Science goals and objectives
History: The Draconid shower is caused by debris from short period Jupiter-family comet 21P/Giacobini-Zinner, which was visited by NASA's International Cometary Explorer (ICE) spacecraft on 11 September 1985.
1946 Draconid storm as seen from Griffith Observatory between 3:45 and 4:02 UT, October 9. Photo: T. Cook, Griffith Observatory.
The Draconid shower is known for its spectacular storms in 1933 and 1946, when rates increased to ZHR = 10,000 per hour. Even in the strong moonlight of both years, the shower was a sight to behold, with many slow (20.5 km/s) meteors still visible when the next one appeared.
The 1933 and 1946 storms were caused by debris released in the returns of 1900 and1907. That was in the same year as the comet's first sighting in December of 1900. Michel Giacobini (Nice, France) discovered the comet in Aquarius on 1900 December 20.81. Ernst Zinner (of Bamberg, Germany) recovered the comet on 1913 October 23, two returns later.
Event: The Earth is expected to encounter the same 1900 ejected dust on October 8, 2011. But not again in the next 40 years.
Operational interest:The potential high impact rates are a concern to satellite operators. Also, the known impact speed of the meteoroids would make it possible to study the re-entry conditions for sample return capsules in a very high 20.5 km/s entry. If any debris survives, it would settle into the stratosphere, dus enabling a low-cost comet sample return.
Scientific interest: The 1933 and 1946 Draconids were exceptional in being very fragile. The grains fell appart high in the atmosphere, had peculiar light curves, released sodium early, and produced a strong debris wake. Later Draconid outbursts in 1985 and 1998 did not show these effects quite as dramatically. The 2005 Draconids, on the other hand, displayed many of the fragile characteristics again [article on physical properties of 2005 Draconids by Jiri Borovicka et al. (2007)].
Comet 21P/Giacobini-Zinner in an image by the Kitt Peak 0.9 m telescope on November 1, 1998. Photo: N. A. Sharp/NOAO/AROA/NSF.
Hypothesis to be tested: According to Peter Jenniskens, it is possible that the dust responsible for the 1933 and 1946 Draconids was created in a breakup event during the return of 1900, releasing dust particles with ice still embedded. When the ice sublimated, it left behind very fragile grains. That disruption made the comet first active, leading to its discovery.
Data needed: To test this hypothesis, we are very keen on observing the 2011 Draconid outburst, which is caused by the same debris cloud form 1900. There is also an encounter with older (pre-1900) dust, if that exists.
- If the comet was inactive prior to 1900, this older dust cloud would not manifest, while the 1900 peak would produce frail grains with peculiar light curves, early sodium release, falling appart high in the atmosphere.
- On the other hand, if the comet was active before 1900 (simply too faint to be detected), then two shower peaks will be observed (around 17h and 20h UT) and the meteors will look similar.