Shoemaker Levy 9, the first time we can see the Biggest impact of a comet
In July 1994, a vast comet 2 km in diameter hit Jupiter with the force of 300 million
atomic bombs, followed by another 20 impacts that set fire to the clouds of the gaseous
planet for six successive days. This was the first time in history that humanity managed
to witness live what a planetary collision of colossal magnitudes can do. What happened
to Jupiter after impact, and what have we learned since then?
let's go to start! "Introduction" THE GREAT DISCOVERY
In 1993 a group of astronomers formed by the couple Carolyn and Eugene Shoemaker and David
Levy was conducting research at the Palomar Observatory in California in the USA, when
they discovered a massive spot by pure chance in the image records.
It was nothing more and nothing less than a vast periodic comet 2 km in diameter that
had been captured by the gravitational pull of Jupiter, which was named Shoemaker-Levy9
in honor of the discoverers. This was an extremely unusual event because although hundreds of
comets are known in the solar system, this was the first time that one captured by the
gravity of a planet instead of the gravity of the sun was observed.
Usually, periodic comets are those that orbit the sun in less than 200 years, but Jupiter
is so massive and its gravitational attraction force so great that it can capture any object
that gets too close to it; in fact, astronomers believe that many of its moons are asteroids
that were captured by Jupiter and never managed to escape its gravitational field.
The image of the discovery gave the first proof that it was a strange comet since it
had multiple nuclei in a region approximately 50 arcseconds long; for reference, common
comets usually have a single nucleus. In contrast, Shoemaker-Levy9 had about 20, which indicated
that something must have happened in the past that fragmented it into several pieces.
Brian Marsden of the Central Bureau for Astronomical Telegrams later noted that the comet was only
4 degrees from Jupiter and that its apparent motion indicated that it was approaching that
planet on an inevitable collision trajectory. Where did it come from?
The scientific community cataloged the discovery of comet Shoemaker-Levy9 as a stroke of luck
or fate since it was discovered only because the Palomar Observatory had begun a search
for near-Earth objects (NEOs); if we had not started the search in that same year, we would
never have managed to see this comet. Since from the moment of its discovery until its
collision with Jupiter, it was only with us for little more than a year.
Tracing the comet's trajectory back in time, it was found that it had been orbiting Jupiter
for some time, where it was most likely captured from a solar orbit in the early 1970s, although
it may well have happened much earlier, in the mid-1960s.
Through more extensive analysis of images taken before March 24 by the Precovery method,
some observers also found the comet in a March 15 photograph. The Precovery method is an
astronomical term that describes the process by which a known object is identified in archival
images or photographic plates to calculate an orbit more accurately in both the past
and the future, to know where it came from and what its trajectory will be in the years
to come. The volume of space for an object to be said
to have been in the orbit of a planet is defined by the Hill sphere.
The Hill sphere is the gravitational sphere of influence of a celestial body. The concept
was defined by American astronomer George William Hill (1838-1914). However, it is also
called the Roche sphere because it was also described independently by the French astronomer
Édouard Roche. The Hill sphere involves three main force
fields: 1. Gravity due to the central body
2. Gravity due to the second body 3. The centrifugal force that keeps the two
bodies away from each other. The Hill sphere is the sphere within which
the sum of the three fields is directed toward the second body, keeping the more petite body
trapped in its gravitational field. When comet SL9 approached Jupiter in the mid-1960s
and early 1970s, it entered its aphelion and encountered Jupiter's Hill sphere; When this
happened, the planet's gravity pulled on the comet, pulling it in and capturing it with
its gravity. Because the comet's motion was minimal relative
to that of the planet, Shoemaker-Levy 9 rushed into Jupiter's atmosphere in an almost rectilinear
motion, causing it to end up orbiting the planet's core with a reasonably high eccentricity,
that is, with a reasonably slight curvature. Comet Shoemaker-Levy 9 passed close to Jupiter
on July 7, 1992, just 40,000 km above the planet's clouds and within Jupiter's Roche
boundary. The Roche boundary is an area within which the tidal force is strong enough to
fragment anybody object that remains there. While the comet had had close approaches to
Jupiter before, the July 7 encounter appeared to be the closest, and the comet's partition
is thought to have occurred at that time, which is why SL9 had a nucleus fragmented
into several pieces rather than a solid nucleus like most comets.
Each of the pieces to which the comet had been reduced was named with a letter of the
alphabet, from "fragment A" to "fragment W," a practice established by astronomers to facilitate
its further study. Astronomer Zdeněk Sekanina analyzed each fragment and concluded that
the original comet may have had a nucleus up to 5 km in diameter.
THE EVENT OF THE CENTURY When it became official that the comet's trajectory
was on a collision course with Jupiter, the news caused great excitement in the astronomical
community because the impact of two bodies of that magnitude in the solar system had
never been observed. SL9 would give astronomers a unique opportunity
to peer into Jupiter's dense atmosphere, as the collisions were expected to cause eruptions
of material from the layers usually hidden beneath clouds.
Before the impact, one of the big debates was whether these effects would be visible
from Earth or if, for example, they would disintegrate as giant meteoroids. Other suggested
effects include that the impacts would generate seismic waves that would propagate across
the planet, an increase in the amount of fog in the stratosphere due to dust, and an increase
in the mass of the ring system. Everyone was excited, it was an event that
can only be seen once in a lifetime, and it was necessary, if not obligatory, to use all
the observation technology we had to study in detail every second of the impact, as this
would help us to understand these events better when a similar threat heads towards Earth.
THE BIG IMPACT As the date for the collisions approached,
astronomers prepared their telescopes, including the Hubble Space Telescope, the X-ray observation
satellite ROSAT, and, of course, the Galileo space mission. On its rendezvous journey with
Jupiter set for 1996. Successive impacts of the 23 fragments were
scheduled to occur between 20:00:40 UTC on July 16 (fragment A) and 07:59:45 UTC on July
22 (fragment W). Everything was prepared; no one was going to miss this historic moment.
The long-awaited day began with fragment A's impact, which hit Jupiter's southern hemisphere,
creating a hole in the clouds that caused a spot more significant than the "Great Red
Spot." "Place at this time video label on the great
red spot of Jupiter." The instruments on the Galileo mission discovered
a bolide that reached a maximum temperature of about 24,000 K, which contrasts with the
temperature of the upper clouds of Jupiter's atmosphere, which have, in general, a typical
temperature of about 130 K, then about 40 seconds later the temperature dropped rapidly
to about 1500 K. The impacts proved impressive: the fragments
(about 21 in total) plunged into Jupiter's atmosphere for six consecutive days. When
they hit, they traveled at a speed of about 37 miles per second (60 kilometers per second)
and heated the atmosphere to at least 53,000 degrees Fahrenheit (30,000 degrees Celsius).
Like the splash that occtheurs when a rock is thrown into a pond, the impacts created
giant columns of material from Jupiter's lower atmosphere, which rose to 1,900 miles (3,000
kilometers) above the clouds, up to the stratosphere. As a result, the splash created a scar in
Jupiter's atmosphere with dark debris clouds from the impact that could be seen for months
as Jupiter's winds gradually scattered them. As planned, the impacts ended on July 22,
when the W fragment hit the planet. Astronomers had predicted they see the effects of impacts
from Earth but had no idea how visible the atmospheric effects of each collision would
be; the largest of these was generated by fragment G on July 18 at 07:34 UTC. This impact
created a big dark spot more than 12,000 km in diameter. It was estimated as an explosion
of energy equivalent to 6,000,000 megatons of TNT, six hundred times the nuclear arsenal
of Earth. The black spot that generated fragment G was so dark that amateurs could see it and
were able to blind some of the telescopes that observed it.
WHAT HAVE WE LEARNED FROM THIS EVENT? Astronomers learned many things thanks to
the impact of this comet on Jupiter. On the one hand, those dark clouds of impact debris
acted as markers of winds in Jupiter's stratosphere. Following their movement over time, scientists
could measure those high-altitude winds to estimate their nature.
SL9's impact caused temporary changes in Jupiter's aurora, showing scientists that particles
from impacts influenced Jupiter's magnetosphere. According to Dr. Fast, today, we can still
see changes in Jupiter's atmosphere due to impacts. When the fragments of Shoemaker-Levy
9 crashed into Jupiter, depositing their chemical compounds, the impact processes also produced
some chemicals inside Jupiter, and others were unearthed from the lower atmosphere.
Some molecules, such as ammonia, were destroyed by sunlight during the weeks and months after
the impacts, but others, such as hydrogen cyanide and water, are still seen today. All
of that tells scientists how chemistry works in Jupiter's atmosphere and how comets can
deposit vast amounts of minerals on a planet, bolstering the theory that Earth's water comes
from comets. Comet Shoemaker-Levy 9 showed us that significant
impacts still occur in the solar system, which was an essential factor in the development
of NASA programs aimed at addressing the risk that one day, one of these bodies will be
heading for a collision with Earth. From comet science to Jupiter-related science and impact
science, the legacy of that serendipitous discovery by Carolyn and Gene Shoemaker and
David Levy continues to this day and extends into the future.