Just look at ’em. Too cute. Photos of Pluto’s tiny moon Kerberos were just sent back this week from New Horizons probe, prompting NASA to create a sibling portrait. They range in size from the comparatively huge Charon at 751 miles (1,212 km) to tiny Styx and Kerberos, roughly 6-7 miles (10-12 km) across their longest dimension.
Kerberos surprised. It turned out to be smaller than scientists expected and has a highly-reflective surface, counter to predictions prior to the Pluto flyby in July. The tiny moon also has a double-lobed shaped that may have resulted from the merger of two separate, smaller moonlets or asteroids. The reflectivity of Kerberos’s surface is similar to that of Pluto’s other small moons — about 50% which is 20% brighter than Earth — and strongly suggests Kerberos, like the others, is coated with relatively clean water ice.
Before New Horizons’ encounter, astronomers had used the Hubble Space Telescope to attempt to weigh Kerberos based on its gravitational effects on neighboring moons. Because it appeared to have a significant tug, they naturally assumed it must be relatively large and massive. But now we see that’s it really quite small. Why remains a mystery.
Meanwhile, New Horizons forges toward its next potential target, the 28-mile-wide (45 km) 2014 MU69, located in the Kuiper Belt, a region beyond Neptune’s orbit home to a legion of icy asteroids. Although this new, post-Pluto mission still awaits approval, the spacecraft has carried out the second in a series of four maneuvers propelling it toward the encounter. The third maneuvers was expected today with the final on Nov. 4th. MU69 orbits a billion miles farther from the sun than Pluto..
The New Horizons team will submit a formal proposal to NASA for the extended mission in early 2016. Scientists hope to bring the spacecraft closer to MU69 than it came to Pluto back in July during a close flyby encounter with MU69 on Jan. 1, 2019.
Today, New Horizons is cruising along at more than 32,000 miles per hour. It’s now about 76 million miles (122 million km) beyond Pluto and 3.16 billion miles (5.09 billion km) from Earth. All systems are healthy and the spacecraft continues to transmit data stored on its digital recorders from the July flyby.