Many of us were taught a mnemonic to remember the eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Maybe it was, ‘My Very Excited Mum Just Served Us Noodles,’ or your mum is instead Very Educated and Serves Nachos instead.
But scientists have long suspected that there could be a ninth planet deep in the solar system, far beyond Neptune. And they may have just found it.
Well, kind of. Researchers at the Vera C Rubin Observatory revealed last week that they have discovered a new dwarf planet, named 2026 ED138.
The icy world is just large enough to be round but not large enough to pave other things out of the way in its orbital neighbourhood.
If confirmed, ED138 would be the sixth dwarf planet discovered so far, following Ceres, the largest asteroid; Pluto; Eris and two icy balls beyond Neptune, Haumea and Makemake.
What is 2026 ED138?
The Vera C. Rubin Observatory, perched on a mountain in Chile, is always scanning the night sky.
On March 4, stargazers spotted a bright speck. When they looked again a few weeks later, it had moved. And it kept moving – again and again – until this pattern of dots revealed ED138’s orbit.
The cosmic racetrack was discovered last month using computer software built by Rubin Operations team member Matthew Holman.
His team found that the dot was also visible in earlier images taken by other telescopes.
Holman estimates that ED138 could be 930 miles wide, making it among the largest and brightest bodies on the outskirts of the solar system.
The way its orbit is tilted suggests it was squished together somewhere around Jupiter and Saturn before being hurled outward by a gas giant.
So, is it Planet 9?
ED138 isn’t the long-fabled Planet Nine, nor is it proof that such a celestial object could be lurking nearby.
But it does show that there are still things waiting to be discovered in the solar system, Dr Edward Bloomer, an astronomer at the Royal Observatory Greenwich in London, tells .
‘Over the years since Pluto’s discovery – at the time, the ninth planet, but recategorised since then- there have been many ideas about “what else is out there?”, and another planet is a sort of big prize in most peoples’ imaginations,’ says Dr Bloomer.
‘It’s worth pointing out that we haven’t stopped exploring: the tally of planetary moons and asteroids is vastly different since the date of Pluto’s discovery!’
Planet 9, sometimes called Planet X, isn’t just wishful thinking – there is some science behind it.
It would explain, among other things, why there are six objects in groovy orbits beyond the solar system’s Kuiper Belt, a minefield of icy debris.
Despite there only being a one in 14,000 chance of this happening, their orbits all point roughly in the same direction and they huddle together.
An elusive planet slightly larger than Earth could be gravitationally herding them all, lapping around the sun every 17,000 years or so.
In other words, despite planets being pretty large to us, it’s tiny by cosmic standards and could be really, really far away if its orbit is badly timed.
Still, astronomers did just discover even smaller than that, ED138, adds Dr Bloomer.
The International Astronomical Union, which once stripped Pluto of its planethood, has yet to confirm ED138 is a dwarf planet.
If and when they do – which will depend on further observations of ED138 – stargazers will get the chance to name it.
‘There tends to be an underworld theme to the outer solar system, so perhaps “Donn” after the Irish god of the dead,’ says Dr Bloomer.
‘Or, if I could get away with it, just drop the “138” and pretend it is named after me.’
And one big question sci-fi fans may be asking: could life call planet Ed home?
‘Never say never!’ Ed, the astronomer, not the dwarf planet contender, says.
‘But they’d be very unusual from our point of view, able to live somewhere more than 200°C below zero, in much less than 0.1% of the brightness of our daylight.
‘But that’s one of the points of doing proper science: collecting data and ascertaining facts, so we know what’s really going on.’
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