Sen—Twenty years ago this month, there occurred one of the most astonishing events ever witnessed in our Solar System.
A comet that had disintegrated into a parade of fragments began bombarding mighty planet Jupiter—and the results were plain to see.
The comet was named Shoemaker-Levy 9, after the astronomers who discovered it on a photographic plate, Carolyn and Eugene Shoemaker, and David Levy, in March 1993.
But this was no ordinary comet. For one thing, it had several bright nuclei, showing that it must be in many pieces. And another oddity was that tracking data showed it to be in orbit around Jupiter.
It became clear that this comet had been torn to pieces by the planet’s powerful gravitational pull. Calculating back, it could be worked out that this catastrophic event had happened when the comet previously passed close to Jupiter in July 1992.
But studies of the comet’s track under Jupiter’s influence revealed something even more dramatic—Shoemaker-Levy 9 was actually going to collide with the planet from 16 to 22 July, 1994, the year after its discovery.
Comet Shoemaker-Levy 9 looked like a string of pearls when it was imaged by Hubble on 17 May, 1994. Image credit: NASA, ESA, and H. Weaver and E. Smith (STScI)
With such a momentous event in the offing, professional astronomers everywhere turned their telescopes on the comet, including Hubble in orbit. They continued to watch fascinated as the comet fragments drifted through space like a string of pearls.
The event will live in my memory for as long as I live because I was lucky enough to have a ringside seat. At the time I was a regular visitor to Puimichel, a hilltop village in a beautiful rural region of south-east France in the foothills of the Alps.
Surrounded by lavender fields, on a high point just outside the village, stood an observatory with a 1-metre reflecting telescope, built for amateur use by Belgian telescope maker, Dany Cardoen, with the support of his partner Arlette Steenmans.
And so it was that I headed to Puimichel. This was an event not to be missed!
As the date of the first impacts approached, no one really knew what we were going to see. There was no doubt that the comet chunks would hit Jupiter, but would anything be visible from Earth or would the fragments disappear without a trace into the planet’s opaque cloud belts?
Astronomical CCD cameras were then still in their infancy. Instead we hired an only moderately bulky Sony video camera from the photographic shop in the nearest town, and hooked it up to the telescope and a TV monitor. Then we waited, all seated around the edge of the telescope dome.
It was known that the impacting fragments would hit Jupiter just out of sight on the planet’s far side. When the crash sites rotated into view, soon after, we could scarcely believe our eyes. It was as if the gas giant had been given a series of black eyes, with the impact scars clearly visible in the planet’s cloud tops.
We watched transfixed as more and more markings became visible—Jupiter spins quite rapidly in just under 10 hours. Then, to everyone’s surprise, they remained visible as new features in the cloudtops for several months before finally fading away.
Since then, a number of smaller impacts have been observed or captured on camera by amateur planetary imagers, showing how the giant planet is something of a magnet for asteroids and the like.
When I lived in London, I was a regular visitor to Puimichel and had my most memorable astronomical nights there. Highlights included two great comets—Hyakutake in 1996 and Hale-Bopp a year later.
Hyakutake, whose spring-onion tail grew noticeably in length from night to night as it approached the Earth, is still the only comet I have seen reflected in a puddle. And it was most impressive to see Hale-Bopp rise tail-first over the distant Swiss Alps.
I saw some memorable meteors too, including a strong return of the Perseids in 1993, an awesome and unexpected night of Leonid fireballs in 1998, then a storm of largely fainter meteors from the same shower a year later.
You will understand why Puimichel has a special place in my heart!