Observations of Comet 9P/Tempel 1 around the Deep Impact event by the OSIRIS cameras onboard Rosetta

Abstract

The OSIRIS cameras on the Rosetta spacecraft observed Comet 9P/Tempel 1 from 5 days before to 10 days after it was hit by the Deep Impact projectile. The Narrow Angle Camera (NAC) monitored the cometary dust in 5 different filters. The Wide Angle Camera (WAC) observed through filters sensitive to emissions from OH, CN, Na, and OI together with the associated continuum. Before and after the impact the comet showed regular variations in intensity. The period of the brightness changes is consistent with the rotation period of Tempel 1. The overall brightness of Tempel 1 decreased by about 10% during the OSIRIS observations. The analysis of the impact ejecta shows that no new permanent coma structures were created by the impact. Most of the material moved with ~200 ms -1 . Much of it left the comet in the form of icy grains which sublimated and fragmented within the first hour after the impact. The light curve of the comet after the impact and the amount of material leaving the comet (4.5-9 x 10 6 kg of water ice and a presumably larger amount of dust) suggest that the impact ejecta were quickly accelerated by collisions with gas molecules. Therefore, the motion of the bulk of the ejecta cannot be described by ballistic trajectories, and the validity of determinations of the density and tensile strength of the nucleus of Tempel 1 with models using ballistic ejection of particles is uncertain.

A ballistics analysis of the Deep Impact ejecta plume: Determining Comet Tempel 1's gravity, mass, and density

“…19 also indicates that the highest speed ejecta particles (shown in the lower right end of these curves) should have been moving at speeds of hundreds of meters per second. This is consistent with the findings via remote sensing, which measured speeds for the leading edge of the ejecta plume (as seen from their perspective) of ∼190 m s −1 (Mason et al, 2007); ∼200 m s −1 (Milani et al, 2007); 197 ± 16 m s −1 (Bauer et al, 2007); 200-230 m s −1 (Knight et al, 2007); <230 m s −1 (Schleicher et al, 2006); ∼200 m s −1 (Keller et al, 2007); and 230-250 m s −1 , to name a few of these observations. As Fig.…”

Activity evolution, outbursts, and splitting events of comet 73P/Schwassmann-Wachmann 3

“…For the grain-size distribution, we used a power-law relationship, n(r) ∼ r −a , with exponent a = 2.6, obtained from a reanalysis of the 1P/Halley Giotto data by Fulle et al (2000). An exponent of ∼3 was also found by using inverse modeling of the dust tails of comet Hyakutake 1996 B2 (Fulle et al 1997), JF comets 46P/Wirtanen and 103P/Hartley 2 (Fulle 2000;Epifani et al 2001), and comet 2P/Encke (Epifani et al 2001), and in the ejecta dust cloud caused by the Deep Impact experiment on the JF comet 9P/Tempel 1 (Keller et al 2007). Since the composition influences the final shape of the phase function, we corrected the observed flux according to three possible compositions: pure silicates made by four components (amorphous and crystalline pyroxene, and amorphous and crystalline olivine), pure organic refractories, and a 1:1 in mass mixture of organics and silicates.…”

Photometric observations of comet 81P/Wild 2 during the 2010 perihelion passage

“…Indeed, it was shown by observational and theoretical works that an exponent ∼3 can be considered typical of dust in cometary comae (e.g. Fulle et al 1997;Fulle 2000;Fulle et al 2000;Epifani et al 2001;Keller et al 2007). Moreover, analyzing the properties of the dust emitted by 81P, Price et al (2010) derived specific values of a, modeling the flux of impacts by dust particles on aluminum foils onboard the Stardust spacecraft during the 2004 flyby.…”