For years, astronomers have suspected there might be a large, unseen planet lurking in the outer reaches of our solar system, nicknamed Planet 9. Now, exciting new research analyzing decades-old infrared data has identified a single compelling candidate that could potentially be this elusive world. This isn’t final proof, but it’s a significant step in the ongoing search for the solar system’s missing member.
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The Curious Case of the Solar System’s Edge
Our solar system seems neat and orderly, with planets orbiting the Sun like marbles on a track. But far beyond Neptune, in the cold, dark Kuiper Belt, some icy objects move in strange, clustered paths. It’s as if something massive is gently nudging them around. This gravitational “shepherding” is one of the main clues suggesting a hidden giant – Planet 9.
Artist's impression showing planets orbiting a star, illustrating the structure of a solar system.
Based on these celestial clues, Planet 9 is theorized to be a planet roughly the size of Neptune, possibly orbiting hundreds of times further from the Sun than Earth does. That’s incredibly distant.
Why Finding Planet 9 is Like Looking for a Ghost
So, why haven’t we seen it already? Imagine trying to spot a small, dark pebble reflecting faint sunlight from across a huge field at night. That’s similar to the challenge of finding Planet 9 using visible light telescopes. The sunlight has to travel all the way out, bounce off the planet, and travel all the way back to Earth, losing intensity drastically over the immense distance. If Planet 9 is 10 times further than Neptune, it would appear 10,000 times fainter in visible light.
Conceptual artwork depicting the hypothetical Planet Nine in the distant outer Solar System.
Compounding the problem, we don’t know exactly where it should be in the sky. Its predicted orbit has a lot of uncertainty, making it hard to know precisely where to point telescopes.
A Different Light: Searching in Infrared
But planets don’t just reflect light; they also emit their own heat in the form of infrared radiation. This thermal glow only has to travel one way to us. For a distant world like Planet 9, its emitted infrared light would be roughly 100 times brighter than its reflected visible light. This makes infrared telescopes a much better tool for the job.
Illustration of a large, icy gas giant planet, similar in appearance to Neptune, in the deep cold of space.
This is exactly the approach taken by Terry Long Phan at National Tsing Hua University in Taiwan and his collaborators. They decided to look for Planet 9’s heat signature in data from two pioneering infrared space telescopes: IRAS and AKARI.
Digging Through Decades of Data
The Infrared Astronomical Satellite (IRAS) mapped the entire sky in infrared in 1983. The AKARI satellite did the same starting in 2006. The crucial difference? There were 23 years between their observations.
If Planet 9 exists at the predicted distance (over 300 AU), it would move incredibly slowly across the sky. So slowly, in fact, that it would likely appear stationary in the data from either single mission. But over 23 years, it should have shifted slightly between the IRAS and AKARI maps.
Artist's concept of the Infrared Astronomical Satellite (IRAS) spacecraft, which mapped the sky in infrared light.
Using special software, Phan and his team sifted through the vast catalogues of infrared sources detected by both telescopes, looking for pairs that showed the tiny, expected movement. This automated search yielded 13 potential candidates.
They then manually checked each pair, ruling out false alarms and other known objects. After this meticulous process, only one candidate pair remained.
The Faint Pinprick of Hope
This single promising source moved by 47.5 arcminutes over the 23 years between the IRAS and AKARI missions. To put that in perspective, that’s about one and a half times the width of the full Moon as seen from Earth – a tiny shift over two decades, consistent with a very distant, slow-moving object.
Comparison view of infrared sky maps from the IRAS and AKARI surveys, highlighting the apparent shift of a potential Planet 9 candidate over 23 years.
This candidate source matches the expected infrared brightness of a Neptune-sized planet far out in the solar system.
What’s Next? More Eyes on the Sky
Does this mean we’ve found Planet 9? Not yet. Finding two points doesn’t give us enough information to definitively calculate the object’s orbit or confirm it’s a planet. It could still be something else, though a compelling candidate.
This potential detection is incredibly exciting, but it’s just the first step. The next crucial phase is follow-up observations. Telescopes like the powerful DECam (Dark Energy Camera) on the Victor M Blanco Telescope in Chile could be used to take a closer look at this specific spot in the sky and see if they can confirm the object and track its movement further.
If confirmed, this infrared pinprick could finally reveal the long-sought ninth planet, adding a new giant world to our cosmic neighborhood. The search continues!
