Search For Planet 9 In Solar System Yields Nothing

A theorized huge, ninth planet beyond the orbit of Neptune once again wasn't found in a new survey of the solar system's outer reaches, Elizabeth Howell reported for Space.com.

Photo Insert: The search found many tentative candidate sources — about 3,500 of them — but none could be confirmed.

Astronomers scanned a large portion of the sky using the 6-meter Atacama Cosmology Telescope (ACT) in Chile to search for Planet 9. The quest came up empty, according to the scientists behind the research, although they acknowledged that more sensitive searches would make the result more definitive. A study based on the research was published in December 2021 in Astrophysical Journal.

"Their search found many tentative candidate sources — about 3,500 of them — but none could be confirmed. There were no statistically significant detections," the Harvard-Smithsonian Center for Astrophysics said on Mar. 11.

That said, in the scanned area of the sky, scientists were "able to exclude with 95% confidence" a world with the supposed properties of Planet 9, the release added, "results that are generally consistent with other null searches for Planet 9."

It's the latest in a string of fruitless searches since 2016 when a team of astronomers argued that such a large world might explain a strange large gravity source in deep solar space. Astronomers Konstantin Batygin and Mike Brown of the California Institute of Technology found six trans-Neptunian objects whose orbits, to the scientists, suggested the presence of a large unseen world far out in the solar system.

The team behind the new research acknowledged how tough the search would be to find such a planet. In theory, Planet 9 appears to be five to 10 times the size of Earth and roughly 400 to 800 Earth-sun distances away from the sun. (The Earth and sun are on average, 93 million miles or 150 million kilometers apart.)

The existence of a roughly Neptune-mass Planet Nine could explain why the few known extreme trans-Neptunian objects seem to be clustered together in space. A small planet so far away would be tough to spot in optical searches because the world would see very little sunlight at such great orbital distances.

Even searching for infrared or heat signatures is tough, as infrared surveys such as the Wide-field Infrared Explorer (WISE) were unable to find Planet 9 in past attempts, the team noted.

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