A NASA probe closing in on Pluto for a close flyby next week has snapped the first close-up glimpse of the little-understood dwarf planet's nooks and crannies.

The space agency's New Horizons probe won't make its closest approach with Pluto until Tuesday, but the spacecraft has already sent back photos showing unprecedented details of the dwarf planet's surface, particularly a mysterious spot.

These images have revealed a dark whale-shaped blotch near the tiny world's south pole.

See also: How our view of Pluto and its moons has transformed through the decades

A particularly striking new image, taken on July 9 when the spacecraft was about 3.3 million miles from Pluto, shows the "whale's tail," a seemingly geologically complicated area of the dwarf planet, according to NASA.

Some of the geological features on Pluto seen by New Horizons. Image: NASA

“We’re close enough now that we’re just starting to see Pluto’s geology,” New Horizons program scientist Curt Niebur said in a statement.

The whale's tail is located on the side of Pluto that always faces the dwarf planet's largest moon Charon. The July 9 image also shows other possible geological features like polygons near the planet's equator and a strange-looking pattern that stretches for about 1,000 miles on Pluto, according to NASA.

New Horizons launched to space in 2006 and has had to travel more than 3 billion miles to the small world. On Tuesday, it will make its closest approach with the dwarf planet, when the probe passes about 7,750 miles from the surface of the world.

“After nine and a half years in flight, Pluto is well worth the wait," New Horizons principal investigator Alan Stern said in a statement.