A billion miles beyond Pluto, the New Horizons spacecraft is just a few weeks out from a historic flyby of the Kuiper Belt object, 2014 MU69 – also known by the far more dramatic nickname, Ultima Thule. After weeks of scans for any potential hazards, NASA has now given New Horizons the all-clear to buzz the object on an optimal path, which will bring it in closer for a much better look.
At 12:33 am EST on January 1, 2019, New Horizons will ring in the new year by passing within about 2,200 mi (3,500 km) of Ultima Thule. This path was deemed the optimal route to provide an unprecedented look at the planetoid, which is set to become the most distant object ever visited by a spacecraft.
But it wasn't necessarily a given that this best-case path would be possible. Since it's so far away, we don't really know if Ultima Thule has any small moons or ring systems that could potentially damage New Horizons if it passes too close. For the last few weeks, a hazard watch team has been searching for any sign of danger – and, thankfully, has come up empty. The alternative would have required the craft to maneuver itself further away from the body, reducing the detail of data that could be collected.
To give the all-clear, the team used the craft's Long Range Reconnaissance Imager (LORRI), which would have picked up any moon more than about 2 miles (3.2 km) wide or dusty rings reflecting as little as five 10-millionths of the sunlight hitting them. There may still be objects very close to Ultima, but the team says these would be out of the way and won't pose a risk.
"Our team feels like we have been riding along with the spacecraft, as if we were mariners perched on the crow's nest of a ship, looking out for dangers ahead," says Mark Showalter, lead of the hazards watch team. "The team was in complete consensus that the spacecraft should remain on the closer trajectory, and mission leadership adopted our recommendation."
The hazard watch team was assembled in 2011, to perform the same function before New Horizons' flyby of Pluto in July 2015. Concerns had been raised about the dwarf planet's then newly-discovered moons, which may have been spreading potentially-damaging debris across New Horizon's path. The team declared smooth sailing ahead, and the end result was the treasure trove of close-up photos and data on Pluto we were treated to over the months and years following the flyby.
This new flyby should give us similarly clear views of a far lesser-known object, which is extremely exciting.
"The spacecraft is now targeted for the optimal flyby, over three times closer than we flew to Pluto," says Alan Stern, New Horizons Principal Investigator. "Ultima, here we come!"
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