Interesting news in extra-solar planetary astronomy today:
“…it was a tremendous surprise this week when astronomers discovered planets orbiting a metal poor star.
The discovery was made by a team of researchers from the University of Texas using the 9.2-metre Hobby-Eberly Telescope at McDonald Observatory. They found a system of two Jupiter-like planets orbiting a star that’s so low in metals that it shouldn’t have planets at all.”
This surprise has some very exciting implications. Metal poor stars are born earlier than metal rich stars like our sun are. The metal abundance (elements heavier than H or He) comes primarily from the supernova explosions of stars which were born in the first waves of star formation in the Universe and the galaxies. (The metals are formed via fusion in the incredible explosive forces of the super-nova. Any thing made out of elements heavier than H and He comes from the remnants of such an explosion – including things like you and me.)
If there are planets orbiting such early stars, then planets are probably much more common than we’ve previously thought and there are way more stars have them then we imagined.
That will lead to changes in one of the values of the Drake Equation which is used to predict the likelihood of finding other life in the galaxy.
Read the rest here: Metal Poor Star Found With Planets
(Via Universe Today.)
Yes, that is a bit of a surprise. One possibility that occurs to me is that the cores of those bodies are made entirely of ices, since the CNO cycle happens even in relatively early generation stars. What would be weird is if transit observations showed strong absorptions in SiH or FeH, i.e., the planets turned out to be somewhat more metallic than the star. (Unfortunately, the observing spectrometers aren’t that good yet…).
Good point Caelius, but still, even though you’ve got CNO in the stellar interior, wouldn’t the products still be in the stellar atmospher rather than in a planetary accretion disk?
If the planets were in fact more metallic, they could have been captured – but you’d still have the problem of where *they* came from. (Though if the star is in the galactic disk than this wouldn’t be as surprising. I guess I’m thinking the star’s in the halo somewhere, but I haven’t looked it up.)
(You’re certainly more up on this branch than I am – so I may be missing your point… /me says as a form of disclaimer).
Fascinating. It seems to me there is also the possibility that these planets are captured; as I understand it many “rogue” bodies are thrown off in the period of formation and wander about…Well, I thought I was being smart until I read the rest of Fr. Nick’s comment.
I don’t think you have to worry about not being smart Christopher… Grin. You’ve certainly pointed out a number of things to me along the way.
Nick, I can’t tell you how deeply I appreciate this amazing report which, even if only for a few brief moments, diverts my attention from the Lambeth 2008 guest list!
No, seriously, I do love your scientific reports and your blog in general.
I’m afraid my point wasn’t very clear. It’s not the CNO cycle in the particular star that’s the issue. It’s the degree of enrichment in C,N,O possible in its initial composition by 10 Ga (when this star apparently formed). Its metallicity is 21% of that of the Sun, so if my grasp of nucleosynthesis is correct, C,N,O should be somewhat less depleted relative to H than Mg, Fe, and Si are depleted relative to H (the CNO cycle being active a few stellar generations earlier than the fusion reactions leading to the rock-forming elements.) Thus, you could form two 10 Earth mass ice cores instead of rock-ice mixtures.
The funny part is metallicity still isn’t a very straightforward measurement since folks started finding planets very near their stars. If you have the possibility of orbital migration of disk material into the star, the metallicity could be a bit contaminated…
Ah then. I get your point about the ice cores – but still… how would the heavier material get out the stellar interior and into the planetary disk?
Unless the star in question isn’t a first-generation star?
Oh wait, nevermind. Of course it isn’t a first generation star if it has 21% the metal content of Sol…
I second Mary Clara’s bit. I love reading your science posts. And did you hear about Enceladus?
These ice-water worlds are fascinating in their own right. Does anyone have any thoughts about what such a world would be like if it were in a habitable zone?
My officemate is working on this particular problem at the moment. I’m not sure what he’ll conclude until I hear his talk next week, but it doesn’t sound particularly fun. It’s heads or tails whether such planets will freeze or boil.