The Crash of 1994

The Impact of Comet Shoemaker - Levy / 9 on Jupiter in July 1994

The Prediction

This was billed as the astronomical event of the century, perhaps even the millennium, when, for the first time, mankind was to witness a comet crashing into a planet. Jupiter acts as a sort of cosmic vacuum cleaner, sweeping up into its gravitational field a proportion of comets that enter the inner Solar System. Indeed, some calculations suggest that the presence of Jupiter directly benefits life on Earth by collecting comets that could otherwise crash into Earth in "Dinosaur-killer" scale events.

The comet, discovered in 1993 was named Shoemaker - Levy / 9, after its co-discoverers. When first discovered the comet presented String of Beadsa very puzzling sight, and was likened to a string of beads. It was quickly realised that the comet was in orbit around Jupiter, not the Sun. Its highly elliptical orbit had carried it so close to the planet in July 1992 (just 16,000 miles) that the tidal forces had torn the nucleus apart into many fragments.

Calculations working backwards in time suggested that the comet had been captured by Jupiter in the 1920s or 30s. Each orbit was slightly different, as the comet was pulled by Jupiter's Galilean moons each time it swung round the planet, and by the Sun and other planets as it wandered chaotically in a gravitational "no-mans-land" when far from Jupiter. Running the calculation forward it was realised that the next visit to Jupiter, in July 1994, would be its last.

The individual fragments of SL/9, each following a slightly different orbit following its break-up two years earlier, would crash into Jupiter like machine-gun bullets. The first, named A was due to arrive on 16th July, and the last, W, on 22nd July. While their size and mass was not accurately known, their speed of 141,000 mph (63km per second) suggested that they would cause massive disruption on Jupiter as they plunged into the atmosphere and exploded.

Unfortunately the impact point on Jupiter was just out of sight of the Earth, but the planet's fast rotation would carry it into view a few minutes later. Telescopes on Earth and in space were therefore trained on Jupiter to record the unfolding drama...

The Outcome

The power and size of the explosions of most fragments far exceeded most predictions. Although the visible flashes were out of sight, in infra-red the huge mushroom clouds, some bigger than the entire Earth, could be seen rising up over the edge of Jupiter. The power of the biggest explosion, that of fragment G, was estimated at 250 million megatons of TNT, 17 billion times bigger than the bomb dropped on Hiroshima in 1945 (yield 15 kilotons). Even the biggest hydrogen bomb ever exploded by mankind, 50 megatons, is tiny by comparison.

The picture right shows one such fireball rising on the lower left of the planet, and the sites of previous impacts still glowing hot in infra-red.

SL/9 Plume and impact sites on Jupiter

For images of the event taken from the Hubble Space Telescope, the Galileo spacecraft that was on its way to Jupiter, and from large ground-based telescopes, visit Jet Propulsion Laboratory or National Space Science Data Center.

My Observations

The devastation caused by these huge explosions was plain to see even in ordinary telescopes, as each impact point was marked by a black "hole" in the atmosphere. This was before the days of digital cameras, and with conventional photography at the telescope being a bit hit and miss, I decided to draw what I saw instead. The pictures below are the results at the eyepiece of my 8.75 inch telescope, which I set up my garden in Kettering.

In each case, the picture has been turned round to give a view in keeping with those on the external websites, i.e. north to the top and east to the right. The impacts occur to the lower left (at a latitude of 44 degrees south on Jupiter) and the planet's rapid rotation brings them into view from left to right.

To make it possible see how the impact sites changed over the course of a month I have initially stacked the pictures in sequence according to the approximate longitude of the centre of the disk. Jupiter's rotation period of just under 10 hours meant that at one time or another it was possible to view every part of Jupiter, though poor weather and other commitments some evenings meant that coverage of some longitudes was better than others.

Click on each picture to take you to a full description of what is being seen and when it was made...

Longitude (degrees west of Central Meridian)
305 270 - 220 170 - 125 020 - 060
20 Jul 1994 (304 degrees) 22 Jul 1994 (220 degrees) 29 Jul 1994 (172 degrees) 28 Jul 1994 (022 degrees)
25 Jul 1994 (310 degrees) 8 Aug 1994 (215 degrees) 31 Jul 1994 (122 degrees) 14 Aug 1994 (036 degrees)
  13 Aug 1994 (246 degrees) 17 Aug 1994 (126 degrees) 19 Aug 1994 (039 degrees)
  23 Aug 1994 (270 degrees)   24 Aug 1994 (060 degrees)

Remember that Jupiter is a large planet, about 11 times the diameter of the Earth. Therefore the impact scars I recorded were huge, roughly the size of the Earth itself. This compares closely with the size of some of the observed fireballs created at the moment of impact. Although Jupiter does not have a solid surface, so the explosions took place entirely within the atmosphere, the scale of devastation has worrying implications should an asteroid or comet hit the Earth at a similar speed - an entirely possible event!

20 Jul 1994

Impact scars of Q1, G and L; 20 Jul 1994

Jupiter, with impact sites (left to right) from fragments Q1, D / G complex and L; 20 Jul 1994, 21:40UT

Q crashed into Jupiter just 1h 25m before I drew this picture and is now coming into view on the left hand side of the disk. The older scars of D (crashed 11:50UT on 17th) and G (07:30UT on 18th), which landed almost on top of each other so cannot be distinguished, and L (22:20UT on 19th),are much more obvious. The view of 25th July shows the same longitude but with additional scars caused by later impacts.

System II longitude = 304 degrees.

22 Jul 1994

Impact scars of L and K/W/U; 22 Jul 1994

Jupiter, with impact sites (left to right) L and K / W / U complex; 22 Jul 1994, 21:00UT

This view shows more eastern longitudes - whereas the scar from L is on the right of the 20th July picture, here it is on the left. The double scar to the right was caused by fragments K (10:20UT on 19th Jul), W (08:00UT on 22nd) and U (21:48 on 21st), which almost crashed into the same spot on Jupiter over a period of 2 days. Two weeks later, on 8th August, this view remained almost unchanged.

System II longitude = 220 degrees.

25 Jul 1994

Impact scars of H, Q1, R/S/D/G and L; 25 Jul 1994

Jupiter, with impact sites (left to right) H, Q1, R / S / D / G complex and L; 25 Jul 1994, 21:00 - 21:20UT

This view corresponds almost exactly to that of 20th July but shows additional scars from later impacts. H (19:30UT on 18th) is visible to the extreme left, Q1 is now more visible, the D and G site has been joined by further impacts nearby of R (05:30UT on 21st) and S (15:15UT on 21st), and L is visible to the right much as before. No further view was obtained of this longitude, a shame given how many impacts were visible.

System II longitude = 310 degrees.

28 Jul 1994

Impact scars of E, H, Q1 and R/S/D/G; 28 Jul 1994

Jupiter, with impact sites (left to right) E, H, Q1 and R / S / D / G complex; 28 Jul 1994, 20:30 - 20:45UT

This view is further west of 25th July - the R / S / D / G multiple impact site is disappearing off to the right hand side, and Q1 appears double now. H appears to be fading, but the scar from fragment E (15:12UT on 17th), which crashed 11 days previously, is still very prominent.

System II longitude = 022 degrees.

29 Jul 1994

Impact scars of K/W/U and C; 29 Jul 1994

Jupiter, with impact sites (left to right) K / W / U complex and C; 29 Jul 1994, 20:30 - 20:45UT

This view is further east of 22nd July - the K / W / U multiple impact site is to the left and still appears much as it did a week earlier, complete with an adjacent darkening of the South Temperate Belt. A previously unseen scar C (07:12UT on 17th) is visible to the right.

System II longitude = 172 degrees.

31 Jul 1994

Impact scars of K/W/U, C and E; 31 Jul 1994

Jupiter, with impact sites (left to right) K / W / U complex, C and E; 31 Jul 1994, 20:15 - 20:30UT

This view lies between the longitudes seen on 28th and 29th July - the K / W / U multiple impact site is to the far left, C is to the right of centre but less visible than two days ago, and the scar of E is still clearly visible on the right despite being two weeks old. Amazingly they were still visible two and a half weeks later on 17th August.

System II longitude = 122 degrees.

8 Aug 1994

Impact scars of S/G/D, L and K; 8 Aug 1994

Jupiter, with impact sites (left to right) S / G / D complex on extreme left, L and K / W / U complex; 8 Aug 1994, 20:00 - 20:15UT

This view is almost exactly the same as that of 22nd July and shows that despite nearly two and a half weeks having elapsed the impact sites are still clearly visible. The S / G / D multiple impact site, seen almost edge on, appeared almost as a dent in the left hand side of the planet.

System II longitude = 215 degrees.

13 Aug 1994

Impact scars of S/G/D, L and K/W/U; 13 Aug 1994

Jupiter, with impact sites (left to right) S / G / D complex, L and K / W / U complex; 13 Aug 1994, 20:00 - 20:15UT

Jupiter has rotated 30 degrees to the right compared to the view of 8th August, so the S / G / D multiple impact site has moved further into view, but K / W / U is disappearing off to the right. Few details are visible on the Jupiter compared to earlier pictures because atmospheric turbulence spoilt the view. A view of similar longitudes on 23rd August proves that the impact sites are long-lived.

System II longitude = 246 degrees.

14 Aug 1994

Impact sites of E, H, Q, R and S/D/G; 14 Aug 1994

Jupiter, with impact sites (left to right) E, H, Q1, R and S / D / G complex; 14 Aug 1994, 20:00 - 20:15UT

This view is of the same part of Jupiter as 28th July, but poor atmospheric conditions meant that I saw almost nothing. Although the impact sites are now starting to become more fuzzy as the debris is spread out by winds in Jupiter's atmosphere, another view of the same longitude on 19th August shows that they can still be seen.

System II longitude = 036 degrees.

17 Aug 1994

mpact scars of K/W, C and E; 17 Aug 1994

Jupiter, with impact sites (left to right) K / W, C and E; 17 Aug 1994, 20:00 - 20:15UT

This view is of the same part of Jupiter as 31st July, but again poor atmospheric conditions hampered visibility. The scars of K / W and C can still be seen as dark patches, though E, created nearly a month ago, is less visible now.

System II longitude = 126 degrees.

19 Aug 1994

Impact sites of E and Q1; 19 Aug 1994

Jupiter, with impact sites (left to right) E and Q1; 19 Aug 1994, 19:15 - 19:45UT

The same longitude as 14th August, but whereas I saw almost nothing that night, now the atmosphere was steady and I was able to see a lot of detail on Jupiter. Several giant storms show up as light ovals in the dark Equatorial Belts.The impact sites can still be seen although are definitely starting to become less well defined now, and by the 24th August are becoming harder to see.

System II longitude = 039 degrees.

23 Aug 1994

Impact scars of S/G/D, L and K/W; 23 Aug 1994

Jupiter, with impact sites (left to right) S / G / D, L and K / W; 23 Aug 1994, 19:00 - 19:15UT

A view 25 degrees west of the view on 13th August, with the same sites visible but shifted to the right. A month has now elapsed since the last impacts, and, although the scars are more diffuse now, they are still visible.

System II longitude = 270 degrees.

24 Aug 1994

Impact sites of E and Q1; 24 Aug 1994

Jupiter, with impact sites (left to right) E and Q1; 24 Aug 1994, 19:00 - 19:15UT

A view 20 degrees west of the view on 19th August. The impact sites have almost disappeared now, but several other weather features, most notably the dark cloud in the Southern Temperate Zone adjacent to the white oval Southern Equatorial Belt, are similar to 5 days earlier.

System II longitude = 060 degrees.

So ended my run of observations. As you can see from the times of each picture I had to progressively bring my observations forward as Jupiter set earlier each day. I eventually lost it in the evening twilight as the Sun caught up with Jupiter in mid September.

By the time Jupiter re-emerged into the dawn sky in October little remained to be seen of the impacts, though big telescopes followed the evolution of the impact sites for several more months. Not having a convenient view to the East, I did not make any more drawings. Those that I did make while Jupiter was still in the evening sky serve as a record of an awesome event which, had it taken place on Earth, would have resulted in the extinction of almost every living thing. Let us hope that Jupiter continues to do a good job clearing the skies of dangerous comets!

Jupiter Gallery Jupiter 2001/02

This page last modified