The hunt for an Earth-like planet shielded with a protective atmosphere has so far eluded scientists, but a new detection by the James Webb Space Telescope could be the first.
Astronomers are taking a closer look at GJ 486b(opens in a new tab), relatively close to our solar system at just 26 light-years away in the constellation Virgo. Discovered two years ago, it's a rocky exoplanet(opens in a new tab) about 30 percent larger than Earth, orbiting a red dwarf star(opens in a new tab) every 1.5 days.
Despite its being so close to its host star and having a scorching-hot temperature of about 800 degrees Fahrenheit, the planet shows signs of having water vapor — a hint that the alien world may have an atmosphere swaddling the planet.
"Water vapor in an atmosphere on a hot rocky planet would represent a major breakthrough for exoplanet science," said Kevin Stevenson, the principal investigator of the study from the Johns Hopkins University Applied Physics Laboratory, in a statement(opens in a new tab). "But we must be careful and make sure that the star is not the culprit."
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Why do we need an atmosphere?
NASA has playfully called Earth's atmosphere its "security blanket(opens in a new tab):" Without it, the type of life flourishing on the planet wouldn't exist. This cocoon holds oxygen in the air and filters out harmful ultraviolet radiation from the sun, all while keeping our world warm and habitable. Furthermore, it creates pressure that allows liquid water to exist on Earth's surface.
Water vapor has been discovered on gassy exoplanets(opens in a new tab) before, but never for a rocky or terrestrial planet akin to Earth, Mars, Mercury, and Venus.
Perhaps surprisingly, though, another possible explanation for the vapor detected by Webb is that water is coming from the outer layer of the nearby red dwarf star — cooler than the sun — not from the planet at all. Scientists will need more observations to determine if the exoplanet indeed has an atmosphere and how much water is present.
Even the sun sometimes has water vapor in sunspots because these areas are much cooler compared to the surrounding surface of the star. Given that the recently found exoplanet's star is much cooler than the sun, Webb researchers say it's even more plausible water vapor would concentrate within its starspots. That means no one yet knows whether the star is mimicking the signal they'd see from a planet's atmosphere.
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“Water vapor in an atmosphere on a hot rocky planet would represent a major breakthrough for exoplanet science."
The new Webb research will be published (opens in a new tab)in The Astrophysical Journal Letters.
How does Webb study exoplanets?
Webb, a collaboration of NASA, the European Space Agency, and the Canadian Space Agency, is the most powerful infrared telescope in space. Astronomers say its scientific capabilities are igniting a golden age in our understanding of the universe. One of its key missions is to peer into the atmospheres of other worlds. Discoveries of water and methane, for example — important ingredients for life as we know it — could be signs of potential habitability or biological activity.
The Webb researchers used a technique called transmission spectroscopy(opens in a new tab) to study the exoplanet. When these worlds cross in front of their host star, starlight is filtered through their atmospheres. Molecules within the atmosphere absorb certain light wavelengths, or colors, so by splitting the star’s light into its basic parts — a rainbow — astronomers can detect what light segments are missing to discern the molecular makeup of an atmosphere.
After observing two instances of the planet crossing in front of its star, the researchers used three different methods to analyze the data. All were consistent in showing a strong likelihood for a water vapor signal, according to a post(opens in a new tab) by the Space Telescope Science Institute, which operates the instrument.
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"We didn’t observe evidence of the planet crossing any starspots during the transits. But that doesn’t mean that there aren’t spots elsewhere on the star," said Ryan MacDonald, a co-author from the University of Michigan in Ann Arbor, in a statement(opens in a new tab). "And that’s exactly the physical scenario that would imprint this water signal into the data and could wind up looking like a planetary atmosphere."
If you're thinking this means Earthlings have found a Plan B planet, don't get too excited: Scientists say GJ 486b appears to be too close to its star to be habitable. But if it does have an atmosphere, they hope to learn whether such a rocky planet could maintain the protective cocoon, even as its super-close star cooks it away with heat and solar radiation.
How could such a planet replenish its atmosphere?
One theory suggests volcanoes spewing steam from deep within the planet.
