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Author Topic: Could a "hot jupiter" exist in an orbit 1 AU from a star like our own, and if so  (Read 322 times)

Offline Cobalt-Blue

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Could a "hot Jupiter" or "super earth" exist in an orbit 1 AU from a star like our own, and if so, could an Earth size planet be in its L4 or L5 position without being tidally locked to either the planet or the star?


 

Offline syhprum

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The blackbody temperature at 1 AU is about 250K what would keep a hot Jupiter hot ?
 

Offline evan_au

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Quote from: Cobalt-Blue
"hot Jupiter"
This term is generally reserved for large planets (the size of Jupiter) but in orbits very close to their star (0.015-0.5AU), with radiation from their star being much stronger than what we receive on Earth.

But I guess a Jupiter-sized planet in Earth's orbit (1AU) is not so far from the usual upper limit (0.5 AU). It is certainly a long way from where astronomers expected gas giants like Jupiter and Saturn to form (and they presumed, to stay there, once they were formed).

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Could a "hot Jupiter" or "super earth" exist in an orbit 1 AU from a star like our own?
Yes. Astronomers were surprised to see them so close to their parent star. But if they can get that close, they could certainly be in a 1 AU orbit.

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if so, could an Earth size planet be in its L4 or L5 position without being tidally locked to either the planet or the star?
Tidal friction is quite weak at the distance of the L4 & L5 points (the time to become tidally locked increases as the 6th power of the orbital distance). If the Earth has not become tidally locked to the Sun by now, it would not become tidally locked to a Jupiter-sized planet at the same distance.
See: https://en.wikipedia.org/wiki/Tidal_locking#Timescale

Of more concern is the stability of the L4 and L5 points. The strength of the tidal interaction is fairly weak, and disturbance from other planets can set up a resonance in the body at the L4 & L5 point which breaks it out of this stable zone.

Being in the same orbit as a Jupiter-sized body is a perilous place to be - the Earth-sized moon could crash into the planet, be flung out of the planetary system, into the star, or an unbearably hot or cold orbit.

So you would have to assume that there are no other large planets in close orbits which could disturb the delicate balance in the L4 & L5 position. Small rocky planets in distant orbits would not disturb the L4/L5 positions of a Jupiter-sized planet excessively.

Quote from: syhprum
The blackbody temperature at 1 AU is about 250K what would keep a hot Jupiter hot ?
For an extrasolar Hot Jupiter: An orbit of 0.015 AU (well inside Mercury's orbit) produces an incredibly high black-body temperature.

For the real Jupiter in our Solar System: Leftover heat from its formation. Radioactive decay from a rocky core. Potentially a tiny amount of Hydrogen fusion in its Hydrogen core. The bigger the body, the longer it holds its heat (all other things being equal).

The Real Jupiter has a "cloud-top" temperature of about 340K, which is well above the black-body temperature at it's icy orbit in the Solar System.
See: https://en.wikipedia.org/wiki/Jupiter#Internal_structure
 

Offline Cobalt-Blue

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Thank you for the information.
 

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