Speeding ever closer to its rendezvous with Pluto, NASA's New Horizons spacecraft has spotted two of the dwarf planet's tiny moons, giving astronomers their first good look at Nix and Hydra.
The NASA probe snapped images of the small bodies, two of Pluto's known five moons, from around 120 million miles away, the space agency said.
NASA released the photos on Wednesday, exactly 85 years to the day after the discovery of Pluto by American astronomer Clyde Tombaugh while working at the Lowell Observatory in Flagstaff, Arizona.
New Horizons will make a historic flyby of Pluto in July.
"It's thrilling to watch the details of the Pluto system emerge as we close the distance to the spacecraft's July 14 encounter," New Horizons science team member John Spencer, of the Southwest Research Institute in Boulder, Colorado, said in a NASA release. "This first good view of Nix and Hydra marks another major milestone, and a perfect way to celebrate the anniversary of Pluto's discovery."
The moons Hydra and Nix, discovered by the Hubble Space Telescope in 2005, are thought to be between 25 to 95 miles wide, a figure the New Horizons spacecraft will pin down when it passes Pluto in July.
Two other moons, Kerberos and Styx, are even smaller than Hydra and Nix and have not shown up in the New Horizon images taken to date.
Charon, Pluto's other known moon, is a comparative giant at 750 miles wide and is almost half the size of the dwarf planet it orbits.
Because of its larger size, Charon was observed in 1978 using telescopes at the United States Naval Observatory Flagstaff Station in Arizona.
The photos taken by New Horizons' Long-Range Reconnaissance Imager are the first in a planned series of long-exposure shots that will continue into March to help astronomers precisely determine the moons' orbits.
Hydra, the outermost of Pluto's known moons, orbits the dwarf planet every 38 days at a distance of around 40,200 miles while Nix, at a distance of approximately 30,000 miles, orbits every 25 days.
Launched in 2006, New Horizons will pass within 8,500 miles of Pluto's surface when it makes its future flyby.
That may not be the final leg of its journey; team members are hoping to get funding for an extension of its mission that would see the spacecraft visit another object in the Kuiper Belt, the distant ring of an icy object orbiting beyond Neptune where Pluto resides.
