Snowy Owl
Retired in 2010, In Memoriam
Background
Comet 73P/Schwassmann-Wachmann 3 was discovered by Arnold Schwassmann and Arno Wachmann
on May 2, 1930 at Hamburg Observatory in Germany. It approached within 0.062 AU six
weeks after its discovery, when it reached 6th magnitude. The comet has an orbital period
of 5.36 years, but due to uncertainties in its orbit, faint visual magnitudes, and relatively
close approaches to Jupiter in 1953 and 1965 that altered its orbit, it wasn't recovered until
1979. In the fall of 1995 the comet's magnitude brightened dramatically, and then in December
of that year, multiple fragments were discovered. In other words, the comet's nucleus split.
Three of the fragments, B, C, and E, were observed again during the subsequent perihelion passage in 2001.
Fragment C was recovered in August, 2005 and fragment B was recovered in January, 2006.
The comet has since split multiple times, and as of early May, about dozens of fragments
been observed. Fragment B has split into at least one large fragment and a cloud of smaller ones.
In contrast, fragment C apparently has not split (yet).
During May, 2006 fragments B, C, and most of the others will approach within 0.079 AU.
Fragment E was last observed in December, 2000. It is predicted to approach within 0.051 AU
several days after the other fragments, when we hope to observe it, presuming, of course,
that it still exists.
Sekanina (1989) estimated a pre-breakup (prior to 1995) diameter of about 2 km.
Toth et al. (2005) estimate that fragment C (prior to recent splitting) had a diameter of 1.3 km.
Fragment C is the largest and (as of early May) is already bright enough to see in binoculars.
Fragment B is also visible in binoculars but it's fainter than fragment C. The other fragments
require a telescope to observe.
These will be combined Goldstone and Arecibo observations.
Goldstone observations are scheduled on May 9, 12, 14, 21, and 23 and Arecibo observations are
scheduled on several dates between April 30-May 22. We know little about the sizes and rotation
periods of the fragments, so it's hard to estimate the SNRs. Comet SW3 could be a moderately strong
radar target at Goldstone, and if we're lucky, we may be able to resolve the nucleus with
coarse-resolution ranging. Alternatively, it could be weak, but in any event, we should be able
to detect it.
The approach by Schwassmann-Wachmann 3 will be the closest by any comet since
comet Sugano-Saigusa-Fujikawa approached within 0.063 AU in June, 1983.
Orbital and Physical Characteristics: Fragment C
orbit type Jupiter-family periodic comet
semimajor axis 3.063 AU
eccentricity 0.693
inclination 11.4?
perihelion distance 0.939 AU
aphelion distance 5.186 AU
orbital period 5.360 years
diameter ~1 km (Z. Sekanina, pers. comm.)
rotation period unknown
pole direction unknown
lightcurve amplitude unknown
Orbital parameters for fragment B are similar.
Last updated: 2006 May 07
http://echo.jpl.nasa.gov/asteroids/73PSW3/html/73PSW3.planning.html
Comet 73P/Schwassmann-Wachmann 3 was discovered by Arnold Schwassmann and Arno Wachmann
on May 2, 1930 at Hamburg Observatory in Germany. It approached within 0.062 AU six
weeks after its discovery, when it reached 6th magnitude. The comet has an orbital period
of 5.36 years, but due to uncertainties in its orbit, faint visual magnitudes, and relatively
close approaches to Jupiter in 1953 and 1965 that altered its orbit, it wasn't recovered until
1979. In the fall of 1995 the comet's magnitude brightened dramatically, and then in December
of that year, multiple fragments were discovered. In other words, the comet's nucleus split.
Three of the fragments, B, C, and E, were observed again during the subsequent perihelion passage in 2001.
Fragment C was recovered in August, 2005 and fragment B was recovered in January, 2006.
The comet has since split multiple times, and as of early May, about dozens of fragments
been observed. Fragment B has split into at least one large fragment and a cloud of smaller ones.
In contrast, fragment C apparently has not split (yet).
During May, 2006 fragments B, C, and most of the others will approach within 0.079 AU.
Fragment E was last observed in December, 2000. It is predicted to approach within 0.051 AU
several days after the other fragments, when we hope to observe it, presuming, of course,
that it still exists.
Sekanina (1989) estimated a pre-breakup (prior to 1995) diameter of about 2 km.
Toth et al. (2005) estimate that fragment C (prior to recent splitting) had a diameter of 1.3 km.
Fragment C is the largest and (as of early May) is already bright enough to see in binoculars.
Fragment B is also visible in binoculars but it's fainter than fragment C. The other fragments
require a telescope to observe.
These will be combined Goldstone and Arecibo observations.
Goldstone observations are scheduled on May 9, 12, 14, 21, and 23 and Arecibo observations are
scheduled on several dates between April 30-May 22. We know little about the sizes and rotation
periods of the fragments, so it's hard to estimate the SNRs. Comet SW3 could be a moderately strong
radar target at Goldstone, and if we're lucky, we may be able to resolve the nucleus with
coarse-resolution ranging. Alternatively, it could be weak, but in any event, we should be able
to detect it.
The approach by Schwassmann-Wachmann 3 will be the closest by any comet since
comet Sugano-Saigusa-Fujikawa approached within 0.063 AU in June, 1983.
Orbital and Physical Characteristics: Fragment C
orbit type Jupiter-family periodic comet
semimajor axis 3.063 AU
eccentricity 0.693
inclination 11.4?
perihelion distance 0.939 AU
aphelion distance 5.186 AU
orbital period 5.360 years
diameter ~1 km (Z. Sekanina, pers. comm.)
rotation period unknown
pole direction unknown
lightcurve amplitude unknown
Orbital parameters for fragment B are similar.
Last updated: 2006 May 07
http://echo.jpl.nasa.gov/asteroids/73PSW3/html/73PSW3.planning.html
