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Almost Planet X

Nature volume 411, pages 423–424 (2001)Cite this article

Optical and infrared observations of a bright object in the outer Solar System reveal it to be surprisingly large — almost as big as Pluto's moon. It could be the first of many such discoveries.

When Neptune, the eighth planet in the Solar System, was discovered in 1846, astronomers began looking for a ninth. Inspired by irregularities in Neptune's orbit, Percival Lowell began searching in 1905 for what he called Planet X. But it wasn't until 1930, 14 years after Lowell's death, that Clyde Tombaugh of the Lowell Observatory in Flagstaff, Arizona, discovered Pluto. The search for Planet X was over. Or was it? Pluto turned out to be much smaller than expected, and some astronomers, including Tombaugh, continued to search for a tenth planet, beyond Pluto.

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Figure 1: The size and surface darkness of the ninth planet Pluto, its moon Charon, and the newly discovered object Varuna, the three largest known members of an ancient belt of icy objects that surround the eight planets closest to the Sun.

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Affiliations

  1. Department of Physics and Astronomy, Northern Arizona University, Flagstaff, 86011, Arizona, USA

    S. C. Tegler

  2. Department of Physics and Astronomy, University of Oklahoma, Norman, 73019, Oklahoma, USA

    W. Romanishin

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  1. S. C. Tegler
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  2. W. Romanishin
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Tegler, S., Romanishin, W. Almost Planet X. Nature 411, 423–424 (2001). https://doi.org/10.1038/35078164

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