Asteroids cannot be resolved by ground-based telescopes due to the Earth's atmosphere and their inherently small dimensions. To get detailed physical information about an asteroid, we need some way to resolve it, to obtain the shape, size and spin state, and to constrain the surface composition. Since spacecraft missions are not possible for a large number of objects, I have been working with radar imaging, optical lightcurves, and adaptive optics techniques. Collaborators on this include Steve Ostro, Lance Benner, and Jon Giorgini at JPL, Chris Magri at the University of Maine, Mike Nolan at Arecibo, Shri Kulkarni at Caltech, Petr Pravec at the Czech Academy of Science, and Dan Scheeres at the University of Michigan.

I am currently working on the near-Earth asteroid 29075 (1950 DA), which was observed by radar and optical telescopes in 2001. I have also studied asteroids 10115 (1992 SK), 2000 PN9, and 105 Artemis and assisted with observations of several other targets, including 99942 Apophis and 2004 XP14, which was also just barely resolved by adaptive optics on Keck. A full list of radar targets is maintained at the Asteroid Radar Group website. Radar images provide size, shape and rotation state information, while optical lightcurves can be very useful in combination with good radar data. If we have sufficient radar and optical data, we can construct a unique physical model of an object, including the pole direction and constraints on surface composition as well as the shape of the object:

Collage of six orthogonal views of the best present model of asteroid 10115 (1992 SK). The z-axis is the asteroid's spin axis. Yellow shading denotes areas that were not seen by the radar or the optical observations, or were seen at incidence angles greater than 60 degrees. The shape in this area is poorly constrained.

The shape of an asteroid, combined with its composition and spin state, tells us about its history: a fast-spinning oblate spheroid rubble-pile implies a much different history than an angular shard from a large asteroid being catastrophically disrupted. There are also potentially practical reasons to understand the physical properties of asteroids, which may be summarized as fear and greed.

Fear comes from the asteroid impact hazard. To predict where an asteroid, such as 1950 DA, will be in a century to within a hundred thousand kilometers, we need to know the physical properties of the object in order to compute the magnitude of such things as the Yarkovsky acceleration. In the case of 99942 Apophis, the unknown physical properties of that object cause uncertainties in the trajectory which are drastically magnified by the 2029 close approach.

Greed is not yet a particularly good motivation for asteroid research, but may become so in the future. Nickel-iron meteorites contain relatively high fractions of platinum-group metals and numerous people have suggested mining nickel-iron asteroids for profit. I estimate that current technology is just capable of doing so, provided we know which asteroid to go to. Since radar gives constraints on near-surface bulk density, it can distinguish between metallic and non-metallic objects remotely and relatively cheaply. Metallic objects are rare, however, with only four to six in the present sample of ~300 radar targets.

Busch, M.W., S.J. Ostro, L.A.M. Benner, J.D. Giorgini, R.F. Jurgens, R. Rose, C. Magri, P. Pravec, D.J. Scheeres and S.B. Broschart. 2006. Radar and optical observations and physical modeling of near-Earth asteroid 10115 (1992 SK), Icarus, 181 145-155.

Busch, M.W. 2006. Feasibility of Asteroid Mining, Society of Economic Geologists Newsletter, April 2006.

Shepard, M.K., J. Schlieder, B. Estes, C. Magri, M. C. Nolan, J.-L. Margot, S. J. Bus, E. L. Volquardsen, A. Rivkin, L.A.M. Benner, J. D. Giorgini, S. J. Ostro and M. W. Busch. 2006. Radar, optical, and thermal observations of binary near-Earth asteroid 2002 CE26, Icarus, 184 198-210.

Busch, M.W., S.J. Ostro, L.A.M. Benner, J.D. Giorgini, C. Magri, E.S. Howell, M.C. Nolan, A.A. Hine, D.B. Campbell, I.I. Shapiro, J.F. Chandler. 2006. Arecibo Radar Observations of Phobos and Deimos, Icarus, 186 581-584.

Busch, M.W., S.R. Kulkarni, A.R. Conrad, P.B. Cameron. 2007. Keck adaptive optics imaging of near-Earth asteroid 2004 XP14, Icarus, 189 589-590.

Busch, M.W., J.D. Giorgini, S.J. Ostro, L.A.M. Benner, R.F. Jurgens, M.D. Hicks, P. Pravec, P. Kusnirak, M.J. Ireland, D.J. Scheeres, S.B. Broschart, C. Magri, M.C. Nolan, A.A. Hine. 2007. Physical modeling of near-Earth asteroid (29075) 1950 DA, Icarus, 190 608-621.

Giorgini, J.D., L.A.M. Benner, S.J. Ostro, M.C. Nolan, M.W. Busch. 2008. Predicting the Earth encounters of (99942) Apophis, Icarus, 193 1-19.

Busch, M.W., L.A.M. Benner, S.J. Ostro, J.D. Giorgini, R.F. Jurgens, R. Rose, D.J. Scheeres, C. Magri, J.-L. Margot, M.C. Nolan, A.A. Hine. 2008. Physical Properties of near-Earth asteroid (33342) 1998 WT24, Icarus, in press

Busch, M.W., O. Aharonson. 2008. Measuring subsurface water distribution using the Dynamic of Albedo Neutrons instrument on Mars Science Laboratory, submitted to JGR.

Benner, L.A.M., J.D. Giorgini, S.J. Ostro, R.F. Jurgens and M.W. Busch, IAU Circular 8589: 2005 OE3

Giorgini, J.D., L.A.M. Benner, S.J. Ostro, M.C. Nolan and M.W. Busch, IAU Circular 8593: (99942) Apophis

Benner, L.A.M, J.D. Giorgini, S.J. Ostro, M.C. Nolan and M.W. Busch, IAU Circular No. 8711: (99942) Apophis

Benner, L.A.M, S.J. Ostro, J.D. Giorgini, M.W. Busch, R. Rose, M.A. Slade, R.F. Jurgens, M.C. Nolan, A.A. Hine, G.J. Black, L.M. Carter, IAU Circular No. 8826: 2006 VV2

Busch, M.W., and R.L. Lysak. Auroral Ion Acceleration by Alfven Waves, SM21A-0450, 2004 Fall AGU Meeting, San Francisco, CA, USA.

Busch, M.W., S.J. Ostro, L.A.M. Benner, J.D. Giorgini, R.F. Jurgens, C. Magri, P. Pravec, D.J. Scheeres and S.B. Broschart. Radar observations and physical modeling of near-Earth asteroid 10115 (1992 SK), 2005 DPS Meeting, Cambridge, UK.

Busch, M.W., J.D. Giorgini, S.J. Ostro. L.A.M. Benner, R.F. Jurgens, R. Rose, P. Pravec, D.J. Scheeres, S.B. Broschart, C. Magri, M.C. Nolan, A.A. Hine. Physical Modeling of Near-Earth Asteroid 29075 (1950 DA), 2006 DPS Meeting, Pasadena, CA, USA.

Benner, L.A.M., S.J. Ostro, J.D. Giorgini, M.W. Busch, R. Rose, J.S. Jao, R.F. Jurgens. Radar Observations of Asteroid 2004 XP14: an Outlier in the Near-Earth Population, 2006 DPS Meeting, Pasadena, CA, USA.

Benner, L.A.M., M.W. Busch, M.C. Nolan, S.J. Ostro, J.D. Giorgini, R. Rose, J.S. Jao, G.J. Black, L.M. Carter, M.A. Slade, R.F. Jurgens, and A.A. Hine. Radar Images of Binary Near-Earth Asteroid 2006 VV2, Seventh Catastrophic Disruptions Workshop, Alicante, Alicante province, Spain, June 26-29 2007; 2007 DPS Meeting, Orlando, FL, USA.

Cook, A. M., M.K. Spencer, M.S. Avnet, J.A. Bonetti, K.L. Bryson, M.W. Busch, S.Y. Cheng, Z.A. Crawford, J.E. Edmunson, E.G. Fahnestock, C.R. Fuse, C.J. Hardgrove, C.A. Hier-Majumder, N.M. Johnson, J.A. Mikucki, L.J. Son, S.A. Wilson. SCREAM (Subsurface Characterization Rover for Exobiology Assessment on Mars), 2006 DPS Meeting, Pasadena, CA, USA; 2006 Fall AGU Meeting, San Francisco, CA, USA; 2007 EGU Conference, Vienna, Austria.

Busch, M.W., N.G. Heavens. B.J. Butler, S.R. Kulkarni, I.J. McEwan, M.I. Richardson. Mars' L-Band Radio Emission, 2007 DPS Meeting, Orlando, FL, USA.

Heavens. N.G., I.J. McEwan, M.W. Busch, C.E. Newman, M.I. Richardson. Modeling and Implications of Exotic Martian Radio Emission, 2007 DPS Meeting, Orlando, FL, USA.

Giorgini, J.D., L.A. Benner, S.J. Ostro, M.C. Nolan, M.W. Busch. The Earth Encounters of Apophis in 2029 and 2036, 2007 DPS Meeting, Orlando, FL, USA.