Planetopreprintology
I haven't really been making many of these posts lately, so let's make up for that deficit.
On the formation and migration of giant planets in circumbinary discs by A. Pierens and R.P Nelson, astro-ph 0803.2000
The authors have simulated what happens with giant planets orbiting a binary star (that is, orbiting both stars in a circumbinary or "P"-orbit - around one of the stars the orbit is called an "S"-orbit, I believe), a a planet which has migrated to the edge of the "cavity" formed by the binary. If the gas giant is about Saturn-sized it is likely this orbit will be stable, but for a more massive Jovian world the likely result is that the planet will make close encounter with one of the stars and either (likely) be ejected from the system or be scattered into a more distant and likely inclined orbit. What this means, well. Probably that gas giants around both binary stars are likely to be less massive and if really massive be on distant and strange orbits. So if you want a rationale for that huge gas giant very far away from the light of the sun where the Interstellar Armada has placed their Depot out in the darkness, a binary system might make some sense.
The Supernova Early Warning System by K.Scholberg, astro-ph 0803.0531
This is not a discovery as such, but a brief recap about the state of the supernova early warning system (SNEWS, which apparently amateur astronomers can sign up for) and as such greatly recommended for all you SF people who wonder about what sort of early warning system one can have and the basics of how different neutrino detectors work. Anyway. When a star goes supernova, the neutrino signal of the core collapse is what exits the core collapse first. Photons need to interact before they get loose. So with the supernova SN1987A the neutrino burst preceded the photons by 2.5 hours. Basically we can assume that this burst, some ten seconds long, of neutrinos will give us an advance warning of a pair of or a few hours and put every geek with a telescope on alert. Problem is that only the best detector in the work can tell us roughly in what direction the star goes kablooie. But with better systems we might get better ranges and perhaps with some advanced tech better triangulation.
Anyway, the neutrino burst would of course also work in a SFnal setting with say, a starship around a dying star, and because there's a lot of neutrinos and the ship is close it probably won't need to have a kiloton of pure water as a neutrino detector either. Of course, maybe the FTL drive takes 2.5 hours to engage. Here's my little idea. You have an observatory around a dying star. It is essentially set up to get as much neutrino readings as possible (thus the closeness) from huge tanks of argon and hydrocarbons and whatever. Massive but not very advanced or costly things, so the observatory is essentially sacrificable. It just needs to relay the burst data out and then await the conflagration. You don't know when the star will die, exactly, so perhaps the observatory has been operational for centuries, manned by robots or uploaded intelligences waiting to be sent out with the data burst, or by normal scientists who have a few hours at best to get out on the spacegate or FTL pod or q-state translocator or whatever. Good place for some sort of horror story for a spacey setting, especially if sabotage is involved. Or maybe there's a nice Earth-like world ten light years away which constantly monitor the dying star in order to order people inside for the oncoming radiation, and the two hours are necessary for hitting the shelters.
Oxygen isotope anomalies of the Sun and the original environment of the Solar system by Jeong-Eun Lee, Edwin A. Bergin, and James R. Lyons, astro-ph 0803-0692
Speaking of supernovae, this paper attempts to explain the different values for the oxygen isotopes of the Solar System and comes to support the conclusion that the enrichment can be explained by a close (less than one light year away) O-type star (that is, an extremely bright, massive blue star) going supernova while the solar system still was very young. That star and supernova has been discussed earlier on this LJ, look at the topic index.
Composition of Ices in Low-Mass Extrasolar Planets by U. Marboeuf, O. Mousis, D. Ehrenreich, Y. Alibert, A. Cassan, V. Wakelam, &
J.-P. Beaulieu, astro-ph 0804.0406
Here the authors study the relative abundances of various ices in planets formed in the colder regions of star systems. Unless the planet forms in a quite carbon-enriched star system (those do seem to exist) one can expect, to the contrary of certain SF shows, that normal water ice will be dominant. On cold low-mass icy worlds we can have a subsurface ocean of liquid water between two "shells" of water ice, and expecially if that ocean contains ammonia it might stay liquid for a long time. Otherwise it will freeze in a few billion years unless something adds energy (like say, tidal action). On warmer icy worlds, because they've migrated past the snow line (the rough place in a solar system where ices start to condense) or because the star has become warmer and moved the snow line outward, carbon dioxide fractions (estimated at about 7% of the total ice for solar abundances, it can go up to 25% in a system twice as carbon-enriched as our solar system), we quickly get an impressive greenhouse gas effect preventing the oceans from freezing, because the CO2 available on such a hot-ocean world is a big deal.
In carbon-enriched systems what happens is that they go dry, because the oxygen locks up in organic compounds (mainly methanol) and carbon(di)oxide, so we don't get much water. Enriched in factors 1.6 to 3, we get mainly carbon monoxide ice, above that we get methane ice, and as rocks silicon carbide. So a system where we have an enrichment factor carbon vs oxygen quite a bit above ours would be an alien place for several reasons and a planet in the habitable zone would be a rather strange place.
Planet Formation Around Stars of Various Masses: Hot Super-Earths by Grant M. Kennedy and Scott J. Kenyon, astro-ph 0804.2296
Hot Super-Earths are planets which are very close to the star and have masses somewhere below the smallest gas giants in our solar system. If these planets detected are really rocky worlds, evaporated cores of small gas giants or some sort of icy-ocean world gone very warm is still a bit worthy of discussion, but basically one shouldn't place emphasis on "Earth". Anyway, what the authors look at here is how these planets might form and migrate and what the effects might be. One such result here is that these planets which mainly have been found around stars smaller than the Sun might indeed only migrate inwward around small stars. Bigger stars have the planets grow into gas giants instead. Planets might still form in the inner region even if a planet migrates through, and scattering might send smaller planets on very odd orbits, with highly elliptic orbits with very close periastron approaches - more massive worlds like gas giants might get their orbits circularized, but lower-mass planets are more unlikely to undergo that. (Could be cool around a red dwarf star with a world which at closest is in the habitable zone, but in an extreme orbit with decent temperatures for a few days and then a long winter. However, see below for a complication.)
These massive planets if water-rich would start to evaporate if they get really close to the star, but (as noted above) they could also stay with a supercritical steam atmosphere if slightly farther away and massive enough (like 6 Earth masses or so). Probably not a very nice place to visit.
Assembling the Building Blocks of Giant Planets around Intermediate Mass Stars by K. A. Kretke, D. N. C. Lin, P. Garaud, N. J. Turner, astro-ph 0806.1521
In this paper the authors model the growth of planets around stars more massive than the Sun, from 1.5 up to about 3 solar masses. (Like, say Sirius) What they predict which seems to be consistent with observations is that these stars will have gas giants fairly close (about 1-2AU) and possibly more massive than around solar-type stars, and that there also might be favored conditions for forming more gas giants outside. So these stars would have planet systems fairly different from our own, with several large gas giants closer up, and I guess as the snow line is a fair bit away there would be a decent amount of potential rocky matter to use. Maybe one would get bigger moons too - but these stars have shorter life times than our Sun so they might not be the best for cozy lunar ranching colonies. Though if one can terraform such a place... ...better bring some sunblock, because these stars are likely to put out a good deal of UV.
Tides and the Evolution of Planetary Habitability by Rory Barnes, Sean N. Raymond, Brian Jackson, and Richard Greenberg, astro-ph 0807.0680
This one is rather interesting. If we assume we have a planet on an eccentric orbit (more than 0.53 eccenctricity) around a small star (less than 0.35 of the Sun) and close enough to be in the habitable zone (for the eccentric-averaged flux*), that planet eventually will be in trouble and this could remove a fair deal of red dwarf worlds from the list of habitable places. That's because the tidal action will serve to circularize the orbit and decrease the semimajor axis. Basically the planet will end up inside the warm edge of the habitable zone, and suffer global heating making it uninhabitable. Will take time, sometimes billions of years, but it will happen. Smaller planets survive longer, which could be good news, because the tides might give energy to keep plate tectonics going longer than the mass of the planet might warrant otherwise, so we could still get a good planetary life time out of such a very alien place, and the eccentricity also makes the planet not locked rotation-wise (it locks when the orbit gets circularized), so you could still have say, 8 days in a short year. If the star is very low mass, the time to circularize is less than one billion years, but with the correct numbers you could have a rather interesting evolutionary sequence on a red dwarf world. (It could perhaps also be too cold and circularize into the habitable zone...)
An interesting alternative to the tidal-locked red dwarf world which might feel more static.
That also means that the overheated world just inside the habitable zone around a red dwarf which barely has changed its luminosity (they are very long-lived) could once have been home to some suitably alien civilization living on a world back when it had days and seasons and a verdant biosphere. Might be a good place for some xenoarchaeology...
*F= L / 4*pi*a^2*(1-e^2)^0.5)
.
On the formation and migration of giant planets in circumbinary discs by A. Pierens and R.P Nelson, astro-ph 0803.2000
The authors have simulated what happens with giant planets orbiting a binary star (that is, orbiting both stars in a circumbinary or "P"-orbit - around one of the stars the orbit is called an "S"-orbit, I believe), a a planet which has migrated to the edge of the "cavity" formed by the binary. If the gas giant is about Saturn-sized it is likely this orbit will be stable, but for a more massive Jovian world the likely result is that the planet will make close encounter with one of the stars and either (likely) be ejected from the system or be scattered into a more distant and likely inclined orbit. What this means, well. Probably that gas giants around both binary stars are likely to be less massive and if really massive be on distant and strange orbits. So if you want a rationale for that huge gas giant very far away from the light of the sun where the Interstellar Armada has placed their Depot out in the darkness, a binary system might make some sense.
The Supernova Early Warning System by K.Scholberg, astro-ph 0803.0531
This is not a discovery as such, but a brief recap about the state of the supernova early warning system (SNEWS, which apparently amateur astronomers can sign up for) and as such greatly recommended for all you SF people who wonder about what sort of early warning system one can have and the basics of how different neutrino detectors work. Anyway. When a star goes supernova, the neutrino signal of the core collapse is what exits the core collapse first. Photons need to interact before they get loose. So with the supernova SN1987A the neutrino burst preceded the photons by 2.5 hours. Basically we can assume that this burst, some ten seconds long, of neutrinos will give us an advance warning of a pair of or a few hours and put every geek with a telescope on alert. Problem is that only the best detector in the work can tell us roughly in what direction the star goes kablooie. But with better systems we might get better ranges and perhaps with some advanced tech better triangulation.
Anyway, the neutrino burst would of course also work in a SFnal setting with say, a starship around a dying star, and because there's a lot of neutrinos and the ship is close it probably won't need to have a kiloton of pure water as a neutrino detector either. Of course, maybe the FTL drive takes 2.5 hours to engage. Here's my little idea. You have an observatory around a dying star. It is essentially set up to get as much neutrino readings as possible (thus the closeness) from huge tanks of argon and hydrocarbons and whatever. Massive but not very advanced or costly things, so the observatory is essentially sacrificable. It just needs to relay the burst data out and then await the conflagration. You don't know when the star will die, exactly, so perhaps the observatory has been operational for centuries, manned by robots or uploaded intelligences waiting to be sent out with the data burst, or by normal scientists who have a few hours at best to get out on the spacegate or FTL pod or q-state translocator or whatever. Good place for some sort of horror story for a spacey setting, especially if sabotage is involved. Or maybe there's a nice Earth-like world ten light years away which constantly monitor the dying star in order to order people inside for the oncoming radiation, and the two hours are necessary for hitting the shelters.
Oxygen isotope anomalies of the Sun and the original environment of the Solar system by Jeong-Eun Lee, Edwin A. Bergin, and James R. Lyons, astro-ph 0803-0692
Speaking of supernovae, this paper attempts to explain the different values for the oxygen isotopes of the Solar System and comes to support the conclusion that the enrichment can be explained by a close (less than one light year away) O-type star (that is, an extremely bright, massive blue star) going supernova while the solar system still was very young. That star and supernova has been discussed earlier on this LJ, look at the topic index.
Composition of Ices in Low-Mass Extrasolar Planets by U. Marboeuf, O. Mousis, D. Ehrenreich, Y. Alibert, A. Cassan, V. Wakelam, &
J.-P. Beaulieu, astro-ph 0804.0406
Here the authors study the relative abundances of various ices in planets formed in the colder regions of star systems. Unless the planet forms in a quite carbon-enriched star system (those do seem to exist) one can expect, to the contrary of certain SF shows, that normal water ice will be dominant. On cold low-mass icy worlds we can have a subsurface ocean of liquid water between two "shells" of water ice, and expecially if that ocean contains ammonia it might stay liquid for a long time. Otherwise it will freeze in a few billion years unless something adds energy (like say, tidal action). On warmer icy worlds, because they've migrated past the snow line (the rough place in a solar system where ices start to condense) or because the star has become warmer and moved the snow line outward, carbon dioxide fractions (estimated at about 7% of the total ice for solar abundances, it can go up to 25% in a system twice as carbon-enriched as our solar system), we quickly get an impressive greenhouse gas effect preventing the oceans from freezing, because the CO2 available on such a hot-ocean world is a big deal.
In carbon-enriched systems what happens is that they go dry, because the oxygen locks up in organic compounds (mainly methanol) and carbon(di)oxide, so we don't get much water. Enriched in factors 1.6 to 3, we get mainly carbon monoxide ice, above that we get methane ice, and as rocks silicon carbide. So a system where we have an enrichment factor carbon vs oxygen quite a bit above ours would be an alien place for several reasons and a planet in the habitable zone would be a rather strange place.
Planet Formation Around Stars of Various Masses: Hot Super-Earths by Grant M. Kennedy and Scott J. Kenyon, astro-ph 0804.2296
Hot Super-Earths are planets which are very close to the star and have masses somewhere below the smallest gas giants in our solar system. If these planets detected are really rocky worlds, evaporated cores of small gas giants or some sort of icy-ocean world gone very warm is still a bit worthy of discussion, but basically one shouldn't place emphasis on "Earth". Anyway, what the authors look at here is how these planets might form and migrate and what the effects might be. One such result here is that these planets which mainly have been found around stars smaller than the Sun might indeed only migrate inwward around small stars. Bigger stars have the planets grow into gas giants instead. Planets might still form in the inner region even if a planet migrates through, and scattering might send smaller planets on very odd orbits, with highly elliptic orbits with very close periastron approaches - more massive worlds like gas giants might get their orbits circularized, but lower-mass planets are more unlikely to undergo that. (Could be cool around a red dwarf star with a world which at closest is in the habitable zone, but in an extreme orbit with decent temperatures for a few days and then a long winter. However, see below for a complication.)
These massive planets if water-rich would start to evaporate if they get really close to the star, but (as noted above) they could also stay with a supercritical steam atmosphere if slightly farther away and massive enough (like 6 Earth masses or so). Probably not a very nice place to visit.
Assembling the Building Blocks of Giant Planets around Intermediate Mass Stars by K. A. Kretke, D. N. C. Lin, P. Garaud, N. J. Turner, astro-ph 0806.1521
In this paper the authors model the growth of planets around stars more massive than the Sun, from 1.5 up to about 3 solar masses. (Like, say Sirius) What they predict which seems to be consistent with observations is that these stars will have gas giants fairly close (about 1-2AU) and possibly more massive than around solar-type stars, and that there also might be favored conditions for forming more gas giants outside. So these stars would have planet systems fairly different from our own, with several large gas giants closer up, and I guess as the snow line is a fair bit away there would be a decent amount of potential rocky matter to use. Maybe one would get bigger moons too - but these stars have shorter life times than our Sun so they might not be the best for cozy lunar ranching colonies. Though if one can terraform such a place... ...better bring some sunblock, because these stars are likely to put out a good deal of UV.
Tides and the Evolution of Planetary Habitability by Rory Barnes, Sean N. Raymond, Brian Jackson, and Richard Greenberg, astro-ph 0807.0680
This one is rather interesting. If we assume we have a planet on an eccentric orbit (more than 0.53 eccenctricity) around a small star (less than 0.35 of the Sun) and close enough to be in the habitable zone (for the eccentric-averaged flux*), that planet eventually will be in trouble and this could remove a fair deal of red dwarf worlds from the list of habitable places. That's because the tidal action will serve to circularize the orbit and decrease the semimajor axis. Basically the planet will end up inside the warm edge of the habitable zone, and suffer global heating making it uninhabitable. Will take time, sometimes billions of years, but it will happen. Smaller planets survive longer, which could be good news, because the tides might give energy to keep plate tectonics going longer than the mass of the planet might warrant otherwise, so we could still get a good planetary life time out of such a very alien place, and the eccentricity also makes the planet not locked rotation-wise (it locks when the orbit gets circularized), so you could still have say, 8 days in a short year. If the star is very low mass, the time to circularize is less than one billion years, but with the correct numbers you could have a rather interesting evolutionary sequence on a red dwarf world. (It could perhaps also be too cold and circularize into the habitable zone...)
An interesting alternative to the tidal-locked red dwarf world which might feel more static.
That also means that the overheated world just inside the habitable zone around a red dwarf which barely has changed its luminosity (they are very long-lived) could once have been home to some suitably alien civilization living on a world back when it had days and seasons and a verdant biosphere. Might be a good place for some xenoarchaeology...
*F= L / 4*pi*a^2*(1-e^2)^0.5)
.