2005 AMOS Technical Conference Abstract
Synthetic Lightcurve Signatures of Unresolved Objects: A Comparison with
Observations
Eileen V. Ryan1, William H. Ryan2, Carlos T. Martinez3, and Louis Blackwell4
Correspondence author: Eileen V. Ryan
Titles/Affiliations:
1
Magadalena Ridge Observatory
Project Scientist/Manager, 2.4 meter Telescope Project
New Mexico Institute of Mining and Technology
801 Leroy Place
Socorro, New Mexico 87801
(505) 835-6803
(505) 835-6807 (FAX)
eryan@mro.nmt.edu
2
Magadalena Ridge Observatory
Research Faculty, 2.4 meter Telescope Project
New Mexico Institute of Mining and Technology
801 Leroy Place
Socorro, New Mexico 87801
(505) 835-6646
bryan@nmt.edu
3
University of New Mexico
Graduate Student, Department of Physics and Astronomy
Albuquerque, New Mexico 87131
(505) 835-6646
ctmtz@yahoo.com
4
Research Scientist, NMIMT
AFRL/VSY Civ-IPA
3550 Aberdeen SE, Bldg 423
Kirtland AFB, NM 87117-5776
(505) 853-6742
blackie64@earthlink.net
Category: Non-Resolved Object Characterization; not restricted.
Abstract:
The temporal brightness variations (i.e., “lightcurves”) of unresolved targets such as
asteroids and artificial satellites can be used to develop a powerful tool for general
characterization studies. This information is obtainable with modest instrumentation,
including off-the-shelf commercial telescopes. Analysis of these temporal signatures
permits the extraction of shape, rotation period, and pole orientation for asteroids, and
may provide shape, general health status, and attitude configuration for artificial objects.
In particular, a tri-axial ellipsoid model has proven to be very reliable in determining the
relative dimensions of large asteroids from the inversion of lightcurve signatures
(Drummond et al. 1988). Although the extension of this inversion process to the more
complex shapes of smaller asteroids and artificial satellites provides additional
challenges, especially when the target’s shape has non-convex features, techniques are
being developed to address this as well (Ďurech and Kaasalainen 2003; Lambert et al.
2004). However, in general, the problem of inverting lightcurve data to determine a
unique shape remains a challenging task for irregularly shaped objects.
In this analysis, we build on the large body of work done in the context of asteroid
studies, and investigate an iterative approach to the identification and characterization of
unresolved targets. We have developed a synthetic lightcurve direct model assuming that
the resulting lightcurve is a deterministic function of the target’s physical parameters and
the observer’s viewing geometry, and can therefore provide a definitive lightcurve even
for the most complex objects. This model can be used to construct a library of lightcurve
signatures for a variety of sample objects which, in turn, can be used to provide initial
guesses for the input parameters to an inverse model. The resulting inverse-predicted
shape is then put back into the direct model, compared with observations, and refined as
needed.
We present the results of applying this technique to both asteroid and artificial satellite
targets. In particular, we demonstrate how this has allowed us to identify the existence of
a binary companion to the main belt asteroid 3782 Celle (Ryan et al. 2004). We then
compare the accuracy of model predictions from data obtained with meter-class
telescopes and a portable, 0.35-meter commercially available instrument. As part of this
research, we plan to build upon the single-site lightcurve inversion work reported in
Lambert et al. (2004) by acquiring and analyzing simultaneous lightcurve observations of
selected low Earth orbiting targets from multiple sites having differing viewing
geometries.
References
Drummond, J. D., S. J. Weidenschilling, C. R. Chapman and D. R. Davis, 1988,
Photometric geodesy of main-belt asteroids. II - Analysis of lightcurves for poles,
periods, and shapes, Icarus 76, 19-77.
Ďurech, J. and M. Kaasalainen, 2003, Photometric signatures of highly nonconvex and
binary asteroids, Astronomy and Astrophysics, 404, 709-714.
Lambert, J., K. Luu, and E. Brevdo, 2004, Direct inversion of visible and infrared
signatures, Proceedings of the 2004 AMOS Technical Conference, Hawaii.
Ryan,W.H., E. Ryan, and C. Martinez (2004). 3782 Celle: Discovery of a Binary System
within the Vesta Family of Asteroids. Planetary and Space Science, 52, 1093 -1101.
Short Biography of Presenting Author
Eileen V. Ryan is currently a Research Scientist and Adjunct Faculty at New Mexico
Institute of Mining and Technology for the Magdalena Ridge Observatory Project,
serving as the Project Scientist and Project Manager of the 2.4-meter Single Telescope
initiative. Previously, she was a tenured member of the Physics faculty at New Mexico
Highlands University, and a Research Scientist affiliated with the Planetary Science
Institute in Tucson, Arizona. She completed her Ph.D. at the University of Arizona,
Tucson, in 1992. She also has a M.S. degree in Astronomy from New Mexico State
University, and a B.A. in Physics from Rutgers University. Her research work includes
theoretical and experimental studies of small body collisions in the solar system, microbe
survivability during collisional events, and telescopic observations of asteroids. She has
been successful in securing funding for these programs, has served on senior review
panels for NASA and the National Science Foundation (NSF), and has refereed papers
for journals such as Icarus, Nature, Planetary and Space Science, the Astronomical
Journal, and the Journal of Geophysical Research. She currently has 24 published papers
and 47 meeting abstracts, including 3 review papers in her field of expertise. Asteroid
(9542) ERYAN = 1983 TU1 has been named in her honor, and she has made several
television appearances discussing her research, most recently appearing on the Canadian
Discovery channel detailing her work in astrobiology.
Selected Recent Publications:
Ryan, E.V., and W.H. Ryan (2004). Asteroid Physical Characterization Studies and its
Relation to the Hazard Mitigation of NEOs. Proceedings of the 2004 AMOS Technical
Conference, Hawaii.
Giblin, I., D.R. Davis, E.V. Ryan (2004). On the Collisional Disruption of Porous Icy
Targets Simulating Kuiper Belt Objects. Icarus 171, 487 - 505.
Ryan,W.H., E. Ryan, and C. Martinez (2004). 3782 Celle: Discovery of a Binary
System within the Vesta Family of Asteroids. Planetary and Space Science, 52, 1093 1101.
Asphaug, E., E.V. Ryan, and M. Zuber (2002). Impact Structures and Asteroid Interiors.
In Asteroids III (William Bottke, Alberto Cellino, Paolo Paolicchi, and Richard P.
Binzel, eds. Univ. of Arizona Press).
Holsapple, K., K. Housen, E.V. Ryan, and I. Giblin (2002). Asteroid Impacts:
Laboratory Experiments and Scaling Laws. In Asteroids III (William Bottke, Alberto
Cellino, Paolo Paolicchi, and Richard P. Binzel, eds. Univ. of Arizona Press).
Ryan, E.V. (2000). Asteroid Fragmentation and Evolution of Asteroids. Ann. Rev. Earth
Planet. Sci., 28, 367-389.
Ryan, E.V., D.R. Davis, and I. Giblin (1999). A Laboratory Impact Study of Simulated
Edgeworth-Kuiper Belt Objects. Icarus, 142, 56-62.
Ryan, E.V., and H.J. Melosh (1998). Impact Fragmentation: From the Laboratory to
Asteroids. Icarus 133, 1-24.
Melosh, H.J., and E.V. Ryan (1997). Asteroids: Shattered but not Dispersed. Icarus,
129, 562.