01 / Contract Profile

80NSSC21M0223 Federal Contract Award

Agency code 8000

MANY OF THE SMALL ASTEROIDS IN THE NEAR-EARTH SPACE (SO-CALLED NEAR-EARTH ASTEROIDS OR NEAS) ARE KNOWN TO BE RUBBLE PILES, I.E. COMPOSED OF A GRANULAR MATERIAL. THE UNDERSTANDING OF THE STRENGTH AND DYNAMICS OF THESE RUBBLE PILES IS STRONGLY LINKED TO UNRAVELING THE MYSTERIES OF THE FORMATION OF OUR SOLAR SYSTEM, SUPPORTING ON-GOING NASA MISSIONS TO SMALL BODIES (E.G. OSIRIS-REX, LUCY), AS WELL AS EVALUATING PLANETARY DEFENSE OPTIONS IN CASE OF AN IMPACT THREAT. IN THE PROPOSED PROJECT, WE AIM AT UNDERSTANDING HOW SEISMIC WAVES TRAVEL THROUGH THESE RUBBLE-PILES, MODIFYING THEIR SHAPES AND SURFACES. IMPACT-INDUCED SEISMIC WAVES ARE A SURFACE MODIFICATION PROCESS THAT IS PARTICULARLY IMPORTANT ON SMALL ASTEROIDS DUE TO THEIR LOW SURFACE GRAVITY AND SMALL VOLUME. SEISMIC DISTURBANCES CAN DESTABILIZE LOOSE MATERIAL RESTING ON SLOPES, CAUSING DOWNHILL FLOWS GENERATE CRATER DEGRADATION AND ERASURE, WHICH IMPACTS SURFACE DATING TECHNIQUES SEGREGATE AND SORT PARTICLES VIA THE BRAZIL NUT EFFECT AND POTENTIALLY LIFT PARTICLES OFF THE ASTEROID SURFACE, GENERATING ACTIVITY AS OBSERVED BY OSIRIS-REX ON ASTEROID BENNU. IN ADDITION, SEISMIC WAVES CAN MODIFY THE SHAPE OF SMALL RUBBLE-PILES, HEIGHTENING EQUATORIAL RIDGES OR GENERATING LOCAL PEAKS. A KEY PARAMETER CHARACTERIZING SEISMIC WAVES IS THEIR TRAVEL SPEED IN A GIVEN MATERIAL, THE SPEED OF SOUND. IN GRANULAR MATERIALS, THIS SPEED OF SOUND HAS BEEN SHOWN TO DEPEND ON THE GRAIN COMPOSITION AND SIZE, AND IN PARTICULAR ON THE FORCE CHAINS DEVELOPING UNDER A CONFINING PRESSURE. FOR THIS REASON, THE SPEED OF SOUND ALSO DEPENDS ON THE AMBIENT GRAVITY LEVEL, WHICH IS ON THE ORDER OF 10-5G, G BEING THE ACCELERATION OF GRAVITY AT THE SURFACE OF THE EARTH, AT THE SURFACE OF SMALL RUBBLE-PILE ASTEROIDS. DUE TO THE ABOVE, IT IS PROPOSED TO DEVELOP AN EXPERIMENT ON THE ISS TO CHARACTERIZE THE SPEED OF SOUND IN HIGH-FIDELITY SIMULANTS REPRODUCING MATERIAL COMPOSING THESE RUBBLE-PILE ASTEROIDS, IN THE RELEVANT GRAVITY CONDITIONS.