Newfound alien planet has nuclear fusion going in its core

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.
 
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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.
 
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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.
 
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!
 
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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.
 
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.
 
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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.
 
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.
 
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