NASA is releasing new images of Pluto that were taken from its New Horizons spacecraft.

The images were unveiled at a news conference at the Johns Hopkins University Applied Physics Lab outside Baltimore.

New Horizons spent more than eight hours after its closest approach looking back at Pluto for a series of experiments to study the planet's atmosphere and photograph its night-side using light reflected off its primary moon Charon.

Sending back its first post-flyby signal took another four-and-a-half hours, the time it takes radio signals, traveling at light speed, to travel the 3 billion miles (4.88 billion km) back to Earth.

Already, the trickle of images and measurements relayed from New Horizons before Tuesday's pass by Pluto has changed scientists' understanding of this diminutive world, which is smaller than Earth's moon.

Once considered an icy, dead world, the planetoid has yielded signs of geological activity, with evidence of past and possibly present-day tectonics, or movements of its crust.

It will take about 16 months for New Horizons to transmit back all the thousands of images and measurements taken during its pass by Pluto. By then, the spacecraft will have traveled even deeper into the Kuiper Belt, heading for a possible follow-on mission to one of Pluto's cousins.