I’m wondering if a massive planet (maybe 10 times the mass of Jupiter) in the habitable zone of a G type star could have an axial tilt similar to earth or if gravitational forces would erode the tilt the way they do to moons orbiting gas giants?
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1$\begingroup$ Uranus has less mass than Jupiter, far less than "maybe 10 times the mass of Jupiter." Further, Uranus orbits the Sun at about 18-20 AU, whereas the Solar System's habitable zone is usually thought to reach to 10 AU (a bit beyond Saturn's orbit) or much less. But Uranus rotates nearly on its side, with an axial tilt of 97.77 degrees to orbit, far more than Earth's 23.439 degrees, giving the ice-giant seasons unlike any other Solar System planet. I'm unsure if that helps answer your question much, but it may pr $\endgroup$– WPWPWPCommented Sep 19, 2022 at 18:52
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$\begingroup$ I think the phrase ‘habitable zone’ is a strange qualifier for how close this gas giant would be to the star; any planet this size would be a gas giant, as so far as we can tell it doesn’t look like things can live on gas giants, so are you referring more to a hot Jupiter type configuration or something else? $\endgroup$– Justin TCommented Sep 19, 2022 at 19:25
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Yes, planets with an extreme tilt can happen, but we cannot be sure about the probability of that by now. Our own planet Uranus is witness to this that it does, though (even when it is significantly lighter than Jupiter).
Despite our knowledge of over 5000 exoplanets to date, we know little for sure about their spin-orbit alignment or their alignment relative to their host star's rotation axis. There have only recently been reported measurements of the spin-orbit alignment from the Beta Pictoris system (Kraus et al, 2020) which confirms that the planets in this emerging planetary system are spin-orbit aligned wrt their host star. There is another slightly older overview by Campante et al (2016) which confirms this for other systems. However defining the exact obliquity for the planets is even more difficult as it needs well-resolved spatial spectroscopy at levels of quite a bit better than 1AU in the target system of evolving planets (thus those which still have a circum-planetary accretion disc) - or you need to resolve the planet which is beyond our current capability.
There is a probability modelling analysis by Monoz and Perez (2018) which comes to a similar conclusion: all tilts possible, but spin-orbit aligned planets are more likely (how much depends on model assumptions).
As to'erosion'of axial tilt: the sun did not succeed in changing much venus' (177°) or earth's (23°) axial tilt, so it won't impact that of a much larger planet either.
answered Sep 21, 2022 at 9:18