Recent research has found evidence of an atmosphere on 55 Cancri e, a rocky exoplanet just 41 light-years away. Despite its proximity to its sun-like star, which causes extreme heat and a molten surface, the planet likely has a secondary atmosphere formed from volcanic processes. (Artist’s concept.) Credit: SciTechDaily.com
Gas bubbling up from a lava-covered surface on the exoplanet 55 Cancri e may feed an atmosphere rich in carbon dioxide or carbon monoxide.
Located a mere 41 light years from Earth, the exoplanet 55 Cancri e is so intensely hot that scientists once doubted its ability to sustain an atmosphere. However, a recent study conducted by a national team of scientists suggests 55 Cancri e may be the first rocky exoplanet confirmed to have an atmosphere.
Published in Nature, the paper titled “A Secondary Atmosphere on the Rocky Exoplanet 55 Cnc e” was authored by researchers from NASA’s Jet Propulsion Laboratory, the California Institute of Technology, the University of Chicago, the University of New Mexico (UNM).
Unique Orbital Characteristics
The exoplanet 55 Cancri e, orbits a star similar to Earth’s sun, but unlike Earth, it orbits its star from an exceptionally close distance making the planet molten hot and uninhabitable. While it takes Earth about 365 days to orbit the sun, the exoplanet completes its full orbit in less than one Earth day, according to NASA. It’s so close to its star that gravity doesn’t allow it to rotate, 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 be unable to maintain the primordial atmosphere it was born with when it formed. In this study, scientists hypothesize that instead, seas of magma continually replenish and maintain a secondary atmosphere. This secondary atmosphere likely formed later in the planet’s existence, in this case, generated from the intense volcanic activity triggered by the proximity to the star.
This artist’s concept shows what the exoplanet 55 Cancri e could 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, which orbits its star at a distance of only 1.4 million miles (0.015 astronomical units), completing one full orbit in less than 18 hours. (Mercury is 25 times farther from the Sun than 55 Cancri e is 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. Credit: NASA, ESA, CSA, Ralf Crawford (STScI)
Groundbreaking Research and Technology
UNM Physics and Astronomy Assistant Professor Diana Dragomir was part of the recent study, though she was already well-acquainted with the exoplanet after contributing to the discovery of its transits in her doctoral thesis. Exoplanet 55 Cancri e’s density and heat have long led to complex questions for her and others who study exoplanets.
“Ever since its discovery, this planet has defied multiple attempts at understanding its properties and composition. This discovery is the clearest piece of information we have obtained so far for 55 Cancri e,” Dragomir said.
The discovery would not be 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 light emitted by the exoplanet and its star. To do that, they first had to translate the images into light spectra. They then compared the observations to spectra created from different combinations of elements and molecules to hypothesize what potential atmospheric compositions the exoplanet might have. This study is among the first to use data from the Webb telescope for this kind of investigation and the models used in the study could provide future researchers with a process 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 a secondary eclipse.
When the planet is next to the 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 the planet is behind the star, the light emitted by the planet is blocked and only the starlight reaches the telescope, causing the apparent brightness to decrease.
Astronomers can subtract the brightness of the star 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 dayside temperature and infer whether or not the planet has an atmosphere.
The temperature of the planet calculated from this observation is about 1,800 kelvins (around 2,800 degrees Fahrenheit), which is significantly lower than would be expected if the planet has no atmosphere or only a thin rock-vapor atmosphere. This relatively low temperature indicates that heat is being distributed from the dayside to the nightside of the planet, possibly by a volatile-rich atmosphere.
Credit: 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 be composed of vaporized rock rich in carbon, carbon monoxide, and carbon dioxide. While further research is needed to confirm the results, the exoplanet’s light emissions and models of carbon-rich atmospheres seem to align closely. While researchers know 55 Cancri e’s extremely harsh conditions make it uninhabitable, the discovery of its atmosphere confirms that the newest telescopes available to scientists may finally be sensitive enough to study distant rocky planets in detail. Michael Bess, who graduated last Spring with a degree in Astrophysics worked with Dragomir on UNM’s portion of the project translating the images into spectra and running models to help narrow down potential atmosphere compositions.
“Studying the atmospheres of exoplanets can tell us a lot about planets in different stages of formation,” Bess said. “Eventually, we may be able to look at similar planets for habitability because a planet with an atmosphere similar to ours could possibly have life.”
When Bess approached Dragomir about getting involved with her research, he never expected to work on such a large-scale project.
“It was really exciting,” Bess said about working on such a significant 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 amazing people from NASA. It was a lot of fun and a lot of work and I enjoyed every second of it.”
A thermal emission spectrum captured by Webb’s NIRCam (Near-Infrared Camera) in November 2022, and MIRI (Mid-Infrared Instrument) in March 2023, shows the brightness (y-axis) of different wavelengths of infrared light (x-axis) emitted by the super-Earth exoplanet 55 Cancri e. The spectrum shows that the planet may be surrounded by an atmosphere rich in carbon dioxide or carbon monoxide and other volatiles, not just vaporized rock.
The graph compares data collected by NIRCam (orange dots) and MIRI (purple dots) to 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 outgassed from a magma ocean that has a similar volatile content as Earth’s mantle. Both MIRI and NIRCam data are consistent with the volatile-rich model.
The amount of mid-infrared light emitted by the planet (MIRI) shows that its dayside temperature is significantly lower than what it would be if it did not have an 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 absorption of those wavelengths by carbon monoxide or carbon dioxide molecules in the atmosphere.
Credit: NASA, ESA, CSA, Joseph Olmsted (STScI), Renyu Hu (NASA-JPL), Aaron Bello-Arufe (NASA-JPL), Michael Zhang (University of Chicago), Mantas Zilinskas (SRON)
Confirmations and Implications
Several teams, including Bess and Dragomir, each analyzed the data individually and then met to compare results. It was found that the results obtained by all the teams agreed, which supported that the interpretation of the data was correct. It was an exciting moment not only for the entire research team but especially for Bess whose skill level working on the project became on par with that of researchers who had already completed Ph.Ds.
“You’ve got an undergrad student who analyzed the data sets at a level comparable to what his much more senior collaborators did, and he was also able to communicate and coordinate with the entire team independently,” Dragomir said. “I’m really proud of Michael for that.”
Bess will begin his Ph.D. in Astrophysics this Fall at the University of Florida. If he chooses to continue research on 55 Cancri e, there will still be much to discover.
Without an atmosphere to help retain heat, it’s likely the side of 55 Cancri e in eternal night would be around negative 400 degrees Fahrenheit.
New Insights Into a Lava Planet
“The presence of an atmosphere on 55 Cancri e also explains the warmer-than-expected temperature measured on the planet’s nightside. Even though that side never faces the star, the atmosphere helps circulate heat from the dayside all around the planet,” Dragomir said.
This work therefore also confirms previous claims that 55 Cancri e is a lava planet with a likely molten surface. Together with the new knowledge of its atmosphere, scientists can begin to hypothesize about the composition of the rest of the planet.
Further study is necessary to continue unlocking 55 Cancri e’s secrets, but until then, the most recent discovery is out-of-this-world.
More on this research:
Reference: “A 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, 8 May 2024, Nature.
DOI: 10.1038/s41586-024-07432-x
