WASHINGTON, Sept. 7 -- Seven weeks after its historic flyby of Pluto, NASA's New Horizons spacecraft now began to transmit the tens of gigabits of data it collected about the dwarf planet back to Earth.

The transmission rate of the July 14 encounter data, however, is especially slow, at only 1-4 kilobits per second, considering the spacecraft's 4.8 billion-kilometer distance from Earth, which means a radio signal delay of 4.5 hours.

As a result, the data transfer, which resumed on Saturday, is expected to take about one year to complete, NASA said.

Alan Stern, New Horizons' principal investigator said the tens of gigabits of data to be beamed back will help scientists understand Pluto's origin and its evolution.

"What's coming is not just the remaining 95 percent of the data that's still aboard the spacecraft -- it's the best datasets, the highest-resolution images and spectra, the most important atmospheric datasets, and more," Stern said in a statement. "It's a treasure trove."

New Horizons transmitted Pluto photos to Earth immediately following the July 14 flyby, but since late July, it has only been sending back lower data-rate information collected by the energetic particle, solar wind and space dust instruments.