The Oort Cloud is a spherical cloud of comets believed to lie roughly 50,000 AU, or nearly a light-year from the Sun, which places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun. The Kuiper belt and scattered disc, the other two known reservoirs of trans-Neptunian objects, are less than one thousandth the Oort cloud’s distance. The outer extent of the Oort cloud defines the boundary of our Solar System.
Objects in the Oort cloud are largely composed of ices such as water, ammonia and methane. Astronomers believe that the matter comprising the Oort cloud formed closer to the Sun, and was scattered far out into space by the gravitational effects of the giant planets early in the Solar System’s evolution.
The cometary membrane of the Oort Cloud and Kupier Belt actively feeds water to the interior planets, with some 20 to 40 ton water-ice comets hitting the earth’s atmosphere 5 to 30 times per minute. Simulations show that Kuiper belt comets simply don’t fall directly toward Earth’s neighborhood but plod their way toward the inner solar system in stairstep fashion. It turns out that the massive outer planets are almost exactly spaced so that they “hand-off” comets from one to the other. At each step the powerful gravitational field of Neptune, Uranus, Saturn and Jupiter might either eject the comet from the solar system or pass it onto the next planet inside their orbit.
A “minor planet” with the awesomely poetic name 2006 SQ372 is just over two billion miles from Earth, a bit closer than the planet Neptune has been discovered in the inner Oort Cloud. This lump of ice and rock is beginning the return leg of a 22,500-year journey that will take it to a distance of 150 billion miles, nearly 1,600 times the distance from the Earth to the Sun, according to a team of researchers from the Sloan Digital Sky Survey (SDSS-II).
The orbital paths of the major planets are nearly circular, but the orbit of 2006 SQ372 is an ellipse that is four times longer than it is wide, said University of Washington astronomer Andrew Becker, who led the discovery team. The only known object with a comparable orbit is Sedna — a distant, Pluto-like dwarf planet discovered in 2003 — but 2006 SQ372’s orbit takes it more than one-and-a-half times further from the Sun, and its orbital period is nearly twice as long.
The new object is much smaller than Sedna, Becker said, probably 30-60 miles across instead of nearly 1,000. “It’s basically a comet, but it never gets close enough to the Sun to develop a long, bright tail of evaporated gas and dust.”
Andy Becker and Nathan Kaib of the University of Washington in Seattle traced the origins of 2006 SQ372, modeling its orbit on a computer. What they found was, that a region no further out than 20,000 AU from the Sun “is the only place in the solar system that can produce these orbits efficiently.”
“It could have formed, like Pluto, in the belt of icy debris beyond Neptune, then been kicked to large distance by a gravitational encounter with Neptune or Uranus,” said Kaib. “However, we think it is more probable that SQ372 comes from the inner edge of the Oort Cloud.”
As we continue to reach further out into space, using more powerful tools, we’re more and more likely to encounter more former-residents of the inner Oort cloud. “I would expect them to discover thousands of such objects, and with a data set so large, we could do a pretty good job in finding out what the inner Oort cloud looks like,” Kaib said.
Posted by Josh Hill.