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13-Billion-Year-Old Alien Worlds Discovered
astroengine writes "Two exoplanets have been discovered by scientists at the Max-Planck Institute for Astronomy orbiting the star HIP 11952. But according to conventional thinking, these worlds shouldn't exist. You see, HIP 11952 is a 'metal-poor star and planetary formation is hindered around stars with low metallicity (PDF). This isn't the only thing; as metal-poor stars were the first stars to form when the Universe was very young, these two worlds also formed around the same time. They are therefore the most ancient exoplanets discovered to date."
"Planets form around sun" certainly was news 13 billion years ago, it just took this long to reach Slashdot's front page.
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I am astounded by the amount of rhetoric and vitriol that surrounds astronomical discoveries. Whether or not they are correct, the truth boils down to: we don't have shit for current time observations of anything in the universe. I truly believe that we are on the right path, and models fit observation, but why get so skeptical about everything? By the time we all die, the universe will basically be in the same state. Let's enjoy the limits of our observation, explore and expand them, and then maybe one of our lineage will be able to explore it.
Koalas. They're telepathic. Plus, they control the weather. -Margaret
Didn't get one thing: the article says the star is 13 billions yo, but it's 375 ly from our solar system.
I always have thought that distance meant age. Which other technique there is to tell a star's age?
Distance is... well, distance. The number of light years something is away means that we are looking at what happened that many years ago. In this case, what we see happened 375 years ago. It has nothing to do with the age of the object. However, if we see a galaxy 13 billion light years away, we know that the galaxy is 13 billion years old since nothing is that much older, provided it still exists. We don't really know as we would be seeing it as it existed 13 billion years ago. To see how it looks today, we'll have to wait another 13+ billion years and look at it again.
As for judging the age of a star, I'll take a stab at it, although IANAA. If I recall correctly, there are several methods used to judge the age of a star. We know by looking at what the star is composed of which developmental stage it is currently at. We know by its size and energy output how fast it is burning its fuel. So, if we see a large, bright, hydrogen star, we know that it is fairly young since large hydrogen stars don't last long. We can be more accurate by figuring out how fast it burns its fuel and how much it has left (helium to hydrogen ratio). If we see that it is composed mostly of helium, we know that it is in its second stage. We can judge by its size how long it was in its hydrogen stage before it fused it all to helium.
I have not RTFA, but I believe they are judging that this star was one of the first out of gate judging by how much metal it has in its core, meaning that it is very, very old.
Take with salt. Like I said, I'm no astrophysicist.
What I don't understand is how do the scientist know that these were not rogue planets, formed much later and then became trapped by the star's gravity. Just because a star has planets orbiting it, doesn't mean that those planets formed along with the star.
There is no "I disagree" mod for a reason. Flamebait, Troll, and Overrated are not substitutes.
Early supernovae wouldn't help - the star is formed from the same material as the planets would, and the star demonstrably has almost no metals. Early supernovae would just mean that this star didn't exist (in its current chemistry), or that it is even younger than currently estimated, so as to form before the supernovae.
Interstellar captures are very difficult. Generally speaking, you need three gravitationally interacting bodies to allow a capture, as you need one to carry away some energy. Basically this requires the wanderer planet to turn up just when the star is passing close to another one, and even then to get really lucky. (Most often it is the lowest mass object of the three which gains energy, but we need the planet to lose energy.) Another possibility is you could lose that energy through tidal losses, but this requires the wanderer has very small positive energy initially, and passes very close to the star. Either way, the odds of such a capture are very low.
In addition, we have the fact that this star has two planets, which makes the odds against capture polynomially* smaller. Finally, if two planets were captured, we'd expect them to have different orbital planes. Given that they were detected by the 'wobble' method, I'd expect this could be measured, and would be mentioned if it had been so. However I can't promise that there aren't gravitational interactions which would bring the orbital planes into alignment over 13Gyr. Captures would also initially have highly elliptical orbits, which again the wobble method should notice, and again I don't know if 13Gyr is long enough to circularize the orbits by tidal effects or planet-planet interactions.
* This word brought to you by the Committee Against The Misuse Of The Word 'Exponentially'
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Nothing is "ageless".
How old is time itself?
I don't think that's a well-formed question. It's like asking "how long is distance?".
Sheesh, evil *and* a jerk. -- Jade
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