Video Caption: Most inner moons in the solar system keep one face pointed toward their central planet; this animation shows that certainly isn’t the case with the small moons of Pluto, which behave like spinning tops. Pluto is shown at center with, in order, from smaller to wider orbit: Charon, Styx, Nix, Kerberos, Hydra.

NATIONAL HARBOR, Md. (NASA PR) — The New Horizons mission is shedding new light on Pluto’s fascinating system of moons, and their unusual properties. For example, nearly every other moon in the solar system — including Earth’s moon — is in synchronous rotation, keeping one face toward the planet. This is not the case for Pluto’s small moons.

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Pluto’s moons Nix and Hydra. (Credit: NASA/JHUAPL/SWRI)

LAUREL, Md. (NASA PR) — Pluto has five known moons. In order of distance from Pluto they are: Charon, Styx, Nix, Kerberos, and Hydra.

While Pluto’s largest moon Charon has grabbed most of the lunar spotlight, two of Pluto’s smaller and lesser-known satellites are starting to come into focus via new images from the New Horizons spacecraft. Nix and Hydra – the second and third moons to be discovered – are approximately the same size, but their similarity ends there.

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A portrait from the final approach. Pluto and Charon display striking color and brightness contrast in this composite image from July 11, showing high-resolution black-and-white LORRI images colorized with Ralph data collected from the last rotation of Pluto. Color data being returned by the spacecraft now will update these images, bringing color contrast into sharper focus. (Credits: NASA-JHUAPL-SWRI)

LAUREL, Md. (NASA PR) — NASA’s New Horizons mission has answered one of the most basic questions about Pluto—its size.

Mission scientists have found Pluto to be 1,473 miles (2,370 kilometers) in diameter, somewhat larger than many prior estimates. Images acquired with the Long Range Reconnaissance Imager (LORRI) were used to make this determination. This result confirms what was already suspected: Pluto is larger than all other known solar system objects beyond the orbit of Neptune.

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New Horizons’ last look at Pluto’s Charon-facing hemisphere reveals intriguing geologic details that are of keen interest to mission scientists. This image, taken early the morning of July 11, 2015, shows newly-resolved linear features above the equatorial region that intersect, suggestive of polygonal shapes. This image was captured when the spacecraft was 2.5 million miles (4 million kilometers) from Pluto. (Credit: NASA/JHUAPL/SWRI)

MEET PLUTO
New Horizons Pluto Flyby Press Kit

General

• First dwarf planet discovered by an American, Lowell Observatory astronomer Clyde Tombaugh in 1930.
• It is the final classical planet in the solar system to be visited by a spacecraft.
• Pluto has five known moons — Charon, discovered in 1978; Nix and Hydra, discovered in 2005; Styx, discovered in 2011; and Kerberos, discovered in 2012.
• Charon is so large (half of Pluto’s size, same diameter as Texas) that the Pluto-Charon system makes up a “double planet,” the only one in our solar system. Together Pluto and Charon orbit around their common center of gravity in the space between them.
• Pluto is unusually difficult to study from Earth because it is so small and far away. It is 50,000 times fainter than Mars, with less than 1% of the red planet’s apparent diameter when viewed from Earth.
• Pluto is the largest and brightest known member of the Kuiper Belt — the solar system’s third zone — the vast region of ancient, icy, rocky bodies stretching almost 2 billion miles beyond Neptune’s orbit.
• The International Astronomical Union controversially opted in 2006 to classify Pluto and recently discovered large Kuiper Belt Objects as dwarf planets; debate continues on Pluto’s planetary classification.

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This illustration shows the scale and comparative brightness of Pluto’s small satellites. The surface craters are for illustration only and do not represent real imaging data. [Credit: NASA/ESA/A. Feild (STScI)]

“Hubble has provided a new view of Pluto and its moons revealing a cosmic dance with a chaotic rhythm,” said John Grunsfeld, associate administrator of NASA’s Science Mission Directorate in Washington. “When the New Horizons spacecraft flies through the Pluto system in July we’ll get a chance to see what these moons look like up close and personal.”

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