|
|
|
Thread Tools | Display Modes |
#1
|
|||
|
|||
New planet GJ 1214 b
A new planet, GJ 1214 b, has been found some 40 l.y. away with 2.678 Earth radius and 6.55 Earth mass. [It was found using a 16-in telescope and a commercially available camera, kind of something someone could have done in his backyard, that's cool even if the planet is hot]. What surprises me is its density, about 1870 kg/m^3, which is consistent with 75% water and 25% rock. I'm no expert in this area, but so much water (or other low density liquid or solid) seems improbable to me. Does anyone know about how the radius was measured? Is it possible that it would be a much denser planet with a very large atmosphere. The atmosphere giving it nearly half its radius? Does anyone think that 75% water for such a large planet is a likely scenario. Alain Fournier |
#2
|
|||
|
|||
New planet GJ 1214 b
In article ,
Dan Birchall wrote: (Alain Fournier) wrote: What surprises me is its density, about 1870 kg/m^3, which is consistent with 75% water and 25% rock. I'm no expert in this area, but so much water (or other low density liquid or solid) seems improbable to me. I'm not a planetary scientist either, but I googled, and this density is roughly comparable to that of our outer planets - Neptune's density is 1760 kg/m^3, Pluto's is 2030 kg/m^3. The planet's orbital radius and temperature would probably help shed light on what elements would most likely be found there in solid, liquid or gaseous forms. The six most common elements in the universe are hydrogen, helium, oxygen, carbon and neon*. If a world isn't massive/cold enough to hold onto H2 (and given that neither helium nor neon will form chemical compounds) the most common chemical compounds should be made up of combinations of H, O and C. In other words, water should be pretty common. * From memory, by mass it's something like 70% H, 24% He, 11% O, 4.5% C 1% Ne. -- http://www.livejournal.com/users/james_nicoll http://www.cafepress.com/jdnicoll (For all your "The problem with defending the English language [...]" T-shirt, cup and tote-bag needs) |
#3
|
|||
|
|||
New planet GJ 1214 b
James Nicoll wrote:
In article , Dan Birchall wrote: (Alain Fournier) wrote: What surprises me is its density, about 1870 kg/m^3, which is consistent with 75% water and 25% rock. I'm no expert in this area, but so much water (or other low density liquid or solid) seems improbable to me. I'm not a planetary scientist either, but I googled, and this density is roughly comparable to that of our outer planets - Neptune's density is 1760 kg/m^3, Pluto's is 2030 kg/m^3. The planet's orbital radius and temperature would probably help shed light on what elements would most likely be found there in solid, liquid or gaseous forms. The six most common elements in the universe are hydrogen, helium, oxygen, carbon and neon*. If a world isn't massive/cold enough to hold onto H2 (and given that neither helium nor neon will form chemical compounds) the most common chemical compounds should be made up of combinations of H, O and C. In other words, water should be pretty common. * From memory, by mass it's something like 70% H, 24% He, 11% O, 4.5% C 1% Ne. But this planet is near to its star and not very big. Close to the star water not already on a planet there is likely to be a gas and blown away. So I have a hard time imagining water accreting to form a planet there. I would expect that you would need a big rock core before it can hold on to water. Being so close to the star the hypothesized 25% rock seems barely enough. Mars has a hard time holding on to its water and it is much colder, Venus didn't hold on to much water. I guess the planet could have been formed in two steps. 1- The 25% rock forms a nucleus (that is a little more than Earth's mass). 2- The 75% water can now accrete to the nucleus. But I have a hard time imagining the water staying in low stellar orbit long enough for that to happen, wouldn't it be blown away? Alain Fournier |
#4
|
|||
|
|||
New planet GJ 1214 b
In article ,
Alain Fournier wrote: James Nicoll wrote: In article , Dan Birchall wrote: (Alain Fournier) wrote: What surprises me is its density, about 1870 kg/m^3, which is consistent with 75% water and 25% rock. I'm no expert in this area, but so much water (or other low density liquid or solid) seems improbable to me. I'm not a planetary scientist either, but I googled, and this density is roughly comparable to that of our outer planets - Neptune's density is 1760 kg/m^3, Pluto's is 2030 kg/m^3. The planet's orbital radius and temperature would probably help shed light on what elements would most likely be found there in solid, liquid or gaseous forms. The six most common elements in the universe are hydrogen, helium, oxygen, carbon and neon*. If a world isn't massive/cold enough to hold onto H2 (and given that neither helium nor neon will form chemical compounds) the most common chemical compounds should be made up of combinations of H, O and C. In other words, water should be pretty common. * From memory, by mass it's something like 70% H, 24% He, 11% O, 4.5% C 1% Ne. But this planet is near to its star and not very big. Close to the star water not already on a planet there is likely to be a gas and blown away. So I have a hard time imagining water accreting to form a planet there. I would expect that you would need a big rock core before it can hold on to water. Being so close to the star the hypothesized 25% rock seems barely enough. Mars has a hard time holding on to its water and it is much colder, Venus didn't hold on to much water. I guess the planet could have been formed in two steps. 1- The 25% rock forms a nucleus (that is a little more than Earth's mass). 2- The 75% water can now accrete to the nucleus. But I have a hard time imagining the water staying in low stellar orbit long enough for that to happen, wouldn't it be blown away? My impression is that worlds like these form beyond the frost line and then migrate. In our solar system, there's reason to think Uranus and Neptune have migrated outwards but in other systems, large worlds can be seen in orbits where it appears unlikely they could have formed. Presumably they migrated in. A popular account of this process can be found he http://en.wikipedia.org/wiki/Planetary_migration -- http://www.livejournal.com/users/james_nicoll http://www.cafepress.com/jdnicoll (For all your "The problem with defending the English language [...]" T-shirt, cup and tote-bag needs) |
#5
|
|||
|
|||
New planet GJ 1214 b
Alain Fournier wrote:
A new planet, GJ 1214 b, has been found some 40 l.y. away with 2.678 Earth radius and 6.55 Earth mass. [[...]] The key technical papers are Charbonneau et al, "A super-Earth transiting a nearby low-mass star" http://arxiv.org/abs/0912.3229 and Rogers & Seager "Three Possible Origins for the Gas Layer on GJ 1214b" http://arxiv.org/abs/0912.3243 -- -- "Jonathan Thornburg [remove -animal to reply]" Dept of Astronomy, Indiana University, Bloomington, Indiana, USA "Space travel is utter bilge" -- common misquote of UK Astronomer Royal Richard Woolley's remarks of 1956 "All this writing about space travel is utter bilge. To go to the moon would cost as much as a major war." -- what he actually said |
#6
|
|||
|
|||
New planet GJ 1214 b
In article ,
Alain Fournier writes: But this planet is near to its star and not very big. Close to the star water not already on a planet there is likely to be a gas and blown away. So I have a hard time imagining water accreting to form a planet there. There's a press release with a few more details at http://www.cfa.harvard.edu/news/2009/pr200924.html and of course the full article is in this week's _Nature_. The article doesn't actually say, but the planet diameter ought to come from the transit timing and independently from the transit depth. In any case, the ratio of planet to star diameter has an error bar of less than one percent according to the article. The error bar on planet density (which includes a variety of other uncertainties) is about 21%. The authors consider the time for atmospheric escape and estimate a maximum of 700 Myr, whereas the age of the system is likely 3-10 Gyr. The authors suggest that either the planet may have had much more massive atmosphere in the past (most of which has now been lost) or that the current atmosphere has recently been outgassed from the planet's core. It wouldn't surprise me if there are other possibilities. The authors say nothing about formation, but we can speculate that the planet may have formed relatively far from the star and migrated inwards. It still seems to me that preserving a volatile atmosphere for such a long time is difficult to explain. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#7
|
|||
|
|||
New planet GJ 1214 b
Thanks to James Nicoll, Jonathan Thornburg and Steve Willner for their interesting replies. I went to read the article http://arxiv.org/abs/0912.3229 provided by Jonathan, I had search for the article earlier but got to a site where one has to pay to have access, I thought I would have to wait until I went to work (where we have subscriptions to a great variety of scientific journals) to see the article, but thanks to Jonathan's link I got to see it today. They state both the 75% water 25% rock hypothesis I saw in the press release and the much denser planet with a large atmosphere as I was hypothesizing in my original post. Alain Fournier |
#8
|
|||
|
|||
New planet GJ 1214 b
So this is a planet which can be detected with amateur's instruments. (16-in telescope and off the shelf commercial camera) But it doesn't seem to be known whether it is a mostly gas planet with a small heavy core or a 25% rock 75% water planet. How could we distinguish between these two possibilities? Alain Fournier |
#9
|
|||
|
|||
New planet GJ 1214 b
In article ,
Alain Fournier writes: it doesn't seem to be known whether it is a mostly gas planet with a small heavy core or a 25% rock 75% water planet. How could we distinguish between these two possibilities? Observe transits at a wavelength where the atmosphere is expected to be transparent? It wouldn't surprise me if the authors have already requested Director's Discretionary Time to observe with _Spitzer_, but no programs are in the database as of now. Proposals for General Observer time will be due in April. However, depending on the atmospheric composition, I'm not sure it will be transparent at 3.6 microns, much less at 4.5 microns. -- Help keep our newsgroup healthy; please don't feed the trolls. Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA |
#10
|
|||
|
|||
Quote:
A strong planetary magnetic field also drastically cuts atmosphere loss due to solar wind. Neil |
|
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Discoverer of Xena and 14 Other Planet Candidates Still Thinks Official Planet Count Should Be 8! | Double-A | Misc | 0 | August 23rd 06 05:15 AM |
Planet Earth only known planet to harbor life per NY Times Newspaper | nightbat | Misc | 11 | August 12th 06 03:51 AM |
Planet finders use much faster instrument to discover distant planet(Forwarded) | Andrew Yee | Astronomy Misc | 0 | January 13th 06 12:32 AM |
Planet finders use much faster instrument to discover distant planet(Forwarded) | Andrew Yee | News | 0 | January 13th 06 12:03 AM |