We’re closer than ever before to knowing whether there is a ninth planet whooshing around the sun – and, alas, it’s not Pluto.
Planet X, also called Planet Nine, is a hypothetical planetary body seven times the mass of Earth lurking behind Pluto.
If found, this gassy, icy beast some 155 billion miles away from the sun would explain why some objects beyond the Kuiper Belt orbit so strangely.
And that day could be soon. Or not, experts told Metro.
Inside the Vera C Rubin Observatory in Chile, the largest digital camera in history will be powered up in May to look up at the stars, giving Planet Nine believers their biggest shot yet at being proved right.
There are eight official planets (sorry, Pluto) in our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
But astronomers have spent the better part of a century wondering if there’s anything beyond our cosmic outskirts.
‘It’s tempting to think that since we can observe incredibly distant galaxies, detect faint gravitational waves and even image black holes, that we should have a complete A-Z of our solar system,’ Dr Ed Bloomer, senior astronomy manager at the Royal Museums Greenwich in London, told Metro.
‘Relatively speaking, that’s just the local neighbourhood, right? But actually, it’s a very difficult job trying to locate everything.’
One hint that there could be more to the solar system than we realise is the weird goings-on outside the Kuiper Belt, a doughnut-shaped ring of icy debris nearly 3,000,000,000 miles from the sun, said Dr Bloomer.
For the most part, anything beyond this region is empty space – literally – but stargazers have spotted six objects in orbit over the years.
These Kuiper objects – dwarf planets and hefty chunks of ice – huddle together and roughly point in the same direction as they do a cosmic lap around the Sun. At one point, they all dip below their plane of orbit.
Scientists have been hard-pressed as to why these bodies have such groovy orbits, let alone why they’re even there at all.
Michael Brown, a professor of planetary astronomy at the California Institute of Technology, first pitched the idea of so-called ‘Planet Nine’ in 2016.
He called this elusive gas giant ‘Planet Nine’ after Pluto – first thought to be about the size of Earth – was demoted to a dwarf planet in 2006.
Brown’s thinking is that a planet-sized object in the darkest reaches of the solar system could be tugging on the orbits of the Kuiper objects.
‘By observing the motion of other objects in the solar system, mathematical modelling suggests that there is a chance the best explanation for their orbits is the presence of a thus-far undetected planet,’ said Dr Bloomer.
‘Now, that’s all pretty non-committal language (and various astronomers will have strong feelings one way or the other) because what we’re lacking is direct observation.’
According to Brown, Planet X could be the fifth most massive planet in the solar system, similar in composition to icy Neptune and orbits the sun every 10,000 years.
Finding this planet is easier said than done, warned Dr Bloomer. ‘The modelling suggests that Planet Nine – if it exists – is incredibly far away from the sun,’ he explained.
‘And broadly speaking, the problem is that this means it is going to be very, very dim: unlike a star, say, which would be producing light, Planet Nine will only really be reflecting light from our Sun.’
In other words, if you were looking up at the night sky from Planet X, the sun would look no different from the thousands of other stars around it.
‘A detection isn’t impossible though, you just need to monitor the right part of the sky at the right time with the right equipment,’ Dr Bloomer added.
The observational equipment at Rubin Observatory could do just that – at least, Brown hopes and Dr Bloomer thinks there’s a chance it can.
The observatory will spend 10 years snapping shots of the Southern Hemisphere sky bit by bit, giving astronomers massive amounts of data to work with.
Brown told Live Science that his fabled planet could be found within ‘two years’. If not, the chances it really is out there are slim to none.
Not everyone is convinced. ‘The available data are subject to many selection effects and observational biases. Therefore, we tend not to take claims as evidence,’ Michael Smith, a professor of astronomy at the University of Kent, told Metro.
‘We take the interpretations of convinced scientists as interesting or with a pinch of salt. However, some of the speculations will, of course, turn out to be verified.
‘That is a selection effect also: if you make enough claims, you are bound to get one right.’
But if it does happen, the day Planet X is discovered could be a tad anticlimactic.
As Dr Bloomer put it: ‘Directly discovering a “Planet Nine” in our solar system might start with an astronomer noticing (or being told by their computer), “Hey, that pixel is brighter than it was a few days ago.
‘”I should make sure to check what it looks like a couple of days from now.”‘
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