Astronomers may have found the first promising candidate for the elusive Planet Nine, using data from retired satellites. But doubts remain among experts.
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| Astronomers identify a potential Planet Nine candidate in satellite data, fueling debate over the existence of a hidden giant planet beyond Neptune. Photo: LS |
HSINCHU, Taiwan – May 17, 2025:
Astronomers may have taken a significant step in the decades-long search for Planet Nine, identifying what they call a “good” candidate for the mysterious world thought to lurk in the farthest reaches of our solar system.
In a new study published on April 24 on the preprint server arXiv and accepted by the Publications of the Astronomical Society of Australia, a team led by Terry Phan, a doctoral student at National Tsing Hua University in Taiwan, revealed the discovery of a moving infrared object in old satellite data that could match predictions for Planet Nine.
The candidate emerged from a meticulous analysis of archival data from two retired satellites: the 1983 Infrared Astronomical Satellite (IRAS) and Japan’s AKARI satellite, operational between 2006 and 2011. Researchers looked for faint objects moving slowly—just as Planet Nine, theorized to orbit billions of miles beyond Neptune, would.
“I felt very excited,” Phan said in an interview with Science. “It’s motivated us a lot.”
After filtering out known celestial bodies, the team zeroed in on one promising candidate—a small dot in the infrared spectrum appearing consistently across both datasets with similar color and brightness.
However, not everyone is convinced.
Dr. Mike Brown, the Caltech astronomer who first proposed the Planet Nine hypothesis in 2016, told Science that the object's tilted orbit—approximately 120 degrees from the solar system’s plane—is inconsistent with his Planet Nine model, which predicts a tilt of only 15 to 20 degrees.
“It doesn't mean it's not there, but it means it's not Planet Nine,” Brown said. He noted that such an object might even contradict the conditions needed for Planet Nine to exist, making it either a new planetary discovery or a Planet Nine alternative.
Planet Nine was first hypothesized to explain the unusual orbits of distant Kuiper Belt objects. If real, it could be much larger than Earth and take thousands of years to complete an orbit around the sun. But no direct evidence of its existence has ever been confirmed.
This new infrared signal may be a breakthrough—or a false alarm. The research team has called for follow-up observations to better determine the object’s orbit and verify its planetary status.
Looking ahead, astronomers are hopeful that the soon-to-be-operational Vera C. Rubin Observatory in Chile could finally settle the Planet Nine debate. Equipped with the world’s largest digital camera, the observatory is expected to start scanning the sky later this year, potentially locating distant objects with unprecedented clarity.
Until then, the mystery of Planet Nine continues—its fate hanging between speculation and discovery, as science inches closer to unveiling what lies in the cold darkness beyond Neptune.