July 14--New Horizons' long journey to Pluto ended in an instant early this morning, when the NASA spacecraft went screaming past the dwarf planet at 30,800 mph -- but the mission is far from over.
Even as the spacecraft speeds deeper into the Kuiper belt, its instruments will continue to search for signs of faint rings around the small world and take measurements of the dust and plasma in Pluto's neighborhood.
And then there's all the new data that it has to get back to Earth.
New Horizons stopped communicating with ground control at 8:17 p.m. Pacific time Monday, and it is not expected to resume contact again until 6:02 p.m. Tuesday.
The 22-hour period of silence was deliberate. The flyby window was extremely brief and mission architects wanted all of New Horizons' power to be focused on data collection, rather than checking in with Earth.
If all goes well, the spacecraft will keep its 6:02 p.m. appointment, and send a 16-minute phone-home signal to the ground team, letting them know that all the instruments are still working and that it survived its encounter with the Pluto system unscathed.
The first batch of new data from the flyby will start to arrive on Earth at 2:32 a.m. Wednesday, and it will include the highest-resolution images taken by the spacecraft, when it was less than 7,800 miles from Pluto's surface.
These black-and-white pictures will be so clear that if you were looking at a similar picture of Earth you could make out the runways of LAX and the ponds of New York's Central Park.
"We know the world is excited to see them, but this is a safety issue," said Henry Throop, a scientist on the New Horizons team. "These are the images that we will get the most science from, and we want it to be the first to come down."
The data will be received by one of three 70-meter antennas in NASA's Deep Space Network, but the information will be coming down at a slow trickle of just 1,000 to 4,000 bits per second.
That's about the speed of your old computer modem from 20 years ago, Throop said. He added that it will take 90 minutes for just one of these images to get fully downloaded.
New Horizons will continue to send the highest priority images in a compressed state for the next two weeks. Beginning in August it will start sending raw data back to Earth for eight hours a day. Mission scientists say it will take 16 months to get everything off the spacecraft.
But even then, when New Horizons has nothing more to tell us about Pluto and its immediate environment, its work may not be over.
New Horizons' principal investigator, Alan Stern, is hopeful that the spacecraft will journey to another object in the Kuiper belt -- one that is smaller than Pluto and closer in size to the comets that zip through our solar system.
The spacecraft is powered by plutonium, and it has enough left to keep it operational through the mid-2030s, Stern said.
Now that the flyby is over, the New Horizons team will work with NASA to choose among three potential Kuiper belt objects to send the spacecraft to next, and possibly fire its engines to point it in the right direction.
All three candidates are another billion miles beyond Pluto, and it would take New Horizons two or three years to get there.
Even after a visit to a second object, the mission could still have legs.
"We could send it to a planetesimal" -- a much smaller object -- "and then have it explore the deep regions of the heliosphere," the immense magnetic bubble enveloping the solar system, Stern said. "It would be like Voyager, but with much more modern instruments."
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