For decades, scientists have been proposing the existence of another planet in our solar system. New mathematical models are now also pointing strongly towards the same. Let's take a look about this 'supposed' member of our system.
What is Planet 9?
Why is the proposal being made?
Well, this can't be put any simple. Let's get back to the basics of our Solar System.
We all know how our system looks like. There is Sun in the center followed by Mercury, Venus, Earth & Mars. Then we have the asteroid belt which is home to a billion billion rocks of various sizes. After that comes Jupiter, Saturn, Uranus & Neptune. We do have Pluto after Neptune but it is no longer considered a planet. After this is where things get interesting. Just after Pluto begins the Kuiper Belt - thought to be remains (or leftovers) of our solar system after it was fully formed.
Out of the many objects (like asteroids, comets, etc) that come hurling inside our system, a significant number of them is considered to be coming from the Kuiper Belt. By analyzing the orbits of a number of these objects, the team predicted the possibility of a large, previously undiscovered planet far beyond the orbit of Pluto that is influencing the objects orbit.
You say it is 'proposed'. Has it not been discovered yet?
True. It hasn't been discovered yet. The existence is only predicted due to the mathematical model proposed by the Caltech team. We all know the basics of gravity - a body with excess mass can exert more gravitational pull on its near by objects. In the grand scale of universe with objects as massive as our Sun and the planets, this gravity affects the orbits of a lot of other objects too (this is how Jupiter has so many moons, it gravitational field is so powerful that it pulls a lot of the objects coming at us i.e. Earth towards itself). As we discussed earlier, when scientists analyzed the orbits of certain Kuiper Belt objects (called extreme trans-Neptunian objects), it lead them to conclude that only a massive body as large as a planet can put those objects on the path they are in now.
Where is it located? And details about the planet itself?
Hypothetically, it is located way beyond Pluto. It is very distant indeed, about 400 - 800 Astronomical Unit (the unit to measure distance in space. 1 AU = roughly the distance of Earth from Sun i.e. about 150 million kms). In comparison the distance of Pluto from Sun is around 50 AU and hence the difficulty in finding it. Accordingly, it will take about 10-20,000 years for this planet to complete one revolution around the Sun (Pluto takes 248 years).
It is considered to be about 10 times as massive as our Earth (also called as Super Earth). There are several [proposed] theories about its origin but the most popular ones are that it was a rogue planet (planets that wander around and are not orbiting any star) pulled by our solar system as it was passing by or it was pulled from another star system as it crossed by our system millions of years ago.
How was the proposal only made now?
Well, you would be wrong to think that. Theories about Planet 9 have been around for decades since the speculation after the discovery of Neptune in 1846. After Pluto was discovered in 1930, it was found too small to affect the orbit of its nearby bodies. The discovery of Sedna and its peculiar orbit is what again flamed the interest on Planet 9.
While more & more scientists are now supporting the Planet 9 hypothesis there are also groups of them which outright deny the existence of a ninth planet. Also, given its distance it is very difficult to track it using current technology. The search is on and only time will tell. After all, disproving someone with facts & proof is the most exciting part of science.
What are your thoughts on this? Do you believe that we will discover a ninth Planet in our lifetime? Let me know all about it in the comments below.