Approach Phase 2, which began when New Horizons was 100 days from Pluto, is just finished. Some LORRI images from Apr 12-18, showing a full orbit of Charon around Pluto and one revolution of Pluto (like the Earth’s Moon, Charon keeps the same face towards Pluto as it orbits), also reveal possible surface features on Pluto, in particular a possible light colored polar region.
Between April 25 and May 1, at a range of 90 million Kilometers, New Horizons spacecraft photographed Kerberos and Styx, the smallest and faintest of Pluto's five known moons, for the first time. Following the spacecraft's detection of Pluto's giant moon Charon in July 2013, and Pluto's smaller moons Hydra and Nix in July 2014 and January 2015, respectively, New Horizons can now see of all the known members of the Pluto system.
Styx (green), Nix (yellow), Kerberos (orange) and Hydra (red)
Drawing even closer to Pluto in mid-May, New Horizons will begin its first search for new moons or rings that might threaten the spacecraft on its passage through the Pluto system.
Kerberos and Styx were discovered in 2011 and 2012, respectively, by New Horizons team members using the Hubble Space Telescope. Styx, circling Pluto every 20 days between the orbits of Charon and Nix, is likely just 4 to 13 miles (approximately 7 to 21 kilometers) in diameter, and Kerberos, orbiting between Nix and Hydra with a 32-day period, is just 6 to 20 miles (approximately 10 to 30 kilometers) in diameter. Each is 20 to 30 times fainter than Nix and Hydra.
By the end of AP2, it’s possible that the LORRI camera will reach a point called “BTH” when it will be close enough to take better images of the Pluto system than the Hubble Space Telescope can from Earth orbit.
New Horizons has two cameras. The Long-Range Reconnaissance Imager (LORRI) has a field of view of about one quarter of degree and takes black-and-white ("panchromatic") images. The Ralph Multispectral Visible Imaging Camera (MVIC) has a field of view nearly six degrees wide and takes both panchromatic and color images. It has panchromatic, near-IR, red, blue, and methane filters, but no green filter.
On May 15, New Horizons will stop its continuous observation of the Pluto system for the second time this year and, again, turn its large antenna toward Earth for 15 days to transmit all the data in its solid state recorders. Once the recorders are emptied, 47 days before reaching Pluto, Approach Phase 3 will begin, on May 28. More instruments are being turned on, the imaging campaign shifts from navigation and long distance studies of color and brightness to obtaining higher and higher resolution images of the surface features of Pluto and Charon.
