JFC talk for Horncastle Astronomy Weekend 2010

1. By Ryan Laird
PhD Supervisor: Dr Stephen Lowry
Horncastle Astronomy Weekend
11th September 2010
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Comets: Delving into the Heart ofComets: Delving into the Heart of
the Matterthe Matter
Survey of Ensemble Physical Properties ofSurvey of Ensemble Physical Properties of
CCoometary Nuclei (SEPPCoN)metary Nuclei (SEPPCoN)

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OUTLINE OF TALKOUTLINE OF TALK
Introduction
Jupiter-Family Comets
Size distribution
Albedo
Colour distribution
Rotation and bulk density
SEPPCoN
Concluding remarks
Comets: Delving into the Heart of the Matter
By Ryan Laird

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IntroductionIntroduction –– Oort Cloud and Kuiper BeltOort Cloud and Kuiper Belt
Comets: Delving into the Heart of the Matter
By Ryan Laird

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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.
Jupiter-Family CometsJupiter-Family Comets
Comets: Delving into the Heart of the Matter
By Ryan Laird

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Investigation of the nuclei of a large sample of Jupiter-
family comets (JFCs) – a subset of the known cometary
population.
Dynamical studies have placed their subset in a source
region within the Kuiper Belt.
JFCs can provide a valuable insight into the physical and
compositional properties of small KBOs.
Jupiter-Family CometsJupiter-Family Comets
Comets: Delving into the Heart of the Matter
By Ryan Laird

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Information on the distributions of the:
• Size
• Shape
• Spin-rate
• Albedo
• Surface composition
of JFCs are critical for understanding their origins and
evolutionary processes affecting them as they
dynamically evolve from the Kuiper Belt.
Jupiter-Family CometsJupiter-Family Comets
Comets: Delving into the Heart of the Matter
By Ryan Laird

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Most cometary nuclei have both small radii ~1-3 km and
dark albedo ~4%.
Only possible to observe the nuclei when they are far
enough from the Sun (when greater than 3 AU) and
where the sublimation levels are small or negligible and
the nuclei dominate the observed flux. Method has
proven very successful.
Jupiter-Family CJupiter-Family Coometsmets
Comets: Delving into the Heart of the Matter
By Ryan Laird

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Size DistributionSize Distribution
100 targets. A third of the known JFC population.
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.
Comets: Delving into the Heart of the Matter
By Ryan Laird

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Size DistributionSize Distribution
One of several size distributions estimated for JFCs (Weissman & Lowry 2003).
Comets: Delving into the Heart of the Matter
By Ryan Laird

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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
Comets: Delving into the Heart of the Matter
By Ryan Laird

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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
Comets: Delving into the Heart of the Matter
By Ryan Laird

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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
Comets: Delving into the Heart of the Matter
By Ryan Laird

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Rotation and Bulk DensityRotation and Bulk Density
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 gcm3
with the exception of the large object 2003
EL61.

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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.
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.
Comets: Delving into the Heart of the Matter
By Ryan Laird

15. Comets: Delving into the Heart of the Matter
By Ryan Laird
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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.

18. Comets: Delving into the Heart of the Matter
By Ryan Laird 18
P/2010 A2P/2010 A2
P/2010 A2: Unusual Asteroid Tail Implies Powerful Collision
Credit: NASA, ESA, D. Jewitt (UCLA)

19. Comets: Delving into the Heart of the Matter
By Ryan Laird 19
Thank you
and
clear skies!