New Horizons Crosses Halfway Point To Pluto

It's been nothing less than the fastest ever sprint across the solar system.

The half-ton NASA New Horizons probe -- the fastest manmade object ever built -- today crosses the halfway mark on its nearly decade-long odyssey to the dwarf planet Pluto.

Today the probe is equidistant between Earth and Pluto; approximately 1.525 billion miles from both worlds. (The spacecraft won't be equidistant between the sun and Pluto until later in 2010.)

The craft is now traveling at 36,900 miles per hour relative to the sun. It is climbing out of the clutches of the sun's "gravity well" fast enough to escape the solar system forever. Now that's a real "getaway special."

If we were traveling along with the probe today, we'd look back and see the sun about 1/15th its diameter as seen from Earth, and less than 1/200th as bright. It shines in the constellation Gemini, and forms a nearly equilateral triangle with the bright red winter stars Betelgeuse and Aldebaran. Earth glimmers as a diamond almost lost in the sun’s glare. Jupiter and Saturn flank the sun. Even at the halfway point Pluto still cannot be seen with the naked eye.

Launched in January 2006, New Horizons swung by Jupiter a little more than a year later and picked up a boost in speed. In June 2008 the probe crossed the one billion mile milepost –- the approximate distance of Saturn from the sun.

It's due to pass Uranus' orbit in 2011, and Neptune's orbit in August 2014. No more than 11 months later the probe will barrel through the Pluto system. The Hubble Space Telescope may even be used to search for other Kuiper belt targets beyond Pluto for New Horizons to visit along its outbound path.

The Pluto flyby will be one of the most celebrated astronomical close encounters in human history. It will likely reveal Pluto as a complex and dynamic world. Today’s pedantic fuss over planetary semantics will seem naive and irrelevant.

Like a science fiction space traveler, the probe's computers and electronics are in hibernation for about 90 percent of the long journey. Mission controllers at the Johns Hopkins University Applied Physics Lab near Columbia, Maryland wake up the spacecraft in November and January every year to re-point its antenna toward Earth and to conduct some maintenance activities. A radio message now takes over two hours to reach the star-streaking probe.

The probe's runaway speed essentially buys it immortality. New Horizons will drift among the stars forever. Regrettably the probe does not carry a plaque or recorded message as it sister runaways Pioneer 11 & 12, and Voyager 1 & 2 do. New Horizons does carry a DVD with the names of over 450,000 people and some of the ashes of the astronomer who discovered Pluto in 1930, Clyde Tombaugh. Even if aliens were clever enough to pinpoint the probe in interstellar space and retrieve it, I can't imagine what they could learn about us from these mementos.

It seems pretty unlikely any aliens could find these interstellar notes-in-bottles, but who can imagine the capabilities of an advanced extraterrestrial civilization?

These plucky robots are monuments to our curiosity that will vastly outlast the Egyptian pyramids. They will be the last surviving artifacts of an inquisitive bipedal race called Homo sapiens that once lived in the galaxy's Orion spur.

The probes' odysseys also humble our dreams about interstellar travel. It will take New Horizons approximately 80,000 years to reach the distance of the nearest star. Any entity capable of traversing such a vast gulf of space certainly cannot be made of flesh and blood.