Must a Hot Jupiter be relatively young?

[jscroft]

Must a "Hot Jupiter" be relatively young?

A large proportion of exoplanets so far discovered are "hot Jupiters," large gas giants orbiting very close (< 0.1 AU) to their primaries.

It seems to me that a gas giant orbiting at such a close distance ought to experience significant friction as it passes through its primary's coronal envelope. I also imagine that any orbital eccentricity on the part of the planet or wobble on the part of the primary would generate significant tidal pumping within the body of the planet, damping these motions by converting their energy to heat, which would cause the planet's gas envelope to expand and add to its drag coefficient.

Finally, I suppose that the plasma composition of the coronal medium—being electrically active—would also facilitate energy transport, although I'm not sure in which direction.

The upshot is that I wonder whether such a planet could orbit its primary for very long before orbital decay removed it from observation? And, if not, what might that say about (a) the mechanism of hot Jupiter genesis—formation? ejection? capture?—and (b) the likelihood of same.

 

[zhermes]

I wonder whether such a planet could orbit its primary for very long before orbital decay removed it from observation?

This is an open question in exoplanet research. Conventional wisdom quickly suggests (as you describe) that there are numerous things dissipating the orbital energy of the planet---tending to both tear apart the planet, and have it inspiral into its host. Observationally there seems to be a cutoff at about 0.05 AU, within which there aren't any planets.
The question is whether this is perfectly consistent with in-spiral (i.e. closer in planets merge with the star so quickly they are rarely seen), or whether there is a mechanism preventing planets from moving closer in. Most of the evidence seems to go along with the former, but the latter still has a good backing.

Some papers that might be interesting:
http://arxiv.org/abs/1009.1352v1"
http://adsabs.harvard.edu/abs/2009ApJ...698.1357J"

 

[jscroft]

Thanks for the references.

I note that neither addresses the question of the electrically active coronal medium. If both the primary and the exoplanet have significant magnetic fields—as do our own Sun and gas giants—then it seems that the interaction of these fields within and across the coronal medium would create effects of a magnitude that might actually dwarf those generated by gravitational interaction.

I realize that I'm evoking Velikovsky here, but whatever you think of his ideas of the origin of Venus etc., the hot-Jupiter scenario DOES seem to lend itself particularly well to analysis from the electrodynamic perspective.

Are you aware of any exoplanet-related work along these lines?