Impact events on Jupiter

Comet Shoemaker-Levy 9's scar on Jupiter (dark area near Jupiter's limb)

In modern times, various impact events have been observed on Jupiter, the most significant of which was the impact of comet Shoemaker-Levy 9 in 1994.

Jupiter is the most massive planet in the Solar system, and because of its large mass has a vast sphere of gravitational influence, the region of space where an asteroid capture can take place under favorable conditions.

Jupiter is able to capture comets in orbit around the Sun with a certain frequency. In general, these comets travel some revolutions around the planet following unstable orbits as highly elliptical and perturbable by solar gravity. While some of them eventually recover a heliocentric orbit, others crash on the planet or, more rarely, on its satellites.

In addition to the mass factor, its relative proximity to the inner solar system allows Jupiter to influence the distribution of minor bodies there. For a long time it was believed that these characteristics led the gas giant to expel from the system or to attract most of the wandering objects in its vicinity and, consequently, to determine a reduction in the number of potentially dangerous objects for the Earth. Subsequent dynamic studies have shown that in reality the situation is more complex: the presence of Jupiter, in fact, tends to reduce the frequency of impact on the Earth of objects coming from the Oort cloud, while it increases it in the case of asteroids and short period comets.

For this reason Jupiter is the planet of the solar system characterized by the highest frequency of impacts, which justifies its reputation as the "sweeper" or "cosmic vacuum cleaner" of the solar system. 2009 studies suggest an impact frequency of one every 50–350 years, for an object of 0.5–1 km in diameter; impacts with smaller objects would occur more frequently. Another 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 (0.99 mi) in diameter do so just once in every 6,000 years.

About Jupiter

A chain of craters on Ganymede, probably caused by a similar impact event. The picture covers an area approximately 190 km (120 mi) across

Jupiter is a gas giant and as such has no solid surface: the lowest atmospheric layer, the troposphere, gradually transitions into the inner layers of the planet.

The impact of a comet or an asteroid generates phenomena, more or less significant depending on the size of the impacting object, which have a transitory character and which are progressively masked by the action of the winds. Therefore, it is not possible to have news relating to any impacts except through direct and almost immediate observation of the event itself or of the phenomena associated with it.

The cratered surfaces of the major satellites provide information on the most remote epochs. In particular, the discovery (during the Voyager missions) of 13 crater chains on Callisto and three on Ganymede and the testimony of the impact of comet Shoemaker-Levy 9, constitute consistent evidence that some comets have been fragmented and are collided with Jupiter and its moons in ancient times. While the chains of craters observed on the Moon often radiate from major craters and are commonly believed to have been created by secondary impacts of the material ejected from the main collision, those present on the Jovian moons are not connected to a main crater, and it is likely that they were created by the impact of a series of cometary fragments.

The first evidence of impacts on the giant planet dates back to the seventeenth century: the Japanese amateur astronomer Isshi Tabe discovered among the correspondence of Giovanni Cassini's observations some drawings representing a dark spot, which appeared on Jupiter on December 5, 1690, and then follow the evolution over 18 days; it could therefore constitute evidence of the observation of an impact on Jupiter prior to that of Shoemaker-Levy 9.

The impact of a meteoroid on Jupiter was first captured by the Voyager 1 spacecraft in 1979, which recorded a rapid flicker of light in the planet's atmosphere.

Impacts by years

Jupiter impact events

Event	Date (UTC)	Rough original size (meters)	Latitude (°)	Longitude (°)
May 2017 event	2017/05/26 19:25	13	+51.2	?
Mar 2016 event	2016/03/17 00:18:33	15	+4	?
Sep 2012 event	2012/09/10 11:35:00	30	+2	345
Aug 2010 event	2010/08/20 18:22:12	10	+11	?
Jun 2010 Jupiter impact event	2010/06/03 20:31:20	12	−16.1	342.7
Jul 2009 Jupiter impact event	2009/07/19 13:30	300	−57	305
Jul 1994 Comet Shoemaker–Levy 9	1994/07/16-22	1800	−65	?

1994 impact

Main article: Comet Shoemaker–Levy 9

Jupiter in ultraviolet (about 2.5 hours after R's impact). The black dot near the top is Io transiting Jupiter.

Anticipation grew as the predicted date for the collisions approached, and astronomers trained terrestrial telescopes on Jupiter. Several space observatories did the same, including the Hubble Space Telescope, the ROSAT X-ray-observing satellite, the W. M. Keck Observatory, and the Galileo spacecraft, then on its way to a rendezvous with Jupiter scheduled for 1995. Although the impacts took place on the side of Jupiter hidden from Earth, Galileo, then at a distance of 1.6 AU (240 million km; 150 million mi) from the planet, was able to see the impacts as they occurred. Jupiter's rapid rotation brought the impact sites into view for terrestrial observers a few minutes after the collisions.

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.

Hubble Space Telescope images of a fireball from the first impact appearing over the limb of the planet

Animation of Shoemaker-Levy 9's orbit around Jupiter
  Jupiter ·    Fragment A ·   Fragment D ·   Fragment G ·   Fragment N ·   Fragment W

Astronomer Ian Morison described the impacts as following:

The first impact occurred at 20:13 UTC on July 16, 1994, when fragment A of the [comet's] nucleus slammed into Jupiter's southern hemisphere at about 60 km/s (35 mi/s). Instruments on Galileo detected a fireball that reached a peak temperature of about 24,000 K (23,700 °C; 42,700 °F), compared to the typical Jovian cloud-top temperature of about 130 K (−143 °C; −226 °F). It then expanded and cooled rapidly to about 1,500 K (1,230 °C; 2,240 °F). The plume from the fireball quickly reached a height of over 3,000 km (1,900 mi) and was observed by the HST.

A few minutes after the impact fireball was detected, Galileo measured renewed heating, probably due to ejected material falling back onto the planet. Earth-based observers detected the fireball rising over the limb of the planet shortly after the initial impact.

Despite published predictions, astronomers had not expected to see the fireballs from the impacts and did not have any idea how visible the other atmospheric effects of the impacts would be from Earth. Observers soon saw a huge dark spot after the first impact; the spot was visible from Earth. This and subsequent dark spots were thought to have been caused by debris from the impacts, and were markedly asymmetric, forming crescent shapes in front of the direction of impact.

Over the next six days, 21 distinct impacts were observed, with the largest coming on July 18 at 07:33 UTC when fragment G struck Jupiter. This impact created a giant dark spot over 12,000 km or 7,500 mi (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). Two impacts 12 hours apart on July 19 created impact marks of similar size to that caused by fragment G, and impacts continued until July 22, when fragment W struck the planet.

2009 impact

Hubble image of the scar taken on 23 July 2009 during the 2009 Jupiter impact event, showing a blemish of about 8,000 kilometres long.

Main article: 2009 Jupiter impact event

The 2009 impact event happened on July 19 when a new black spot about the size of Earth was discovered in Jupiter's southern hemisphere by amateur astronomer Anthony Wesley. Thermal infrared analysis showed it was warm and spectroscopic methods detected ammonia. The impact has been studied by NASA's Hubble Space Telescope, and the study suggests that the observed incident was a hit by an asteroid about 500 metres (1,600 ft) wide.

2010 impact

Observations made by NASA's Hubble Space Telescope, 7 June 2010

Main article: 2010 Jupiter impact event

A 2010 impact event occurred on June 3 involving an object estimated at 8–13 meters was recorded and first reported by Anthony Wesley. The impact was have also been captured on video by amateur astronomer Christopher Go in the Philippines.

2012 impact

On 10 September 2012 at 11:35 UT amateur astronomer Dan Petersen visually detected a fireball on Jupiter that lasted 1 or 2 seconds using a Meade 12″ LX200. George Hall had been recording Jupiter with a webcam on his 12" Meade; upon hearing the news Hall checked the video to see if the impact was captured. Hall had indeed captured a 4-second clip of the impact and released the video to the public. The impact's estimated position in the system was longitude = 345 and latitude = +2. Dr Michael H. Wong estimated that the fireball was created by a meteoroid less than 10 metres (33 ft) in diameter. Several collisions of this size may happen on Jupiter on a yearly basis. The 2012 impact was the 5th impact observed on Jupiter, and the fourth impact seen on Jupiter between 2009 and 2012. It was quite similar to the flash observed on 20 August 2010. }}

2016 impact

On 17 March 2016 an impact's fireball observed on Jupiter's limb was recorded by Gerrit Kernbauer, Moedling, Austria with an 8" telescope operating at f/15. This report was later confirmed by an independent observation by amateur John McKeon. The size of impact object estimated to be between 7 and 19 meters.

2017 impact

On May 26, 2017, amateur astronomer Sauveur Pedranghelu observed another flash from Corsica (France). The event was announced the next day, and was quickly confirmed by two German observers, Thomas Riessler and André Fleckstein. The impactor had an estimated size of 4 to 10 meters.

2020 impact

On April 10, 2020, the Juno spacecraft observed a fireball on Jupiter's surface, consistent with a 1–4 metres (3.3–13.1 ft) meteor burning up. Although no other fireballs had been detected by Juno before this, the researchers estimate that Jupiter experiences approximately 24,000 impact events of this size per year (~2.7 per hour). For comparison, Earth experiences only ~1-10 such events per year, depending on the precise size of the meteor that hit Jupiter.

Phenomena associated with the impacts

The phenomena associated with an impact on a gas giant are mainly transitory in nature and depend on the size of the impacting body and its composition.

In the case of small meteoroids, the light emission associated with the penetration into the upper layers of the atmosphere was observed, but in the two cases of 2010 no alterations in the clouds were observed either in the minutes immediately following the impact, nor in the subsequent revolutions, in a similar way to what happens for a fireball in the earth's atmosphere.

In the case of objects with a diameter greater than 100 m, able to penetrate below the visible cloud layer, the phenomenology becomes more complex. A large part of the kinetic energy of the impacting object is transferred to the atmosphere and this determines a rapid increase in the local temperature, which is associated with an intense light emission. The mass of atmospheric gas that is affected expands upwards (where it meets less resistance). Thus, a plume is formed that can reach heights of a thousand kilometers and temperatures of a thousand kelvins in a few seconds (for an object originally of about 2 km). When the expansion stops, the plume precipitates on itself and the impact with the atmosphere causes a new temperature increase. This phenomenology was actually observed in the impacts of the larger fragments of comet Shoemaker-Levy 9. This also leads to the upwelling of material from the deepest areas of the planet. In the case of the comet Shoemaker-Levy 9 impacts, ammonia and carbon disulfide (typically present in the troposphere) remained in the upper atmosphere for at least fourteen months after the event.

The collision can also generate seismic waves, which in the case of the SL9 traveled across the planet at a speed of 450 m / s and were observed for more than two hours after the impact. In some cases, moreover, auroras may appear in the vicinity of the impact site and in the diametrically opposite zone, evaluated with respect to the magnetic field of Jupiter, interpreted as a consequence of the fallout of the plume material. Finally, in the case of the impacts of comet Shoemaker-Levy 9, a marked increase in radio emissions from the planet was detected and interpreted as a consequence of the introduction into the Jupiter magnetosphere of relativistic electrons.

On the impact site, depending on the size of the impacting object and its composition, an extremely dark spot quickly forms when observed in the visible and ultraviolet and bright in the infrared. The size of the patch is related to the intensity of the infrared emissions from the impact plume. In the case of cometary objects 1–2 km in size (as was the case with fragment G of comet Shoemaker-Levy 9), the spot is predominant with respect to the typical formations of the Jovian atmosphere. It consists of two elements: a central ellipse, corresponding to the site of the explosion, and a thicker half-ring, in the opposite direction to that of impact and corresponding to the ejected material. The process leading to the stain formation is unclear. Scholars believe it is mainly composed of debris.

Small spots can disappear in a few days or weeks. The larger spots, however, remain for several months, although deforming over time. In the case of multiple impacts, as was the case with comet SL9, an "impact band" can form in correspondence with the band occupied by the spots. In 1994 it did not form from the union of the spots, but materialized as they began to dissolve and persisted until about the middle of the following year.

Identification of the impacting body

Only in the case of the impact of comet Shoemaker-Levy 9 was it possible to observe the impacting body before the collision with the planet; in all other cases an attempt was made to identify their nature and origin by analyzing the effects on the atmosphere. The information acquired during the impacts of the twenty-one fragments of the comet, therefore, constitute an important touchstone for subsequent studies.

The identification of specific chemical species through spectroscopic analysis of the debris makes it possible to distinguish a comet (rich in water and poor in silicon) from an asteroid. While, the depth of the altitude reached by the disturbance generated in the explosion and the duration of the disturbance itself allow, in turn, to produce estimates of the dimensions of the impacting body.

This information is useful for developing models of comet and asteroid populations near the orbit of Jupiter. In this regard, the impact of 2009 was particularly important and could change our knowledge of the number of Jupiter-crossing asteroids if it were statistically significant. On the other hand, the identification may not be correct, thus highlighting a still limited knowledge on the internal composition of cometary nuclei.

Impact frequency

Image of the sign (visible below as a luminous oval) left following the impact of a comet or asteroid with Jupiter, in July 2009. The image was collected by NASA 's Infrared Telescope Facility at a wavelength of 1.65 μm.

The frequency of impact on a planet can be defined as the average interval between two consecutive impacts, so that a high value of it corresponds to a short interval between two consecutive impacts. In 1988, Nakamura and Kurahashi estimated that every 500-1000 years a Jupiter comet with a diameter greater than 1 km could impact the planet. This estimate was revised in light of the impact of Comet Shoemaker-Levy 9, in 1994. In the various subsequent works, values between 50 and 350 years were suggested for an object of 0.5–1 km. However, they are based on some assumptions that have been questioned since the impact of 2009.

In particular, it was believed that the role of asteroids was marginal and it was mainly the Jovian comets that fell on the planet. Furthermore, the time data deriving from the observations has radically changed: in 2008, the only two confirmed observations indicated a time interval of about 300 years between the impact observed by Cassini and that of the SL9. In 2010, the new observation clearly reduces this value, since only fifteen years have passed since the previous impact and it could be possible to estimate, based on the last two observations, even an impact frequency of 10 years for an object of0.5–1 km.

Regarding the impacts with meteoroids, their distribution in the outer solar system is not known and therefore it is not possible to provide a forecast on the frequency of impact without relying on partial data.

Considering a meteoroid of about 10 m in diameter, we would have:

• an impact per year on Jupiter, from considerations relating to the craterisation of the surfaces of the Medicean satellites;
• 30-100 collisions per year, basing the data on asteroid and cometary populations near the planet's orbit.

For comparison, a frequency of impact with an object of this size every 6-15 years has been estimated for the Earth.

In order to estimate the frequency of impacts, observation campaigns were launched with the involvement of various amateurs. Marc Delcroix of the Société Astronomique de France and a group of astronomers from the University of the Basque Country, led by Ricardo Hueso, developed the DeTeCt software to allow rapid identification of any impact and facilitate the rapid spread of the news. In addition, Japanese amateurs from the Association of Lunar and Planetary Observers (ALPO) have activated the "Find Flash" project. The two projects led to an estimate of the minimum impact frequency of meteoroids at about 3,events a year. Astronomer Ricardo Hueso, however, believes that it is more likely that between 10 and 65 impacts per year of meteoroids with a diameter of between 5 and 40 m can occur on the planet. For larger objects capable of leaving a visible scar on the planet's cloud cover for weeks, it provides a frequency of impact every 2-12 years. Even larger objects would impact Jupiter with every 6-30 years.

Following the impact of 10 April 2020 observed by the Juno probe, Rohini S. Giles and colleagues estimated the number of impacts on Jupiter caused by meteoroids with masses between 250 and 5 000 kg.

Search campaigns

As highlighted in the previous sections, from the observation of the impact events on Jupiter it is possible to deduce information on the composition of comets and asteroids, but also on that of the deeper layers of the Jovian atmosphere. The frequency of impacts, on the other hand, provides us with information on the asteroid and cometary populations present in the outer solar system.

You can recognize the recent impact sites for the characteristics that distinguish them, in particular the appearance of dark spots on the planet disc, as happened in 2009. The detectors CCD in visible currently on the market can determine the minimum size of about stains300 km wide. Sanchez-Lavega and colleagues suggest exploiting the brightness of the spots at a wavelength of 890 nm, detectable using CCDs suitable for near infrared, or the one corresponding to the range 2.03-2.36 μm, detectable using K filters.

Different is the case of the meteoroids that do not leave evident impact marks. The light emission that accompanies the entry into the atmosphere in their case lasts a few seconds (1–2 s) and therefore a continuous monitoring of the planet's surface at high frequency is necessary for their identification. Hueso et al. suggest that telescopes with a diameter between 15 and 20 cm are the ideal tools for their detection, if equipped with webcam or other video recording tools.

Finally, more information on the frequency of impact can also be obtained by analyzing the historical observations of Jupiter conducted in the eighteenth and nineteenth centuries in the light of the new knowledge acquired. For example, the Hungarian astronomer Illés Erzsébet, analyzing the correspondence of the observations made at three Hungarian observatories, identified three other possible impact events that occurred in 1879, 1884 and 1897. The proposed identifications need to be confirmed.

Finally, some 2007 studies related the ripples of Jupiter's rings to the impact of comet SL9, analyzing the time evolution recorded by the instruments on board the Galileo, Cassini and New Horizons probes that visited the planet. In the rings, "fossil traces" could therefore be present from which the occurrence of previous impacts could be deduced or, in the future, traces of events not directly observed could appear.

Collisions in mass culture

The direct observation of impact events on Jupiter has led to the growing awareness, even in public opinion, that the impact of a comet or asteroid with our planet would have potentially devastating consequences. Therefore, the possibility of such a fall has become something concrete, from which one must, as far as possible, guard against.

This happened above all thanks to the story of comet Shoemaker-Levy 9, to which extensive media coverage was dedicated and whose historical significance had been highlighted. Among the forms of communication aimed at the general public, there was also the production in 1998 of the films Deep Impact by Mimi Leder and Armageddon by Michael Bay.

The discovery of the subsequent impacts has shown, however, that these events are much more frequent than previously thought. It should also be noted the role played by non-professional astronomers in identifying the signs of impact, [83] also thanks to a reduction in the cost of technologically advanced observation instruments.

Further reading

• Bertrand M. Peek (1981). Faber and Faber Limited (ed.). The Planet Jupiter: The Observer's Handbook. Londra. ISBN 0-571-18026-4. OCLC 8318939.{{cite book}}: CS1 maint: location missing publisher (link)
• Eric Burgess (1982). Columbia University Press (ed.). By Jupiter: Odysseys to a Giant. New York. ISBN 0-231-05176-X.{{cite book}}: CS1 maint: location missing publisher (link)
• John H. Rogers (1995). Cambridge University Press (ed.). The Giant Planet Jupiter. Cambridge. ISBN 0-521-41008-8. OCLC 219591510.{{cite book}}: CS1 maint: location missing publisher (link)
• Reta Beebe (1996). Smithsonian Institute Press (ed.). Jupiter: The Giant Planet (2 ed.). Washington. ISBN 1-56098-685-9.{{cite book}}: CS1 maint: location missing publisher (link)
• AA.VV. (1999). Sky Publishing Corporation (ed.). The New Solar System. Massachusetts: Kelly J. Beatty; Carolyn Collins Peterson; Andrew Chaiki. ISBN 0-933346-86-7. OCLC 39464951.
• D. C. Jewitt, S. Sheppard, C. Porco, F. Bagenal; T. Dowling; W. McKinnon (2004). Cambridge University Press (ed.). Jupiter: The Planet, Satellites and Magnetosphere (PDF). Cambridge. ISBN 0-521-81808-7. Archived from the original (PDF) on 2007. {{cite book}}: Check date values in: |archive-date= (help)CS1 maint: location missing publisher (link) CS1 maint: multiple names: authors list (link)
• Linda T. Elkins-Tanton (2006). Chelsea House (ed.). Jupiter and Saturn. New York. ISBN 0-8160-5196-8.{{cite book}}: CS1 maint: location missing publisher (link)

Scientific articles

• National Space Science Date Center, NASA (ed.). "Comet Shoemaker-Levy 9 Collision with Jupiter".
• K. S. Noll (1995). "HST Spectroscopic Observations of Jupiter Following the Impact of Comet Shoemaker-Levy 9". Science. 267 (5202): 1307–1313. doi:10.1126/science.7871428. PMID 7871428. S2CID 37686143.
• Rogers, J.H. (1996). "The comet collision with Jupiter: II. The visible scars". Journal of the British Astronomical Association. 106 (3): 125–149. Bibcode:1996JBAA..106..125R.
• Martin, T.Z. (1996). "Shoemaker-Levy 9: Temperature, Diameter and Energy of Fireballs". Bulletin of the American Astronomical Society. 28: 1085. Bibcode:1996DPS....28.0814M.
• Nakamura, T. (1998). "Collisional Probability of Periodic Comets with the Terrestrial Planets: An Invalid Case of Analytic Formulation". Astronomical Journal. 115 (2): 848–854. Bibcode:1998AJ....115..848N. doi:10.1086/300206.
• Sánchez-Lavega, A. (2010). "The impact of a large object with Jupiter in July 2009" (PDF). The Astrophysical Journal Letters. 715 (2): L150. arXiv:1005.2312. doi:10.1088/2041-8205/715/2/L155. S2CID 119251280.
• Hueso, R. (2010). "First Earth-based Detection of a Superbolide on Jupiter" (PDF). The Astrophysical Journal Letters. 721 (2): L129–L133. arXiv:1009.1824. Bibcode:2010ApJ...721L.129H. doi:10.1088/2041-8205/721/2/L129. S2CID 37619282.
• Fletcher, L.N. (2010). "Jupiter Impacts in the Thermal-Infrared: Comparing Atmospheric Responses in 1994, 2009 and 2010". American Astronomical Society, DPS Meeting #42, #31.03; Bulletin of the American Astronomical Society. 42: 1010. Bibcode:2010DPS....42.3103F.
• Orton, G.S. (2011). "The atmospheric influence, size and possible asteroidal nature of the July 2009 Jupiter impactor". Icarus. 211 (1): 587–602. Bibcode:2011Icar..211..587O. doi:10.1016/j.icarus.2010.10.010.
• R. Hueso (2018). "Small impacts on the giant planet Jupiter" (PDF). Astronomy & Astrophysics. 617: A68: 1-13. arXiv:1804.03006. Bibcode:2018A&A...617A..68H. doi:10.1051/0004-6361/201832689. S2CID 102339147.

References

The article was partly translated from the Italian Wikipedia article. For original, see it:Eventi d'impatto su Giove.