Finding an exoplanet similar to Earth turned out to be difficult, especially in terms of atmospheric parameters. In all the candidates studied today, it turned out that the atmospheres were extremely small or the observations gave uncertain results. This trend could change the Janssen exoplanet. According to observations of the James Webb space telescope, the atmosphere of this rocky planet is quite thick and has an interesting composition.

Planet Janssen, or 55 Cancer, has long intrigued astronomers. This is one of the first transiting super-Earths discovered (that is, a planet regularly passes between us and the star). There are at least four other planets in its “family”; among them are hot Jupiter and a gas giant with an orbital period of 15 years. They are all flying around a bright yellow dwarf that is part of a binary star. Its companion, the red dwarf, flies at a distance of about 1060 AU.

Yellow dwarf 55 Cancer is one of the few bright stars known to have transiting planets. But it was discovered only by the Janssen transit method, the rest were discovered only by “training” the star, that is, by the method of radial velocities. By the way, the star can be seen with the naked eye under suitable weather conditions. It is located 40 light years away from us.

Rocky Janssen is closest to the star and makes one revolution in less than an Earth day. It is almost twice as large as Earth (1.95 Earth radii) and almost nine times more massive in mass (8.8 Earth masses). Due to its proximity to the armature, the equilibrium temperature reaches 1.7 thousand degrees Celsius (two thousand kelvin). This is comparable to the temperature of the coldest stars.

Astronomers have been observing this planet for a long time in order to understand its structure and composition. The transit method allows you to study the structure of the atmosphere by analyzing changes in the star’s radiation when it passes in front of a planet.

Thus, scientists confirmed that Jansen cannot have a predominantly hydrogen atmosphere, that is, an atmosphere “given to it from birth”. First, this is not evident in observational data. The latter “evaporated” long ago due to being so close to the star.

Analyzing the possible date and conditions of Janssen’s evolution, astronomers even concluded that the planet was probably “naked.” Other scientists have hypothesized that if an atmosphere exists, it is “secondary”, saturated with compounds resulting primarily from volcanic processes on the planet. All of these studies were conducted before the launch of the James Webb Space Telescope. Given the many years of interest in this exoplanet, it is not surprising that the telescope program devoted time to studying Janssen. And so scientists shared the results of the first observations.

In the new study published in the journal Natureresearchers processed data collected by “James Webb”. Despite the resolution and capabilities of the telescope, it was not easy to clear the obtained values ​​from the noise of the star and other nearby sources. The analysis was performed independently by several groups. There were two datasets: NIRCam in the near-infrared (observations in 2022) and MIRI in the mid-infrared (observations in 2023).

To reject the hypothesis of a “bare” planet, the planet’s temperature and “brightness” were first investigated. Molten lava cannot give such indicators, so heat must be dissipated by an atmosphere of significant volume, a thickness of a few percent of the planet’s radius.

To determine the composition of this atmosphere, scientists checked “cleaned” observation data with different ratios of compounds in many computer models. An atmosphere rich in carbon monoxide and carbon dioxide is best suited to the indicators. In some models, the match was even better when water, sulfur dioxide and phosphine were added.

As the study’s authors show, Janssen could support such an atmosphere with a magma ocean. In such cases, even the powerful radiation of the star cannot “evaporate” it. Moreover, the observed “fluctuations” in the planet’s radiation can be explained by emissions from the lava ocean – both volatile substances that affect the heating of different layers of the atmosphere, and compounds that can condense into short clouds.

To confirm these results, the study’s authors called for continuous observation of the planet’s atmosphere using the James Webb telescope.