Maybe even with life: red dwarf stars have three types of planets

Maybe even with life
Red dwarf stars have three types of planets

9/9/2022 at 2:07 pm

Red dwarfs are the most common star in the Milky Way. So far, astronomers have known two classes of planets in their vicinity. Now the researchers have identified a third group. The discovery could affect the search for life in space.

Orbiting red dwarf stars, which are smaller and cooler than our Sun, are three different types of planets: those with dense atmospheres, planets with very high water content in liquid or solid form, and rocky Earth-like planets. This is evidenced by careful analysis of archive data, in particular files TESS space telescope (Transiting Exoplanet Survey Satellite), by two astrophysicists from Spain. All of these planets are good candidates for analyzing their atmospheres using the new James Webb Space Telescope — also to search for extraterrestrial life, according to the research team. In the magazine “Science”.

Red dwarf stars are of particular interest to astronomers searching for planets for a number of reasons: They are the most common type of star in our Milky Way. It is easier to see the planets passing in front of them as seen from Earth than it is to see the larger stars. Because it covers a larger part of the star during such a “transit” and thus weakens its light even more.

TESS, a space telescope launched by NASA in 2018, specializes in looking for such a periodically weakening of starlight. Rafael Luc of the Andalusian Institute of Astrophysics and Enrique Ballet of the University of La Laguna in Tenerife have subjected the red dwarf planets discovered by TESS to a detailed analysis. The researchers focused on planets no more than four times the size of Earth.

Accurate data in the archive

Previous research indicated that there are two different types of planets in this region. Astronomers believe that while the smaller planets are rocky Earth-like planets, the larger planets have extensive helium and hydrogen atmospheres, and therefore appear larger. However, in order to verify this conclusion, the mass of the planets and therefore their density must also be known. That’s exactly what Luque and Pallé did—and came to the surprising conclusion that there are not two, but three different types of planets in red dwarf stars.

While the planet’s size can be read directly from the amount of light attenuation during transit, determining its mass is tricky. Because this requires accurate measurements of the motion of the red dwarf star: strictly speaking, the planet does not revolve around its star, but both move around their common center of gravity, however, the star is much less due to its greater mass – this makes this motion more difficult to measure.

However, for a total of 34 planets near the red dwarfs, Luque and Pallé were able to find sufficiently accurate measurements in the data archive and thus determine the mass and density of these celestial bodies. In addition to the already known rocky planets and a few of them with an extensive gaseous envelope, the researchers found a large number of planets with densities consistent with a mixture of about half rock and half water. These water-rich planets may have formed farther from the star—because there was more water in the formation stage—and only entered closer orbits later, Lock and Paley suggest. This is also supported by the fact that pure rocky planets are always closer to the star than water planets.

Depending on the distance of a planet from its star, conditions favorable for life for all three species can be visualized. This makes all of these planets suitable targets for searching for “biosignatures” in their atmosphere – that is, for materials that indicate the presence of life.