Last of Pluto’s moons — mysterious Kerberos — revealed by New Horizons

Pluto’s moon Kerberos appears to be smaller than scientists expected and has a highly reflective surface, which suggests it’s coated with relatively clean water ice.

This image of Kerberos was created by combining four individual Long Range Reconnaissance Imager (LORRI) pictures taken on July 14, approximately seven hours before New Horizons’ closest approach to Pluto, at a range of 245,600 miles (396,100 kilometers) from Kerberos. The image was deconvolved to recover the highest possible spatial resolution and oversampled by a factor of eight to reduce pixilation effects. Kerberos appears to have a double-lobed shape, approximately 7.4 miles (12km) across in its long dimension and 2.8 miles (4.5km) in its shortest dimension.

NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

Images of Pluto’s tiny moon Kerberos taken by NASA’s New Horizons spacecraft — and just sent back to Earth this week — complete the family portrait of Pluto’s moons.

Kerberos appears to be smaller than scientists expected and has a highly reflective surface, counter to predictions prior to the Pluto flyby in July. “Once again, the Pluto system has surprised us,” said Hal Weaver from the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

The new data, downlinked from the New Horizons spacecraft on October 20, show that Kerberos appears to have a double-lobed shape, with the larger lobe approximately 5 miles (8 kilometers) across and the smaller lobe approximately 3 miles (5km) across. Science team members speculate from its unusual shape that Kerberos could have been formed by the merger of two smaller objects. The reflectivity of Kerberos’ surface is similar to that of Pluto’s other small moons — approximately 50 percent — and strongly suggests Kerberos, like the others, is coated with relatively clean water ice.

Before the New Horizons encounter with Pluto, researchers had used Hubble Space Telescope images to “weigh” Kerberos by measuring its gravitational influence on its neighboring moons. That influence was surprisingly strong, considering how faint Kerberos was. They theorized that Kerberos was relatively large and massive, appearing faint only because its surface was covered in dark material. But the small bright-surfaced Kerberos now revealed by these new images shows that that idea was incorrect, for reasons that are not yet understood.

“Our predictions were nearly spot-on for the other small moons, but not for Kerberos,” said Mark Showalter from the SETI Institute in Mountain View, California. The new results are expected to lead to a better understanding of Pluto’s fascinating satellite system.

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