The search for one of the most mysterious objects of our solar system.

Absence of evidence is not evidence of absence — Carl Sagan.

A few months ago, I remember sitting for my lectures and used to get extremely bored with certain topics so I had this habit of checking the latest news related to Technology, Space science, Astronomy, Physics, etc. One such day, I remember there was this title of an article — ‘ If Planet Nine exists, why has no one seen it?’. And I just stopped. I did know that Pluto was removed from the list of planets that we learnt in school. But the title sparked a curiosity in me and I wanted to read it! And you know what? The article was astonishing! I searched on Youtube about this and got to listen to a wonderful Tedx Talk with a similar name, ‘The search for Planet 9’ by Dr. Renu Malhotra. I was like- Wow!!

Now, not everyone one of you must be knowing or familiar with Pluto being removed as the 9th planet especially why it was removed. Let me explain a bit about it.

Why is Pluto no longer a planet of the Solar system or Nav Grah?

There is a union called the International Astronomical Union (IAU) which does the job of safeguarding all the research in astronomy and promotes it. So for every planet to be called a full-sized planet, they have a total of 3 major criteria. If the astronomical object satisfies all the 3 criteria, it is recognized as a full-sized planet in the solar system.

The 3 Criteria are:

1. It is in orbit around the sun.
2. It has sufficient mass to assume hydrostatic equilibrium. (a nearly round shape in layman’s terms)
3. It has “cleared the neighbourhood” around its orbit. ( basically, the planet has a good amount of gravity so that there are no other bodies comparable to its size other than its satellites.)

Pluto could not satisfy the 3rd criteria hence its removal as the 9th planet. It was demoted to being called a dwarf planet in 2006.

So now that pluto was demoted, how will we have that 9 planets, symmetry and the perfect solar system that we want? This question marked the journey of looking for an actual planet out there in the far outskirts of our solar system — Planet 9.

So what is so peculiar about this unknown so-called Planet 9?

Before going into the depths of this planet, I would like to give a short overview of the formation of distant objects of our solar system i.e. Uranus, Neptune, Pluto and the Kuiper Belt.

Starting with Uranus, an astronomer called William Herschel in the 1700s was looking up at the night sky every day and he noticed that the position of one object was changing continuously. With every night it was deviating from where it was supposed to be. Herschel thought it might be a comet or a star but later discovered that it was a distant, huge planet- Uranus. The discovery of Neptune was also amazing. Initially, a mathematician, Urbain Le Verrier, predicted Neptune’s mass, orbit, and location all on paper by using a normal telescope and surprisingly the planet was found within 1° of the predicted position.

As we found these planets, the insatiable human curiosity to know more and find more secrets about our universe was increasing. So in 1846, Clyde Tombaugh discovered Pluto. At that time, not much was known, so we didn’t know whether it was a huge or a dwarf planet. But then after Pluto, no peculiar object was discovered in our solar system till the 1990s.

Though there were predictions of objects beyond Pluto.

Around 1990, two astronomers from MIT, David Jewitt and Jane Luu decided to look for more. These people just asked one question, ‘Why is our outer solar system so empty?’ Finally, after 5 years of intense observation, they found that there is a doughnut-shaped structure consisting of small rocks, icy objects having peculiar orbits beyond Pluto. This structure was none other than ‘The Kuiper Belt.’

Now starts the true story of our topic of discussion i.e. Planet 9.

A peculiar thing about a few Kuiper Belt objects (KBOs) was that when they were orbiting, the alignment of these objects, i.e. their trajectories, pointed in a similar direction as if influenced by some object of a good amount of gravitation.

One of the first such objects was Sedna discovered by Mike Brown in 2004.

This person, Mike Brown and Konstantin Batygin, brilliant astronomers at Caltech started their search for more of these peculiar objects.

They did a what we can say blind search for Trans-Neptunian Objects (TNOs) — these are minor/dwarf planets that rotate around the sun beyond the orbit of Neptune. These TNOs are all at distances like 30–50 AU where the Kuiper Belt is ( this is pretty much a big length — 1 AU = 150 million Kms!)

The second prominent planet similar to Sedna in terms of orbit was called 2012 VP 113. Further, a lot more were discovered and the most interesting fact about these TNOs was that most of them were all pointing in the same direction or else in a normal case, they would have been distorted.

If we consider these objects of the outer solar system, they would have been scattered long ago, but something kept these objects intact in the orbit in a particular direction. A huge gravitational influence and one of the best guess was Planet 9.

If Planet 9 exists, it’s got to be huge, with a mass exceeding that of Earth and should take around 10,000 years to orbit the sun.

The Caltech duo ran simulations right from the time of the formation of our solar system, fast-forwarding it w.r.t. Earth and there was an interesting observation. A few Kuiper Belt objects or “Planets” were thrown out of the Interstellar medium and those which stayed were confined in the exact opposite direction to which they were tossed apart. So it was weird how the orbits are scattering continuously but a few pointing in the same direction.

The peculiarity of these orbits was that they followed a complicated dynamic ride like the orbit flips upside down, they come back and follow a path (Please try imagining that ;), personally, it took me a while to understand this ride!)

5 objects along with Sedna and 2012 VP 113 were found to exhibit such orbits. So one of the most obvious answers again was that Planet 9 takes these objects, tilts them upside down and brings them back to the same position. Such kind of geometry.

But these were initial predictions.

Now there’s a small twist here. Like I said Planet 9 must be something of huge gravitational influence and all.

But further observations and simulations by the Caltech Duo were that this theory was partially wrong.

They saw that as few objects were tossed out during simulation, there might be the case that these objects were tossed inside the solar system and not outside in the Interstellar medium. What exactly happened was there was the orbit of Neptune, a predicted orbit of Planet 9 and one KBO. Every time the KBO came close to the orbit of Neptune, it got scattered and scattered in (not outside) until it parked/stalled itself into a constant perpendicular orbit.

This is interesting like how they thought something was influencing these objects in a particular direction as shown above. Now, they have discovered that the KBOs take a perpendicular orbit like the green coloured orbit in the picture below. The orange-coloured orbit is supposed to be the predicted orbit for Planet 9.

The planet 9 discovery is going to be huge because its peculiarity as far as I have comprehended is about its geometry. Like huge orbit ( more than 300 AU), 5 Earth Mass object, 10,000 years around the sun.

Generally, 5 Earth Mass objects are common, like if we consider the solar system, apart from the big planets, others are somewhat similar to Earth. So if we find planet 9, we might be able to find the missing link of the formation of our solar system more widely.

What method is being used by the Caltech duo — Mike and Konstantin to find Planet 9?

Well, they are using the shifting and stacking method.

Shifting — Taking pictures of the sky for predefined sets of certain orbital paths.

Stacking — Stacking/clipping all these images together to get a faint light that will reveal a particular pathway of a moving object beyond Neptune.

They have predicted that it might take them around a decade to solve and actually get a real location and picture of Planet 9 since the region beyond Neptune is huge, almost endless.

Till then, the mystery continues!!

Below is the picture of the Caltech Duo!

P.S: If this blog got you interested in planet 9, just watch YT videos of either Mike Brown or Konstantin Batygin ( the Caltech Duo) or anyone researching it. I personally referred one of Konstantin’s talks to make notes for writing this blog. Trust me 1/2 or 1 hour would be gone in a jiffy with lots of learning and curiosity!!