50 years ago, scientists had hints of a planet beyond Pluto

Excerpt from the May 6, 1972 issue of Science News

a photo of the Atacama Cosmology Telescope scanning the night sky with the Milky Way overhead

Astronomers have used the Atacama Cosmology Telescope in Chile to scan nearly 90 percent of the Southern Hemisphere’s sky in search of Planet Nine.

Jon Ward/University of Pennsylvania

cover of the May 6, 1972 issue of Science News

Cometary evidence of a planet beyond Pluto Science News, May 6, 1972

There have been suggestions that our solar system might have a tenth planet…. In the April Publications of the Astronomical Society of the Pacific, a mathematician … presents what he says is “some very interesting evidence of a planet beyond Pluto.” The evidence comes from calculations of the orbit of Halley’s comet.

Update

The 1972 evidence never yielded a planet, but astronomers haven’t stopped looking — though it became a search for Planet 9 with Pluto’s 2006 switch to dwarf status. In the mid-2010s, scientists hypothesized that the tug of a large planet 500 to 600 times as far from the sun as Earth could explain the peculiar orbits of some objects in the solar system’s debris-filled Kuiper Belt (SN: 7/23/16, p. 7). But that evidence might not stand up to further scrutiny (SN: 3/13/21, p. 9). Researchers using the Atacama C­osmology Telescope in Chile to scan nearly 90 percent of the Southern Hemisphere’s sky had no luck finding the planet, the team reported in December 2021.

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