An article published in the journal “Nature” reports the results of a study of the exoplanet 55 Cancri e, formally called Janssen, which confirms the presence of an atmosphere that is considered secondary, which means that it derives from emissions coming from the planet itself. A team of researchers led by NASA’s Jet Propulsion Laboratory (JPL) used observations conducted with the James Webb Space Telescope to detect traces of an atmosphere that may be rich in carbon monoxide or carbon dioxide.
The image (NASA, ESA, CSA, J. Olmsted (STScI), A. Bello-Arufe (JPL)) shows a diagram of a secondary eclipse and a graph of the resulting change in brightness over time in the 55 Cancri system based on detections by the James Webb Space Telescope’s MIRI instrument.
The exoplanet 55 Cancri e was discovered almost twenty years ago and is about 40 light-years away from Earth, so it’s in the cosmic neighborhood. The conditions existing on its surface are hellish due to the fact that it’s very close to its star, to which it always shows the same face.
The temperature on 55 Cancri e’s surface was estimated in the past from previous observations. The average of around 2,300° Celsius on the dayside and between 1,300° and 1,400° Celsius on the nightside make it one of the most extreme planets known. These are reasons that placed it at the center of many studies with various instruments, and it was inevitable that the James Webb Space Telescope would also be used.
In particular, the NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument) instruments were used to understand whether 55 Cancri e has an atmosphere, as suggested in an article published in November 2017 in the journal “The Astronomical Journal” based on observations conducted with NASA’s Spitzer Space Telescope, JPL’s Renyu Hu was one of the authors of that study and is the lead author of the one just published.
The researchers used the technique of secondary eclipse spectroscopy, that is, they used the MIRI and NIRCam instruments to measure emissions from the 55 Cancri system when 55 Cancri e was behind its star and when it was in front of it. The difference in brightness indicates which emissions are coming from the planet’s dayside.
The results indicate a lower temperature than previous estimates, at around 1,540° Celsius. That’s a value that suggests a distribution of heat caused by the presence of an atmosphere, probably rich in volatile elements. Spectroscopic results suggest an abundance of carbon monoxide or carbon dioxide.
Temperature values on the exoplanet 55 Cancri e’s dayside, along with the intense emissions from its star, remain sufficient to wipe out any atmosphere it may have had when it formed. For this reason, the researchers believe that the traces detected by the James Webb Space Telescope are of a secondary atmosphere, generated and renewed by emissions coming from the planet itself. This super-Earth has a surface made up of a magma ocean that continually releases gases dissolved in that magma.
Due to its extreme characteristics, the exoplanet 55 Cancri e represents an interesting study object for studying the interactions between the atmosphere, the surface, and the interior of a rocky planet. Primordial rocky planets are probably covered in magma, so 55 Cancri e can be useful for understanding the conditions that existed when Earth, Venus, and Mars had just formed.
Concerning the atmosphere of the exoplanet 55 Cancri e, the analyzes of the data collected continue. The different results obtained with different telescopes and the difficulty in precisely interpreting the data obtained with a powerful instrument such as the James Webb Space Telescope show how difficult it is to understand exactly the composition of an exoplanet’s atmosphere. Astronomers are slowly learning how to best collect this data and interpret it. It’s a type of study that is still developing and progress is still slow.
