[5] This generated a large amount of coverage in the popular media, and the comet was closely observed by astronomers worldwide.

The collision provided new information about Jupiter and highlighted its possible role in reducing space debris in the inner Solar System.

While conducting a program of observations designed to uncover near-Earth objects, the Shoemakers and Levy discovered Comet Shoemaker–Levy 9 on the night of March 24, 1993, in a photograph taken with the 46 cm (1.51 ft) Schmidt telescope at the Palomar Observatory in California.

[11] However, as his team were expecting comets to be inactive or at best exhibit a weak dust coma, and SL9 had a peculiar morphology, its true nature was not recognised until the official announcement 5 days later.

[16] The most optimistic prediction was that large, asymmetric ballistic fireballs would rise above the limb of Jupiter and into sunlight to be visible from Earth.

[8] Anticipation grew as the predicted date for the collisions approached, and astronomers trained terrestrial telescopes on Jupiter.

[19] Two other space probes made observations at the time of the impact: the Ulysses spacecraft, primarily designed for solar observations, was pointed toward Jupiter from its location 2.6 AU (390 million km; 240 million mi) away, and the distant Voyager 2 probe, some 44 AU (6.6 billion km; 4.1 billion mi) from Jupiter and on its way out of the Solar System following its encounter with Neptune in 1989, was programmed to look for radio emission in the 1–390 kHz range and make observations with its ultraviolet spectrometer.

[21][22]A few minutes after the impact fireball was detected, Galileo measured renewed heating, probably due to ejected material falling back onto the planet.

This impact created a giant dark spot over 12,000 km or 7,500 mi[26] (almost one Earth diameter) across, and was estimated to have released an energy equivalent to 6,000,000 megatons of TNT (600 times the world's nuclear arsenal).

[28] Observers hoped that the impacts would give them a first glimpse of Jupiter beneath the cloud tops, as lower material was exposed by the comet fragments punching through the upper atmosphere.

[29] As well as these molecules, emission from heavy atoms such as iron, magnesium and silicon were detected, with abundances consistent with what would be found in a cometary nucleus.

[30] As predicted, the collisions generated enormous waves that swept across Jupiter at speeds of 450 m/s (1,500 ft/s) and were observed for over two hours after the largest impacts.

[32] This was thought to be due to synchrotron radiation, caused by the injection of relativistic electrons—electrons with velocities near the speed of light—into the Jovian magnetosphere by the impacts.

The cause of these emissions was difficult to establish due to a lack of knowledge of Jupiter's internal magnetic field and of the geometry of the impact sites.

High resolution spectroscopic studies found that variations in the ion density, rotational velocity, and temperatures at the time of impact and afterwards were within the normal limits.

By far the most massive planet in the Solar System, Jupiter can capture objects relatively frequently, but the size of SL9 makes it a rarity: one post-impact study estimated that comets 0.3 km (0.19 mi) in diameter impact the planet once in approximately 500 years and those 1.6 km (1 mi) in diameter do so just once in every 6,000 years.

During the Voyager missions to the planet, planetary scientists identified 13 crater chains on Callisto and three on Ganymede, the origin of which was initially a mystery.

[47] On July 19, 2009, exactly 15 years after the SL9 impacts, a new black spot about the size of the Pacific Ocean appeared in Jupiter's southern hemisphere.

Thermal infrared measurements showed the impact site was warm and spectroscopic analysis detected the production of excess hot ammonia and silica-rich dust in the upper regions of Jupiter's atmosphere.

Scientists have concluded that another impact event had occurred, but this time a more compact and stronger object, probably a small undiscovered asteroid, was the cause.

Astronomers have speculated that without Jupiter's immense gravity, extinction events might have been more frequent on Earth and complex life might not have been able to develop.

In 2009, it was shown that the presence of a smaller planet at Jupiter's position in the Solar System might increase the impact rate of comets on the Earth significantly.

A planet of Jupiter's mass still seems to provide increased protection against asteroids, but the total effect on all orbital bodies within the Solar System is unclear.