U.S. space researchers say it is "amazing" and "fun" to see the images sent back by the New Horizons probe as it gradually moves closer to Pluto.
The probe will make its closest pass to Pluto on Tuesday when it will be just about 12,500 kilometers (about 7,800 miles) from the surface.
But scientists have been thrilled by what New Horizons has sent back so far, calling it a whole new view of Pluto.
Pluto is pictured in this July 7, 2015, handout image from New Horizons' Long Range Reconnaissance Imager (LORRI).
"It's just amazing what we are seeing now," NASA's John Spencer said Saturday. "We are seeing these crazy black-and-white patterns. We have no idea what those mean. We are seeing a lot of circular things that we are wondering are those craters or are they something else. ... We are having a lot of fun just really speculating."
The planets in the solar system travel in elliptical orbits, not perfect circles, so the distance between their paths changes. Right now, Pluto is about 4.8 billion kilometers, or almost 3 billion miles, from Earth.
NASA launched New Horizons in 2006, just before the International Astronomical Union reclassified Pluto as a "dwarf" planet. The Union said Pluto lies in a region of the outer solar system beyond the other planets called the Kuiper Belt. Other astronomers still regard Pluto as a full planet.
NASA scientists say this first close-up exploration of the Kuiper Belt will give them a look at what the solar system was like just after it was formed and possibly more information on how life on Earth developed.