There were plenty of collisions in the early solar system. There’s reason to believe that comet collisions were probably what caused elements other than hydrogen and helium to get to Jupiter. But sizeable impacts inside the solar system are now a pretty rare event, with one occurring only every few centuries.
In fact, the first observed collision of two solar system bodies took place only in 1994. The collision took place between comet Shoemaker-Levy 9 and the giant planet Jupiter between July 16, 1994 and July 22, 1994.
Named after its discoverers
American astronomer Carolyn Shoemaker discovered Shoemaker-Levy 9 along with her geologist husband Eugene Shoemaker and Canadian amateur astronomer David Levy. It was discovered on March 24, 1993 based on a photograph taken with the 0.4 metre Schmidt telescope at Mt. Palomar. Named after its discoverers, it was the ninth short-period comet discovered by the trio.
The first comet observed orbiting a planet rather than the sun, it had already been torn into more than 20 pieces and was travelling around Jupiter in a two-year orbit at the time of discovery. Orbital studies confirmed that the comet (believed to be a single body at the time) had passed within Jupiter’s Roche limit in July 1992, thereby being torn apart into at least 21 fragments by the planet’s tidal forces.
Galileo’s view
While the disruption of a comet into many fragments was in itself unusual, observing a captured comet in orbit around Jupiter was even more rare. If that weren’t enough, astronomers soon learnt that the comet’s orbit would pass within Jupiter in July 1994, thus smashing into the giant planet. With NASA having a spacecraft in position to watch this as it unfolded, excitement reached fever pitch.
It proved worthy every bit as a spectacular event unfolded from July 16, 1994. With NASA’s Galileo orbit then en route to Jupiter, it was able to capture the event in unprecedented detail. The fragments of the comet, labelled A through W, smashed into Jupiter’s cloud tops, starting on July 16 and ending on July 22. Earth-based observatories and orbiting spacecraft like the Hubble Space Telescope and Voyager 2 also studied the impact and the aftermath.
Force of 300 million atomic bombs
On the same day when the world’s first atomic bomb was successfully tested in 1945 as part of the Trinity test, the fragments of the comet started smashing into Jupiter with the force of 300 million atomic bombs. Not only did these fragments create gigantic plumes that were 2,000 to 3,000 km high, but they also heated the Jovian atmosphere to temperatures as high as 30,000 to 40,000 degrees Celsius. The impacts of the comet left dark, ringed scars on Jupiter that were later erased by the planet’s winds.
While people from around the world followed the event, it enabled scientists to learn a lot, including the fact that the comet supplied water to Jupiter’s atmosphere. Based on a number of studies, this water is still there, decades later.
Scientists tracked high-altitude winds on Jupiter for the first time by observing the dust, left floating following the collision, spread across the planet. Scientists also studied the changes in the magnetosphere with changes in the Jovian atmosphere after the impact.
Additionally, they were able to find out the composition and structure of the original comet, with calculations revealing that it would have been 1.5 to 2 km wide. If an object of that size were ever to hit our Earth, it would be catastrophic. Just ask the dinosaurs!
