NASA cau­tious on Pluto flyby

Haz­ards could emerge as a space­craft ap­proaches in mid-July, of­fi­cials say.

Los Angeles Times - - THE WORLD - By Deb­o­rah Netburn deb­o­rah.netburn @la­times.com Twit­ter: @Deb­o­rahNet­burn

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.

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