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NASA sizing up “weird” asteroid candidates for capture

June 19, 2014
Courtesy of the Jet Propulsion Laboratory
and World Science staff

As­tro­no­mers us­ing NASA’s Spitzer Space Tel­e­scope have meas­ured the sizes of two as­ter­oid “can­di­dates” for NASA’s pro­posed mis­sion to cap­ture a small as­ter­oid, or boul­der from an as­ter­oid. 

The idea is to put it in or­bit around the moon.

Both can­di­date as­ter­oids turned out to be “to be really weird—not at all like the one sol­id rock that we ex­pected. We’re scratch­ing our heads,” said Da­vid Trilling of North­ern Ar­i­zo­na Uni­vers­ity, who leads the team of as­tro­no­mers in the The As­ter­oid Re­di­rect Mis­sion.

In­stead, the as­ter­oids con­sist of about two-thirds emp­ty space, the mea­sure­ments show.

The lat­est can­di­date as­ter­oid meas­ured, called 2011 MD, was meas­ured at roughly 20 feet (6 me­ters) wide. Spitzer’s in­fra­red-light vi­sion was key to siz­ing up the ob­ject. “From its perch up in space, Spitzer can use its heat-sensitive in­fra­red vi­sion to spy as­ter­oids and get bet­ter es­ti­mates of their sizes,” said Mi­chael Mom­mert of North­ern Ar­i­zo­na Uni­vers­ity, lead au­thor of the lat­est stu­dy, ap­pear­ing June 19 in the journal As­t­ro­phys­i­cal Jour­nal Let­ters.

Val­id can­di­dates are as­ter­oids with the right size, weight and spin rate to be fea­sibly cap­tured by a robotic space­craft. Two oth­er “val­id” can­di­dates have been iden­ti­fied so far. Com­bined in­fra­red and visible-light ob­serva­t­ions of the new can­di­date led to a meas­ure­ment of its weight and dens­ity, or com­pact­ness. As­tro­no­mers think it might be a col­lec­tion of loosely bound rocks, like a fleet of fly­ing boul­ders, or a sol­id rock with sur­round­ing fi­ne de­bris.

Sci­en­tists found a si­m­i­lar type of com­po­si­tion for as­ter­oid 2009 BD, anoth­er can­di­date con­sid­ered val­id. Trilling and col­leagues used Spitzer to help pin down the size of that as­ter­oid to roughly 10 to 13 feet (3 or 4 me­ters).

The team said the small as­ter­oids probably formed as a re­sult of col­li­sions be­tween larg­er as­ter­oids, but they don’t un­der­stand how their un­usu­al struc­tures could have aris­en. They plan to use Spitzer to study more of the ti­ny as­ter­oids, both as pos­si­ble tar­gets for as­ter­oid space mis­sions, and for a bet­ter un­der­standing of the many as­ter­oid denizens mak­ing up our so­lar sys­tem.


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Astronomers using NASA’s Spitzer Space Telescope have measured the sizes of two asteroid “candidate” for NASA’s proposed mission to capture a small asteroid, or boulder from an asteroid. The idea is to put it in orbit around the moon. Both candidate asteroids turned out to be “to be really weird—not at all like the one solid rock that we expected. We’re scratching our heads,” said David Trilling of Northern Arizona University, who leads the team of astronomers in the The Asteroid Redirect Mission. Instead, the asteroids consist of about two-thirds empty space, the measurements show. The latest candidate asteroid measured, called 2011 MD, was measured at roughly 20 feet (6 meters) wide. Spitzer’s infrared-light vision was key to sizing up the object. “From its perch up in space, Spitzer can use its heat-sensitive infrared vision to spy asteroids and get better estimates of their sizes,” said Michael Mommert of Northern Arizona University, lead author of the latest study, appearing June 19 in the Astrophysical Journal Letters. Valid candidates are asteroids with the right size, weight and spin rate to be feasibly captured by a robotic spacecraft. Two other “valid” candidates have been identified so far. Combined infrared and visible-light observations of the new candidate led to a measurement of its weight and density, or compactness. Astronomers think it might be a collection of loosely bound rocks, like a fleet of flying boulders, or a solid rock with surrounding fine debris. Scientists found a similar type of composition for asteroid 2009 BD, another candidate considered valid. Trilling and colleagues used Spitzer to help pin down the size of that asteroid to roughly 10 to 13 feet (3 or 4 meters). The team said the small asteroids probably formed as a result of collisions between larger asteroids, but they don’t understand how their unusual structures could have arisen. They plan to use Spitzer to study more of the tiny asteroids, both as possible targets for asteroid space missions, and for a better understanding of the many asteroid denizens making up our solar system.