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Dwarf planet seen at edge of solar system

Three images of the night sky, taken two hours apart, then combined. The first image was artificially coloured red, the second green, the third blue. The new dwarf planet can be seen moving while the more distant stars and galaxies in the background do not move and appear white. Picture courtesy: Scott Sheppard, Carnegie Institution for Science

New Delhi, March 26: Two American astronomers have discovered a dwarf planet far beyond the orbit of Pluto, adding a new member in the Sun’s family album and bolstering the evidence for a vast cloud of icy bodies girdling the solar system.

The new object, provisionally named 2012VP113, is a 450km wide world at the edge of the solar system, 2.5 times further away than Pluto, in a region so distant from the Sun that the temperatures there never rise above minus 240C.

“This region was originally thought to be the solar system’s no man’s land,” Scott Sheppard, a faculty member at the Carnegie Institution of Science in the US and one of the two astronomers told The Telegraph.

The object appears to be a smaller version of another dwarf planet named Sedna spotted 10 years ago in the outskirts of the solar system, the astronomers said. Their finding will be described in the journal Nature tomorrow.

The astronomers said the two dwarf planets appear to be part of the inner Oort cloud, a vast shell of thousands of comets and icy bodies predicted decades ago to be surrounding the solar system at a great distance from the Sun but with no hard evidence.

“The discovery of 2012VP113 shows that Sedna is not unique — both are likely to be objects of the inner Oort cloud,” said Sheppard, who specialises in the history and formation of the solar system.

The astronomers, using a telescope in the highlands of Chile, first noticed the new object in November 2012 and tracked its movement for over a year. Their calculations suggest that 2012VP113’s closest orbital point to the Sun is about 80 times the distance of the Earth to the Sun, a measure called Astronomical Unit (AU), and its furthest point is about 450AU.

“What’s really interesting is that neither Sedna nor 2012VP113 come close to the Sun, they always stay very far out,” said Chadwick Turjillo, the second astronomer at the Gemini Observatory in Hawaii.

“This is a puzzle because we don’t know how they can get so far out — it is possible they formed closer to the Sun and were thrown out by gravitational influences during the last stages of the formation of the solar system,” Turjillo told The Telegraph in a telephone interview, speaking from Hawaii.

Their calculations of the orbital behaviour of the new dwarf planet and Sedna also suggest that a massive super-Earth-like object may exist even further beyond, at the extreme edge of the solar system about 250AU from the Sun. “This is a tenuous possibility — it would be hard to explain how an even bigger planet could have formed at an even greater distance from the Sun,” Turjillo said.

An Indian astronomer not associated with the finding said a super-Earth in the outermost realms of the solar system would challenge current theories of the formation of the planets.

“One way to explain this would be that the solar system captured a rogue planet from another stellar system,” said Sujan Sengupta, a scientist at the Indian Institute of Astrophysics, Bangalore.

“But there may be many other explanations for the orbital behaviour of Sedna and 2012VP113,” Sengupta said. “A system of several Sedna-like dwarf planets orbiting each other might explain the observed behaviour.”

Sheppard and Turjillo will get an opportunity to assign a formal name to the dwarf planet. The provisional name follows International Astronomical Union rules. The 2012 specifies the year of discovery, V is assigned to all objects discovered in the first half of November, and P113 is a code that uniquely identifies all asteroids and other objects discovered during that half of the month.

The astronomers will need to study the planet’s orbit in greater detail before they can name it. “In a few years, we’ll name it after some Arctic mythology from the Eskimos or the Inuits,” said Sheppard. “Arctic because these objects are so cold and distant from the Sun.”

While Pluto, discovered in 1930 by an American astronomer Clyde Tombaugh, was labelled the solar system’s ninth planet, discoveries over the past decade have prompted some astronomers to wrest that title away.

“We thought Pluto was unique for over 70 years, we now know it shares its orbit with thousands of other objects in the Kuiper belt,” said Sheppard. The Kuiper belt is a zone of frozen objects beyond Neptune, between 30AU and 50AU from the Sun.

The inner Oort cloud, calculated by some astronomers to begin at about 2,000AU and extend up to 20,000AU, is believed to be part of the Oort cloud, predicted by a Dutch astronomer Jan Oort in 1950, a shell of comets that extends to nearly 50,000AU or nearly half-way to the nearest star.