Near worlds: The red dwarf Gliese 887, only eleven light years away, has a planetary system, as astronomers discovered. It is surrounded by two, maybe even three super earths. Because this red dwarf is unusually inactive, these planets could have dense, protective atmospheres and be exposed to little hard radiation. At least the two outer super-earths would be a good target for the search for life.
In our cosmic neighborhood, astronomers have already discovered a number of exoplanets around red dwarfs, including the two worlds around our neighboring star Proxima Centauri or the seven “earth twins” around the star TRAPPIST-1 40 light years away. So far, however controversialhow life-friendly such systems are. Because red dwarfs produce frequent, strong bursts of radiation, which then cover their planets with high-energy UV and X-rays – this would be of little help for extraterrestrial life.
Red dwarf eleven light years away
But as it turns out, there are also nearby red dwarfs who are far calmer – and who have promising planets. The star Gliese 887 (GJ 887) is just under eleven light years away and is the brightest red dwarf in the sky. Sandra Jeffers from the University of Göttingen and her colleagues took a closer look at him with the HARPS spectrograph at the Very Large Telescope (VLT) of the European Southern Observatory in Chile.
In order to find out whether GJ 887 is orbited by planets, the astronomers looked for slight, periodically repeated shifts in the spectral lines in the star’s spectrogram. They form when the star “wobbles” slightly due to the influence of one or more planets. This radial velocity method was used to track down more than 90 percent of all potentially life-friendly exoplanets known to date.
Two, maybe three super earths
The astronomers also found what they were looking for in GJ 887: “We discovered signals with a period of 9.3 days, 21.8 days and 50.7 days,” report Jeffers and her team. Closer analysis confirmed that the first two of these signals are most likely from planets. With the third signal, on the other hand, astronomers cannot yet rule out that it is only a disturbing effect.
That means: The nearby red dwarf has two planets, maybe even three. The two inner worlds GJ 887b and GJ 887c are super earths with 4.2 and 7.6 earth masses, so they are only slightly larger than the earth. GJ 887b is in orbit only 0.07 astronomical units (AU) from its star. This means that this super earth with a temperature of almost 200 degrees is probably too hot for life.
The second planet, GJ 887c, on the other hand, could give hope. Because with an orbit of 0.12 astronomical units, it moves only slightly within the habitable zone, which starts at 0.19 astronomical units. Astronomers estimate that the temperatures on GJ 887c are around 75 degrees. If there was the third planet around this red dwarf, its orbit would even be in the middle of the habitable zone – it would be a good candidate for the search for life.
Hardly any outbreaks of rays
Also positive: In contrast to most other red dwarfs, Gliese 887 is a particularly quiet specimen of its star class. Data from NASA’s TESS space telescope showed that the radiation intensity of this star fluctuates only minimally. In addition, the astronomers found only a smaller group of star spots – this also indicates low activity and few radiation outbreaks.
The planets in this system would therefore be exposed to little hard radiation and could have a thick, protective atmosphere due to the weak star wind. “If someone had to live near a red dwarf, they would want a quieter star like GJ 887,” Melvyn Davies from Lund University in Sweden wrote in a supplementary comment.
Rewarding observation object
Because of its proximity to Earth, the uniform brightness of the star and the possibly three super-earths in orbit around GJ 887, this planetary system could become a particularly worthwhile observation object for astronomers in the future. As early as 2021, NASA’s James Webb space telescope could clarify whether the third planet exists and also provide information about the atmospheres of these worlds.
“If further observations confirm the existence of the third planet in the habitable zone, then GJ 887 could become one of the most intensively researched systems in the solar neighborhood,” comments Davies. (Science, 2020; doi: 10.1126/science.aaz0795)
Source: University of Göttingen
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