University of Kent School of Physical Sciences Colloquium Talk 2011

1. Comets: Delving Into the
Heart of the Matter
By Ryan Laird
PhD Supervisor: Dr Stephen Lowry
School of Physical Sciences
Postgraduate Colloquium
Friday 23rd September, 2011 1
Survey of Ensemble Physical
Properties of Cometary Nuclei
(SEPPCoN)
Optical ObservationsOptical Observations

2. SEPPCoN
S. C. Lowry (UKC) (Supervisor)
Y. Fernández (UCF)
M. F. A’Hearn (U-Md)
J. M. Bauer (JPL)
H. Campins (UCF)
A. Fitzsimmons (QUB)
O. Groussin (LAM)
H. Hsieh (QUB)
M. Kelley (U-Md)
P. Lamy (LAM)
J. Licandro (IAC, UL)
C. M. Lisse (JHU/APL)
K. J. Meech (UH-IfA)
J. Pittichová (UH-IfA, AI)
W. T. Reach (Caltech/IPAC)
C. Snodgrass (ESO/MPI)
I. Toth (K. Obs.)
H. A. Weaver (JHU/APL)
P. Weissman (JPL)
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SEPPCoNSEPPCoN
School of Physical Sciences Colloquium 2011
By Ryan Laird
• SEPPCoN (Survey of the Ensemble Physical Properties of Cometary Nuclei)
This is a survey to understand the sizes, albedos, colours, shapes, and spin rates of Jupiter-
Family comets - critical for understanding their origins and evolutionary processes as they
dynamically evolve from the Kuiper Belt.
• Spitzer Large Proposal – 100 hrs – MIPS & IRS imaging obtained during SST Cycle 3,
July 2006 – July 2007
• Ground based optical data (3.5-10m telescopes), ~42 nights – BVRI photometry

3. School of Physical Sciences Colloquium 2011
Ryan Laird
SEPPCoNSEPPCoN –– Ground-Based Optical CampaignGround-Based Optical Campaign (400-790 nm), CCD imaging
ESO – 8.2m VLT
Antu, FORS
(3 nights)
ESO – 3.6m NTT
with
EMMI/EFOSC2
(11 nights)
Apache Point
Observatory ARC 3.5m,
New Mexico (1.5 nights)
2m Robotic
Liverpool
Telescope, La
Palma (0.1 night)
Palomar
Observatory:
5m Hale Telescope
with LFC, California
(14.2 nights)
UH 2.2m (2
nights) and Keck
10m (2 nights),
Mauna Kea
2.6m, Nordic
Optical
Telescope, La
Palma (0.2
nights)
SOAR 4.1m at
Cerro Pachón,
Chile (2.8 nights).
4.2m William
Herschel
Telescope,
La Palma (5
nights)
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4. 4
Jupiter-Family CometsJupiter-Family Comets
Jupiter-Family Comets
• Orbital period < 20 years
• Direct orbits with inclination < 40 degrees
• Most observationally accessible of the comet groups
• Heliocentric distances 3 AU <Rh< 7 AU
• Tisserand parameter, 2 <TJ< 3 => dynamically distinct group.
For a small body with semimajor axis, a, eccentricity, e, and
inclination, i, relative to the orbit of a perturbing larger body
(Jupiter) with semimajor axis aP
School of Physical Sciences Colloquium 2011
Ryan Laird

5. JFCs
6P/d'Arrest
7P/Pons-Winnecke
11P/Tempel-Swift-LINEAR
14P/Wolf
15P/Finlay
16P/Brooks 2
22P/Kopff
31P/Schwassmann-
Wachmann 2
32P/Comas Sola
33P/Daniel
37P/Forbes
43P/Wolf-Harrington
47P/Ashbrook-Jackson
48P/Johnson
50P/Arend
51P/Harrington-A
54P/de Vico-Swift
56P/Slaughter-Burnham
57P/du Toit-Neujmin-
Delporte
62P/Tsuchinshan 1
68P/Klemola
69P/Taylor
74P/Smirnova-Chernykh
77P/Longmore
78P/Gehrels 2
79P/du Toit-Hartley
89P/Russell 2
93P/Lovas 1
94P/Russell 4
101P/Chernykh
107P/Wilson-Harrington
113P/Spitaler
118P/Shoemaker-Levy 4
119P/Parker-Hartley
120P/Mueller1
121P/Shoemaker-Holt 2
123P/West-Hartley
124P/Mrkos
127P/Holt-Olmstead
129P/Shoemaker-Levy 3
130P/McNaught-Hughes
131P/Mueller2
132P/Helin-Roman-Alu 2
137P/Shoemaker-Levy 2
138P/Shoemaker-Levy 7
139P/Vaisala-Oterma
141P/Machholz 2
143P/Kowal-Mrkos
144P/Kushida
146P/Shoemaker-LINEAR
148P/Anderson-LINEAR
149P/Mueller4
152P/Helin-Lawrence
159P/LONEOS
160P/LINEAR
162P/Siding Spring
163P/NEAT
168P/Hergenrother
169P/NEAT
171P/Spahr
172P/Yeung
173P/Mueller5
P/1998 VS24 (LINEAR)
P/1999 WJ7 (Korlevic) (203P)
P/2000 Y3 (Scotti)
P/2001 CV8 (LINEAR) (216P)
P/2001 R6 (LINEAR-Skiff)
P/2001 YX127 (LINEAR) (228P)
P/2002 JN16 (LINEAR) (221P)
P/2002 LZ11 (LINEAR) (219P)
P/2002 O8 (NEAT) (215P)
P/2002 S1 (Skiff) (223P)
P/2002 X2 (NEAT)
P/2003 HT15 (LINEAR)
P/2003 KV2 (LINEAR) (197P)
P/2003 O3 (LINEAR)
P/2003 S1 (NEAT)
P/2003 S2 (NEAT)
P/2004 A1 (LONEOS)
P/2004 DO29 (Spacewatch-LIN.)
P/2004 F3 (NEAT)
P/2004 H2 (Larsen)
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Jupiter-Family CometsJupiter-Family Comets
P/2004 T1 (LINEAR-NEAT)
P/2004 V3 (Siding Spring)
P/2004 V5 A+B(LINEAR-Hill)
P/2004 VR8 (LONEOS)
P/2005 GF8 (LONEOS)
P/2005 JD108 (Catalina-NEAT)
P/2005 JQ5 (Catalina)
P/2005 K3 (McNaught)
P/2005 L4 (Christensen)
P/2005 Q4 (LINEAR)
P/2005 R1 (NEAT)
P/2005 R2 (Van Ness) (213P)
P/2005 S3 (Read)
P/2005 T5 (Broughton)
P/2005 W3 (Kowalski)
C/2005 W2 (Christensen)
P/2005 Y2 (McNaught)
P/2005 XA54 (LONEOS-Hill)
School of Physical Sciences Colloquium 2011
Ryan Laird

6. SEPPCoNSEPPCoN –– Survey of Ensemble Physical Properties of Cometary NucleiSurvey of Ensemble Physical Properties of Cometary Nuclei
1. Use complementary ground-based visible-wavelength and thermal-IR
observations to derive the nuclei’s geometric albedos and sizes.
2. Test for correlations between the albedos and other properties of the
nuclei, such as composition and dynamical age.
3. Compare the cometary albedo distribution with those of Centaurs, TNOs,
Trojans, and extinct comet candidates to test the proposed evolutionary
processes.
4. Resolve once and for all the question of just how safe it is to assume an
albedo for a cometary nucleus. A cautionary tale is the TNO albedo story,
where 4% was long assumed and turned out to be very wrong.
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School of Physical Sciences Colloquium 2011
Ryan Laird

7. SEPPCoNSEPPCoN –– Survey of Ensemble Physical Properties of Cometary NucleiSurvey of Ensemble Physical Properties of Cometary Nuclei
5. Investigate the colour distribution of JFCs to help constrain the
composition and surface processes of JFC nuclei.
6. Determine the rotation and bulk density of JFC nuclei to compare with
other minor bodies to investigate any possible trends.
7. Determine the most robust size distribution of JFCs in relation to
ascertaining the KBO size distribution.
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School of Physical Sciences Colloquium 2011
Ryan Laird

8. 8
Size DistributionSize Distribution
Size and Rotation Period
Distributions:
• Is it influenced by collisional
history? By erosion? By
fragmentation? Is it at all similar to
Trojans?
• Is there a paucity of sub-km
objects?
• How does the spin-rate
distributions compare to KBOs, and
what can be learned about their
internal structure?
• We investigate the size distribution
down to ~ 1km. Size distributions
truncated < 2km. Most of targets <
2km by observational and theoretical
indications (Meech at al. 2004,
Samarasinha 2001) so to constrain
low end of size distribution is
dependent on sample.
School of Physical Sciences Colloquium 2011
Ryan Laird
One of several size distributions estimated for JFCs (Weissman & Lowry 2003).

9. Rotation and Bulk Density• We can use the rotation
period and elongation of
the nucleus to put limits on
the bulk density of the
nucleus (Pravec & Harris.
2000).
• Time-series photometry
and light curve amplitude
compared between JFCs
and all available data for
KBOs and Centaurs.
• Together this can reveal
information about the
internal structure of minor
body populations.
Rotation and Bulk DensityRotation and Bulk Density
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School of Physical Sciences Colloquium 2011
Ryan Laird
Available cometary nucleus light-curve data (Snodgrass, 2006). Comet data
are shown as open circles, KBOs as filled circles and Centaurs as filled
triangles. Like comets, KBOs all lie above 0.6 gcm-3
with the exception of the
large object 2003 EL61.

10. Summary of SEPPCoN
findings
Summary of SEPPCoN findingsSummary of SEPPCoN findings
To date we have attempted observations of 91% of our sample of 100
JFCs, at least 64 of those were successfully detected. Of those 64
detected comets just 16 showed signs of outgassing. In most cases
the comets were at heliocentric distances between 3.0 and 6.5 AU.
Examples of processed optical R-band imaging of three comets successfully detected at
the ESO 3.6-m NTT telescope in May 2007. Comet Lovas 1 shows clear signs of
activity, whereas comets NEAT and Klemola appear unresolved.
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School of Physical Sciences Colloquium 2011
Ryan Laird

11. EPSC Abstract
11

12. Investigating colours allows us to constrain composition
and surface properties.
Groupings have been reported between Centaurs and
KBOs.
Large scale survey from ESO imply a taxonomy of KBOs
based on their composition.
We look for trends in JFC nuclei, developing compositional
links with KBOs.
Colour DistributionColour Distribution
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School of Physical Sciences Colloquium 2011
Ryan Laird

13. Lamy et al. 2004 – review of 65 ecliptic comets. Albedo
range for cometary nuclei narrow, namely 0.02 to 0.06.
Looking for trends in this narrow range is difficult.
Evolutionary processes such as solar-UV, cosmic ray
darkening, space weathering, collisions, and
resurfacing from outgassing can alter the original
albedo of a comet.
Hypotheses show a trend of albedo with time that elapsed
since the object left the KBO region.
AlbedoAlbedo
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School of Physical Sciences Colloquium 2011
Ryan Laird

14. Size DistributionSize Distribution
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School of Physical Sciences Colloquium 2011
Ryan Laird
Reflectance Properties:
– How good is the 4% albedo assumption?
– What are the colourand albedo distributions?
Thermal Properties: – Do all comets have the same thermal properties (e.g. like Tempel 1) ?
(See Lowry et al. 2008. In TheSolarSystemBeyondNeptune)