We're closer than ever to finding the mysterious Planet Nine

Artist's impression of Planet Nine

Tom Ruen/ESO

Via wired.co.uk by Abigail Beall

In January 2016, a pair of astronomers published a paper that changed the direction of modern astronomy. The paper predicted the existence of another, huge planet lurking far beyond Neptune, in the most distant realms of our solar system.

The pair dubbed this mysterious planet Planet Nine. Some perceived this name as a snub to the planet Pluto, our old ‘ninth planet’, which one of these very astronomers had played a part in demoting to ‘dwarf planet’ status ten years previously. But aside from this, everyone was excited.

Since the publication of that paper, astronomers over the world have spent time searching both using telescopes and computational models for any sign of Planet Nine. Now, the most detailed prediction yet of Planet Nine’s orbit and influence on our solar system has been released.

Konstantin Batygin, a Caltech professor of planetary science and co-author of the original paper, decided it was time that paper got an update.

“There have been new detections of distant Kuiper belt objects since the publication of our original paper,” Batygin says. ”We now better understand how the expanded observational dataset shaped by the gravity of Planet Nine.”


Batygin and Alessandro Morbidelli, from the University of Côte d'Azur, developed an up to date computer simulation, which takes into account the latest observational data, in a new paper uploaded to the server arXiv.

The important result of this paper is that it defines the exact orbit and behaviour of Planet Nine, rather than the vague notion there is another planet lurking somewhere. This is defined by how it influences the orbits of other, smaller objects that exist beyond Neptune, called trans-Neptunian objects.

“Remember that over the last 170 years, there have been numerous authors that have proposed variants of trans-Neptunian planets,” Batygin says. “What separates each proposition is the data a given hypothesis aims to explain - in our case, the physical clustering of the distant orbits - and the dynamical mechanism through which the planet generates its observational signatures.”

The new paper describes this mechanism mathematically, Batygin says. “I’ve always tried to be explicit about the fact that what we are proposing is not just the existence of a planet. Rather, it is the existence of a planet that sculpts a specific orbital pattern through a rather distinct physical mechanism.”

The paper narrows down the hunt for the planet. “With our new understanding of how Planet Nine sculpts the observed patterns in the data, we have been able to zoom in on its true orbit further,” Batygin says.

The search is still on. At the end of last month Batygin and Mike Brown, co-author of the original paper and the man behind Pluto’s demise, spent five nights in Hawaii. They used the Mauna Kea Observatory, and were searching for signs of Planet Nine.

“We had a genuinely fantastic observational run with Mike,” Batygin says. “In total, we covered about ~20% of the sky that we need to cover and the weather was for the most part, in our favour.”

However, it may still be some time before this data is published. For now, we will have to wait and keep wondering.

“Frustratingly, we do not yet know if we found Planet Nine this time around. The data is still in the process of being processed and analysed, there is a lot of data. So nothing observational to share yet.”

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