"Long before it's in the papers"
October 01, 2015

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“Test run” planned for mission to push asteroid off-course

Oct. 1, 2015
Courtesy of the European Planetary Science Congress
and World Science staff

Sci­en­tists are plan­ning a proj­ect to test the wa­ters for what might some­day be a mis­sion needed to save the Earth­—by push­ing an as­ter­oid off-course.

The cur­rent mis­sion just in­volves diverting a mini-as­ter­oid—or more pre­cise­ly, the moon of an as­ter­oid, which is also an as­ter­oid, just small­er.

The idea is to shift the rocky ob­ject in­to a new or­bit around the same par­ent as­ter­oid it al­ready goes around. Pre­sumably this can’t cre­ate a threat to Earth, such as might oc­cur, say, if some­one ac­ci­den­tally knocked a sub­stanti­al as­ter­oid in­to the path of our own blue world.

The mis­sion is a step to­ward pro­tect­ing Earth “from po­ten­tially haz­ard­ous im­pacts,” said Pat­rick Mi­chel, lead­er of the in­ves­ti­ga­t­ion team for the Eu­ro­pe­an Space Agen­cy’s As­ter­oid Im­pact Mis­sion, one of two space­craft be­ing planned as part of the de­flec­tion proj­ect.

For that, he added, “we need to un­der­stand as­ter­oids much bet­ter—what they are made of, their struc­ture, ori­gins and how they re­spond to col­li­sions.” The over­all mis­sion, called AIDA, is “the first to test wheth­er we can de­flect an as­ter­oid through an im­pact with a space­craft.”

Be­cause as­ter­oid struc­ture is­n’t well un­der­stood, sci­en­tists have scratched their heads about what would be the best way to de­flect an as­ter­oid, should it some­day be nec­es­sary. One po­ten­tial prob­lem is that as­ter­oids may be more like float­ing rub­ble piles than sol­id rocks. If so, the sim­ple gam­bit of us­ing a space­ship to bump an as­ter­oid off-course might not work so well, al­though many al­ter­na­tive meth­ods of de­flec­tion have been pro­posed.

The new mis­sion will al­so be the first “to study an as­ter­oid bi­na­ry sys­tem,” that is, an as­ter­oid with a small part­ner as­ter­oid, or moon, Mi­chel said. The Eu­ro­pe­an craft is to join a NASA space­ship called the Dou­ble As­ter­oid Redi­rec­tion Test in vis­it­ing the Didy­mos as­ter­oid and its small sat­el­lite, nick­named “Didy­moon.”

The Eu­ro­pe­an part of the mis­sion “will study the struc­ture of Didy­moon and the or­bit and rota­t­ion of the bi­na­ry sys­tem, pro­vid­ing clues to its or­i­gin and evo­lu­tion,” Mi­chel said. “As­ter­oids rep­re­sent dif­fer­ent stages in the rocky road to plan­e­tary forma­t­ion, so of­fer fas­ci­nat­ing snap­shots in­to the So­lar Sys­tem’s his­to­ry.”

Af­ter the ma­chine has stud­ied both as­ter­oids and mapped Didy­moon, the U.S. probe is to bump Didy­moon, and the Eu­ro­pe­an craft would as­sess its ef­fec­tive­ness in chang­ing the moon’s or­bit around Didy­mos.

Sci­en­tists dis­cussed the AIDA mis­sion Sept. 30 at the Eu­ro­pe­an Plan­e­tary Sci­ence Con­gress 2015 in Nantes, France. The Eu­ro­pe­an part of the mis­sion is planned for launch in 2020 and to reach its des­tin­ation two years lat­er. 

Bi­na­ry sys­tems make up an es­ti­mat­ed 15 per­cent of the as­ter­oid popula­t­ion. The egg-shaped Didy­moon, es­ti­mat­ed as 160 me­ters (170 yards) wide, or­bits the diamond-shaped Didy­mos as­ter­oid, which is al­most five times wid­er, eve­ry half an Earth-day at a dis­tance of 1.1 km (0.7 miles).

While small, Didy­moon is al­ready an es­ti­mat­ed eight times wid­er than than the space rock that burst over Chel­ya­binsk, Rus­sia on Feb. 15, 2013, cre­at­ing a shock wave that sent over a thou­sand peo­ple to the hos­pi­tal. The speed of an ob­ject mat­ters too, of course, not just its size.

Ground-based ob­serva­t­ions in­di­cate that, like the Chel­ya­binsk me­te­or, Didy­mos is probably a com­mon “chon­drite,” or stony as­ter­oid formed of dust from the prim­i­tive so­lar sys­tem. Didy­moon’s weight and com­pact­ness are un­known.

The Eu­ro­pe­an space­craft is to pho­to­graph the moon, study its in­te­ri­or us­ing ra­dar and de­ploy a small lan­der to probe the in­ter­nal struc­ture by ex­chang­ing ra­di­o sig­nals through Didy­moon.

Re­cent mis­sions have shown that as­ter­oids are ex­tra­or­di­narily di­verse in their ge­ol­o­gy, struc­ture and ev­o­lu­tion. All seem to be co­vered by soil, but this varies from fi­ne grains to peb­bles. Most as­ter­oids seem to be ag­gre­gates of ma­te­ri­al, rath­er than sol­id bod­ies, but it’s not clear wheth­er they’re filled with large rocks and empty pock­ets, or grav­el.


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Scientists are planning a project to test the waters for what might someday be a mission needed to save the Earth—by pushing an asteroid off-course. The current mission involves knocking a mini-asteroid—or, more precisely, the moon of an asteroid—off its natural path. The idea is to shift the rocky object into a new orbit around the same parent asteroid it already goes around. Presumably this can’t create a threat to Earth, such as might occur, say, if someone accidentally knocked a substantial asteroid into the path of our own blue world. The mission is a step toward protecting Earth “from potentially hazardous impacts,” said Patrick Michel, leader of the investigation team for the European Space Agency’s Asteroid Impact Mission, one of two spacecraft being planned as part of the deflection project. For that, he added, “we need to understand asteroids much better—what they are made of, their structure, origins and how they respond to collisions.” The overall mission, called AIDA, is “the first to test whether we can deflect an asteroid through an impact with a spacecraft.” Because asteroid structure isn’t well understood, scientists have scratched their heads about what would be the best way to deflect an asteroid, should it someday be necessary. One potential problem is that asteroids may be more like floating rubble piles than solid rocks. If so, the simple gambit of using a spaceship to bump an asteroid off-course might not work so well, although many alternative methods of deflection have been proposed. The new mission will also be the first “to study an asteroid binary system,” that is, an asteroid with a small partner asteroid, or moon, Michel said. The European craft is to join a NASA spaceship called the Double Asteroid Redirection Test in visiting the Didymos asteroid and its small satellite, nicknamed “Didymoon.” The European part of the mission “will study the structure of Didymoon and the orbit and rotation of the binary system, providing clues to its origin and evolution,” Michel said. “Asteroids represent different stages in the rocky road to planetary formation, so offer fascinating snapshots into the Solar System’s history.” After the machine has studied both asteroids and mapped Didymoon, the U.S. probe is to hit Didymoon, and the European craft would assess its effectiveness in changing the moon’s orbit around Didymos. Scientists discussed the AIDA mission Sept. 30 at the European Planetary Science Congress 2015 in Nantes, France. The European part of the mission is planned for launch in 2020 and for rendezvous with the asteroid system two years later. Binary systems make up an estimated 15% of the asteroid population. The egg-shaped Didymoon, estimated as 160 meters (170 yards) wide, orbits the diamond-shaped Didymos asteroid, which is almost five times wider, every half an Earth-day at a distance of 1.1 km (0.7 miles). While small, Didymoon is already an estimated eight times wider than than the space rock that burst over Chelyabinsk, Russia Feb. 15, creating a shock wave that sent over a thousand people to the hospital. The speed of an object matters too, of course, not just its size. Ground-based observations indicate that, like the Chelyabinsk meteor, Didymos is probably a common “chondrite,” or stony asteroid formed of dust from the primitive solar system. Didymoon’s weight and compactness are unknown. The European spacecraft is to photograph the moon, study its interior using radar and deploy a small lander to exchange radio signals through Didymoon to investigate the internal structure. Recent missions have shown that asteroids are extraordinarily diverse in their geology, structure and evolution. All seem to be covered by soil, but this varies from fine grains to pebbles. Most asteroids seem to be aggregates of material, rather than solid bodies, but it’s not clear whether they’re filled with large rocks and pockets of empty space, or gravel.