45th Lunar and Planetary Science Conference (2014) 1 1571.pdf

Binary Asteroid in-situ Explorer Mission (BASiX): A Mission Concept to Explore a Binary Near Earth Asteroid System, Robert. C. Andersona, Daniel Scheeresb, Steven Chesleya, and the BASiX Science Team, aJet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, bUniversity of Colorado Boulder, CO 80203, Department of, USA, [email protected]

Motivation: The Binary Asteroid in-situ both spatially and temporally. They were Explorer (BASiX) Mission will actively probe present in the early solar system when proto- the geophysics of a near-Earth Asteroid (NEA) planetary materials were interacting with each in a controlled and repeatable manner. BASiX other forming the initial planetesimals [2] and will make the first quantitative measurements of continue to be present today in planetary rings an asteroid’s strength and seismic properties, [3] and on the surfaces and interiors of asteroids and be the first to explore a binary asteroid and comets [4]. In these micro-gravity system’s mass morphology. environments, physical phenomena other than gravity, such as van der Waals and electrostatic Introduction: In the decade since the NEAR forces, may play a crucial or even dominant role mission explored Asteroid 433 Eros, ground- for the mechanics of solar system aggregates [5]. based and spacecraft observations of Near-Earth The direct study of micro-gravity physics on an and small main belt asteroids (NEAs and MBAs) asteroid surface – the best attainable physical have caused a profound shift in our analogue of early planetesimals – would understanding of these bodies: 1) NEAs are revolutionize our understanding of aggregate “rubble-piles,” aggregates of components mechanics in all of the realms they inhabit forming a size distribution ranging from micron- across the solar system. sized particles to decameter-sized boulders, 2) NEA surfaces are driven by seismic phenomena This lack of knowledge about the strength, and change by regolith migration, segregation, cohesion, and seismic properties of asteroids and space weathering processes, 3) NEAs also limits our ability to plan and prepare for commonly split apart to form new asteroids that future exploration missions. Such information either escape from each other or form stable has been idenfitied by NASA as key Strategic binary systems, and 4) the geophysics of rubble Knowledge Gaps crucial for the exploration of pile bodies are expected to be fundamentally these bodies. This information is also different than planetary bodies [1]. fundamental for the development of mitigation technologies to divert hazardous asteroids. Despite the clear evidence that small asteroids undergo drastic physical evolution, the Until we can address this gap in our science, our geophysics and mechanics of these processes understanding of asteroids as physical bodies remain a mystery due to a lack of scientific data will remain at a crossroads with fundamental on the mechanical properties of small asteroids questions concerning them remaining open. in the unique micro-gravity regime they inhabit, What is a Rubble Pile Asteroid? A rubble pile on their mass distribution and morphology, and asteroid is an object that is not made up of a on their sub-surface and global geophysics. single piece of rock, but consists of numerous Previous explorations of NEAs stopped at smaller particles (a size distribution of boulders remote observation or sample capture, and did and grains that extends from microns to not take the next step: direct interaction to decameters). These are rock fragments that have measure how an asteroid responds to its coalesced following catastrophic collisions environment. This has led to a profound gap in between larger asteroids. Rubble pile asteroids our knowledge of asteroid geophysics that were first identified because they have low BASiX will address. density (high porosity), presumably due to a The implications of the BASiX investigations go high number of voids. Many of the calculated beyond understanding rubble pile asteroids. The densities for this family of asteroids were interaction of aggregates in micro-gravity significantly less than those identified for settings has occured throughout the solar system, meteorites, which in some cases where 45th Lunar and Planetary Science Conference (2014) 21571 .pdf

determined to be pieces of specific asteroids by spectra across its surface and subsurface their chemical and spectral analysis. Such high Target Selection: 1996 FG is a primitive Near- porosities may be sustained by weak molecular 3 Earth minor planet in the Apollo Group. 1996 cohesive forces between components of the size FG is an accessible binary asteroid that was distribution, which can become dominant in this 3 previously the target for both the JPL/APL microgravity environment. Galahad and Marco-Polo-R sample return BASiX Objectives: BASiX addresses missions. It is well characterized in terms of fundamental questions concerning asteroids and size, spin and orbit and has also been mapped aggregates in micro-gravity environments by spectrally and found to be heterogeneous with focusing on two main scientific goals: 1) significant spectral variations [6]. Understanding the unique geomorphology, The BASiX Team: BASiX is a joint proposal dynamics, and evolution of a binary Near-Earth between the University of Colorado, JPL and asteroid, and 2) Determine the strength, seismic, Ball Aerospace, and has significant and space weathering properties of the surface contributions from CNES. The PI is Dan and sub-surface of a Near-Earth asteroid. Scheeres (CU), the Deputy-PI is Steve Chesley Science Implementation Goals: To carry out (JPL), and the Project Scientist is Bob Anderson these objectives BASiX will focus on carrying (JPL). The Science Team has eminent scientists out clear and simple experiments in this novel from across the globe, who are well prepared to environment: implement and execute the fundamental investigations that are envisioned. • Explain and explore the unique global morphology of binary asteroids by carrying out detailed imaging and tracking campaigns SUMMARY: The BASiX mission will perform in the binary system the first geophysics science exploration of a • Quantify the strength and cohesion of an primitive asteroid system. It will open a new asteroid surface by detonating calibrated blasts understanding on the evolution aggregates in the solar system, enable future exploration of on the surface and characterizing the surface asteroids, and provide key information necessary and subsurface response for the mitigation of hazardous asteroids. • Constrain and measure the seismic properties of a small solar system body by sensing REFERENCES: [1] Goldreich & Sari, ApJ calibrated experiments with surface packages 691, 2009. [2] Johansen et al., Nature 448, 2007; • Explore the fundamental geophysics of a Cuzzi et al., ApJ 687, 2008. [3] Esposito, Ann. Rev. EPS 38, 2010. [4] Fujiwara et al., Science rubble pile body by characterizing the rate at 312, 2006; Miyamoto et al., Science 316, 2007. which tides dissipate energy [5] Scheeres et al., Icarus 210, 2010. [6] Binzel • Explore space weathering and compositional et al., LPI Abstract 43: 2222, 2012; deLeon et al., A&A 530, 2011; Rivkin et al., LPI Abstract heterogeneity on the surface and interior of a 43:1537, 2012. rubble pile asteroid by mapping colors and

Binary Asteroid 1996 FG3 as seen by the Arecibo Observatory in 2011 (L.A.M. Benner, private communication)