[Space] Trojan Objects

[AlexanderHowl]

Yes, all that matters is the size of the primary planet in the system. Even with primary planet the mass of Uranus though, you could still support two Standard Terrestrial Trojan Planets 50% the mass of Earth (80% the diameter).

[Phantasm]

Originally Posted by Anthony

That still allows a super-earth for a Jovian or Super-Jovian.

Seeing as how Saturn's moon Dione has a trojan body in its L4 (or is it L5? I forget) space, which we've known of since Voyager 2 passed through, this isn't inconceivable.

(It's probably not inconceivable for a moon to have a moon, if the planet was a Jovian and the moon a Small or Standard size, even if the moon's moon is merely a Phobian moonlet.)

[johndallman]

Originally Posted by Phantasm

Seeing as how Saturn's moon Dione has a trojan body in its L4 (or is it L5? I forget) space, which we've known of since Voyager 2 passed through, this isn't inconceivable.

One in each of L4 and L5, actually. Tethys also has L4 and L5 trojan moons, but those are all the examples discovered so far.

[Anthony]

Originally Posted by Phantasm

Seeing as how Saturn's moon Dione has a trojan body in its L4 (or is it L5? I forget) space, which we've known of since Voyager 2 passed through, this isn't inconceivable.

The question is whether it's possible for a large object to actually form there. Once it's there it can stay.

[AlexanderHowl]

While it is unlikely in a resource poor star system like our own, we have found star systems that possess dozens of times as much planetary mass as our own, so I am sure that it is not only possible but probable. In addition, an interstellar civilization that discovers a couple of standard terrestrial major moons in orbit around a Large Gas Giant in the habitable zone of a star system might prefer that they were not being constantly subjected to radiation and move them over the course of a couple of centuries from their parent planet to the Trojan Points, so Trojan Planets might be evidence of Precursor civilizations. It would probably require less energy than constructing a planet in the same Trojan Point (since you could use the other bodies in the star system to assist your efforts).

[Jovus]

My impression is that, for superjovians of about 50 MJ or more, radiation pressure ends up making the trojans unstable over planetary timescales. But then it's been a while since I was doing astro, and I was focused more on ULXs at the time, so take that with a grain of salt.

[AlexanderHowl]

Superjovians cannot exceed 15 Jupiter-Masses before undergoing deuterium fusion, so an object of 50 Jupiter-Masses is a brown dwarf rather than a gas giant. I agree that a brown dwarf will likely not have Trojan Planets, at least not within any habitable zone of a primary star, just because the radiation pressure will probably destabilize them. It might be possible though for a brown dwarf that orbits a higher mass star to have habitable planets orbiting them.

A 5 billion year old G2V star would have a habitable zone of around 0.8 AU-1.2 AU. A 50 Jupiter-mass brown dwarf of similar age would have a luminosity of 0.0119, meaning that its habitable zone would be 0.08 AU-0.12 AU. If a brown dwarf orbited a G2V star at 4 AU and had a planet orbiting at 0.4 AU, the planetary orbit would be stable and the planet would be habitable (though the seasons would be very, very complicated). The brown dwarf would prevent the formation of planets around the G2V star from 1.3 AU to 12 AU, meaning that the G2V star would not have a planets that corresponded to the orbits of Mars, the Main Belt, Jupiter, or Saturn. The system could still be rich in asteroid belts and gas giants within 1.3 AU or beyond 12 AU though.

[RyanW]

Originally Posted by AlexanderHowl

If a brown dwarf orbited a G2V star at 4 AU and had a planet orbiting at 0.4 AU, the planetary orbit would be stable and the planet would be habitable (though the seasons would be very, very complicated).

Are you sure it would be habitable? I'm getting a blackbody temperature of about 160 K, assuming I remember how to do multiple star systems. It would likely be tidelocked to the brown dwarf, making its seasons dominated by a day/night cycle (with respect to the primary star) a little longer than an Earth year.

[Daigoro]

Originally Posted by RyanW

Are you sure it would be habitable? I'm getting a blackbody temperature of about 160 K, assuming I remember how to do multiple star systems. It would likely be tidelocked to the brown dwarf, making its seasons dominated by a day/night cycle (with respect to the primary star) a little longer than an Earth year.

It seems that irradiation temperature is only part of the equation- atmospheric insulation, and possibly hydrospheric thermal inertia, also play a big part. By the standard insolation equations, I recall that Earth's blackbody temp is somewhat below freezing too.

[Anthony]

Originally Posted by AlexanderHowl

A 5 billion year old G2V star would have a habitable zone of around 0.8 AU-1.2 AU. A 50 Jupiter-mass brown dwarf of similar age would have a luminosity of 0.0119, meaning that its habitable zone would be 0.08 AU-0.12 AU. If a brown dwarf orbited a G2V star at 4 AU and had a planet orbiting at 0.4 AU, the planetary orbit would be stable and the planet would be habitable

No it wouldn't be. It's getting 6.3% as much energy as Earth from the star, and another 7.4% from the brown dwarf, for a total of 13.7%. You need to be a lot closer (also, since brown dwarfs cool significantly over time, it might have been problematically hot during early planet formation).