Sen—NASA's New Horizons spacecraft, which is fast approaching Pluto, has released the most detailed images so far of the dwarf planet.
The surface shows dark and brighter patches, and a brighter area around one of the poles that could be a polar ice cap.
"These new images show us that Pluto's differing faces are each distinct, likely hinting at what may be very complex surface geology or variations in surface composition from place to place," said New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute in Boulder, Colorado, in a statement released with the images.
"These images also continue to support the hypothesis that Pluto has a polar cap whose extent varies with longitude. We'll be able to make a definitive determination of the polar bright region's iciness when we get compositional spectroscopy of that region in July."
The images were taken between May 8-12 by the probe's Long-Range Reconnaissance Imager (LORRI) instrument from distances ranging from 80 million km (49.7 million miles) on May 8, to 75 million km (46.6 million miles) on May 12.
The New Horizons team released comparisons between the images taken in mid-May and those just a month earlier to highlight the difference in sharpness now that the spacecraft is about 30 million km (20 million miles) closer to its target.
A process known as deconvolution is used by the team to sharpen the raw unprocessed pictures sent back by the probe.
New Horizons will be at its closest to Pluto when it flies past on July 14. The spacecraft is now 56 million km from Pluto, approaching its target at about 15 km per second (about 50,000 km per hour).
Pluto has five known moons, all of which have been spotted in images released last week. Pluto's largest moon Charon is nearly half the size of Pluto, whilst the other four moons—Nix, Hydra, Styx and Kerberos—are much smaller, ranging from a few hundred down to just tens of kilometres in diameter.
New Horizons launched in January 2006 to study Pluto and the Kuiper belt, a region of icy bodies that orbit beyond Neptune.
When New Horizons launched it was on its way to study Pluto as the ninth planet of our Solar System. However, in 2006 Pluto, along with other similar bodies such as Ceres, Eris, Sedna, Makemake and Haumea, were classified as dwarf planets by the International Astronomical Union.
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