Pluto-Bound Probe Sprints Across Uranus' Orbital Path

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The fastest man-made object ever built, the half-ton NASA New Horizons spacecraft, crosses the orbit of Uranus today on its nearly decade-long odyssey to the dwarf planet Pluto.

The probe is now 1.8 billion miles from Earth, but still has nearly 1.2 billion miles to go before encountering Pluto. To underscore the enormity of that distance, it now takes a radio signal 2.5 hours to travel back to Earth from the spacecraft.

The nuclear-powered craft is hurtling though the interplanetary void at 35,000 miles per hour. That’s fast enough to escape the solar system forever and join the ranks as one of our earliest starships (albeit poking along so slowly it will take 80,000 years to reach the distance of the nearest star).

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If you were traveling along with the probe today, you’d look back and see the sun at a small spot of light that is only 1/400th as bright as seen from Earth.

At this distance Earth is almost lost in the sun’s glare. Jupiter and Saturn flank the sun at two brilliant diamonds at nearly their greatest western and eastern elongation, respectively. Even beyond the halfway point, the ultimate destination, Pluto, still cannot be seen with the naked eye.

Like a science fiction space traveler, the probe’s computers and electronics are in hibernation for about 90 percent of the long journey. The spacecraft will be awaken from its current sleep on May 9 for its fifth checkout (since launch) that involves testing of all the onboard instruments to see if they are still healthy.

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The New Horizons team at the Johns Hopkins University Applied Physics Lab near Columbia, Maryland will also do a “lunar occultation” experiment while the craft is awake. The Earth’s moon will pass across the line-of-sight between Earth and the spacecraft on May 20th. At that time, NASA’s Deep Space Network will send radio signals from Earth to the probe. This transmission will “blink out” when the moon crosses the sightline. This will be a dress rehearsal for what happens when New Horizons passes into the shadows of Pluto and its largest moon Charon in 2015.

Launched in January 2006, New Horizons sprinted out to Jupiter in little more than a year. The probe picked up a boost in speed by robbing momentum from Jupiter.

In June 2008, the probe crossed the one billion mile milepost — roughly the distance of Saturn from the sun.

New Horizons is due to cross Neptune’s orbit in August 2014. No more than 11 months later the probe will speed through the Pluto system for a long-awaited but flirtatiously brief encounter.

High-definition Hubble Space Telescope images meticulously processed over the past several years reveal that Pluto is a variegate planet with a mottled mix of snow-white patches and darker molasses-colored terrain.

New Horizons won’t get a view of Pluto that is sharper than Hubble’s until the craft is just six months from closest encounter. Hubble’s snapshots suggest that New Horizons will unveil Pluto as a complex and dynamic world — befitting of a planet, dwarf or otherwise.

Image credit: NASA