- May 10, 2008
- Reaction score
- Dallas, TX
Those would be most conveniently specified as 'at L4 (or L5)' and placed using a Lagrange point finder (surprise, I have one of those as well...)
I'm interested in things like the effect of librational dynamics on climate, so I'm interested in arbitrary orbits in the vicinity of the L4/L5 point (thus the word approximately in my previous post).
I've never heard that you can have planets developing there though... it seems kinda hard to accumulate enough mass, usually it's just debris that's been captured
The literature seems to be undecided on whether Trojan planets can actually form (highly sensitive to modeling assumptions and things like grid resolution, cartesian vs. cylindrical coordinates, etc) and fairly confident that they can remain stable over gigayear timescales once formed or captured. The possibility is taken seriously enough that empirical searches are being performed.
Meanwhile, the giant impactor that whacked Earth to form the moon is believed to have formed as a Trojan and been perturbed into a collision with Earth by Jupiter and/or Venus (in that case it wasn't stable for gigayears).
Those you already asked and I answered - they're interesting and can be done.
(In fact, you can cheat a bit and specify a 'star' with the temperature and luminosity of a gas giant, let that orbit your companion star and you get the results with the existing code and interface)
But temperature and luminosity for a gas giant are dependent on climate, and different on the day vs. night side. Depending on if and at what lattitudes water clouds form, albedo can be markedly different (if you're too warm for clouds, you end up with a dark blue color from Raleigh scattering). So being able to model them as planets will be useful.
I guess for me the point is - of course there's all sorts of weird situations where orbital dynamics is interesting. But most of these cases would be rare and exotic. Whereas what is a major influence and not rare at all is... atmosphere. So I'm actually more interested in spending my time with improving the atmosphere simulation and see whether one can tease some gross weather patterns out for instance (like the (non)-existence of a jet stream) than coding an interface for arbitrarily weird situations (also with extending the solver to 3d - the issue isn't so much the solver, 3d is easy there, the issue is interface and analysis tools, they become much more complicated and messy without providing much more insight - most systems would be near-planar problems..)
The jury is still out on Trojan configurations, and the fact that so many hot jupiters show up suggests that gas giants migrate aggressively, which means we can anticipate a fair number of terrestrial planets captured into resonances. Resonant configurations will tend to pump up eccentricity, which will affect climate, and the Kozai mechanism will then tend to drive up inclination and drive the longitude of periapsis to +/- 90 degrees, which will then be vital to keeping the resonance stable if eccentricity gets high enough for the orbit of the terrestrial planet to approach or cross that of the gas giant. Even in the Solar system, the 2/3 resonance with Neptune defines the Plutinos, and a significant fraction of them have significant eccentricities and inclinations.
And then there's all the red dwarfs with multi-planet resonance chains, and the solar system has the Galilean moons in their 1:2:4 chain, and not just any 1:2:4 arrangement will work, it depends on particular phase relationships for stability.
Point being, I'm not sure that interesting configurations that depend on orbital phases or non-planarity are as rare as you think. And even for the circular, non-resonant, near-planar case, inclinations of less than a degree are sufficient to cause significant seasonal changes in binary-star eclipses, and for moons, to give a worked example, the angular diameter of Jupiter is about 13 degrees at 2 light seconds (a bit less than the orbit of Europa). A coplanar eclipse in this configuration can be expected to last roughly 1/27th of the orbit, which works out to about an extra 2 hours and 30 minutes of darkness in a 70 hour day for the planet-facing side of the moon (assuming that the planet has the mass of Jupiter and the moon is tidally locked), or an hour of darkness in a 27-hour day, (for a more massive planet of the same radius*). In such a configuration, an inclination of five degrees to the ecliptic would be sufficient to cause significant variation in the length of eclipses with the seasons.
*We can assume that the radius is about equal to Jupiter because a planet twice as massive as Jupiter is only very slightly larger, and 2 Jupiter masses of hydrogen has the largest radius that any object can have without significant support from thermal pressure, so the smallest red dwarves are actually slightly smaller than Jupiter, and then get larger with more mass as heat from fusion puffs them up.