Like a traveler on a very long road trip, a deep space probe has passed the last sign post before its destination. NASA has announced that its New Horizons probe has passed the orbit of Neptune – its last milestone before it flies by Pluto on July 14 next year. Launched in 2006, the piano-sized unmanned spacecraft is almost 2.75 billion mi (4.42 billion km) from Earth and is the fastest man-made object ever sent into space.
NASA says that the the craft passed the Neptunian orbit at 10:04 pm EDT on Monday, occurring on the 25th anniversary of Voyager 2’s flyby of Neptune in 1989. But where Voyager came within 3,080 mi (4,950 km) of the gas giant, New Horizons was still 2.45 billion mi (3.96 billion km) away.
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Despite New Horizon’s vast distance from the planet, its Long Range Reconnaissance Imager (LORRI) was still able to capture images of Neptune and its giant moon Triton. NASA says that Triton may be very similar to Pluto and that the information gathered by Voyager 2 a quarter of a century ago may be helpful in the coming encounter.
"There is a lot of speculation over whether Pluto will look like Triton, and how well they’ll match up," says Ralph McNutt of the Johns Hopkins University Applied Physics Laboratory. "That’s the great thing about first-time encounters like this – we don’t know exactly what we’ll see, but we know from decades of experience in first-time exploration of new planets that we will be very surprised."
The first mission in NASA’s New Frontiers program, the US$650 million New Horizons mission was launched on January 19, 2006 atop an Atlas V rocket from Cape Canaveral, Florida. It broke the record for the fastest man-made object on lift off with a speed of 36,373 mph (58,536 km/h). The 478 kg (1,054 lb) spacecraft was sent on a 9.5-year mission to fly by Pluto – a distance so far that radio signals from the nuclear-powered probe take four hours to reach Earth.
Sent on a slingshot trajectory using the gravitational pull of Jupiter, which tacked on another 9,000 mph (14,480 km/h) to its speed, New Horizons is scheduled to rendezvous with Pluto on July 14 of next year, which it will pass at a distance of 13,000 km (8,000 mi). After this encounter, it will continue on out of the Solar System, during which it will study objects in the distant Kuiper belt.
The video below discusses New Horizon's upcoming encounter with Pluto.