LAUREL (United States) • After a long day celebrating the arrival of Nasa's New Horizons spacecraft at Pluto and wondering about its fate while it was out of radio contact, mission controllers finally received confirmation yesterday morning that the spacecraft had performed its scientific tasks.
On schedule, at 8.53am Singapore time, a message from the spacecraft arrived at Mission Control at the Johns Hopkins Applied Physics Laboratory. "We are in lock with carrier," said Ms Alice Bowman, the missions operations manager. "Stand by for telemetry."
Some moments later, when she confirmed that data was coming down, cheers erupted for the second time.
New Horizons has shipped back a trove of tantalising images, showing the dwarf planet in unprecedented detail as a reddish globe with varied terrain, ice caps and an oddly perfect heart shape on its surface. The remaining images and data will be sent back to Earth over the course of the next 16 months.
Scientists have already learnt from New Horizons that Pluto is 19km to 29km larger than previously thought, with a radius of 1,184km. They have also confirmed the existence of a polar ice cap on Pluto and found nitrogen escaping from the dwarf planet's atmosphere.
New Horizons, a nuclear-powered spacecraft, launched from Cape Canaveral, Florida, in 2006. The mission was hailed as a milestone in space exploration because it was the first spacecraft to visit Pluto, a mysterious celestial body of which little is actually known.
The greatest hazard faced by the spacecraft was the possibility of encountering space debris that may have been knocked off Pluto's moons by meteorite strikes. A collision with a particle just the size of a grain of rice could destroy the spacecraft, which would be a tremendous loss, given that about 99 per cent of the data has still not been transmitted. The risk of such an incident was, however, low, at about one in 10,000.
"Pluto just had its first visitor," President Barack Obama posted on Twitter. "Thanks, Nasa. It's a great day for discovery and American leadership."
After a voyage of 91/2 years at a speed of 49,000 kmh, the probe is about 4.8 billion km away, where radio signals, even travelling at light speed, need 4.5 hours to reach Earth.
Following the success, New Horizons principal investigator Alan Stern told reporters: "We have completed the initial reconnaissance of the solar system, an endeavour started under President (John F.) Kennedy more than 50 years ago, continuing today under President (Barack) Obama."
The head of Nasa's science mission directorate, Mr John Grunsfeld, said images beamed back by New Horizons showed Pluto to be an "extraordinarily interesting and complex world", according to The Guardian. "It's truly a hallmark in human history," he said. "It's been an incredible voyage."
The spacecraft has enough fuel to carry on its exploration, and Mr Stern plans to ask Nasa for funding to continue using New Horizons beyond its Pluto mission, to study more objects in the Kuiper Belt.
NEW YORK TIMES, AGENCE FRANCE-PRESSE, REUTERS, XINHUA
