Comet Activity and Comet Activity and CompositionComposition

K. MeechK. Meech

Ast 734 SeminarAst 734 Seminar

8/30/048/30/04

Dirty SnowballsDirty SnowballsHH22OO 100100 CHCH44 0.60.6

COCO 1-201-20 CC22HH22 0.10.1

COCO22 3-203-20 CC22HH66 0.30.3

HH22COCO 0.1-10.1-1 NHNH33 0.60.6

CHCH33OHOH 1-71-7 HCNHCN 0.20.2

HCOOHHCOOH 0.050.05 CHCH33CNCN 0.020.02

HNCOHNCO 0.10.1 HCHC33NN 0.030.03

NHNH22CHOCHO 0.010.01 HH22SS 1.51.5

Inactivity to ActivityInactivity to Activity Ionization Ionization gas tail gas tail Activity developsActivity develops

Km-scale nucleusKm-scale nucleus Coma ~ 10Coma ~ 1055 km km Tail ~ 10Tail ~ 1066-10-1077 km km

Sublimation of gasesSublimation of gases Drags dust from nucleusDrags dust from nucleus

Gravity lowGravity low Most dust escapesMost dust escapes Solar radiation pressure Solar radiation pressure

coma coma tail tail

Photodissociation of gasPhotodissociation of gas

Dust Coma DevelopmentDust Coma Development

q-620 dy; Af = 14 cm

q+590 dy; Af = 13 cmq+300 dy; Af = 83 cmq+210 dy; Af = 87 cm

q-150 dy; Af = 105 cmq-350 dy; Af = 31 cm

01/19/99 r=3.1AU

11/12/01 r=4.4 AU09/30/00 r=2.8 AU08/22/00 r=2.6 AU

04/06/98 r=4.3 AU 07/15/99 r=2.2 AU

Who Cares?Who Cares?

““extragalactic student”extragalactic student”

““extragalactic astronomers observing a comet”extragalactic astronomers observing a comet”

Cosmic Solar System HistoryCosmic Solar System History

>4.6 Gy>4.6 GyISM dark cloudISM dark cloud

Planetesimals condensePlanetesimals condensePlanets accretePlanets accreteForm few x100 million yearsForm few x100 million years

Earth in the HadeanEarth in the HadeanOceans & rocks formOceans & rocks form~4.4 Gy ago~4.4 Gy ago

Late planetary bombardmentLate planetary bombardmentComets, asteroids bring water &Comets, asteroids bring water &Organics to EarthOrganics to Earth

The Archean EpochThe Archean EpochOldest life on EarthOldest life on Earth3.5-3.8 Gy ago3.5-3.8 Gy ago

The Oort CloudThe Oort Cloud 1717thth century physics: century physics:

Brahe, Kepler & NewtonBrahe, Kepler & Newton EEorbitorbit = - = -/2a/2a

Distribution of 1/aDistribution of 1/aoriginaloriginal

22 long-period comets22 long-period comets Strongly peaked Strongly peaked

Source 50,000-150,000 AUSource 50,000-150,000 AU Contains 10Contains 101111 comets comets

Width very narrowWidth very narrow Fading ProblemFading Problem ““Volatile Frosting”Volatile Frosting” Different chemistryDifferent chemistry

Oort, J. (1950) B.A.N. 408, 91-110.Oort J. H. & M. Schmidt (1951) B.A.N. 419, 259-270

The Modern Oort CloudThe Modern Oort Cloud

Outer Oort Cloud 15,000-10Outer Oort Cloud 15,000-1055 AU AU Stellar perturbations > 10Stellar perturbations > 1044 AU AU

Inner Oort Cloud 2000-15,000Inner Oort Cloud 2000-15,000 Galactic TidesGalactic Tides

Dynamically inert 50-2000 AUDynamically inert 50-2000 AU Kuiper Belt 35-50 AUKuiper Belt 35-50 AU

Stable, dynamically activeStable, dynamically active Classical, 3:2, scatteredClassical, 3:2, scattered

Dynamically new Dynamically new 1/a1/aorigorig < 100x10 < 100x10-6-6 AU AU-1-1

Long PeriodLong Period P > 200 yrP > 200 yr Short Period P < 200 yrShort Period P < 200 yr

Halley family – Oort cloud originHalley family – Oort cloud origin Jupiter family – KBO originJupiter family – KBO origin

Centaurs transition objectsCentaurs transition objects

The Evidence for FadingThe Evidence for Fading

Morehouse 1908 IIIGreat Comet 1577 Halley 1910 Delavan 1914

Different types of evidenceDifferent types of evidence Really bright comets are all long-periodReally bright comets are all long-period Distant comets Distant comets narrow tails (large dust) narrow tails (large dust) volatile gases volatile gases New comets tend to split more frequently (more volatiles)New comets tend to split more frequently (more volatiles) Non-gravitational motion (jets)Non-gravitational motion (jets)

ProblemsProblems Non uniform data setsNon uniform data sets Non-linear detectorsNon-linear detectors

SP Comets 3.4-14.5 AUSP Comets 3.4-14.5 AU

Comet Activity Levels Comet Activity Levels Trends Trends

Evidence for DifferencesEvidence for Differences

Dots = All SP obsDots = All SP obs Squares = HalleySquares = Halley Triangles = DN cometTriangles = DN comet

Sublimation of Volatiles?Sublimation of Volatiles?

Delsemme’s original work: albedo too highDelsemme’s original work: albedo too high Water-activity out beyond JupiterWater-activity out beyond Jupiter

Water Ice PhysicsWater Ice Physics Phase I: P < 2700 atmPhase I: P < 2700 atm Ih – hexagonalIh – hexagonal Ic – cubic (low T, low P Ic – cubic (low T, low P

phase)phase) High P forms: II to XIVHigh P forms: II to XIV Amorphous TAmorphous Tcondcond< 100K< 100K

Traps gasesTraps gases ClathratesClathrates

Mechanical trapping in Mechanical trapping in cagescages

Comet FormationComet Formation

100K100K

64K64K

31K31K

00 1010 100 AU100 AU

Low Temperature CondensationLow Temperature Condensation Ices in comets Ices in comets

condensed T< 100Kcondensed T< 100K Amorphous formAmorphous form Trapped other gasesTrapped other gases Amounts depend on Amounts depend on rr

Release of gasesRelease of gases 137K amorphous 137K amorphous

crystalline phase changecrystalline phase change Annealing (30-35K)Annealing (30-35K) Sublimation 160-180KSublimation 160-180K

CHCH44

NN22

ArAr

COCO

Gas release at large distances: controlled Gas release at large distances: controlled by Waterby Water

Heat Transfer Heat Transfer in Cometsin Comets

Conduction lowConduction low Depends on porosity Depends on porosity

(unknown)(unknown) RadiationRadiation Gas phase conduction Gas phase conduction

(recondensation)(recondensation) SinteringSintering

Changes the Changes the conductivityconductivity

Volatile re-distributionVolatile re-distribution Insulating layersInsulating layers

The Halley OutburstThe Halley Outburst

Gas Laden amorphous ice modelGas Laden amorphous ice model Heat from perihelion penetrates to ice layerHeat from perihelion penetrates to ice layer Exothermic transformation (137K)Exothermic transformation (137K) Released gases build up pressure Released gases build up pressure outburst outburst

Chiron’s BehaviorChiron’s Behavior

Amorphous ice modelAmorphous ice model 60% dust60% dust 40% amorphous ice40% amorphous ice 0.1% trapped CO0.1% trapped CO

Matches observationsMatches observations Density < 0.4 g/cmDensity < 0.4 g/cm33

Mass loss rates & dustMass loss rates & dust CO fluxes match obsCO fluxes match obs TTsurfacesurface matches obs matches obs Activity sporadic Activity sporadic not not

refreshing surfacerefreshing surface

Hale BoppHale Bopp

Active at large rActive at large r Discovered 7.2 AU Discovered 7.2 AU

(1995)(1995) Pre-discovery image Pre-discovery image

13.0 AU (1993)13.0 AU (1993)

Dynamically youngDynamically young Large CO fluxes seenLarge CO fluxes seen Molecules of different Molecules of different

volatilities appear at volatilities appear at similar timessimilar times

Thermal models: Comet Hale BoppThermal models: Comet Hale Bopp

Amorphous ice crystallization modelAmorphous ice crystallization model Porosity 0.65Porosity 0.65 4% by mass trapped CO4% by mass trapped CO

Activity at Larger r?Activity at Larger r?

Distance for T ~ 137KDistance for T ~ 137K Beginning near 10 AUBeginning near 10 AU

Mechanisms at r > 10 AUMechanisms at r > 10 AU Solid volatiles (e.g. CO, COSolid volatiles (e.g. CO, CO22) )

sublimationsublimation AnnealingAnnealing

C/2003 A2 GleasonC/2003 A2 Gleasonq = 11.43 AUq = 11.43 AU1/a = 42 x 101/a = 42 x 10-6-6 AU AU-1-1

KBO1996 TOKBO1996 TO6666 – Activity? – Activity? OrbitOrbit

Q = 48.6, q = 38.5Q = 48.6, q = 38.5 q: 5/3/1910 Q: 2/1/2054q: 5/3/1910 Q: 2/1/2054

Lightcurve periodLightcurve period 1997: 2 peak 6.25 +/- 0.03 1997: 2 peak 6.25 +/- 0.03

hr, hr, m = 0.12 magm = 0.12 mag 1998: single peak, 1998: single peak, m = 0.33 m = 0.33

Consistent with activityConsistent with activity Blue colorsBlue colors

Vary with rotation in 1999Vary with rotation in 1999

ObservationsObservations Subaru 8m + Suprime CamSubaru 8m + Suprime Cam

8x12 K CCD mosaic8x12 K CCD mosaic 0.2”/pixel, 0.250.2”/pixel, 0.25oo FOV FOV

Target SelectionTarget Selection 15 blue-neutral objects15 blue-neutral objects Select smallest r = 33.8 AUSelect smallest r = 33.8 AU 1997QJ1997QJ44: V-R = 0.296 (Plutino): V-R = 0.296 (Plutino) r = 33.8 AU, Hv=7.5 (rad = 80 km)r = 33.8 AU, Hv=7.5 (rad = 80 km)

October 3, 4 2002 UTOctober 3, 4 2002 UT

Nt 1 phot, Nt 2 clouds Nt 1 phot, Nt 2 clouds SensitivitySensitivity

S/N = 3, V=28 12000sS/N = 3, V=28 12000s

Composite Composite ImageImage

Single exp, Single exp, 400 sec400 sec

Composite Composite ImageImage

Single exp, Single exp, 400 sec400 sec

12000s sum12000s sum

Composite Composite ImageImage

Single exp, Single exp, 400 sec400 sec

12000s sum 12000s sum (zoomed 80”)(zoomed 80”)

Composite Composite ImageImage

Single exp, Single exp, 400 sec400 sec

12000s sum 12000s sum (zoomed 80”)(zoomed 80”)

Median Median combinedcombined

Composite Composite ImageImage

Single exp, Single exp, 400 sec400 sec

12000s sum 12000s sum (zoomed 80”)(zoomed 80”)

Median Median combinedcombined

Shift & sum Shift & sum for KBO ratefor KBO rate

Composite Composite ImageImage

Single exp, Single exp, 400 sec400 sec

12000s sum 12000s sum (zoomed 80”)(zoomed 80”)

Median Median combinedcombined

Shift & sum Shift & sum for KBO ratefor KBO rate

Median star Median star subtractedsubtracted

Surface BrightnessSurface Brightness

F = SF = Sooaagrgr22ppvvQQ/ 2r/ 2r2222vvgrgr

Constants: SConstants: So o r r Assume: aAssume: agrgr = 0.1 = 0.1 m (max lifted off)m (max lifted off)

ppvv = 0.04, v = 0.04, vgrgr = 0.1 km/s (CO) = 0.1 km/s (CO)

Result: Q < 0.01 kg/sResult: Q < 0.01 kg/s

Comet ParadigmsComet Paradigms

““Comets are the most Comets are the most pristine things in the pristine things in the Solar System”Solar System”

““Comets tell us about Comets tell us about the formation of the the formation of the Solar SystemSolar System