NASA cautious on Pluto flyby
Hazards could emerge as a spacecraft approaches in mid-July, officials say.
After a journey of 9 1⁄2 years across 3 billion miles, NASA’s New Horizons spacecraft is about three months away from its closest approach to the dwarf planet Pluto.
The mission has gone according to plan, but NASA officials said hazards could emerge as the spacecraft plunges deeper into the Pluto system.
“This is no simple flyby,” Jim Green, director of planetary science at NASA, said during a panel discussion in Washington. “We are flying into the unknown.”
When the New Horizons mission got the green light in 2001, astronomers knew Pluto to have only one moon, Charon, which is about the size of Texas.
Since then, four smaller moons have been discovered — Hydra, Nix, Styx and Kerberos.
Alan Stern, principal investigator for the mission, said there may be other satellites around Pluto that are too small to be seen by telescopes in and around Earth.
The New Horizons team is not worried about the spacecraft crashing into one of Pluto’s moons, but there is a chance the spacecraft could get hit by debris from a collision between one of the moons and another object.
Stern explained that the Pluto system is hurtling through a collection of icy bodies called the Kuiper Belt at the speed of a bullet. If Pluto or Charon got hit by one of those objects, their gravity would trap the ejecta, causing it to settle back to the surface.
But smaller moons do not have enough gravity to keep the ejecta from floating off into space. Stern said it was likely that moon dust eventually gets captured into orbit around Pluto, perhaps leading to the formation of rings around the dwarf planet.
If Pluto does have rings, it could pose a hazard to the mission. “Even tiny particles the size of a grain of rice can be lethal to the New Horizons spacecraft because we are traveling so fast,” Stern said.
Four years ago, he said, he put together a hazard analysis team to calculate how much danger the spacecraft would face around the time of closest approach.
He said that the best estimates suggested the probability of a debilitating runin with a bit of moon dust was significantly less than 1%.
Still, no one wants to take any chances.
During the panel discussion, Stern described a few precautionary measures, including a series of watch campaigns, when controllers will use New Horizons’ instruments to look for potential hazards.
New Horizons’ closest approach to Pluto is scheduled to occur in mid-July.
Stern said the team had also plotted two alternative approach trajectories that might provide less science value but would be safer.
“We are taking this very seriously,” he said.
The Mars rover Curiosity had “seven minutes of terror” when it landed. “I like to refer to our approach to Pluto as seven weeks of suspense.”
AS IT ENTERS the Pluto system, the New Horizons probe will be “f lying into the unknown,” NASA says.