Collision of Comet Shoemaker-Levy 9 with Jupiter
Post-Impact Questions and Answers
Last Updated on February 2, 1996
This is a continuation of the pre-impact FAQ which contains information about the comet's discovery, orbit, tidal breakup, and fragment sizes. The answers to questions Q3.2 to Q3.6 below were provided by Mark Boslough and David Crawford. Send additions, corrections or comments to astro@tamu.edu. A text version of this FAQ list is available at ftp.tamu.edu.
Impact Questions and Answers
Q3.1: What were some of the effects of the collisions?
Q3.2: What causes the fireballs?
Q3.3: How does this differ from other phenomena called "fireballs"?
Q3.4: What is the difference between a "fireball" and a "plume"?
Q3.5: Why was there a gap between the apparent limb of Jupiter
and the plumes or fireballs in the Hubble images?
Q3.6: How deep did the fragments penetrate into Jupiter's atmosphere?
Q3.7: What is the dark material at the impact sites?
Q3.8: How can the structure of the impact sites be explained?
Q3.9: What were the impact times and locations?
Q3.10: Where can I find more information and GIF images?
Impact Questions and Answers
Q3.1: What were some of the effects of the collisions?
Just before the the first comet fragment hit Jupiter, Zdenek Sekanina wrote that based on Hubble Space Telescope observations in early July 1994 the fragments had effective diameters generally between 1 and 2 kilometers: "Although the evidence points to an apparently continuing disintegration of the large fragments in numerous discrete events, objects a few km across still seem to have been present in early July, and the temporal variations in the effective diameters are likely to be primarily a rotational effect of strongly irregular shape." [58] Would some of the fragments remain intact and create large fireballs or would the comet nuclei shatter before they reached Jupiter? Perhaps both were true. Some fragments created large fireballs that rose above the limb of Jupiter and left giant dark marks on the planet, while other fragments seem to leave little trace of their impact.
Fragment A struck Jupiter with its kinetic energy equivalent to about 225,000 megatons of TNT creating plume which rose about 1000 km above the Jovian cloudtops. It was not long before the Hubble Space Telescope images of the fireball and impact site of fragment A were downloaded by thousand of observers. Many were surprised to see any effects from Earth. "We were thinking that we were going to have to go in with a microscope and you know stretch the image as hard as we could to pull out anything, but its just blasting away at us...unbelievable." - Hal Weaver
Fragment B was about the same brightness as fragment A in the pre-impact images but its impact left a small mark on Jupiter that was observed by only a few observatories. Then fragments C, D, and E left marks similar the impact of fragment A while the impact of F was difficult to detect. The real show-stopper was fragment G which struck Jupiter with an estimated energy equivalent to 6,000,000 megatons of TNT (about 600 times the estimated arsenal of the world). The fireball from fragment G rose about 3000 km above the Jovian cloudtops and was observed by many observatories (mostly in infrared). As it turned out, visible-light-radiating fireballs were seen with large telescopes and many observers reported seeing the dark impact scars with telescopes as small as 5 cm in diameter.
Observers have detected some of the collisions using radio telescopes [57] but it appears that the light emitted during the entry of the fragments into the Jovian atmosphere was not observed from the ground in reflection from Jupiter's moons as predicted. The Galileo spacecraft images of impact W have now been downloaded and do show a light flash that lasted a few seconds, but it was not particularly strong and would probably not have been detected in reflection from a moon by the available ground-based instruments [56].
Many of the later impacts hit near the sites of earlier ones and the resulting features soon became very complex. The development of the new features on Jupiter has since been followed by many observers. While the smaller features have almost disappeared the larger complexes are still visible even in small telescopes. Currently it appears that some of the dark impact sites are overlapping to form a partial band. No one really knows how long the features will continue to be visible, but perhaps this band will still be visible during the next observing season.
In summary, some of the fragments of comet Shoemaker-Levy 9 disappeared before they reached Jupiter (J, M and P1), some impacts were generally difficult to detect (B, F, N, P2, Q2, T, U, and V), some fragments created dark impact sites that measured about half of an Earth-diameter across (A, C, D, E, H, Q1, R, S, and W) and others created impact sites that were at least an Earth-diameter across (G, K, and L). Clearly not all of the fragments of comet Shoemaker-Levy 9 were the same. The size of fragment A is thought to have been about 1 km across and the diameter of fragment G is thought to have been about 3 km.
Back to List of Questions
Q3.2: What causes the fireballs?
isc.tamu.edu |
