SEDNA: Dwarf Planet on the outer regions of Solar System

Sedna is a dwarf planet on the far outer reaches of the solar system.

Credit: NASA

Sedna is a dwarf planet that is one of the most distant bodies found in our solar system.

The object's closest approach to the sun is far greater than Pluto's distance away from Earth, at a spot where the sun is so tiny, according to NASA, that you could blot it out with a pin.

At 8 billion miles (12.8 billion kilometers) away, it's hard to figure out things such as surface features, but one thing astronomers have been able to identify is Sedna's distinct reddish colour.

Mike Brown

In 2004, it was described as the second-reddest object in our solar system, after Mars.

Sedna was discovered by a team led by Mike Brown, an astronomer at the California Institute of Technology.

The discovery of Sedna and other objects similar to it was a large impetus behind demoting Pluto from planetary status in 2006.

Image of Sedna, taken by Hubble Space Telescope

Discovery and basic statistics
Brown's team found Sedna in 2003 as part of a larger survey of the solar system that began in 2001.

Using the Samuel Oschin Telescope at the Palomar Observatory (east of San Diego) as well as Palomar's Quasar Equatorial Survey Team (QUEST) camera, the astronomers would take pictures of a tiny spot in the sky, one per hour for three hours, and see if they could find something that moved, Brown said in an explanation page about the discovery.

"The many billions of stars and galaxies visible in the sky appear stationary, while satellites, planets, asteroids, and comets appear to move. Objects in the inner Oort Cloud are extremely distant and so move extremely slowly," he said.

The Oort Cloud expands from a narrow belt on its inner edge
 into a large sphere farther from the Sun.

The Oort Cloud is a theorized area far in the solar system that is supposed to contain billions of icy objects that, if they receive a gravitational push toward the sun and warm up, turn into comets as the sun's energy melts the ice.

Sedna, however, was much bigger than a comet. Estimates for Sedna's size vary, but it is believed to be slightly smaller than the size of Pluto (1,400 miles or 2,250 kilometers in diameter).

Sedna takes some time to orbit the sun, not only because of its vast distance but also because its orbit is so elliptical or oval-shaped.

The dwarf planet takes roughly 10,000 years to complete one circuit around the sun. At the time of its discovery, it was at one of the closest points of its orbit to the sun, making it easier to spot.

Credit: Nasa

More Information: An explanation page about the SEDNA discovery

DLR Portal: FAQ on ROSAT mission

Since its launch on 1 June 1990, friction due to Earth's upper atmosphere has been causing the X-ray satellite ROSAT to lose altitude continuously.

When the spacecraft re-enters the atmosphere, which is expected to occur in October 2011, the satellite will disintegrate and most of the fragments will burn up in the extreme heat caused by atmospheric friction.

This FAQ provides answers to the most common questions about the ROSAT mission and its re-entry.

NASA's Quest for space life a focus for the future

US space agency NASA is pondering 28 potential missions focusing on finding life beyond Earth inside our solar system, a US researcher said Wednesday.

"Astrobiology and the search for life is really central to what we should be doing next in the exploration of the solar system," Steve Squyres, a researcher at Cornell University in Ithaca, New York, said in a telephone press briefing.

"We are looking for a total of 28 different missions.... They cover everything from Mercury landers to fly-by of objects in deep outer space of the solar system -- and they are particularly relevant to looking for life," he explained.

Among other objects of interest: a three-stage Martian mission that would bring Martian soil samples back to Earth, said Squyres, who worked on the Spirit and Opportunity rovers, still active six years after their arrival on the Red Planet.

"Those samples might reveal a great deal of whether Mars once or today (has) forms of life," he said.

Another part of the mission would be to look at the origin of methane in the planet's atmosphere, and whether or not it is organic, he said.

Methane breaks down quickly in the Martian atmosphere, but scientists discovered plumes of methane on Mars in 2003, raising the prospect that the planet is not entirely dead.

"So we will send a mission potentially to look at the sources of the methane and consider the possibility that they could be from biological origins," Squyres added.

Further out in the solar system, scientists are very interested in Europa, a moon of Jupiter, he said.

"It's believed that Europa may have an ocean of liquid water underneath its icy crust. And we are looking at a Europa robot mission that would have, among other things, the capability to use a radar system that can penetrate through that ice, find the ocean if it exists, identify places where you might go to the surface to learn more" about the ocean, Squyres said.

Likewise Titan, a moon of Saturn, has scientists' attention.

It is "a moon we know to be very rich in organic materials. We are looking long term at a mission that will study Titan in great deal, including an orbiter, a balloon in Titan atmosphere and a lander to land in some of the lakes of liquid methane," the Cornell scientist added.

Another mission under consideration is one to return samples from a comet, the researcher said. "Comets are believed to be rich in organic materials, rich in building blocks of life. Most of the organic material on earth was probably delivered to earth by comets."

The number of projects needs to be whittled down, he said, before a recommendation will be made on what missions NASA should prioritise.