New clues about the possible atmosphere of the exoplanet 55 Cancri e

Artist's concept of the exoplanet 55 Cancri e and its star (Image NASA/JPL-Caltech)
Artist’s concept of the exoplanet 55 Cancri e and its star (Image NASA/JPL-Caltech)

An article published in the magazine “The Astronomical Journal” describes a research on the exoplanet 55 Cancri e. This super-Earth is one of the most studied among the planets in other solar systems but its extreme characteristics and the often experimental nature of the studies carried out provided partial and sometimes contradictory results. Now a analysis of data gathered using NASA’s Spitzer Space Telescope convinced a team of researchers that 55 Cancri e has an atmosphere and could have a composition similar to that of the Earth.

55 Cancri e – in December 2015 officially named Janssen – is a very dense planet, so its size is twice the Earth’s but its mass is eight times greater. Its orbit is very close to its star, which means that its year only lasts 18 hours and its rotation is synchronous so its day lasts as long as its the year.

The authors of the new research used an improved model of the energy flow across the planet 55 Cancri e and its irradiation into space. Among the results there are new estimates of the temperatures on the surface, very different on the day and night side exactly because it always shows the same face to its star. On the day side it’s estimated that the average temperature is about 2,300° Celsius (4,200° Fahrenheit), while on the night side the average is between 1,300° and 1,400° Celsius (2,400 to 2,600° Fahrenheit).

The difference between the two faces is lower than estimated by a mapping of the planet’s climate described in an article published in the journal “Nature” in April 2016. That difference was considered a clue that the atmosphere of the planet 55 Cancri e was thin or even absent, if it was really exaggerated, that statement would also have to be revised.

According to a research described in an article published in “The Astrophysical Journal” in February 2016 the atmosphere of the planet 55 Cancri e is composed mainly of hydrogen and helium. The newly published research brings new clues to the existence of the atmosphere but also proposes an alternative composition, more like the Earth’s atmosphere with nitrogen, water and even oxygen.

One of the clues of the existence of the planet’s 55 Cancri e’s atmosphere is given according to the researchers by the characteristics of the lava lakes existing on its surface due to the very high temperatures. If those lakes were exposed directly to space, they’d create local hotspots of high temperatures but the observations made with the Spitzer Space Telescope suggest a different situation. Renyu Hu of NASA’s JPL, one of the authors of the article, explained that the lava should cover the entire planet but would be hidden from our view by a thick atmosphere.

The model used by the researchers was previously applied only to hot Jupiter exoplanets, which are gas giant very close to their stars. For the first time it was used to study the atmosphere of a super-Earth very close to its star. The result is the possibility that the atmosphere is thick and rich in volatile elements, which might explain the estimated temperatures.

Every new research on the planet 55 Cancri e seems to contradict some previous ones. In some ways that’s inevitable because it’s “just” 40 years light from Earth and its relative proximity makes it ideal to try new types of study that can have high error margins.

The extreme conditions on the planet 55 Cancri make it even harder to understand exactly its characteristics. For example, due to the proximity to its star, similar to the Sun, it’s hit by considerable amounts of radiation that should strip its atmosphere away.

All of these factors make the study of the planet 55 Cancri e more difficult but also very interesting. Understanding the characteristics and evolution of such a planet could be very helpful to obtain more general information on the evolution of rocky planets such as the Earth.

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