NASA can breathe again now that its New Horizons Pluto probe has phoned home. The unmanned nuclear-powered probe re-established contact with the Deep Space Network at 8:54 pm EDT – 13 hours and five minutes after today's historic flyby of the distant dwarf planet. This marks the successful completion of New Horizons' exploration of Pluto and provides scientists with information that should shed new light on the origins of the Solar System.

The long delay between the flyby and confirmation of New Horizons' status was due to the tremendous distances involved. Because Pluto is currently 4.77 billion km (2.97 billion mi) from Earth, radio signals from New Horizons take four hours and 25 minutes to reach Earth. In addition, during the flyby and immediately after the spacecraft was positioned to bring its suite of seven scientific instruments to bear on the planet and its moons, so the probe's main antenna wasn't pointing in the right direction to transmit to Earth.

One frustrating aspect of reestablishing communications has been that a treasure trove of information remains locked in the spacecraft's memory banks. Because data downloads from New Horizons are restricted to two kilobits per second, NASA is now concentrating on returning status updates from the spacecraft. But an agency spokesman said on Twitter that new high resolution images could be received sometime tomorrow. According to NASA, it will take a total of 16 months to transmit back all the data gathered during the flyby.

The confirmation signal took 4 hours and 25 minutes to reach Earth(Credit: NASA)

Despite this, data sent back before the flyby is already beginning to pay scientific dividends. From images returned during the hours that New Horizons approached its close encounter, mission scientists have been able to finally settle the 85-year old debate about exactly how large Pluto is. Using data from the Long Range Reconnaissance Imager (LORRI), it was possible to work out the diameter of the dwarf planet, which is 2,370 km (1,473 mi). This makes Pluto larger than previous estimates and settles it as the largest known object in the Solar System beyond Neptune.

The highest-resolution image returned yet, which was collected 16 hours before the flyby, has also shed new light on Pluto and its history. A plain-like feature informally called "the heart", which borders darker equatorial regions, was discovered measuring 1,600 km (1,000 mi) across. The heart is relatively featureless, with surrounding areas dominated by meteor impacts, indicating age on a scale of billions of years.

As to the future of New Horizons, NASA has identified two possible rendezvous targets in the Kuiper belt that the spacecraft could visit in the next four years, but that will depend upon available funding and, more importantly, fuel left for making course corrections.

New Horizons was launched on January 19, 2006, from Launch Complex 41 at Cape Canaveral Air Force Station, Florida atop a Lockheed Martin Atlas V-551 rocket. It's the fastest spacecraft ever launched, reaching the distance of lunar orbit in only nine hours. After a February 2007 gravity assist from the planet Jupiter, it reached a speed of 83,600 km/h (52,000 mph) relative to the Sun. On July 14, following a nine and a half year voyage through deep space, it passed Pluto at a distance of 12,500 km (7,750 mi) and a speed of 14 km/sec (31,000 mph), making it the final classical planet to be visited by a spacecraft.

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