NMT Pilot Project
Statement of Work
06-09-05
Title: Synthetic Lightcurve Signatures of Unresolved Objects: A Comparison with
Observations
Period of Performance: June 2005 – May 2006
Total Budget (actual, in-kind, & matching funds): $200,000
Principal Investigator: Eileen V. Ryan, Ph.D.
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
Co-Investigator: William H. Ryan, Ph.D.
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
1
TABLE OF CONTENTS
Synthetic Lightcurve Signatures of Unresolved Objects: A Comparison with Observations
Proposal Cover Page……………………………………………………………………. 1
Table of Contents………………………………………………………………………. 2
Statement of Work……………………………………………………………………...
3
Expected Milestones & Accomplishments ……………………………………………
6
References ……………..………………………………………………...…………….
7
Short Biography: Principal Investigator …………………….………………………... 8
Budget Details/Matching Funds ………………………………………………………... 9
2
STATEMENT OF WORK
INTRODUCTION
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.
PREVIOUS WORK
Observational Studies
During the first funded stage of this project, 81 nights of observing time were awarded using
the 1.8-meter Vatican Advanced Technology Telescope (VATT). Over this time phase,
periods were determined for 15 Vesta family members, and for 6 of these chips we obtained
3
multi-apparition data. Partial lightcurves were obtained for an additional 15 asteroids.
Lightcurve rotation periods range from very short (~2.4 hours) to greater that 10 hours. A
typical lightcurve indicating the quality of data obtained is shown in Figure 1. The
lightcurves have also displayed peak-to-trough variations that vary from very simple to quite
complex (Figure 2, asteroid 3155 Lee). As yet, no sub-two-hour periods (which would
definitively imply a monolithic rather than rubble-pile fragment) or period-to-period
variations (which would imply 'tumbling', and hence put an upper limit on the age of the
Vesta family) have been observed.
Figure 1. Composite lightcurve for 1933 Tinchen. Error bars indicate both photon noise and
photometric scatter of the comparison stars.
Figure 2. Lightcurve data for asteroid 3155 Lee showing an example of complex peak-to-trough
variations. The rotation rate for this Vesta chip is 8.310 hours.
Shape Inversion
Asteroid lightcurves can traditionally provide three important pieces of information: rotation
rate, spin axis orientation, and shape. Determining an asteroid's spin rate is straightforward:
its reflected light is recorded as the asteroid proceeds along its orbital path, and a cycle of its
rotation becomes evident as the light intensity dips and peaks in a clear pattern. Spin axis
4
orientation and shapes, however, are somewhat more difficult to discern, but reliable
methods have been developed (Kaasalainen et al., 2002). By comparing shapes computed for
951 Gaspra using lightcurve-based data with those determined from Galileo spacecraft
images, Barucci et al. (1992) have shown that available lighcurve inversion techniques are
very successful. Their groundbased shape analysis was accomplished using three lightcurves
obtained at ecliptic longitudes of 60°, 230°, and 31°. A similar pre-Galileo shape
determination for Gaspra was performed by Magnusson et al. (1992) using the above
lightcurves plus one recorded at 10° ecliptic longitude. From these studies, it was shown that
an accurate shape determination is possible with a minimum of two lightcurves recorded 90°
apart in ecliptic longitude. More recently, Kaasalainen et al. (2001) have developed a
polyhedron inversion technique that yields relatively detailed models of the convex features
of asteroid shapes. However, this technique requires considerably more lightcurve data as
input.
The observational portion of this proposal is centered on the continuation of the CCD
photometric survey to perform a spin-rate and shape analysis of the asteroids in the Vesta
family. The specific goals include the following:
1) Obtain data for a total of three apparitions for the 15 objects that already have
one or more complete lightcurves.
2) Obtain additional data at various phase angles for at least three objects.
3) Utilize the rotational rate estimates obtained by our partial coverage of the 15
additional targets (mostly slow rotators) to strategically plan observations of
these asteroids.
4) Modify current observing strategy of faster rotators to include longer coverage
in an attempt to identify any additional binary systems.
5) Perform an extended study of 3782 Celle during its 2004 apparition.
6) Scan all images for new asteroids and perform follow-up astrometry if
observing time permits.
Item 1 should allow us perform a first estimate of the shapes for at least 15 Vesta chips. Item
2 will be needed to develop an amplitude-phase relationship for Vesta-type asteroids that will
be needed to effectively utilize some of our higher phase angle data. Depending on the
quality of the resulting curve, it is also possible that this will provide information regarding
the surface characteristics of typical Vesta-like asteroids. Item 3 will allow us to determine
spin rates for many of the slower rotating Vesta chips that are not in our shape analysis
priority list. Item 4 represents the lesson learned by the discovery of a binary system during
the first phase of the project. Item 5 will allow us to develop a more detailed model of the
3782 Celle binary system. Finally, Item 6 is just a routine procedure that will be performed
having the by-product of contributing to the catalog of known asteroids.
5
The challenging task to be undertaken is the determination, or at least constraint, of the
shapes of the Vesta-family asteroids and their spin axis orientation. Under the most ideal
geometric circumstances, a minimum of two lightcurves, obtained 90º apart in ecliptic
longitude is required to determine the asteroid's shape. However, as pointed out previously
by the reviewers, it is highly unlikely that the observer would stumble upon the 'right'
geometric conditions that would make this possible. The renewal of this proposal would
facilitate the acquisition of lightcurves for an additional two apparitions of our targets that
already have at least one complete lightcurve - resulting in 3-4 apparitions worth of data for
these objects. This should permit at least a preliminary tri-axial ellipsoid shape model and
spin axis determination to be performed for 15 of the Vesta chips during the period of
performance of this grant.
Lightcurve inversion techniques have matured considerably (Kaasalainen, et. al., 2002) since
this survey was initially undertaken. In particular, a convex polyhedron inversion technique
has been developed that has need successful in developing rather detailed asteroid shape
models from lightcurve data (Kaasalainen, et. al., 2001). However, this technique generally
works best for objects with data from four or more apparitions and at a variety of solar phase
angles. Although this level of data coverage might be achieved for a few of our targets, we
will in general concentrate on getting one (composite) lightcurve per apparition for each
object, permitting the use of traditional amplitude-aspect modeling techniques (Drummond,
et al., 1988). Although this method will result in a cruder, triaxial ellipsoid model, it will
yield spin axis orientations and facilitate the acquisition of data for more objects. This should
provide the first indication of whether our Vesta members are spalls or not, and form a basis
for a more detailed shape study in the future.
April 20, 2005
Memorandum For the Record
Subject: AFRL Phillips Research Site and NMT Magdalena Ridge Observatory Joint Project – Light Curve
Inversion Pilot Study
Background
The New Mexico Institute of Mining and Technology (NMT), Magdalena Ridge Observatory (MRO) will
include two instruments: (a) a 2.4m telescope with rapid tracking capability and (b) a multi-aperture optical
interferometer. Language in congressional appropriations for MRO requires that the facility be of use both in
scientific applications in astronomy and to the Department of Defense, including applications in Space Situation
Awareness (SSA.)
During March-April 2005 a survey analysis of applications in SSA for MRO was conducted by a team of
individuals from NMT led by Dr Eileen Ryan and Dr Louis Blackwell. Collaboration with AFRL SSA efforts
was coordinated with Dr Barry Hogge, SSA technology lead for AFRL/DE directorate. The project effort has
identified numerous applications in SSA to which MRO may be able to contribute and has further identified a
joint ‘pilot project’ which shows technical promise of contributing to the state of the art for SSA. Recognizing
that the MRO will be a new facility with no practical background in SSA and the inherent potential security
considerations of observations supporting SSA, this project will provide significant training for the MRO 2.4meter Telescope team in expanding their understanding of SSA.
6
A further benefit of the pilot project is that the MRO team, working with SSA elements of the Air Force, will
explore the structure and functions of becoming a “contributing site” in the SSA community by conducting the
pilot project. This knowledge will be applied when the MRO 2.4m facility comes on line in FY 2007.
The pilot project will also contribute to the state of the art in SSA and extend recent work on ground based
observations of satellites using ‘lightcurve’ inversion – a technique well known in observations of asteroids.
Recent work has investigated the benefit of single location lightcurve signatures of satellites collected over
multiple passes.
The pilot project will extend this work by performing simultaneous observations of the same resident space
objects (RSOs) from differing locations – and combining the resulting lightcurves for inversion. The
observations will be conducted by AFRL sites (SOR and/or AMOS (details to be defined)) in collaboration with
an MRO portable telescope. Analytic prediction of light curves using a direct model will be conducted based
on knowledge of the resident space objects (RSOs) – details on the candidate RSOs will be provided by
AFRL/DE. An available set of light curve prediction tools at NMT will be used in collaboration with
AFRL/DE tools.
The project is anticipated to require as much as a year to complete. If the pilot project proves the merit of
multiple simultaneous observation, then follow on phases are possible. A paper based on the project is already
proposed for presentation at the AMOS Technical Conference (covering SSA topics) in Maui September 5 - 9,
2005.
7
EXPECTED ACCOMPLISHMENTS AND MILESTONES
-Identified a research project for a new satellite characterization method
-Simultaneous observation by multiple sites
-Apply well known ‘light curve inversion’ from asteroid research
(Builds on recent single site ‘light curve inversion’ results by Lambert, et al)
-Proposed as a joint AFRL/MRO SSA project
Conduct pathfinder experiment using 14” Meade telescope to establish credible approach
to Light Curve inversion
-Estimate light collection based on satellite signature model
-Collect measurements in collaboration with SOR
Phase I
-Choose a RSO for experiment with 14” instrument
-Estimate light curve inversion results
-Extrapolate performance expectations for MRO instrument
-Collaborative measurement simultaneous with SOR
-Comparison between measurements and model
Demonstrate potential for meeting SSA goals of satellite characterization
Develop operational concepts and procedures for 2.4m
Pilot Project will:
-- Analytically investigate shapes and light curve inversion
-- Select known satellites/objects for data collection
-- Obtain simultaneous “lightcurves” with 14” Meade Telescope and additional sites
(SOR/AMOS)*
-- SOR obtain simultaneous AO images on selected observations (for ground truth)
-- Acquire 4-color visible spectrum photometric data
-- Spectroscopy if budget allows
-- Invert lightcurves for shape & pole orientation; evaluate benefit of simultaneous two site
collection
NMT will provide
 Personnel and funding for a twelve month effort and will provide an available Meade telescope as one
of the observing instruments to gather data on resident space objects.
 Analytic tools to predict light curves and analysis and inversion of gathered light curve information
 Project leadership – Dr. Eileen Ryan, MRO
 Project reporting and documentation
8
AFRL will provide





Information and candidate listing of RSOs to be considered for experimental collection
Support by personnel at SOR (e.g., Dr. Jack Drummond)
Support by Personnel at MSSS (e.g., Paul Kervin)
Simultaneous light curve collection in collaboration with the NMT/MRO instrument
If feasible, simultaneous imagery of an RSO during lightcurve collection
9
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.
Kaasalainen, M., S. Mottola, and M. Fulchignoni 2002, Asteroid Models from Disk
Integrated Data, In Asteroids III, (Bottke, W.F., Cellino, A., Paolicchi, P., and Binzel, R. P.,
Eds., University of Arizona Press, Tucson) 139-150
M. Kaasalainen, J. Torppa, and K. Muinonen 2001, Optimization methods for asteroid
lightcurve inversion. II. The complete inverse problem. Icarus 153, 37.
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.
10
SHORT BIOGRAPHY OF PRINCIPAL INVESTIGATOR
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. Proc. 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 EdgeworthKuiper 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.
11
BUDGET DETAIL AND MATCHING FUNDS
New Mexico Tech AFRL/VS Funding:
Direct Costs:
1.
Professional Salaries: (0.45 FTE)
Fringe benefits: (33%)
Subtotal:
= $32,548
= $10,741
= $43,289
2. Travel:
(AMOS Conference, 2 people)
= $ 3,400
3. Equipment:
(Video rate CCD plus associated
Equipment for 14” Meade
Telescope)
= $ 4,000
SUBTOTAL:
=
Indirect Costs:
Overhead (15.6%)
TOTAL (AFRL/VS Funds):
= $50,000
New Mexico Tech Matching Funds:
1. NASA HQ Planetary Astronomy Grant: ''CCD Photometry of the Vesta Family of Asteroids II:
More Lightcurves and a Search for Satellites”
Professional Salaries & Fringe
Graduate Student Support
Travel, Materials, Supplies
SUBTOTAL:
= $54,144
= $12,000
= $ 6,000
= $72,144
2. NASA HQ: "South-West Internet Program for the Enhancement of Minority Education"
Equipment (14” Meade Telescope)
= $ 7,500
3. NMT Tech R&ED:
Administrative support, computer facilities:
= $20,356
TOTAL (NM Tech Matching Funds):
= $100,000
AFRL/DE In-kind Support:
AFRL/MSSS: Salaries and telescope usage:
AFRL/SOR: Salaries and telescope Usage:
=$
=$
12