NASA will release more pictures from the New Horizons flyby of Pluto. Scientists promise to show further close-ups, and talk about some of the other types of data acquired during Tuesday’s close pass. Already, there are strong indications that Pluto and its main moon, Charon, have been active in the recent past.
Meanwhile, the probe itself continues to monitor the diminutive world and its five satellites. Even though it has gone more than three million km beyond the Pluto system, there is still much to learn by looking in "the rear-view mirror".
New Horizons is attempting to study the crescent Pluto, to see if there are hazes and even clouds in its tenuous atmosphere. It is also hunting for rings. It is possible Pluto is surrounded by concentric circles of dusty, icy particles, and these would scatter sunlight in a way that might be easier to detect from "behind" the dwarf planet.
On Thursday Nasa released another view of Charon, as a tease ahead of Friday’s briefing. This zoomed in on a rectangular area approximately 390km long. The terrain has remarkably few craters, but what really catches the eye is a large mountain that sits in a depression – like a castle surrounded by a moat.
"This is a feature that has geologists stunned and stumped," said Jeff Moore, a Nasa scientist who leads New Horizons’ geology, geophysics and imaging team. The probe has so far sent back only a tiny amount of its stored flyby data.
The vast distance to Pluto (4.7 billion km) and the modest transmitter/antenna system (12W) onboard makes for very slow bit rates – an average of one kilobit (125 bytes) per second. The three-axis stabilised spacecraft can boost this if it switches off its power-hungry inertial measurement unit and spins itself up. However, it cannot do this and take images at the same time.
Not until the probe has observed Pluto for another two full rotations will it make this change. And given that a "Pluto day" is 6.4 Earth days, this means the command to stop imaging and spin-up is at least a fortnight away.