In the last two and a half decades, astronomers have confirmed the existence of thousands of exoplanets. In recent years, thanks to improvements in instrumentation and methodology, the process has slowly changed from the discovery process to the characterization. In particular, astronomers hope to obtain spectra from exoplanet atmospheres that will indicate their chemical composition.
This is not an easy task as direct imaging is very difficult, and the only other method is to make observations during transits. However, astronomers from the CARMENES consortium recently reported that the discovery of a hot rocky super-Earth revolves around the nearby red dwarf star. Although extremely hot, this planet has retained some of its original atmosphere, making it unique for observations using next-generation telescopes.
Part of the problem with characterizing exoplanets is that those considered the most habitable are rocky exoplanets orbiting near their stars. Any light that is reflected by their atmosphere and surfaces is thus overwhelmed by the light of their parent star. As such, direct imaging is usually only possible when it comes to gas giants with long orbits.
Sometimes astronomers are able to study light that travels through an atmosphere of a planet as it moves in front of its parent star (even though passages). It also presents challenges, as rocky planets have relatively thin atmospheres compared to gas giants (assuming they are at all). As a result, many of the current atmospheric models for rocky planets remain untested.
Astronomers have used both Transit Photometry and Radial velocity measurements – currently the two most effective methods (especially in combination) – to confirm the existence of Gliese 486b. This was done using data from Transiting Exoplanet Survey Satellite (TESS), the 1.52 m Telescopio Carlos Sánchez at the Teide Observatory, the Las Cumbres Observatory Global Telescope (LCOGT) network and other instruments.
This latest planet discovered by the CARMENES consortium is known as Gliese 486b, a super-Earth orbiting an M-type (red dwarf) star, just 26 light-years away. This planet is about 2.8 times the mass of Earth, is similar to the composition of Earth and Venus and orbits 2.5 million km (1.55 million miles) from its star – about 1.6% of the distance between the earth and the sun. It takes 1.5 days to complete an orbit.
Between the proximity of the Earth, the rocky composition, the tight orbit with its parent star and the fact that it retains an atmosphere, this exoplanet meets all the requirements for follow-up observations by the next generation of telescopes. Since Gliese 486b has a sidereal rotation that is the same as its orbital period (1.5 days), it is tide-locked with its parent star (one side always looks at it).
Trifon Trifonov, a planetary scientist at the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, was the lead author of the research study. As he explained in a recent press release from MPIA:
‘The proximity of this exoplanet is exciting, as it will be possible to study it in more detail with powerful telescopes, such as the upcoming James Webb Space Telescope and the future extraordinarily large telescopes.
‘We can hardly wait until the new telescopes are available. The results will help us understand how well rocky planets can hold their atmosphere, what it consists of and how it affects the energy distribution on the planets. ”
Although Gliese 486 is a relatively faint and cool star (compared to the Sun), the amount of radiation to which it is exposed is so intense that the planet experiences surface temperatures up to 700 K (430 ° C; 806 ° F). From all this, the surface of Gliese 486b probably looks a lot like Venus, with a hot and dry landscape and traversed by glowing lava rivers.
One big difference, however, is that Gliese 486b has a soft atmosphere (while Venus has an incredibly dense atmosphere). This is impressive when we consider that our current planetary models indicate that radiation tends to strip planets of their gas envelopes. In this case, any atmosphere the planet still has will be maintained by the gravity of the super-Earth.
As José A. Caballero of the Centro de Astrobiología (CSIC-INTA, Spain) and a co-author of the article concluded:
‘The discovery of Gliese 486b was a stroke of luck. One hundred degrees warmer and the entire surface of the planet would be lava. Its atmosphere would consist of evaporated rocks. On the other hand, if Gliese 486b were a hundred degrees colder, it would have been unsuitable for follow-up observations. ”
In the future, the CARMENES team hopes to observe Gliese 486b as it makes doors in front of its star (compared to ours). At this point, small amounts of light will pass through the thin atmosphere of the planet, which is noticeable as James Webb. A second series of spectroscopic measurements are performed when the Gliese 486b orbit takes it behind its star.
At this point, light reflected from the planet’s surface can be studied to obtain emission spectra. Between these two types of spectroscopic observations, astronomers will be able to test the methods that enable them to limit the search for habitable planets. Ground-based observatories such as the Extremely Large Telescope (ELT) and Giant Magellan Telescope (GMT) will also allow direct imaging and spectroscopic studies.
The Calar Alto High Resolution Search for M Dwarfs with Near-Infrared Exoearths and Échelle Spectrographs (CARMENES) Consortium consists of more than 200 scientists and engineers from 11 institutions in Spain and Germany. The study, which describes their finding, a nearby transit rocky exoplanet suitable for atmospheric exploration, ‘recently appeared in the journal Science (Vol. 371, No. 6533).
Further reading: MPIA, Science