Comets: Delving into the Heart of the Matter

By Ryan Laird

PhD Supervisor: Dr Stephen Lowry

Horncastle Astronomy Weekend 11th September 2010

1

Comets: Delving into the Heart of Comets: Delving into the Heart of the Matterthe Matter

Survey of Ensemble Physical Properties of Survey of Ensemble Physical Properties of CCoometary Nuclei (SEPPCoN)metary Nuclei (SEPPCoN)

2

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 MatterBy Ryan Laird

3

Introduction Introduction –– Oort Cloud and Kuiper Belt Oort Cloud and Kuiper Belt


4

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


5

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.



6

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.



7

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


8

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.


9

Size DistributionSize Distribution

One of several size distributions estimated for JFCs (Weissman & Lowry 2003).


10

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


11

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


12

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


13

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.

14

SEPPCoN SEPPCoN –– Survey of Ensemble Physical Properties of Cometary Nuclei Survey 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.



15

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.

Comets: Delving into the Heart of the MatterBy Ryan Laird 18

P/2010 A2P/2010 A2

P/2010 A2: Unusual Asteroid Tail Implies Powerful CollisionCredit: NASA, ESA, D. Jewitt (UCLA)

Comets: Delving into the Heart of the MatterBy Ryan Laird 19

Thank you

and

clear skies!

Comets: Delving into the Heart of the Matter

Science

Transcript of Comets: Delving into the Heart of the Matter