First Exo-Moon may have been Discovered

#1
Given the huge number of exoplanets out there, it's assumed that there must be even more exo-moons. But none have yet been seen.

That may have changed, since the discovery of an exomoon is being reported by two astronomers at Columbia University.

http://advances.sciencemag.org/content/4/10/eaav1784

It's a biggie: they estimate this moon might be about the same mass as Neptune. The planet it's orbiting is apparently several Jupiter masses. (I'm not sure if that would be a planet-moon situation or a double planet situation. It presumably depends on whether the common center of gravity they both orbit is located inside the bigger planet.

It and its parent planet are orbiting a seemingly very stable star (Kepler 1625) with Sun-like characteristics, but about twice as old.

The discoverers say that this is just the "lowest hanging fruit", since big moons are the easiest to detect. There should be lots of smaller moons out there waiting to be discovered.

They say

"One jarring aspect of the system is the sheer scale of it. The exomoon has a radius of ~ 4 Earth radii, making it very similar to Neptune or Uranus in size... This Neptune-like moon orbits a planet with a size fully compatible with that of Jupiter at 11.4 plus or minus 1.5 Earth radii, but most likely a few times more massive... as a likely gaseous pair of objects, there is not much prospect of habitability here, although it appears that the moon can indeed be in the temperature zone for optimistic definitions of the habitable zone.

What is particularly interesting about the star is that it appears to be a solar-mass star evolving off the main sequence.... We find that the star is certainly older than the Sun, at ~ 9 gigayears in age... The luminosity was likely close to solar for most of the star's life...

A mass ratio of 1.5% is certainly not unphysical from in situ formation using gas-starved disk models, but it does represent the very upper end of what numerical simulations form... Impacts between gaseous planets leading to captured moons are not well studied but could be worth further investigation... If confirmed, Kepler 1625b-i will certainly provide an interesting puzzle for theorists to solve."
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#2
(Oct 4, 2018 02:47 AM)Yazata Wrote: [...] It's a biggie: they estimate this moon might be about the same mass as Neptune. The planet it's orbiting is apparently several Jupiter masses. (I'm not sure if that would be a planet-moon situation or a double planet situation. It presumably depends on whether the common center of gravity they both orbit is located inside the bigger planet. [...]


At least the AstroCrank community hasn't seized upon it yet as a possible alien megastructure (Hollow Moon hypothesis).

And the gargantuan size of this particular satellite would surely inhibit even them from proposing another camouflaged spaceship ("Spaceship Moon" and Soviet Scientific Politics ).

~
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