Comets in our solar system have always been an interesting phenomenon. The unique characteristics, chemical properties, and the search for life outside Earth are all explored through comets as well as other celestial objects. However, some of these comets have collided and exploded very close to our planet. While this does present a threat to our planet, it makes it even more questioning as to what would happen if any celestial object collided with Earth. One such comet has been Shoemaker-Levy9 which broke into 21 individual pieces.
Overview of the Shoemaker-Levy 9 Comet
Comet Shoemaker-Levy 9 was discovered by astronomers Carolyn Shoemaker and Eugene Shoemaker on 24th March 1993. The official name of this comet was D/1993 F2. The comet got its popularity in science and astronomy because it broke into 21 pieces after colliding with the planet Jupiter.
This was the first time any celestial object collision was observed by scientists. It was also the first time a cosmic event was given press attention and the collision was shown all over the media as well. The collision aided the study of celestial objects as well as an idea about the strong gravitational force of Jupiter as well as its associated properties. As Jupiter is a wild planet with many interesting characteristics, the predicted collision of SL9 with Jupiter was quite significant.
Discovery of Comet Shoemaker-Levy 9
Shoemaker-Levy 9 was discovered by husband and wife Eugene Shoemaker and Carolyn Shoemaker. Along with them was David Levy as well. The three were researching to find out near-Earth objects and it was just too unexpected when they saw the Shoemaker-Levy 9 comet.
On the night of 24th March 1993, the three of them first discovered the comet with the help of the Schmidt Telescope located at Palomar Observatory in California. By that time, it was orbiting the planet Jupiter and was captured in its orbit in a very strong manner. Although this telescope was only 46 cm, it was able to take a good enough picture to make valuable judgments about the properties, orbit, and ongoing collision path of Comet Shoemaker-Levy 9.
The first photographs of the comet showed that it was quite a rare comet as it had multiple nuclei in elongated regions. These nuclei measured 50 arcseconds long by 10 arc seconds wide. Upon a closer inspection by Brian G Marsden, it was found out that the comet was just 4 degrees from Jupiter as seen from Earth which indicated that the comet was in orbit of Jupiter or just too close to it. The discovery was announced in the International Astronomical Union Circular on 26th March 1993 with which, the comet got popular and gained media attention as well.
Pre-Collision Observations of Shoemaker-Levy 9
Scientists did not know from the start that this comet is on a collision course. The first orbital studies showed that this planet had a Jovian Orbit which meant that it was orbiting around the planet Jupiter unlike many of the comets which orbit around the sun. The orbital period was estimated to be roughly around 2 years and an apoapsis. The orbital distance was considered 0.33 astronomical units. Scientists, from this point, started to trace back the appearance of this comet from various astronomical records.
The initial observations showed that the comet had been orbiting Jupiter for some time. Some studies suggested that it was orbiting Jupiter since the mid-1960s when the planet captured it from solar orbit. This was because of the strong gravity of Jupiter which obstructed the orbital path of Shoemaker-Levy 9. Previous images of this comet were also found.
Further studies showed that the comet passed the planet Jupiter extremely close in 1992 when it was just around 40,000 km away from the planet, but not close to its center. This was so close that the strong forces of Jupiter could have disrupted the comet with the strong gravity. The main nucleus of the comet broke and the comet was segregated into 21 fragments with a highly eccentric two-year obit.
However, this encounter was still not as close to breaking away the entire comet or having it collide with the planet. Further studies showed that if the comet continued its orbit, it would collide with Jupiter in 1994. This was because the comet was about to pass the center of Jupiter at a distance of just 45,000 km. It was also evaluated that the nuclei of the comet would plow into Jupiter in a total of 5 days.
Collision Prediction
Once it was confirmed that the collision is highly likely with Jupiter, the comet got mass attention from astronomical organizations all over the world. Many astronomers started to pursue theories of collision as well as predict the collision course of the comet as well as possible aftereffects. This was the first time that people on Earth were going to witness the collision of two celestial bodies, which is why astronomers from all over the world were interested in it.
After thorough studies and countless tests, the collision course and theories were finalized. Astronomers predicted that collision would cause the eruption of material from layers that are normally hidden below the clouds of a certain planet’s atmosphere. This would provide a better idea about Jupiter as a planet as well.
Astronomers predicted that upon collision, there would be ballistic fireballs that would rise above Jupiter into the sunlight. This would make these fragments possible to be seen from Earth. Possible impacts of the collision were predicted to be huge. The seismic waves would be created that would travel across the planet. However, due to the massive size of Jupiter planet, it would not affect it in any way. There was no chance that this comet would possibly impact Earth in any way pre or post-collision.
The Collision of Shoemaker-Levy 9 Comet
As time passed, astronomers started to predict more precise dates of the collision. Apart from that, preparations were underway on Earth as this was the first time a celestial object collision was to be noticed. Many spacecraft were already in space and were set in direction to observe the collision. This includes the Hubble Space Telescope, Galileo Spacecraft, and Voyager 2 as well.
The collision between Shoemaker-Levy 9 and Jupiter occurred on 16th July 1994 at 20:13 UTC. Fragment A hit the southern hemisphere of planet Jupiter at a speed of 60km/s which is equivalent to 216,000km/h. As per the prediction, there was a fireball coming out of Jupiter that had a temperature of approximately 23,700 degrees Celcius or 42,700 Fahrenheit. The fireball’s fume reached a height of 3,000km and was then observed by the Hubble Space Telescope. As soon as the fireball rose, it deposited dark clouds on top of the Jovian clouds.
Each fragment had a collision with a gap of 7 to 8 hours. In total, the fragments collided over the period of 21 days. Fragment G was considered as the heaviest one as it had the most impact upon collision and the fireball coming from Fragment G was the brightest. It also had an estimated diameter of between 300 and 600 meters. Upon collision and cloud formation, Fragment G left a cloud that was bigger than the entire Earth and had a diameter of 12,000km. Astronomers suggested that this Fragment alone delivered an impact of 48 billion tons of TNT which is several times the nuclear power present on Earth, to date.
As opposed to the predictions, the collision occurred on a sight that could not be viewed from the Earth. However, spacecraft were able to observe it from a different viewing angle. Galileo, Voyager 2, and Hubble Space Telescope were able to capture images that were then seen by astronomers. Astronomers on Earth could only see the post-impact view and not exactly the time of impact. The clouds that had formed over Jupiter vanished from Jupiter’s winds in the next few days / weeks.
Post-Collision Analysis
Most astronomers were amazed to watch the collision. Many studies went underway later on to evaluate the atmospheric conditions of Jupiter as well as Shoemaker-Levy 9. According to the official statement of NASA “Comet Shoemaker-Levy, 9 indicated that large impacts can still happen in the solar system which is why NASA needs to develop programs to assess the counter the risk that these events pose on Earth”.
Spectroscopic studies showed that there are few absorption lines in the Jovian region occurring due to diatomic sulfur and carbon disulfide. It was the first time that these two elements were found in the atmosphere of Jupiter. Ammonia and Hydrogen sulfide were also detected in the post-collision study. Apart from common elements and molecules, heavy atoms such as iron and silicon were also detected which were obvious from the nucleus of the comet.
As per the prediction, there were major waves that went across Jupiter at a speed of 450m/s equivalent to 1620km/h. Due to a stable layer pattern of the waves, scientists concluded that the waves had either reached the water layer or were spreading within the stratosphere. One astonishing fact was that water was found but not in as much quantity as the scientists predicted.
About the Discoverers – The Shoemakers and David Levy
Eugene Merie Shoemaker was born on 28th April 1928 and died on 18th July 1997. He was an American geologist who studied various phenomena of Earth as well as major comets, meteors, and other celestial objects in space. Among the notable contributions of Eugene Shoemaker is the discovery of the Shoemaker-Levy Comet and Barringer Meteor Crater. Carolyn Shoemaker was his wife who was an Astronomer and discovered 31 comets other than Shoemaker-Levy as well as more than 500 asteroids.
David Howard Levy is a Canadian astronomer who was born on 22 May 1948. He was also a co-discoverer of SL9. He also discovered other comets and minor planets during his career.
Conclusion
The Shoemaker-Levy 9 was one of the most astonishing comets in our solar system. It had several aspects from its first discovery to the collision to a post-collision impact. The SL9 was quite helpful for the astronomical community to study many other comets as well as devise coherent opinions on the planet Jupiter. To date, it stands as one of the most interesting events in the history of space exploration.