The images were obtained by combining pictures from the probe’s high-resolution, “black and white” camera, Lorri, and its lower-resolution, colour imager known as Ralph. What is outstanding in the picture that pops out are four dark spots on the 2,300km-wide dwarf planet. Each spot is about 500km across. Quite why they should be so similar in size and spacing is not clear.
New Horizons will not be passing through the their hemisphere during its close flyby on 14 July. However, there may be other opportunities to observe those spots in detail later on.
“It’s a real puzzle – we don’t know what the spots are, and we can’t wait to find out,” said New Horizons principal investigator, Alan Stern, of the Southwest Research Institute.
“Also puzzling is the longstanding and dramatic difference in the colours and appearance of Pluto compared to its darker and greyer moon Charon.”
If, as scientists think, Pluto and Charon are the products of a collision between two primitive bodies in the early Solar System, one might expect them to look more similar.
NASA is now drawing closer to the dwarf plant Pluto and its five moons.
The moment of closest approach on the 14th will take place at 11:49 GMT, when the probe is just 12,500km above the surface.
It is moving too fast – at 13.7km/s – to go into orbit, and it will simply scream past the dwarf and its satellites, gathering as much data as it can.
No pictures will be sent back to Earth on the day itself; the spacecraft will be too busy executing its pre-programmed observation campaign.
Instead, the first images from the flyby should be presented on the following day, on 15 July.
New Horizons was commanded to make a thruster burn earlier this week, to speed it up ever so slightly.
This will ensure the spacecraft reaches a precise point in space and time to carry out the pre-programmed observation sequence.
The probe must spin around to take pictures of all the different targets, and if its navigation is off by even a small amount it will be looking in the wrong direction at the critical moment.