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An Optical Search for Small Comets R. L. Mutel & J.D. Fix University of Iowa. Small Comet Detection Papers. DE-1 (April 1986). Polar (May 1997). Small Comet Scenario (From L. Frank Website). Small Comet Parameters (from Frank and Sigwarth 1993, Small comet Web site)
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R. L. Mutel & J.D. Fix
University of Iowa
DE-1 (April 1986)
Polar (May 1997)
(from Frank and Sigwarth 1993, Small comet Web site)
Mass: 20,000 – 40,000 kg
Size: 4 – 10 m
Density: ~ 0.1 x H20
Number density: (3 ± 1) · 10-11 km-3
Flux at Earth: 1 every 3 seconds (107 per yr.)
Composition: Water ice with very dark mantle (albedo 0.01-0.02)
Orbit: Confined to ecliptic, prograde
Speed: ~10 km-sec-1 at 1 a.u.
Origin: Hypothesized comet belt beyond Neptune
FWHM = 4.2"Visual Magnitude Calibration using Standard Stars:ADU counts vs. V, FWHM
16.7Visual Magnitude Detection vs. Trail Length(20 April 1999, 60 s: fixed & 30 pixel trailed
Visual Detection Calibration Using Synthetic Trails
V = 16.4
V = 15.1
Sample Synthetic Comet Calibration Images
Rejected density region
Allowed density region
n = 0.05 n0
n = 0.25 n0
1. Visual magnitude m correction for distance (55,000 km vs. 137,000 km) is 2.0 magnitudes.
2a. Visual magnitude m as function of solar phase angle , scattering parameter Q, phase function () [Lumme & Bowell 1981]:
2b. Best fit phase function for solar system objects is:
2c. For Q ~ 0, magnitude difference between previous searches (fixed phase angle 20) and present search (4< < 9 ) is:
Small comet albedo range
8 average solar phase angle
Q = 0.6
Q = 0.0
Magnitude difference between IRO search and previous searches at fixed = 20
Implications for Physical Characteristics of Small Comets
The magnitude limit can be converted to limits on the physical properties of small comets. Assuming a single scattering function Q = 0 and and a mean solar phase angle of 8°, the allowed range of geometrical albedo and density for a mass of 20,000 kg (Frank et al. 1990) is shown below.
Darkest solar system objects (Iapetus)
Darkest part of Halley nucleus
Frank et al. (1990) estimated mass range
V = 16.5
V = 17.0
Physical Conditions of Small Comets
Alternatively, assuming a mass density of 0.1 gm-cm-3 (e.g. Frank and Sigwarth 1993), the mass-albedo allowed range is shown below.
n < 0.05 (99% confidence)
of the value claimed by Frank and Sigwarth (1990).