Extra sunlight with large center

Exoplanet is small and lightweight, making it very difficult to detect using common methods. Astronomers have now discovered one of the lightest and smallest known known solar eclipses 31 light years away. GJ 367b is only half the size of Mars and the mass of Earth. From the mass to size ratio, the researchers conclude that the iron core of this exoplanet should occupy most of its interior – as in Mercury, the core makes up 80 percent of the diameter. However, the GJ 367b is not ideal for life: its surface temperature is well over 1500 degrees, as it orbits very close to its star, the red dwarf.

Since the discovery of the first solar planet in the 1990s, astronomers have discovered thousands of other worlds orbiting extraterrestrial stars. Some of them were manifested by the effects of gravity on their star, while others made themselves noticeable by going directly in front of their star and thereby obscuring it from time to time. However, in general, larger asteroids closer to their star are more easily detected using these methods than smaller ones. Rocks smaller than Earth or smaller are more difficult to detect because they only exert less gravitational effects on their stars, and with bright stars, traffic is often difficult to see at a light bend. .

Shading around a red dwarf

But red dwarfs – a very common type of star, especially in our immediate cosmic environment, provide excellent opportunities for observing small things like this. These relatively cool, dimly lit stars make up less than 60 percent of the Sun’s radius. Christine Lam and her colleagues at the University of Technology in Berlin explain that “the traffic signal of a planet orbiting such a M dwarf star is relatively larger than that of a star of the same size as the Sun.” This opens up the possibility of identifying even the smallest planets orbiting near the star. With the help of the Transiting Exoplanet Survey Satellite (TESS) 31 light years away, astronomers have found a candidate for such a sub-Earth.
Observations have suggested that there may be a planet around the nearby red dwarf GJ367 with a radius of only 0.75 Earth.

To investigate this suspicion and to learn more about this potential exoplanet, Lam and his team further evaluated TESS data and observed the planet’s candidate and its star through the Harpes Spectrograph of the La Silla Laboratory at the European Southern Laboratory in Chile. “We did a lot of testing to make sure this candidate was not a false positive,” they explain. But new observations have confirmed that the red dwarf’s light is constantly dark every 0.32 days. From the time and shape of this depression in the light curve, astronomers conclude that this shadow must have come from a planet.

Small, dense and very warm

Analysis shows that around the Red Dwarf is a planet about 9,000 kilometers in diameter – no larger than Mars. At about 0.55 Earth masses, GJ 367b was baptized as one of the lightest known extraterrestrials to date. “From the precise determination of radius and mass, we conclude that GJ 367b must be a rocky planet,” says Lam. “It belongs to the terrestrial sub-Earth and goes one step further in the search for a second Earth.” However, in terms of its climate, the GJ 367b is not very Earth-like. It orbits its star in very close orbit and requires only 0.32 days per orbit – only eight hours per year. Although its core star is relatively cold and dim, the planet receives 576 times more radiation from its star than Earth. As a result, the temperature on its day side is about 1500 degrees Celsius. “It is hot enough to melt or evaporate silicates and metals,” astronomers explain.

From the mass and size of GJ 367b, researchers were also able to determine the density of the planet. It weighs 8.1 grams per cubic centimeter, which is significantly higher than other exoplanets of similar size. “High density indicates that the planet is dominated by an iron core,” explains Lam’s colleague Silard Sismadia. According to the group’s calculations, this metal center will take up 85 percent of the planet’s radius. “In which it is like Mercury, the large center of iron and nickel in its proportions distinguishing it from all other terrestrial celestial bodies in the solar system.” Circles not yet described.

Quelle: Christine Lam (TU Berlin) et al., Science, doi: 10.1126 / science.aay3253

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