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."

Comments

Re:Astronomers are so funny

[ArcherB]

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.