A new study has revived the hunt for Planet Nine, the long-hypothesised world thought to be lurking at the outermost edge of the solar system. Astronomers poring over two decades-old sky surveys believe they may have spotted something moving just enough to suggest it could be the elusive planet. If confirmed, it would be the best candidate yet: larger than Neptune, and currently orbiting around 700 times further from the Sun than Earth.
A Different Kind Of Planet X
The idea of a hidden planet beyond Neptune isn’t new. Past theories linked an undiscovered giant to periodic mass extinctions on Earth, though those claims have largely fallen apart. The modern version, Planet Nine, was proposed in 2016 to explain the clustered orbits of several icy objects beyond Pluto. The theory suggests a massive planet on a stretched-out orbit, far enough from the Sun to make detection painfully difficult, especially in visible light. But in infrared? That’s where things get interesting.
Spotting A Shadow In The Archive
The latest search was led by Terry Long Phan of National Tsing Hua University in Taiwan. His team analysed data from two infrared satellites, IRAS, launched in 1983, and AKARI, which operated between 2006 and 2011. They looked for a faint object that moved ever so slightly between the two surveys, just enough to indicate its presence over the 23-year gap. After sifting through hours of sky scans, they found a lone candidate: a dim dot that fits the predicted motion and distance of Planet Nine, moving about 47 arcminutes between the two observations, consistent with what you’d expect from a planet drifting slowly through space at around 700 astronomical units. The object’s apparent brightness also points to a Neptune-sized world, larger than expected, given many models focus on a super-Earth.
What We Don’t Know (Yet)
At this point, no one’s calling it a discovery. The orbital path is still unknown, and it hasn’t been spotted in more recent data sets like WISE. That’s likely because it’s moved again since 2006, but without a confirmed orbit, astronomers don’t know exactly where to look next. Still, tools like the Dark Energy Camera on Chile’s Blanco telescope, with a wide enough field of view to cover the search area, could help pin it down. There are also big questions about how such an object got there in the first place. It could be a planet that formed closer in and was flung out during the solar system’s chaotic youth. Or it might be a rogue planet, captured from another star during a close encounter billions of years ago.
Phan’s candidate is the second potential Planet Nine to turn up in archival infrared data. The first, found in 2021, hasn’t been confirmed. But this latest detection, seen in two independent surveys, holds more promise. With next-gen observatories like the Vera Rubin and Roman Space Telescopes set to scan the skies with unprecedented depth, if Planet Nine exists, it won’t remain hidden much longer.
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