Explained: How researchers found where to look for Planet Nine

Dr. Brown mentioned in his tweet that the data only tells us the orbital path of Planet Nine but not where in the orbital path it is. “It is more likely to be at its most distant point from the sun, but only because it travels more slowly there."

New computer studies said that Planet Nine could be five Earth masses. (Source: Caltech)

6 min readKochiSep 20, 2021 01:16 AM IST First published on: Sep 19, 2021 at 09:00 AM IST

In August 2006, the International Astronomical Union broke several hearts when it announced that it had reclassified Pluto as a dwarf planet. The decision was based on Pluto’s size and the fact that it resides within a zone of other similarly-sized objects. Currently, there are five dwarf planets: Ceres, Pluto, Eris, Makemake and Haumea.

Scientists have continued their search for new planets and in 2016 Konstantin Batygin and Michael E. Brown, both from the California Institute of Technology, published a paper in The Astronomical Journal, stating that they had evidence for a distant giant planet and nicknamed it Planet Nine. They noted that it could have a mass about 10 times that of Earth.

“Although we were initially quite skeptical that this planet could exist, as we continued to investigate its orbit and what it would mean for the outer solar system, we became increasingly convinced that it is out there,” said Dr Batygin, an assistant professor of planetary science in a release. “For the first time in over 150 years, there is solid evidence that the solar system’s planetary census is incomplete.”

The team continued their study of the planet and in 2019 published a pair of papers on its orbit and influence on other objects.

“The most distant objects that we know of in the solar system are being slightly tugged by some gravitational effects; as far as we can tell, the only plausible explanation is a giant planet out there,” explained Dr Brown in an email to indianexpress.com. He was one of the researchers who helped reclassify Pluto and is the author of the book ‘How I Killed Pluto and Why It Had It Coming.’

New computer studies said that Planet Nine could be five Earth masses. “Planet Nine is likely to be very reminiscent of a typical extrasolar super-Earth,” explained Dr Batygin in a release. “Planet Nine is going to be the closest thing we will find to a window into the properties of a typical planet of our galaxy.”

Is Planet 9 a black hole?

Researchers from across the globe have carried out several studies on Planet Nine and there are several theories about it, including one that stated Planet Nine could in fact be a black hole. The paper published last year in Physical Review Letters argued that the unknown object causing anomalous orbits of the trans-Neptunian objects could be a primordial black hole.

Another study published in 2018 in The Astronomical Journal gave more evidence for the existence of Planet Nine. It noted that a trans-Neptunian object called 2015 BP519 had an unusual trajectory because it was affected by Planet Nine’s strong gravity.

The lead author Juliette Becker had then told The Indian Express: “When we ran a simulation without Planet Nine, we found it was very hard to make objects like BP519. When we ran a different simulation including Planet Nine, we found that it was very easy to make objects like BP519.”

What is the new finding?

Dr. Brown tweeted last month that he has ‘the treasure map’ to find Planet Nine. “Five and a half years after our proposal of the existence of Planet Nine, we have finally accomplished what is perhaps the most important task in aiding the search: we now know where to look,” he wrote in his blog.

The paper posted on arXiv says that Planet Nine has a mass of 6.2 (+2.2/-1.3) Earth masses. The paper also details Planet Nine’s semimajor axis, inclination, and perihelion.

Dr. Brown mentioned in his tweet that the data only tells us the orbital path of Planet Nine but not where in the orbital path it is. “It is more likely to be at its most distant point from the sun, but only because it travels more slowly there. But this is where you should be looking,” he tweeted.

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When asked if there were any ideas on how Planet Nine was formed, he explained: “Our best guess is that it formed in the vicinity of Uranus and Neptune and eventually got too close to Jupiter or Saturn which flung it out into the outer reaches of our solar system.”

The team is continuing their studies and note that the Vera C. Rubin Observatory, currently under construction in Chile, will further help the hunt for Planet Nine. “The observatory will scan the skies night after night and eventually uncover many things, including — we hope — Planet Nine,” concludes Dr. Brown.

Is everyone convinced that Planet Nine exists?

Since 2016, studies have variously concluded that there is more and more evidence of Planet Nine’s exist, or that it does not exist, or that it may in fact be a black hole. A paper published last year in Physical Review Letters argued that the unknown object causing anomalous orbits of the trans-Neptunian objects could be a primordial black hole.

Another study published in 2018 in The Astronomical Journal, on the other hand, cited fresh evidence for the existence of Planet Nine. It noted that a trans-Neptunian object called 2015 BP519 had an unusual trajectory because it was affected by Planet Nine’s strong gravity.