Triggered outburst after the collision of the Deep Impact impactor with Comet 9P/Tempel 1
Abstract
Time variations in velocities and relative amount of material ejected from Comet 9P/Tempel 1 were studied [1-3] based on analysis of the images made by Deep Impact (DI) cameras during the first 13 minutes after the collision of the DI impactor with the comet. The velocities and rate of production of observed ejected material correspond mainly to small (with diameter d<3 micron) icy particles. Results of our studies testify in favour of that the contribution of a triggered outburst to the observed brightness of the ejected cloud (not to the total mass of ejected material) could be considerable. The outburst ejection could be from the entire surface of the crater, while the normal ejection was mainly from its edges. The `fast' outburst could be caused by ejection from the regions inside the comet with gas pressure. `Slow' outburst ejection could be similar to the ejection from a `fresh' surface of a comet and could take place long after the formation of the crater. A considerable increase of the `fast' outburst at te =10 s was characterized by the increase of the ejection rate, the beginning of considerable excessive ejection (rays of ejected material) to a few directions, the quick change of the direction from the place of ejection to the brightest pixel by about 50° , and the increase of brightness of the brightest pixel. Typical projections vp of velocities onto the plane perpendicular to the line of sight at te ∼10-20 s were ∼100-200 m/s. A sharp (by a factor of 1.6) decrease of estimated ejection rate at 55<te <72 s could be caused by a decrease of the `fast' outburst and/or the normal ejection. As a first approximation, the characteristic velocity of the normal ejection at 1<te <100 s can be considered to be proportional to te -α , where α is about 0.7-0.75. For such approximation of velocity, the fractions of observed material ejected (at te ≤6 s and te ≤15 s) with vp ≥200 m/s and vp ≥100 m/s were estimated to be about 0.1-0.15 and 0.2-0.25, respectively, if we consider only material observed during the first 13 min. Time variations in velocities could be smaller (especially, at te >100 s) for the outburst ejecta than for the normal ejecta. The outburst continued at te ∼10 min because the rays of ejected material were still observed in images made at t∼500-700 s. Duration of the outburst (up to 30-60 min) could be longer than that of the normal ejection (not more than a few minutes). This work was supported by NASA DDAP grant NNX08AG25G. [1] 40th LPSC, 2009, 1022. [2] Proc. IAU Symp. 263 "Icy bodies in the Solar System", 2010, in press. [3] http://arxiv.org/abs/0810.1294.
- Publication:
-
38th COSPAR Scientific Assembly
- Pub Date:
- 2010
- Bibcode:
- 2010cosp...38..659I