The hunt for the mysterious “Planet Nine” offers a surprise

It is an evocative idea that has long been unable to scientists: a huge and mysterious planet is hidden in the dark on the edge of our solar system, escaping all our efforts to identify it.

Some astronomers say that the strange orbits grouped with frozen rocks beyond Neptune indicate that something large is there, that they have nicknamed Planet Nine.

Now, a trio based in the United States hunting this elusive world has rather fallen on what seems to be a new dwarf planet in the external expanses of the solar system.

And the existence of this new child on the block could challenge the theory of the new planet, the researchers calculated.

Appointed in 2017 in 2017, the new object is around 700 kilometers (430 miles) in diameter, according to a preparation study, which was not evaluated by peers, published online last week.

This makes it three times smaller than Pluto.

But it is still large enough to be considered a dwarf planet, the author of the main study Sihao Cheng of the Institute of Final Study of New Jersey told AFP.

Traveler

The object is currently three times further from the earth than Neptune.

And its extremely elongated orbit balances more than 1,600 times the distance between the earth and the sun, taking it in the ring of frozen rocks around the solar system called oort cloud.

“It goes so far, he could have gone through stars other than our sun in the past,” said Cheng.

During its 25,000 -year orbit, the object is only close to the earth to be observed about 0.5% of the time, or about a century.

“It is already becoming lower and lower,” said Cheng.

The discovery suggests “there are several hundred similar things on similar orbits” in the Kuiper belt beyond Neptune, said Cheng.

After taking risks to spend more than half year in sorting a set of difficult data in search of Planet Nine, Cheng said he was “lucky” to have found anything.

The researchers ask time to point to telescopes James Webb, Hubble and Alma to discover them.

But Sam Deen, an amateur astronomer of 23 years from California, has already been able to follow the candidate of the dwarf planet via old sets of data.

“From 201 is, in my opinion, probably one of the most interesting discoveries in the external solar system of the last decade,” said Deen to AFP.

And Planet Nine?

The frozen rocks discovered in the Kuiper belt tend to have an orbit in clusters in a particular direction.

Two decades ago, astronomers proposed that this was due to the gravitational attraction of a world up to 10 times larger than the earth, naming it Planet Neuf and launches a debate that has groaned since.

It is also sometimes called Planet X, a name proposed for a hypothetical world beyond Neptune more than a century ago.

In 1930, astronomers sought planet X when they discovered Pluto, which became the ninth planet of our solar system.

But Pluto turned out to be too tiny – it is smaller than the Moon – and was demoted to the status of dwarf planet in 2006.

There are now four other officially recognized dwarf planets, and Cheng thinks that 2017 of 2010 could join their ranks.

When the researchers modeled his orbit, they found that he did not follow the cluster trend of similar objects.

This could be a problem for the theory of the new planet, but Cheng stressed that more data is necessary.

Samantha Lawler of the University of Canada of Regina told AFP that this “great discovery” and others as meant that “the original argument for Planet Nine becomes lower and weaker”.

The Vera Rubin observatory, which should go online in Chile this year, should shed light on this mystery, in one way or another.

Deen said it was discouraging that no sign of Planet Nine has been found so far, but with Vera Rubin “on the horizon, I do not think that we will have to question his existence longer”.

For Cheng, he always hopes that this huge planet is somewhere.

“We are at a time when large telescopes can see almost on the brink of the universe,” he said.

But what is in our “backyard” is still largely unknown, he added.

© 2025 AFP