What factors contribute to the migration of hot Jupiters?

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In summary: I imagine that the paper would be of interest to people who study planet migration and the formation and evolution of giant planets.
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they ran computer simulations of 8500 planetary systems to see how giant planets could sometimes MIGRATE in close to the star

and they got some statistics of what one might expect.

I cannot vouch for this paper, or say how it stacks up compared with other similar papers, but this business of hot Jupiters is a great puzzle so I figure anything along these lines that might give some answers could be interesting.

the paper has been accepted for publication in a peer-review journal so that is one good sign at least. if someone checks it out please let us know how good a paper and if it does help answer why there are so many giant planets are in close to their stars (like as close as Mercury, or closer)

http://arxiv.org/abs/astro-ph/0505234
Giant Planet Migration through the Action of Disk Torques and Planet Scattering
Althea V. Moorhead, Fred C. Adams
46 pages including 15 figures; accepted to ICARUS

"This paper presents a parametric study of giant planet migration through the combined action of disk torques and planet-planet scattering. The torques exerted on planets during Type II migration in circumstellar disks readily decrease the semi-major axes, whereas scattering between planets increases the orbital eccentricities. This paper presents a parametric exploration of the possible parameter space for this migration scenario using two (initial) planetary mass distributions and a range of values for the time scale of eccentricity damping (due to the disk). For each class of systems, many realizations of the simulations are performed in order to determine the distributions of the resulting orbital elements of the surviving planets; this paper presents the results of 8500 numerical experiments. Our goal is to study the physics of this particular migration mechanism and to test it against observations of extrasolar planets. The action of disk torques and planet-planet scattering results in a distribution of final orbital elements that fills the a-e plane, in rough agreement with the orbital elements of observed extrasolar planets. In addition to specifying the orbital elements, we characterize this migration mechanism by finding the percentages of ejected and accreted planets, the number of collisions, the dependence of outcomes on planetary masses, the time spent in 2:1 and 3:1 resonances, and the effects of the planetary IMF. We also determine the distribution of inclination angles of surviving planets and the distribution of ejection speeds for exiled planets."
 
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"5. Conclusion

This paper explores a migration scenario in which multiple giant planets are driven inward through the action of tidal torques in a circumstellar disk. In this case, the outer planet interacts with the disk, which drains energy and angular momentum away from the planetary orbit. As the outer planet migrates inward, it eventually becomes close enough to the interior planet to force it inward and to drive eccentricity growth with increasingly violent interactions. Such systems are generally not stable in the long term and adjust themselves to stability by ejecting a planet, accreting a planet onto the central star, or by having the two planets collide. The surviving planet is left on an eccentric orbit of varying semi-major axis, roughly consistent with the orbits of observed extrasolar planets. On longer time scales, tidal interactions with the central star act to circularize the orbits of the closet planets. We have presented a comprehensive, but not exhaustive, exploration of parameter space for this migration scenario. Our main results can be summarized as follows: [1] This migration scenario results in a wide variety of final systems with a broad distribution of orbital elements. In particular, this migration scenario can fill essentially the entire a-e plane for semi-major axes a smaller than the initial values. The observed extrasolar planets have orbital elements that fill the a-e plane in roughly the same way (see Figs. 9 – 15). When the theoretical ensemble of planets is corrected for additional orbital evolution due to interactions with the circumstellar disk (on approx. 1 Myr time scales) and tidal interactions with the central star (on approx. 1 Gyr time scales), the resulting distributions of theoretical orbital elements are in reasonable agreement with those of the observed sample of extrasolar planets..."

"...This migration scenario produces a full distribution of orbital elements for the surviving planets and is in reasonable agreement with observations. In order for this mechanism to be successful, the systems must have a number of properties, and it is useful to summarize them here: The planets that end up in the currently observed region of the a-e plane are assumed to have formed in disk annulus r = 3 - 7 AU, roughly where Jupiter lives in our solar system..."
 
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It looks like a very good paper to me, marcus. The initial assumptions are few [a big plus in my book] and the results do not appear to suffer from over-analysis.
 

What makes hot Jupiters?

Hot Jupiters are a class of gas giant exoplanets that orbit very close to their parent star, with orbital periods of less than 10 days. They are significantly hotter than Jupiter, hence the name "hot Jupiters". Scientists have been studying these mysterious planets for years, and there are a few common questions that are frequently asked about them.

1. How did hot Jupiters form?

The formation of hot Jupiters is still a subject of ongoing research and debate. One theory suggests that they formed in the outer regions of their planetary systems, where temperatures were cooler, and then migrated inward due to interactions with other planets or gravitational forces from the star. Another theory proposes that they formed close to their stars and never migrated, but this is less likely due to the extreme heat and radiation in such close proximity to the star.

2. What causes hot Jupiters to have such high temperatures?

The close proximity to the parent star is the main reason for the high temperatures of hot Jupiters. They receive a large amount of heat and radiation from their stars, which causes their atmospheres to expand and become inflated. This also contributes to their low densities compared to other gas giant planets.

3. Do hot Jupiters have any similarities to our own Jupiter?

Despite their name, hot Jupiters have a few similarities to our own Jupiter. They are both gas giants, meaning they are primarily composed of hydrogen and helium. However, hot Jupiters are much closer to their stars and have much higher temperatures, so they have very different atmospheres and weather patterns compared to Jupiter.

4. Can life exist on hot Jupiters?

Due to their extreme heat and inhospitable conditions, it is highly unlikely that life could exist on hot Jupiters. However, some scientists have proposed the idea of "hot Jupiter moons", where habitable moons could potentially exist around these planets. These moons would need to have their own atmospheres and be at a safe distance from the planet's intense heat and radiation.

5. How do scientists study hot Jupiters?

Scientists use various methods to study hot Jupiters, including transit photometry, radial velocity measurements, and direct imaging. Transit photometry involves measuring the decrease in a star's brightness as a planet passes in front of it, while radial velocity measurements track the slight wobble of a star caused by the gravitational pull of an orbiting planet. Direct imaging uses telescopes to capture images of the planet itself. By combining data from these methods, scientists can learn more about the composition, atmosphere, and other characteristics of hot Jupiters.

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