as that of its star, meaning it was undoubtedly shaped by the extra gas that was available soon after the star was conceived,” Coulombe said. “Those results are truly important to get an unmistakable image of how weird planets like WASP-18 b, which have no partner in our planetary group, come to exist.”
Nature has published the paper.
More information: Louis-Philippe Coulombe et al, A broadband thermal emission spectrum of the ultra-hot Jupiter WASP-18b, Nature (2023). DOI: 10.1038/s41586-023-06230-1
