NASA says small as­teroid could hold grand an­swers

Mis­sion to Bennu aims to cap­ture clues to life’s ori­gin

Baltimore Sun - - NATION - By Amina Khan amina.khan@la­

Get ready for an in­ter­plan­e­tary trea­sure hunt.

On Thurs­day, NASA will launch its first mis­sion to visit an as­teroid and bring pre­cious sam­ples back to Earth.

OSIRIS-REx, set to launch around 7:05 p.m. EDT, will head to Bennu, a dark rub­ble-pile of an as­teroid that stretches1,614 feet wide.

After the space­craft reaches and or­bits the near-Earth as­teroid in 2018 and car­ries sam­ples back to Earth, sci­en­tists hope to de­velop a de­tailed pro­file to shed light on the early evo­lu­tion of the so­lar sys­tem, clues to the ori­gin of life and tools that will al­low them to ac­cu­rately track as­ter­oids that come un­com­fort­ably close to Earth.

The space­craft, aboard an At­las V rocket, was rolled out to the launch pad Wed­nes­day. “We’re ready to go,” said Ja­son Dworkin, the mis­sion’s project sci­en­tist, “and ex­cited to see the space­craft fly.”

OSIRIS-REx — short for Ori­gins, Spec­tral In­ter­pre­ta­tion, Re­source Iden­ti­fi­ca­tion, Se­cu­rity-Re­golith Ex­plorer — is bring­ing a suite of in­stru­ments that will help it un­der­stand Bennu in un­prece­dented de­tail. It will use sev­eral cam­eras to ex­am­ine the sur­face, a laser al­time­ter to map the 3-di­men­sional to­pog­ra­phy, vis­i­ble- and in­frared-light spec­trom­e­ters to study its chem­i­cal and min­eral com­po­si­tion and an X-ray spec­trom­e­ter to study el­e­men­tal abun­dances.

It also holds an arm with a disc-like de­vice at the end that will care­fully con­tact the sur­face and col­lect some of the dust and rock that sci­en­tists think cover Bennu’s sur­face. “We are ba­si­cally a space vac­uum cleaner,” prin­ci­pal in­ves­ti­ga­tor Dante Lau­retta said in a brief­ing Wed­nes­day.

The eight known plan­ets formed when the so­lar sys­tem was still in its in­fancy, co­a­lesc­ing out of the swirling disc of gas and dust that sur­rounded our nascent star. The as­ter­oids are those bits of rock that never quite made it into one of these worlds; sci­en­tists think the belt of de­bris that stretches between the or­bits of Jupiter and Mars could have been a planet, had the gas gi­ant’s grav­ity not kept it from form­ing.

These as­ter­oids, then, are the left­over build­ing blocks of the so­lar sys­tem — rocks that have never been al­tered by the heat and pres­sure in­side a planet or been chem­i­cally trans­formed by the pres­ence of life. As such, they hold clues to the early de­vel­op­ment of the so­lar sys­tem.

Bennu is par­tic­u­larly in­trigu­ing be­cause its dark sur­face in­di­cates that it’s full of or­ganic mol­e­cules, the kinds of chem­i­cals that could have seeded life on Earth.

Re­searchers have stud­ied pieces of as­ter­oids that have fallen to Earth as me­te­orites, but their plunge through the at­mos­phere and con­tact with the planet con­tam­i­nates them so that it’s dif­fi­cult to tell what chem­i­cal clues are from the sam­ple and which ones are ter­res­trial con­tam­i­na­tion.

Bennu will also al­low sci­en­tists to study the Yarkovsky ef­fect, a strange phe­nom­e­non that es­pe­cially af­fects smaller, dark­col­ored as­ter­oids. The as­teroid’s sur­face ab­sorbs sun­light and then re-emits it later as heat, which acts like a thruster and can al­ter its course.

This makes it dif­fi­cult to pre­dict an as­teroid’s path; for ex­am­ple, Dworkin pointed out, Bennu has veered about 60 miles off course since its dis­cov­ery in 1999. Learn­ing in de­tail how the Yarkovsky ef­fect acts on Bennu could help sci­en­tists bet­ter pre­dict the tra­jec­to­ries of other as­ter­oids whose paths bring them within strik­ing dis­tance of Earth.

“If you want to be able to pre­dict where an ob­ject like Bennu is go­ing to be in the fu­ture, you have to ac­count for this phe­nom­e­non,” Lau­retta said.

As it is with most in­ter­plan­e­tary mis­sions, pa­tience is key: Sci­en­tists will have to wait to an­a­lyze the sam­ple Bennu car­ries back to Earth; the space­craft isn’t slated to re­turn its cargo un­til 2023.


An artist’s ren­der­ing shows the OSIRIS-REx space­craft ap­proach­ing Bennu. The mis­sion is to launch Thurs­day.

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