Press release | 6 December 2021 | pp

Ultra-Light and Super-Fast

GJ367 b is a flyweight among planets. Researchers report on newly discovered extrasolar rocky planet in the journal "Science"

GJ 367 b is remarkable because of its low mass, the lowest in fact yet measured. What also makes it interesting is the time it requires to orbit its sun – just eight hours. This makes it an ultra short period (USP) exoplanet. An exact calculation of its radius and mass also reveals that GJ 367 b is a rocky planet, in other words similar to our own planet. This brings us a step closer to discovering a “second Earth”. A group of 78 authors has now published reports on their research findings in the journal Science. The group is led by Dr. Kristine W. F. Lam und Dr. Szilárd Csizmadia of the Zentrum für Astronomie und Astrophysik at TU Berlin and the Institute of Planetary Research at the German Aerospace Center (DLR).

A quarter of a century after the discovery of the first extrasolar planet (a planet beyond our own solar system orbiting another star), scientists today are mainly concerned with determining the exact characteristics of these planets, as well as finding further examples of course. We now have a far more precise profile of the majority of the 5,000 extrasolar planets currently known to us. Many of these were discovered using the transit method, which measures the minimal differences in luminosity observed when planets pass in front of their own sun. This is also how GJ 367 b was discovered using NASA’s space telescope TESS (Transiting Exoplanet Survey Satellite).

We don’t yet know the origin of this rapid little planet

Researchers have made a number of other discoveries concerning GJ 367b: “This exoplanet is a very fast mover and smaller than the Earth,” explains Dr. Kristine W. F. Lam. “It belongs to the group of ultra short period planets, meaning that it takes less than one day to orbit its sun. We have already discovered a number of these planets, but we don’t yet know how they came to exist. Following the discovery of GJ 367b, we were able to make spectral follow-up observations from the ground. Based on meticulous examinations and the combination of various evaluation methods, we were able to accurately determine that its radius is 72 per cent that of the Earth, and its mass 55 per cent of the Earth's mass.”

Determining its radius and mass with an accuracy of 7 and 14 percent, has also enabled the researchers to discover some facts about the inner composition of the planet: GJ 367b is a low-mass rocky planet with a higher density than Earth. “The high density indicates an iron core,” explains Dr. Szilárd Csizmadia. “This makes it similar to Mercury, whose large iron core is unique among the terrestrial bodies in our solar system.” However, as the planet orbits very close to its sun, it is exposed to a significantly higher level of radiation, more than 500 times that of the Earth. This means that surface temperatures could reach up to 1500 degrees Celsius, a temperature at which all rocks and metals melt.

Red dwarves with usually two to three orbiting planets are particularly common in our cosmic neighborhood

The parent star of the new exoplanet, a red dwarf called GJ 367, is only about half the size of our sun.  This proved advantageous both for discovering the planet as well as for the follow-up measurements, as it means the orbiting planet’s transit signal is particularly strong. Red dwarves are both smaller and cooler than the Sun. This makes it easier to both find their planets and determine their characteristics. They are among the most common objects in our cosmic neighborhood, making them suitable destinations for research on exoplanets. Scientists estimate that every red dwarf, also known as M stars, is orbited by an average of two to three planets, each up to a maximum of about four times the size of Earth.

According to the astrophysicists, the discovery shows how the smallest and lowest-mass planets can be found, leading to a better understanding of the formation and evolution of rocky planets.

The article is published in Science at: Doi-Nr.: 10.1126/science.aay3253

The research was developed as part of DFG priority program SPP 1992 “Exploring the Diversity of Extrasolar Planets”:
https://www-astro.physik.tu-berlin.de/exoplanet-diversity/  

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