Comet Activity and Composition K. Meech Ast 734 Seminar 8/30/04

Dirty Snowballs H2OH2OH2OH2O100 CH 4 0.6CO1-20 C2H2C2H2C2H2C2H20.1 CO C2H6C2H6C2H6C2H60.3 H 2 CO NH CH 3 OH 1-7HCN0.2 HCOOH0.05 CH 3 CN 0.02 HNCO0.1 HC 3 N 0.03 NH 2 CHO 0.01 H2SH2SH2SH2S1.5

Inactivity to Activity Ionization  gas tail Ionization  gas tail Activity develops Activity develops Km-scale nucleus Km-scale nucleus Coma ~ 10 5 km Coma ~ 10 5 km Tail ~ km Tail ~ km Sublimation of gases Sublimation of gases Drags dust from nucleus Drags dust from nucleus Gravity low Gravity low Most dust escapes Most dust escapes Solar radiation pressure  coma  tail Solar radiation pressure  coma  tail Photodissociation of gas Photodissociation of gas

Dust 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 AU07/15/99 r=2.2 AU

Who Cares? “extragalactic student” “extragalactic astronomers observing a comet”

Cosmic Solar System History >4.6 Gy ISM dark cloud Planetesimals condense Planets accrete Form few x100 million years Earth in the Hadean Oceans & rocks form ~4.4 Gy ago Late planetary bombardment Comets, asteroids bring water & Organics to Earth The Archean Epoch Oldest life on Earth Gy ago

The Oort Cloud 17 th century physics: Brahe, Kepler & Newton 17 th century physics: Brahe, Kepler & Newton E orbit = -  /2a Distribution of 1/a original Distribution of 1/a original 22 long-period comets Strongly peaked  Source 50, ,000 AU Contains comets Width very narrow Fading Problem “Volatile Frosting” Different chemistry Oort, J. (1950) B.A.N. 408, Oort J. H. & M. Schmidt (1951) B.A.N. 419,

The Modern Oort Cloud Outer Oort Cloud 15, AU Outer Oort Cloud 15, AU Stellar perturbations > 10 4 AU Stellar perturbations > 10 4 AU Inner Oort Cloud ,000 Inner Oort Cloud ,000 Galactic Tides Galactic Tides Dynamically inert AU Dynamically inert AU Kuiper Belt AU Kuiper Belt AU Stable, dynamically active Stable, dynamically active Classical, 3:2, scattered Classical, 3:2, scattered Dynamically new Dynamically new 1/a orig < 100x10 -6 AU -1 1/a orig < 100x10 -6 AU -1 Long PeriodP > 200 yr Long PeriodP > 200 yr Short Period P < 200 yr Short Period P < 200 yr Halley family – Oort cloud origin Halley family – Oort cloud origin Jupiter family – KBO origin Jupiter family – KBO origin Centaurs transition objects Centaurs transition objects

The Evidence for Fading Morehouse 1908 IIIGreat Comet 1577Halley 1910Delavan 1914 Different types of evidence Different types of evidence Really bright comets are all long-period Really bright comets are all long-period Distant comets  narrow tails (large dust)  volatile gases Distant comets  narrow tails (large dust)  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) Problems Problems Non uniform data sets Non uniform data sets Non-linear detectors Non-linear detectors

SP Comets AU

Comet Activity Levels  Trends

Evidence for Differences Dots = All SP obs Dots = All SP obs Squares = Halley Squares = Halley Triangles = DN comet Triangles = DN comet

Sublimation of Volatiles? Delsemme’s original work: albedo too high Delsemme’s original work: albedo too high Water-activity out beyond Jupiter Water-activity out beyond Jupiter

Water Ice Physics Phase I: P < 2700 atm Phase I: P < 2700 atm Ih – hexagonal Ic – cubic (low T, low P phase) High P forms: II to XIV High P forms: II to XIV Amorphous T cond < 100K Amorphous T cond < 100K Traps gases Clathrates Clathrates Mechanical trapping in cages

Comet Formation 100K 64K 31K AU

Low Temperature Condensation Ices in comets condensed T< 100K Ices in comets condensed T< 100K Amorphous form Trapped other gases Amounts depend on r Release of gases Release of gases 137K amorphous  crystalline phase change Annealing (30-35K) Sublimation K CH 4 N 2 ArCO Gas release at large distances: controlled by Water Gas release at large distances: controlled by Water

Heat Transfer in Comets Conduction low Conduction low Depends on porosity (unknown) Depends on porosity (unknown) Radiation Radiation Gas phase conduction (recondensation) Gas phase conduction (recondensation) Sintering Sintering Changes the conductivity Changes the conductivity Volatile re-distribution Volatile re-distribution Insulating layers Insulating layers

The Halley Outburst Gas Laden amorphous ice model Gas Laden amorphous ice model Heat from perihelion penetrates to ice layer Exothermic transformation (137K) Released gases build up pressure  outburst

Chiron’s Behavior Amorphous ice model Amorphous ice model 60% dust 40% amorphous ice 0.1% trapped CO Matches observations Matches observations Density < 0.4 g/cm 3 Mass loss rates & dust CO fluxes match obs T surface matches obs Activity sporadic  not refreshing surface

Hale Bopp Active at large r Active at large r Discovered 7.2 AU (1995) Discovered 7.2 AU (1995) Pre-discovery image 13.0 AU (1993) Pre-discovery image 13.0 AU (1993) Dynamically young Dynamically young Large CO fluxes seen Large CO fluxes seen Molecules of different volatilities appear at similar times Molecules of different volatilities appear at similar times

Thermal models: Comet Hale Bopp Amorphous ice crystallization model Amorphous ice crystallization model Porosity 0.65 Porosity % by mass trapped CO 4% by mass trapped CO

Activity at Larger r? Distance for T ~ 137K Distance for T ~ 137K Beginning near 10 AU Beginning near 10 AU Mechanisms at r > 10 AU Mechanisms at r > 10 AU Solid volatiles (e.g. CO, CO 2 ) sublimation Solid volatiles (e.g. CO, CO 2 ) sublimation Annealing Annealing C/2003 A2 Gleason q = AU 1/a = 42 x AU -1

KBO1996 TO 66 – Activity? Orbit Orbit Q = 48.6, q = 38.5 Q = 48.6, q = 38.5 q: 5/3/1910 Q: 2/1/2054 q: 5/3/1910 Q: 2/1/2054 Lightcurve period Lightcurve period 1997: 2 peak / hr,  m = 0.12 mag 1997: 2 peak / hr,  m = 0.12 mag 1998: single peak,  m = : single peak,  m = 0.33 Consistent with activity Consistent with activity Blue colors Blue colors Vary with rotation in 1999 Vary with rotation in 1999

Observations Subaru 8m + Suprime Cam Subaru 8m + Suprime Cam 8x12 K CCD mosaic 8x12 K CCD mosaic 0.2”/pixel, 0.25 o FOV 0.2”/pixel, 0.25 o FOV Target Selection Target Selection 15 blue-neutral objects 15 blue-neutral objects Select smallest r = 33.8 AU Select smallest r = 33.8 AU 1997QJ 4 : V-R = (Plutino) 1997QJ 4 : V-R = (Plutino) r = 33.8 AU, Hv=7.5 (rad = 80 km) r = 33.8 AU, Hv=7.5 (rad = 80 km) October 3, UT October 3, UT Nt 1 phot, Nt 2 clouds Nt 1 phot, Nt 2 clouds Sensitivity Sensitivity S/N = 3, V= s S/N = 3, V= s

Composite Image Single exp, 400 sec Single exp, 400 sec

Composite Image Single exp, 400 sec Single exp, 400 sec 12000s sum 12000s sum

Composite Image Single exp, 400 sec Single exp, 400 sec 12000s sum (zoomed 80”) 12000s sum (zoomed 80”)

Composite Image Single exp, 400 sec Single exp, 400 sec 12000s sum (zoomed 80”) 12000s sum (zoomed 80”) Median combined Median combined

Composite Image Single exp, 400 sec Single exp, 400 sec 12000s sum (zoomed 80”) 12000s sum (zoomed 80”) Median combined Median combined Shift & sum for KBO rate Shift & sum for KBO rate

Composite Image Single exp, 400 sec Single exp, 400 sec 12000s sum (zoomed 80”) 12000s sum (zoomed 80”) Median combined Median combined Shift & sum for KBO rate Shift & sum for KBO rate Median star subtracted Median star subtracted

Surface Brightness F = S o  a gr 2 p v Q  / 2r 2  2 v gr Constants: S o   r   Assume: a gr = 0.1  m (max lifted off) p v = 0.04, v gr = 0.1 km/s (CO) p v = 0.04, v gr = 0.1 km/s (CO) Result: Q < 0.01 kg/s

Comet Paradigms “Comets are the most pristine things in the Solar System” “Comets are the most pristine things in the Solar System” “Comets tell us about the formation of the Solar System “Comets tell us about the formation of the Solar System