Using NASA’s space telescope, scientists have discovered an exciting world. It’s about the size of Earth, remarkably close to our solar system, and could be comfortable for life as we know it.
The extrasolar planet, or “exoplanet,” named Gliese 12b orbits a small, cool red dwarf star located only about 40 light-years from Earth in the constellation Pisces. The exoplanet — which the team found using NASA’s Transiting Exoplanet Survey Satellite (TESS) — is estimated to be about 1.1 times the width of Earth, making it similar to our planet and also to Venus, which is often called our world’s solar system. twin.”
Gliese 12b orbits its star Gliese 12 so closely that its year is just 12.8 Earth days long. However, because the red dwarf Gliese 12 is only about a quarter the size of the Sun, it is also much cooler than our star. This means that even though Gliese 12b is at a distance from its red dwarf host, which corresponds to only 7% of the distance between the Sun and Earth, it is still in the habitable zone of its planetary system. The habitable zone, also known as the “Goldilocks Zone,” is the region around a star that is neither too hot nor too cold for planets to host liquid water, a vital component of life as we know it. Although it is important that the two teams behind the discovery of Gliese 12b cannot yet say for sure whether it has an atmosphere. So it remains unclear whether the world could be habitable, but scientists have some cautious optimism.
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“The main interesting thing is that this is a planet that’s really close; in fact, it’s one of the closest transiting planets to Earth,” University College of London scientist Larissa Palethorpe, who led the research with University of Southern Queensland astrophysicist Shishire. Dholakia, he told Space.com. “It’s either in the habitable zone of its star, or it’s right on the edge of it – so it could be habitable.”
If Earth and Venus had a child
Scientists spotted Gliese 12b as it passed, or “transited,” across the face of its red dwarf parent star. These transits cause small dips in light that TESS is adept at detecting. Palethorpe added that when the team went into this project, they didn’t know what the orbital period or size of the planet would be.
“Finding out that it’s as big as Earth was quite a nice surprise,” she continued. “So it was a really nice thing to be able to hang on to, but I think especially knowing that it could lie between Earth and Venus in terms of habitability is really exciting.”
Gliese 12b receives about 85% of the radiation that Venus receives from the Sun, but is thought to have a much cooler surface temperature of 107 degrees Fahrenheit (42 degrees Celsius) compared to Venus’ surface temperature of 867 degrees Fahrenheit (464 degrees Celsius). ).
Although both Earth and Venus are in the Sun’s habitable zone, one can support life and has a favorable atmosphere, while the other is an inhospitable hellscape with temperatures hot enough to melt lead. A study of Gliese 12b might help us understand why this is so.
“Gliese 12b could teach us a lot about how our own solar system evolved,” Palethorpe added.
The team will now investigate whether Gliese has an atmosphere – but early indications are that if it does, it will be relatively sparse. Perhaps surprisingly, however, the absence of a thick atmosphere is good news for the planet’s habitability prospects.
“We know that some planets have a very thick hydrogen atmosphere that covers the entire planet. This very thick layer of gas is actually bad news for habitability,” Vincent Van Eylen of Palethorpe, a researcher at UCL, told Space.com. “Typically these planets are two or three times the size of Earth. Gliese 12b is the actual size of Earth, so it probably doesn’t have this very dense atmosphere.
“It could either have no atmosphere, which wouldn’t be great for habitability, or it could have the thin atmosphere that Earth has.”
Still, even if Gliese 12b does not have an atmosphere, it may still be an important test subject for advancing our search for life elsewhere in the Milky Way. That’s because, as a red dwarf, the star it orbits is the most common form of star in our galaxy—yet we know relatively little about it when it comes to red dwarf planetary systems.
Life around red dwarfs
In the Milky Way, red dwarfs make up the largest family of stars that are still fusing hydrogen with helium in their cores, a process that defines the so-called “main sequence” of a star’s life. An estimated 60% to 70% of the stars in our galaxy are red dwarfs like Gliese 12, and of the 30 stars closest to Earth, at least 20 are red dwarfs.
“It is interesting to know about planets around small stars, what they might be like and whether such planets could have life,” added Van Eylen.
Red dwarfs, officially known as K-type or M-type stars, have between 7.5% and 50% of the mass of the Sun. This low mass relative to the Sun means that such stars burn at a lower temperature, reaching only 6,380 degrees Fahrenheit (3,500 degrees Celsius) compared to our star’s 9,900 degrees Fahrenheit (5,500 degrees Celsius). For example, Gliese 12 has a surface temperature of about 60% that of the Sun.
This lower temperature means that dimly glowing red dwarfs can exist as main-sequence stars much longer than intermediate-mass stars like the Sun. Although the sun is expected to live for about 10 billion years, red dwarfs are predicted to have ten or even a hundred times that lifetime. Sometimes this number can extend up to trillions of years. This means that life would have had more time to develop on planets orbiting red dwarfs than on planets around larger main sequence stars.
But it’s not all good news for the prospects for life on exoplanets orbiting red dwarfs.
Although cooler than the sun in their stellar maturity, red dwarfs are believed to be much wilder than our star. This class of stars is thought to be highly magnetically active and emits frequent and powerful flashes of high-energy light in the form of X-rays. These X-rays can violently remove the atmosphere of a planet close to a red dwarf.
Moreover, recent research has suggested that even red dwarfs that remain quiescent for many years can suddenly explode in superflares 100 to 1000 times more powerful than solar flares. These eruptions are more common in the youth of this class of stars and are also capable of removing atmospheres and boiling liquid water, even in the habitable zones.
At the moment, however, both teams involved in the discovery of Gliese 12b think the red dwarf is relatively calm in orbit, which could be good news for the exoplanet’s chances of gaining an atmosphere.
Red dwarf exoplanets are good targets for TESS
The fact that red dwarfs are cooler than stars like the Sun, and thus their habitable zones are closer to the stars, actually makes it a little easier for TESS and its transit method of planet hunting to detect exoplanets around them.
“We tend to detect planets that are close to their host stars basically just because they transit more often. When we find planets orbiting red dwarfs, because they’re smaller stars, the transit dimming is greater,” Palethorpe said. “Because red dwarfs are slightly cooler, the habitable zone lies closer to the star than it would for our kind of sun, which means that with TESS we are more likely to detect planets in the habitable zone.”
The team will have to turn to instruments other than TESS to explore the planet further. They will also switch to a different exoplanet detection method to better define the characteristics of Gliese 12b. One is called the “radial velocity method,” which uses the tiny wobbles that planets make in the motion of their stars as they pull on those stars gravitationally.
“I think the next thing is to actually determine the mass of the planet. We’re already actively doing that as part of the High Accuracy Radial Velocity Planet Searcher team for the Northern Hemisphere (Harps North), which is a radial velocity telescope,” Palethorpe said. “Then we also got another proposal accepted by the European Southern Hemisphere Astronomical Research Organization (ESPRESSO), which is another radial velocity telescope. And so, hopefully, from the kind of radial velocity observation, we’re going to do this.”
Palethorpe and Van Eylen also hope to get time with the James Webb Space Telescope (JWST) to further study the planet’s atmosphere. This is possible because as Gliese 12b passes the face of its star, the light passing through its atmosphere will carry the characteristic fingerprints of the elements in the atmosphere.
This process is called “transmission spectroscopy,” and Gliese 12b is only one of a handful of Earth-like temperate worlds close enough to be examined this way.
JWST is currently conducting a similar investigation for the seven Earth-like planets of the TRAPPIST-1 system, located about 40 light-years away. These planets are similar to Gliese 12b in that many of them are not only in the habitable zone of their star, but that the star is also a small and cool red dwarf.
“I think with JWST we’ll at least get some clues about the atmosphere of this planet, which I think would be the most exciting thing we could do now that it’s been discovered,” Van Eylen said.
Both scientists are extremely cautious about the possibility that Gliese 12b could host life. After all, it is early for our understanding of this world and the methods that would be able to detect signs of life in the atmosphere of an exoplanet, even one as relatively close as Gliese 12b.
“I think Gliese 12b will teach us a lot about life, but we can’t say anything for sure. I think it’s very exciting and we should definitely look forward to more research coming out of Gliese 12b,” Palethorpe concluded. “Not a bad place to start the hunt for life.
The research by both teams was published Thursday (May 23) in The Monthly Notices of the Royal Astronomical Society and The Astrophysical Journal Letters.
Originally published on Space.com.