© Christine Pulliam (CfA)In this artist's conception, a captured world drifts at the outer edge of a distant star system, so far from its Sun-like host that the star's disk is barely resolvable at upper right. New research shows that one in 20 stars within our galaxy might have captured a free-floating planet.
As crazy as it sounds, free-floating rogue planets have been predicted to exist for quite some time and just last year, in May 2011, several orphan worlds were finally detected. And earlier this year, astronomers estimated that there could be
100,000 times more rogue planets in the Milky Way than stars. Now, the latest research suggests that sometimes, these rogue, nomadic worlds can find a new home, and go into orbit around other stars. Scientists say this finding could explain the existence of some planets that orbit surprisingly far from their stars, and even the existence of a double-planet system.
"Stars trade planets just like baseball teams trade players," said Hagai Perets of the Harvard-Smithsonian Center for Astrophysics.
Astronomers now understand that rogue planets are a natural consequence of both star and planetary formation. Newborn star systems often contain multiple planets, and if two planets interact, one can be ejected in a form of planetary billiards, kicked out of the star system to become an interstellar traveler.
But, later if a rogue planet encounters a different star moving in the same direction at the same speed, be captured in to orbit around that star, say Perets and Thijs Kouwenhoven of Peking University, China, the authors of a new paper in
The Astrophysical Journal.
A captured planet tends to end up hundreds or thousands of times farther from its star than Earth is from the Sun. It's also likely to have a, orbit that's tilted relative to any native planets, and may even revolve around its star backward.
Perets and Kouwenhoven simulated young star clusters containing free-floating planets. They found that if the number of rogue planets equaled the number of stars, then 3 to 6 percent of the stars would grab a planet over time. The more massive a star, the more likely it is to snag a planet drifting by.
While there haven't actually been planets found yet that are definitely a 'captured' world, the best bet would perhaps be a planet in a distant orbit around a low-mass star. The star's disk wouldn't contain enough material to form a planet that distant, Perets and Kouwenhoven said.
The best evidence of a captured planet comes from the European Southern Observatory, which announced in
2006 the discovery of two planets (weighing 14 and 7 times Jupiter) orbiting each other without a star.
"The rogue double-planet system is the closest thing we have to a 'smoking gun' right now," said Perets. "To get more proof, we'll have to build up statistics by studying a lot of planetary systems."
As for our own solar system, there's no evidence at this time that our Sun could have captured an alien world, which would lie far beyond Pluto.
"There's no evidence that the Sun captured a planet," said Perets. "We can rule out large planets. But there's a non-zero chance that a small world might lurk on the fringes of our solar system."
Source: Center for Astrophysics
How more incredible can existence BE.
For this however:
"There's no evidence that the Sun captured a planet,"
There is this:
"Oxygen is the third most abundant element in the cosmos, of which the isotope oxygen-16 makes up 99.67%, oxygen-17 0.04%, and oxygen-18 0.02%. Kelly Beatty writesโ โThe Sun represented a critical missing piece of this isotopic puzzle. Cosmochemists assume that whatever atoms populate the solar wind must be representative of what's in the Sun itself and therefore a sample of the raw mix from which the planets formed. So would the Sun's oxygen ratios match those of Earth or of the ancient meteorites? The very framework of planetary formation hung in the balance.
At the 39th annual Lunar and Planetary Science Conference in Houston, Texas, Kevin McKeegan (UCLA) announced that the Sun has proportionately far more oxygen-16, relative to oxygen-17 and -18, than is present in terrestrial seawater. There's a serious mismatch. Instead, the solar ratios follow the same trend seen in primitive meteorites.
Suddenly, Earth is the odd planet out. "We had little idea what the Sun's ratios should be," McKeegan told me after his presentation. Now, he says, there's "no plausible model" to make Earth with the oxygen ratios it exhibits. "It's always been a challenge to supply Earth with the water it has. And now we're wondering how it got the rocks it has."
That view was echoed by Robert Clayton, a University of Chicago cosmochemist. "The CAIs were thought to be the anomaly and we were normal but this result has turned that idea upside down."
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