New Horizons sends back Kerberos images, adjusts course toward next target
New Horizons returned images of Pluto’s tiniest moon, Kerberos, showing it to be smaller than scientists expected with a highly reflective surface. The spacecraft was also commanded to begin shifting its trajectory to encounter a new Kuiper Belt Object (KBO).
Four pictures were taken by the Long Range Reconnaissance Imager (LORRI) about seven hours before the spacecraft’s closest approach to Pluto on July 14. The images, taken from a range of 245,600 miles (396,100 km), were combined by the mission team to create a composite picture of the small moon.
In order to provide the highest possible spatial resolution and reduce pixelation effects, the composite image was deconvolved and oversampled by a factor of eight.
Smaller than scientists had thought, Kerberos is about 7.4 miles (12 km) across on its longer side and about 2.8 miles (4.5 km) across on its shorter side. Like its larger companion moon, Hydra, and also like Comet 67P/Churyumov-Gerasimenko, Kerberos appears to be composed of two lobes. That suggests that it may have formed through the merger of two separate objects.
A similar formation process may have been responsible for the shape of both Comet 67P and Hydra.
Kerberos’s larger lobe is about 5 miles (8 km) across, whereas its smaller lobe is about 3 miles (5 km) across.
Prior to the flyby, scientists had attempted to determine Kerberos’s size by using the Hubble Space Telescope to measure the small moon’s gravitational influence on the other moons in the Pluto system.
Because Kerberos was found to have a strong gravitational influence on its companions in spite of being very faint, the scientists speculated it was larger and more massive than it appeared to be. Its faintness was ascribed to a suspected coating of dark surface material.
Those predictions turned out to be incorrect, and scientists are not sure why.
“Once again, the Pluto system has surprised us,” said New Horizons project scientist Hal Weaver of Johns Hopkins University Applied Physics Laboratory (JHU-APL).
Instead of being dark, Kerberos’s surface has approximately the same reflectivity as the other moons of the Pluto System – estimated to be around 50 percent.
The brightness of its surface suggests an outer layer of water ice.
“Our predictions were nearly spot-on for the other small moons, but not for Kerberos,” said New Horizons co-investigator Mark Showalter of the SETI Institute.
With images of all the system’s moons now back, the mission team created a “family portrait” composite photo complete with a small section of Charon, the largest moon. Charon and the four smaller moons were photographed using LORRI.
Large enough to be spherical, Charon has a diameter of 751 miles (1,212 kilometers). Nix and Hydra are each approximately 25 miles (40 km) across in their longer dimensions. Kerberos and Styx are even smaller, with longer dimensions of approximately six to seven miles (10–12 km).
Unlike Charon, the four small moons have elongated shapes believed to be characteristic of small KBOs.
As New Horizons sent back the Kerberos images, mission controllers conducted the first of four maneuvers directing it to its next target, a tiny KBO designated 2014 MU69, located around one billion miles past Pluto.
On Oct. 22, at approximately 1:50 p.m. EDT, two of the piano-sized spacecraft’s small hydrazine-fueled thrusters were engaged for about 16 minutes to redirect the spacecraft’s path by about ten meters per second.
The next three maneuvers will be done on Oct. 25, Oct. 28, and Nov. 4. Together, the four maneuvers will alter New Horizons’ trajectory by about 57 meters per second, setting it on course for its encounter with 2014 MU69 on Jan. 1, 2019.
The spacecraft is healthy and has now traveled about 74 million miles (119 million km) past Pluto.
The mission team plans to submit the required proposal for an extended mission to the KBO to NASA early next year.
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.