Alien earths could form earlier than expected

Jun 13, 2012
This artist's conception shows a newly formed star surrounded by a swirling protoplanetary disk of dust and gas. Debris coalesces to create rocky 'planetesimals' that collide and grow to eventually form planets. The results of this study show that small planets form around stars with a wide range of heavy element content, suggesting that their existence might be widespread in the galaxy. Credit: University of Copenhagen/Lars Buchhave

(Phys.org) -- Building a terrestrial planet requires raw materials that weren't available in the early history of the universe. The Big Bang filled space with hydrogen and helium. Chemical elements like silicon and oxygen - key components of rocks - had to be cooked up over time by stars. But how long did that take? How many of such heavy elements do you need to form planets?

Previous studies have shown that Jupiter-sized tend to form around stars containing more heavy elements than the Sun. However, new research by a team of astronomers found that planets smaller than Neptune are located around a wide variety of stars, including those with fewer heavy elements than the Sun. As a result, rocky worlds like Earth could have formed earlier than expected in the universe's history.

"This work suggests that terrestrial worlds could form at almost any time in our galaxy's history," said Smithsonian astronomer David Latham (Harvard-Smithsonian Center for Astrophysics). "You don't need many earlier generations of stars."

Latham played a lead role in the study, which was led by Lars A. Buchhave from the University of Copenhagen and will be published in the journal Nature. The work is being presented today in a press conference at the 220th meeting of the .

Astronomers call heavier than hydrogen and "metals." They measure the metal content, or metallicities, of other stars using the Sun as a benchmark. Stars with more heavy elements are considered metal-rich while stars with fewer heavy elements are considered metal-poor.

Latham and his colleagues examined more than 150 stars known to have planets, based on data from NASA's spacecraft. They measured the stars' metallicities and correlated that with the sizes of the associated planets. Large planets tended to orbit stars with solar metallicities or higher. Smaller worlds, though, were found around metal-rich and metal-poor stars alike.

" prefer metal-rich stars. Little ones don't," explained Latham.

They found that terrestrial planets form at a wide range of metallicities, including systems with only one-quarter of the Sun's metal content.

Their discovery supports the "core accretion" model of planet formation. In this model, primordial dust accumulates into mile-sized planetesimals that then coalesce into full-fledged planets. The largest, weighing 10 times Earth, can then gather surrounding hydrogen and become a gas giant.

A gas giant's core must form quickly since hydrogen in the protoplanetary disk dissipates rapidly, swept away by stellar winds in just a few million years. Higher metallicities might support the formation of large cores, explaining why we're more likely to find a gas giant orbiting a metal-rich star.

"This result fits with the core accretion model of planet formation in a natural way," said Latham.

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User comments : 5

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kevinrtrs
1 / 5 (13) Jun 13, 2012
Once again, people are obfuscating the actual observation[s] with their own brand of origins for stars and planets.

Just because certain types of planets have been observed around certain types of stars, it doesn't therefore imply that they "form" in such preferences. The only real thing that can be said about the planets and stars is that they occur there in those particular relative numbers. Nothing more concrete can be deduced from the occurrence of such relativities. To jump to the conclusion that the objects "form" there is superfluous and unwarranted because it supposes a known history of star and planetary formation which just doesn't exist.
Better to leave out completely how those planets came to be there and rather concentrate on finding and recording the relative frequencies until such time as other observations can actually indicate a substantial history of formation/creation.
aroc91
5 / 5 (7) Jun 13, 2012
The nebular and protoplanetary disc hypothesis was disproved? I was unaware, kevin. Enlighten us.
Torbjorn_Larsson_OM
5 / 5 (8) Jun 13, 2012
This has been hinted by Kepler results for a long time, I believe it may have started with Corot even. It is good to see confirmation, and that the amount of metallicity is so low. The "Rare Earth" idea got stomped again, on numbers and on lateness of Earth.

@ kevintrs:

Creationists shouldn't comment on science. As aroc91 notes, you are babbling on what you don't know first thing about, such as well known facts and theories. But thank you for showing for everyone that the old idea of having religious magic instead of science facts is not only not useful but also ridiculous.
Deesky
5 / 5 (7) Jun 13, 2012
@kev,

Once again, people are obfuscating the actual observations with their own delusional brand of origins for everything.

Just because certain types of planets have been observed around certain types of stars, it doesn't therefore imply that they "form" in such preferences. The only real thing that can be said about the planets and stars is that they occur there in those particular relative numbers because god put them there.

Nothing more concrete can be deduced from actual observation. To jump to the conclusion that the objects weren't created by god is superfluous and unwarranted because it supposes a knowledge-based history of star and planetary formation.

Better to leave out completely how those planets came to be there and rather concentrate on finding the sky fairy until such time as other observations can actually support my makebelieve history of creation.
Parsec
5 / 5 (7) Jun 14, 2012
The nebular and protoplanetary disc hypothesis was disproved? I was unaware, kevin. Enlighten us.

Please don't feed the trolls. kevinrts is a diehyard creationist. He doesn't like science and his posts are uniformly intelligence free.