A team of astronomers has discovered a new dwarf planet, and they weren't even trying to find one.

The dwarf planet, named 2015 RR245 for now, has an unusual orbit — it's very large and looping, and takes 700 years to travel around the sun.

The researchers estimate that little 2015 RR245 is about 700 kilometres in diameter.

The Outer Solar System Origins Survey team, or OSSOS, led in part by researchers at the University of British Columbia, had originally set out to find out how the planets moved into their places when the solar system was young.

They've been studying objects in the Kuiper belt, the outer region of our solar system. During their research, they found this new dwarf planet, said Brett Gladman, the Canada Research Chair in planetary astronomy at UBC and the principal investigator for the project.

When they found what they suspected was the dwarf planet, Gladman said the reaction was "Whoa, there's a bright one!"

Unlike regular planets, which "completely dominate their surroundings," said Gladman, a dwarf planet is not large enough to exert much influence, but it is big enough that gravity pulls it into a sphere shape.

The international team also includes researchers from the the National Research Council of Canada, the University of Victoria, as well as researchers from Tucson, Ariz., France and Taiwan.

Telescope in Hawaii

Gladman and his team have been working with a tool that is incredibly sensitive to light, the Canada-France-Hawaii Telescope, located at the summit of Mauna Kea in Hawaii. The telescope looks for bright, moving objects in space, and a camera takes pictures of what it sees every hour.

Because the telescope records massive amounts of data, the team had to make a program to sift through the photos. Once the program has what Gladman calls candidates of moving objects, the researchers take over and look at the images themselves.

The newly discovered dwarf planet's elliptical orbit is seen in yellow. (Alex Parker/OSSOS Team)

"Sometimes the computer proposes wrong things, but it's pretty good at proposing a bunch of right things," said Gladman. "So that's how we find them."

Even with the computer's assistance, the process of flipping through the pictures is time consuming.

"It was, 'no, no, no, no — yes — no, no, no — whoa, what's that!'" described Gladman when his colleague JJ Kavelaars spotted it.

They've found almost 1,000 objects so far. This discovery, photographed in September and analyzed in February, was surprising because of how big it is.

"This one was a monster. It was incredibly bright for us."

Gladman is careful to point out that 2015 RR245 is technically a candidate dwarf planet — there's a chance that it could be a smaller, very shiny object instead. It's so far away that they can't be 100 per cent sure, although they are confident.

Movement is key

Because the images are taken three hours apart, the team can spot whether objects move or not. And movement gives them a lot of information.

"The rate of the movement across relative to the star field is telling you how far away it is," he said.

This one was a monster. It was incredibly bright for us. - Brett Gladman , UBC astronomist

"An asteroid would be zipping across the field really fast. The fact that this one is moving slower is telling you it's far away."

He said 2015 RR245 is about 65 astronomical units away — much farther than the average object in the Kuiper belt, which tends to be around 30 or 40 astronomical units away.

For reference, an astronomical unit is based on Earth's mean distance from the sun, about 150 million kilometres.

They're also able to map the dwarf planet's "eccentric" orbit, said Gladman. At its closest approach to the sun, which will happen in the year 2096, Gladman said, it will be about 35 astronomical units away. At its farthest, it is nearly 130.

He said 2015 RR245 will gradually appear brighter as it nears, but it's still so far away that only a very sophisticated telescope will be able to see it (although who knows what technology will be available for space viewing in 2096).

Importance of dwarf planets

Most dwarf planets were destroyed or thrown from the solar system in what the researchers call the chaos that ensued when the planets moved into their current positions.

But some of these dwarf planets stuck around and circle the sun, like Pluto, which is one of the largest of them. A couple of dozen dwarf planets have been discovered over the years, and this is the latest one.

Gladman called the dwarf planets the "trapped lucky survivors of a population that must have been hundreds of times bigger."

He said discoveries like this help in understanding how the planets got to their current positions in the solar system "when there was lots of junk around."

"They [dwarf planets] let us piece together the history of our solar system," said Michele Bannister of the University of Victoria, who is a post-doctoral fellow with OSSOS.

Because they discovered the dwarf planet, the OSSOS team can submit name options to the International Astronomical Union. But Gladman said they're going to wait to submit anything until they have more information about the discovery, which he expects they will have by the end of the year.