SL9 Impact G
From the Hubble Space Telescope (HST)
(1.75 hours after impact from fragment G.)
The "G" impact has concentric rings around it with a central dark spot 1,550 miles (2,500 km) in diameter. This dark spot is surrounded by a thin dark ring 4,600 miles (7,500 km) in diameter. The dark thick outermost ring's inner edge has a diameter of 7,460 miles (12,000 km) -- about the size of the Earth. The smaller feature to the top of fragment "G" was the impact created by fragment "D." Photo Credit: Heidi Hammel and HST and NASA.
The thin ring in the above photo is possibly a shock wave in the atmosphere moving outward from where the fragment exploded below the cloud-tops. The dark semi-circles south of the impact points are probably an ejecta blanket composed of fine material condensed from the plume. This material is either from the comet itself, or from Jupiter, and is suspended in the upper atmosphere. Some scientists refer to the dark material as soot, silicates, or tar-like hydrocarbons. In the infrared they look bright because of relected sunlight, and in the visible spectral region they are generally darker than the Jovian clouds.
From Mt. Stromlo and Siding Spring Observatories (MSSSO)
This image was obtained on the Australian National University 2.3m telescope at Siding Spring Observatory near Coonabarabran, Austrailia, using the CASPIR near-infrared array camera on July 18, 1994. The intense impact flash was recorded at 2.34 microns at UT 07:46:17. They estimated the saturated image to be roughly -2 to -5 mag at 2.34 microns. Although the impact flash was first reported as such, it was later found to be a "fireball echo," caused by impact debris falling back on Jupiter's atmosphere at high speed. Photo Credit: MSSSO.
From Mt. Stromlo and Siding Spring Observatories (MSSSO)
This image of impact "G" was obtained on the Australian National University 2.3m telescope at Siding Spring Observatory near Coonabarabran, Austrailia, using the CASPIR near-infrared array camera at 3.09 microns (B), 3.42 microns (G), and 3.99 microns (R) on July 18, 1994. The ring of hot gas was 33,000 km wide, and it was expanding at 4 km/s. Photo Credit: Peter McGregor and Mark Allen and MSSSO.
Impact "G" Summary
Fragment G, the largest and best studied, created a fireball at least 3,000 km high, at least 7,000 degrees Kelvin, and left a black eye twice the diameter of the earth. E. Shoemaker believes G's kinetic energy was equivalent to 6 trillion tons TNT, hundreds of times greater than the world's entire nuclear arsenal. If it struck the Earth instead, it would have left a crater 60 km across. HST spectroscopists found ammonia (NH3), sulfur (S2), and hydrogen sulfide (H2S) in G's cooling fireball, suggesting that the comet managed to dredge up material from the upper two layers of ammonia and ammonium hydrosulfide from Jupiter. No trace of water was detected.[Home Page] [Science Links] [Contents] [Previous] [Next]
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