Newfound alien planet has nuclear fusion going in its core

Artist's illustration of Europe's star-mapping Gaia spacecraft, whose observations helped discover the huge alien planet HD 206893 c.
Artist's illustration of Europe's star-mapping Gaia spacecraft, whose observations helped discover the huge alien planet HD 206893 c. (Image credit: ESA)

An international team of scientists has found a new exoplanet that's the first to be directly imaged thanks to Europe's Gaia spacecraft — and it appears to have nuclear fusion ongoing in its core.

The team, led by Professor Sasha Hinkley at the University of Exeter in England, discovered the exoplanet orbiting roughly 300 million miles (483 million kilometers) away from the star HD 206893, which is located about 130 light-years from Earth and is about 30% larger than our sun. 

The star has a known debris disk around it and was considered a good candidate for finding new extrasolar planets. The European Space Agency's Gaia mission makes extremely precise measurements of the location of stars as they move across the sky, and the astrometric data it provides also means the presence of exoplanets can be inferred by measuring the wobble of stars.

Related: 10 amazing exoplanet discoveries

Following up on Gaia data, the team used the GRAVITY instrument on the Very Large Telescope in the Atacama Desert of northern Chile to directly confirm the presence of the newfound planet, known as HD 206893 c.

What's more, the observation also allowed the researchers to analyze the light spectrum from the planet's atmosphere. The apparent brightening of the object suggests that the core of this giant planet is undergoing nuclear fusion using deuterium, an isotope of hydrogen carrying a neutron. 

The newly discovered exoplanet is likely about 13 times more massive than Jupiter. That enormous size and the evidence of fusion mean it is on the boundary between being a planet and a brown dwarf, a curious cosmic object that forms in the same way as normal stars but does not quite have the mass required to sustain nuclear fusion. The discovery could provide new insight for scientists to distinguish between massive planets and brown dwarfs, study team members said.

"The discovery of HD 206893 c is a really important moment for the study of exoplanets, as ours may be the first direct detection of a 'Gaia exoplanet,'" Hinkley said in a statement (opens in new tab)

The discovery shows that Gaia can point the way to potential exoplanets, which can then be directly detected by follow up observations, either on the ground or by a space-based observatory such as NASA's James Webb Space Telescope.

The new study has been accepted by the journal Astronomy & Astrophysics and is available via ArXiv (opens in new tab). In addition, Hinkley presented the discovery earlier this month at the American Astronomical Society conference in Seattle.

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Andrew Jones
Contributing Writer

Andrew is a freelance space journalist with a focus on reporting on China's rapidly growing space sector. He began writing for Space.com in 2019 and writes for SpaceNews, IEEE Spectrum, National Geographic, Sky & Telescope, New Scientist and others. Andrew first caught the space bug when, as a youngster, he saw Voyager images of other worlds in our solar system for the first time. Away from space, Andrew enjoys trail running in the forests of Finland. You can follow him on Twitter @AJ_FI (opens in new tab).

  • rod
    From the reference paper, ref - Direct Discovery of the Inner Exoplanet in the HD206893 System, https://arxiv.org/abs/2208.04867, 23-Nov-2022. "Long term precise radial velocity (RV) monitoring of the nearby star HD206893, as well as anomalies in the system proper motion, have suggested the presence of an additional, inner companion in the system. Here we describe the results of a multi-epoch search for the companion responsible for this RV drift and proper motion anomaly using the VLTI/GRAVITY instrument. Utilizing information from ongoing precision RV measurements with the HARPS spectrograph, as well as Gaia host star astrometry, we report a high significance detection of the companion HD206893c over three epochs, with clear evidence for Keplerian orbital motion. Our astrometry with ∼50-100 μarcsec precision afforded by GRAVITY allows us to derive a dynamical mass of 12.7 +1.2/−1.0 MJup and an orbital separation of 3.53 +0.08/−0.06 au for HD206893c. Our fits to the orbits of both companions in the system utilize both Gaia astrometry and RVs to also provide a precise dynamical estimate of the previously uncertain mass of the B component, and therefore derive an age of 155±15 Myr. We find that theoretical atmospheric/evolutionary models incorporating deuterium burning for HD206893c, parameterized by cloudy atmospheres provide a good simultaneous fit to the luminosity of both HD206893B and c..."

    b and c are very large exoplanets reported. http://exoplanet.eu/catalog/hd_206893_c/, and http://exoplanet.eu/catalog/hd_206893_b/
    c would be out near the asteroid belt or so in our solar system, and b would be close to Saturn position.
    Reply
  • Mikhail Markeyev
    This is called a "brown dwarf" - a star whose mass can only provide a deuterium fusion reaction, but not hydrogen. And it is not a planet.
    Reply
  • rod
    Mikhail Markeyev said:
    This is called a "brown dwarf" - a star whose mass can only provide a deuterium fusion reaction, but not hydrogen. And it is not a planet.
    Okay, keep in mind the exoplanet sites show exoplanets with much more mass too.

    Example, http://exoplanet.eu/, this site shows 329 with masses 10 or larger Jupiter. HD 131664 b is 135 Jupiters, HR 3549 b is 45 Jupiters as examples.

    https://exoplanetarchive.ipac.caltech.edu/index.html, this site shows 159 with 10 or more Jupiter masses. PH2 b is 80 or so Jupiters. VHS J125601.92-125723.9 b is 32 or so Jupiters.
    Reply
  • Helio
    Wow. I didn't realize there are so many brown dwarfs in the list, but I shouldn't be surprised since it's logical to include BDs (Brown Dwarfs) in the exoplanet list. They might have moons. :)

    But, as noted, they are Brown Dwarfs. There are about 10 BD's listed that range from 12.9 to 13.3 Jupiter masses, ignoring the margins of error. There are 270 exoplanets with 13 or more Jupiter masses, using Rod's first link.
    Reply
  • Pogo
    As far as I know, if it burns hydrogen and heavier elements, it’s a star. If it burns only deuterium, it’s a brown dwarf. If it doesn’t burn anything, it’s a planet. But, of course, if it looks like a planet and we discover it’s hiding a dueterium process inside, we would change its designation.

    But, the designation of things can be dynamic. We may change definitions and create new ones as we learn more. Don’t be surprised!
    Reply
  • Pogo
    I also think that bodies that are destined to be stars go through earlier stages - starting out as a pile of gas and rubble, then a planet as the mass increases. Then given enough mass and rate of infalling material, it’s heated up enough by gravitational collapse to become sorta a plasma planet. As the temperature and pressure get to brown dwarf stage, the deuterium ignites, first as a few hot spots, then eventually enough to be self-sustaining. As it gains more mass, the conditions become enough to ignite the hydrogen cycle. Hence the body goes through all those stages.
    We just can’t see it because of the accretion disc along with other bodies going through the building stage all within a nebula or cloud of stuff making the stars. I imagine once the cloud clears because the bodies that were born consumed most of the material, left behind are stars with planets, some brown dwarves, some interstellar planets and moons, and all kind of rocks and dust just everywhere, all going their destined pathways.
    Reply
  • Helio
    Pogo said:
    I also think that bodies that are destined to be stars go through earlier stages - starting out as a pile of gas and rubble, then a planet as the mass increases. Then given enough mass and rate of infalling material, it’s heated up enough by gravitational collapse to become sorta a plasma planet. As the temperature and pressure get to brown dwarf stage, the deuterium ignites, first as a few hot spots, then eventually enough to be self-sustaining. As it gains more mass, the conditions become enough to ignite the hydrogen cycle. Hence the body goes through all those stages.
    We just can’t see it because of the accretion disc along with other bodies going through the building stage all within a nebula or cloud of stuff making the stars. I imagine once the cloud clears because the bodies that were born consumed most of the material, left behind are stars with planets, some brown dwarves, some interstellar planets and moons, and all kind of rocks and dust just everywhere, all going their destined pathways.
    We actually can see many of these protostars, including their disks, thanks to IR scopes.
    Reply
  • Pogo
    I imagine although we can see them, with all the debris surrounding them, we wouldn’t be able to see them when they light off the deuterium cycle, and again the hydrogen cycle. That would be interesting.
    Reply
  • Helio
    Pogo said:
    I imagine although we can see them, with all the debris surrounding them, we wouldn’t be able to see them when they light off the deuterium cycle, and again the hydrogen cycle. That would be interesting.
    AFAIK, the ignition event is not an event. The stars simply get hot enough from the gravitational energy generated during collapse (as you mentioned), reaching a point in the core that deuterium burning takes place, here and there. The amount of energy released per cubic meter is less than what the human body generates in heat, surprisingly, which is true even for hydrogen fusion.

    What might be interesting is when the star's light finally breaks through its dusty shroud, though this is likely a very slow process, normally.
    Reply