Science case for the Asteroid Impact Mission (AIM): A component of the Asteroid Impact & Deflection Assessment (AIDA) mission

Abstract

The Asteroid Impact & Deflection Assessment (AIDA) mission is a joint cooperation between European and US space agencies that consists of two separate and independent spacecraft that will be launched to a binary asteroid system, the near-Earth asteroid Didymos, to test the kinetic impactor technique to deflect an asteroid. The European Asteroid Impact Mission (AIM) is set to rendezvous with the asteroid system to fully characterise the smaller of the two binary components a few months prior to the impact by the US Double Asteroid Redirection Test (DART) spacecraft. AIM is a unique mission as it will be the first time that a spacecraft will investigate the surface, subsurface, and internal properties of a small binary near-Earth asteroid. In addition it will perform various important technology demonstrations that can serve other space missions.The knowledge obtained by this mission will have great implications for our understanding of the history of the Solar System. Having direct information on the surface and internal properties of small asteroids will allow us to understand how the vaious processes they undergo work and transform these small bodies as well as, for this particular case, how a binary system forms. Making these measurements from up close and comparing them with ground-based data from telescopes will also allow us to calibrate remote observations and improve our data interpretation of other systems. With DART, thanks to the characterization of the target by AIM, the mission will be the first fully documented impact experiment at asteroid scale, which will include the characterization of the target's properties and the outcome of the impact. AIDA will thus offer a great opportunity to test and refine our understanding and models at the actual scale of an asteroid, and to check whether the current extrapolations of material strength from laboratory-scale targets to the scale of AIDA's target are valid. Moreover, it will offer a first check of the validity of the kinetic impactor concept to deflect a small body and lead to improved efficiency for future kinetic impactor designs. This paper focuses on the science return of AIM, the current knowledge of its target from ground-based observations, and the instrumentation planned to get the necessary data.

On the Delivery of DART-ejected Material from Asteroid (65803) Didymos to Earth

“…The Jet Propulsion Laboratory (JPL)'s Solar System Dynamics site 1 lists it as a near-Earth object (NEO, indicating that its perihelion distance lies within 1.3 AU of the Sun) and a Potentially Hazardous Asteroid (PHA, indicating that it poses at least a hypothetical danger of impact, having an Earth MOID less than 0.05 AU and an absolute magnitude H less than 22.0 (Atkinson et al 2000;Stokes et al 2003)) 2 . The Didymos primary itself has H = 18.2 and a diameter of 780 meters (Michel et al 2016).…”

“…The Didymos asteroid pair consists of a primary with a diameter of 780 m, and a 163 m diameter secondary; their individual centers of mass are separated by 1.18 km and their orbital period is 11.92 hours (Michel et al 2016). Material released from Didymos' secondary (informally known as 'Didymoon' e.g.…”

“…Material released from Didymos' secondary (informally known as 'Didymoon' e.g. Michel et al (2016)) by the DART impactor can be expected to show a range of behaviors. Ejecta with speeds less than the escape speed from Didymos (about 1 m/s, Michel et al (2016)) can be expected to remain in orbit around the asteroid and/or re-impact one of the members of the binary.…”

Direct observations of asteroid interior and regolith structure: Science measurement requirements

“…More than 700 near Earth asteroids have been observed by Arecibo and Goldstone radars at 2.4, 7.2 and 8.6 GHz (https://echo.jpl.nasa.gov/asteroids/PDS.asteroid.radar.history.html; Naidu et al, 2016;Slade et al, 2011). The most prominent results consist of orbit, spin vector and shape (Magri et al, 2007) and allow inference of internal structures, e.g from diamond shapes or binary systems (Ostro et al, 2006;Fang and Margot, 2012).…”

“…In the context of the 5 th Medium Class (M5) ESA Cosmic Vision call, the Castalia mission to a Main-belt Comet (Snodgrass et al, 2017), the Heavy Metal mission to Psyche (Wahlund et al, 2016) and the MarcoPolo-M5 sample return mission to a D-type asteroid (Franchi et al, 2017), each include an instrument aimed at internal structure measurements. Such an instrument was also considered for the AIDA technology demonstration mission, composed of a kinetic impactor DART (NASA, Cheng et al, 2016) and of an observing spacecraft AIM (ESA, Michel et al, 2016) to test a deflection scenario and to study the binary near-Earth asteroid system, 65803 Didymos. Unfortunately, the European AIM component was not funded by ESA Member States during the Ministerial council in 2016.…”