Recent research has found evidence of an atmosphere on 55 Cancri e, a rocky exoplanet just 41 light-years away. Despite the proximity of its Sun-like star causing extreme heat and a molten surface, the planet likely has a secondary atmosphere created by volcanic processes. (Concept artist.) Credit: SciTechDaily.com
Gas bubbles from the lava-covered surface on exoplanet 55 Cancri e can feed on an atmosphere rich in carbon dioxide or carbon monoxide.
Located just 41 light-years from Earth, exoplanet 55 Cancri e is so hot that scientists once doubted its ability to sustain an atmosphere. However, a recent study by a national team of scientists suggests that 55 Cancri e may be the first rocky exoplanet to have an atmosphere confirmed.
Published in NatureThe paper, titled “Secondary atmosphere on rocky exoplanet 55 Cnc e,” was written by researchers at NASA’s Jet Propulsion Laboratory, the California Institute of Technology, the University of Chicago, and the University of New Mexico (UNM).
Unique orbital characteristics
Exoplanet 55 Cancri e orbits a star similar to Earth’s sun, but unlike Earth, it orbits its star at an exceptionally close distance, making the planet hot and uninhabitable. While Earth takes about 365 days to orbit the Sun, an exoplanet completes its full orbit in less than one Earth day. NASA. It is so close to its star that gravity prevents rotation, so for billions of years one side has experienced day and the other night. The extreme environment of this planet should mean that it would not be able to maintain the primordial atmosphere it was born with when it was formed. In this study, the researchers hypothesize that instead, seas of magma are constantly replenished and maintain a secondary atmosphere. This secondary atmosphere likely formed later in the planet’s existence, in this case by intense volcanic activity triggered by the star’s proximity.
This artist’s concept shows what exoplanet 55 Cancri e might look like. Also called Janssen, 55 Cancri e is a so-called super-Earth, a rocky planet significantly larger than Earth but smaller than Neptune that orbits its star at a distance of just 1.4 million miles (0.015 AU), thus completing one complete revolution. in less than 18 hours. (Mercury is 25 times farther from the Sun than 55 Cancri e from its star.) The system, which also includes four large gas giant planets, is located about 41 light-years from Earth in the constellation Cancer. Acknowledgments: NASA, ESA, CSA, Ralf Crawford (STScI)
Groundbreaking research and technology
UNM assistant professor of physics and astronomy Diana Dragomir was part of the recent study, even though she was already familiar with the exoplanet after contributing to the discovery of its transits in her doctoral thesis. The density and heat of exoplanet 55 Cancri e have long led to difficult questions for her and others who study exoplanets.
“Since its discovery, this planet has defied many attempts to understand its properties and composition. This discovery is the clearest information we have yet for 55 Cancri e,” said Dragomir.
The discovery would not have been possible without the James Webb Space Telescope, which allows researchers to study exoplanets with greater precision than ever before. The team used images from the Webb Telescope to analyze the light emitted by the exoplanet and its star. To do this, they first had to convert the images into light spectra. They then compared the observations with spectra created from different combinations of elements and molecules to predict what potential composition the exoplanet’s atmosphere might have. This study is one of the first to use data from the Webb Telescope for this kind of investigation, and the models used in the study could provide a process for future researchers to complete similar work for other exoplanets.
This light curve shows the change in brightness of the 55 Cancri system as the rocky planet 55 Cancri e, the closest of the five known planets in the system, moves behind the star. This phenomenon is known as a secondary eclipse.
When a planet is next to a star, the mid-infrared light emitted by both the star and the dayside of the planet reaches the telescope and the system appears brighter. When a planet is behind a star, the light emitted by the planet is blocked and only starlight reaches the telescope, causing a decrease in apparent brightness.
Astronomers can subtract a star’s brightness from the combined brightness of the star and planet to calculate how much infrared light is coming from the dayside of the planet. This is then used to calculate the daily temperature and infer whether the planet has an atmosphere.
The planet’s temperature calculated from this observation is about 1,800 kelvins (around 2,800 degrees Fahrenheit), significantly less than would be expected if the planet had no atmosphere or only a thin atmosphere of rock and vapor. This relatively low temperature indicates that heat is distributed from the day side to the night side of the planet, probably by a volatile-rich atmosphere.
Acknowledgments: NASA, ESA, CSA, Joseph Olmsted (STScI), Aaron Bello-Arufe (NASA-JPL)
Collaborative efforts and future prospects
The research team hypothesizes that the exoplanet’s atmosphere could consist of vaporized rock rich in carbon, carbon monoxide, and carbon dioxide. Although more research is needed to confirm the results, the exoplanet’s light emission and models of carbon-rich atmospheres appear to agree. While scientists know that the extremely harsh conditions make Cancri e uninhabitable, the discovery of its atmosphere confirms that the latest telescopes available to scientists may finally be sensitive enough to study the distant rocky planets in detail. Michael Bess, who graduated last spring with a degree in astrophysics, worked with Dragomir on the part of the UNM project that converted images into spectra and ran models to help narrow down potential compositions of the atmosphere.
“Studying exoplanet atmospheres can tell us a lot about planets at different stages of formation,” Bess said. “Eventually, we may be able to look at the habitability of similar planets, because a planet with an atmosphere similar to ours could have life.”
When Bess approached Dragomir to join her research, he never expected to be working on such a large-scale project.
“It was really exciting,” Bess said of working on such a major project as an undergraduate. “I thought it was so fascinating and new and interesting to be able to work with this brand new amazing telescope and the amazing people at NASA. It was a lot of fun and a lot of work and I enjoyed every second of it.”
The thermal emission spectrum captured by Webb’s NIRCam (Near-Infrared Camera) in November 2022 and MIRI (Middle Infrared Instrument) in March 2023 shows the brightness (y-axis) of different wavelengths of emitted infrared light (x-axis). super-Earth exoplanet 55 Cancri e. The spectrum shows that the planet may have an atmosphere rich in carbon dioxide or carbon monoxide and other volatiles, not just vaporized rock.
The plot compares data collected by NIRCam (orange dots) and MIRI (purple dots) with two different models. Model A in red shows what the emission spectrum of 55 Cancri e should look like if it has an atmosphere made of vaporized rock. Model B, in blue, shows what the emission spectrum should look like if the planet has a volatile-rich atmosphere degassed from a magmatic ocean that has a similar volatile content to Earth’s mantle. Both MIRI and NIRCam data are consistent with a volatile-rich model.
The amount of mid-infrared (MIRI) light emitted by the planet shows that its daytime temperature is significantly lower than it would be if it had no atmosphere to distribute heat from the dayside to the nightside. The dip in the spectrum between 4 and 5 microns (NIRCam data) can be explained by the absorption of these wavelengths by carbon monoxide or carbon dioxide molecules in the atmosphere.
Acknowledgments: NASA, ESA, CSA, Joseph Olmsted (STScI), Renyu Hu (NASA-JPL), Aaron Bello-Arufe (NASA-JPL), Michael Zhang (University of Chicago), Mantas Zilinskas (SRON)
Confirmation and Consequences
Several teams, including Bess and Dragomir, analyzed the data individually and then met to compare the results. The results obtained by all teams were found to agree, supporting the correctness of the data interpretation. It was an exciting moment not only for the entire research team, but especially for Bess, whose skill level while working on the project was on par with researchers who had already completed their Ph.D.
“You have an undergraduate student who was analyzing datasets at a level comparable to what his much older colleagues were doing, and was also able to communicate and coordinate independently with the entire team,” Dragomir said. “I’m really proud of Michael for that.
Bess will begin her Ph.D. in astrophysics this fall University of Florida. If he decides to continue his research on 55 Cancri e, there will still be more to discover.
Without an atmosphere to help retain heat, side 55 Cancri e in eternal night is likely to be around minus 400 degrees Fahrenheit.
New perspectives on a lava planet
“The presence of an atmosphere on 55 Cancri e also explains the higher than expected temperature measured on the night side of the planet.” Even though this side never faces the star, the atmosphere helps circulate the heat from the day side around the planet,” said Dragomir.
Therefore, this work also confirms previous claims that 55 Cancri e is a lava planet with a likely molten surface. Along with new knowledge about its atmosphere, scientists can begin to think about the composition of the rest of the planet.
More study is needed to continue to unravel Cancri e’s 55 secrets, but until then, the latest discovery is out of this world.
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Reference: “Secondary Atmosphere on the Rocky Exoplanet 55 Cancri e” by Renyu Hu, Aaron Bello-Arufe, Michael Zhang, Kimberly Paragas, Mantas Zilinskas, Christiaan van Buchem, Michael Bess, Jayshil Patel, Yuichi Ito, Mario Damiano, Markus Scheucher, Apurva V. Oza, Heather A. Knutson, Yamila Miguel, Diana Dragomir, Alexis Brandeker and Brice-Olivier Demory, 08 May 2024, Nature.
DOI: 10.1038/s41586-024-07432-x