Free Astronomy Magazine July-August 2024

JULY-AUGUST 2024 T he graph compares data collected by NIRCam (orange dots) and MIRI (purple dots) to two different models. Model A, in red, shows what the emis- sion 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. [Illustration: NASA, ESA, CSA, Joseph Olmsted (STScI). Science: Renyu Hu (NASA-JPL), Aaron Bello-Arufe (NASA-JPL), Michael Zhang (University of Chicago), Mantas Zilinskas (SRON)] some confirmation of our work is priceless!” The team thinks that the gases blan- keting 55 Cancri e would be bub- bling out from the interior, rather than being present ever since the planet formed. “The primary atmos- phere would be long gone because of the high temperature and intense radiation from the star,” said Bello- Arufe. “This would be a secondary atmosphere that is continuously re- plenished by the magma ocean. Magma is not just crystals and liquid rock; there’s a lot of dissolved gas in it, too.” While 55 Cancri e is far too hot to be habitable, researchers think it could provide a unique window for study- ing interactions between atmos- pheres, surfaces, and interiors of rocky planets, and perhaps provide insights into the early conditions of Earth, Venus, and Mars, which are thought to have been covered in magma oceans far in the past. “Ulti- mately, we want to understand what conditions make it possible for a rocky planet to sustain a gas-rich atmosphere: a key ingredient for a habitable planet,” said Hu. very strong indication that energy is being distributed from the day- side to the nightside, most likely by a volatile-rich atmosphere.” While currents of lava can carry some heat around to the nightside, they can- not move it efficiently enough to ex- plain the cooling effect. When the team looked at the NIR- Cam data, they saw patterns consis- tent with a volatile-rich atmosphere. “We see evidence of a dip in the spectrum between 4 and 5 microns — less of this light is reaching the telescope,” explained co-author Aaron Bello-Arufe, also from NASA JPL. “This suggests the presence of an atmosphere containing carbon monoxide or carbon dioxide, which absorb these wavelengths of light.” A planet with no atmosphere or an atmosphere consisting only of va- porized rock would not have this specific spectral feature. “We’ve spent the last ten years mod- elling different scenarios, trying to imagine what this world might look like,” said co-author Yamila Miguel from the Leiden Observatory and the Netherlands Institute for Space Research (SRON). “Finally getting By subtracting the brightness during the secondary eclipse, when the planet is behind the star (starlight only), from the brightness when the planet is right beside the star (light from the star and planet combined), the team was able to calculate the amount of various wavelengths of infrared light coming from the day- side of the planet. This method, known as secondary eclipse spectroscopy, is similar to that used by other research teams to search for atmospheres on other rocky exoplanets, like TRAPPIST-1 b. The first indication that 55 Cancri e could have a substantial atmos- phere came from temperature mea- surements based on its thermal emission, or heat energy given off in the form of infrared light. If the planet is covered in dark molten rock with a thin veil of vaporized rock or no atmosphere at all, the dayside should be around 4,000 de- grees Fahrenheit (~2,200 degrees Celsius). “Instead, the MIRI data showed a relatively low temperature of about 2,800 degrees Fahrenheit [~1540 de- grees Celsius] ,” said Hu. “ This is a !