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Starts With A Bang

Does Jupiter protect Earth or endanger it?

Even with all the recent impacts we’ve seen, it might be more “foe” than “friend” to us.
4 seconds of video, looped here, is sufficient to show the entirety of the September 13, 2021 impact event that occurred on Jupiter, as seen from Earth.
(Credit: José Luis Pereira (Brazil))

On September 13, 2021, a brilliant, transient flash briefly illuminated Jupiter’s surface.

At approximately 10:40 PM UT, an impact event occurred on Jupiter on September 13, 2021, which appears as a brief, transient flash of white light near Jupiter’s equator. This marks the first such event observed on Jupiter in over a year, but the 9th since 2009. (Credit: Harald Paleske, Langendorf, Germany,

Lasting only ~2 seconds, no lasting, visible effects lingered.

Taken approximately one hour after the impact was observed with larger and superior equipment, no lingering effects of the September 13, 2021 impact could be seen with either amateur or professional setups. (Credit: E. Enzmann / Damian Peach.)

The culprit? A small, fast spaceborne body striking Jupiter, disintegrating before reaching its lower atmosphere.

This eight-image sequence shows the September 13, 2021 event of an object striking Jupiter and leaving a temporary mark. From the first image to the last image in this sequence, a total of eight seconds have elapsed. No further effects or consequences have subsequently been observed. (Credit: Jean-Paul Arnould, 54-Villey-le-ssec, France/Societe Lorraine d’Astronomie.)

Such events are relatively commonplace there, indicating Jupiter’s possible protective effects.

Drawing of Jupiter in 1690 by G. D. Cassini, reported in 1692 and brought into prominence in 1997 by Isshi Tabe, Jun-ichi Watanabe, and Michiwo Jimbo. (Credit: I. Tabe et al., Publ. Astron. Soc. Japan, 49, L1-L5, 1997.)

Giovanni Cassini’s 1690 observations of Jupiter revealed a darkened region persisting for 18 days.

During Voyager 1’s 1979 flyby encounter with Jupiter, a brief “point” of light was seen on Jupiter’s surface, representing the first observed bolide event in Jupiter’s atmosphere. Jupiter experiences thousands of times as many such events as Earth does, at minimum. (Credit: NASA / JPL / Voyager 1.)

Voyager 1’s 1979 flyby saw a temporary atmospheric streak.

These are the fragments of Comet Shoemaker-Levy 9 on its final, suicidal plunge toward Jupiter. This image was taken in May 1994, just weeks before all of the 21 identified fragments of the comet, which was torn apart by tidal forces, collided with Jupiter, scarring its outer atmospheric surface for month to come. (Credit: H.A. Weaver, T. E. Smith (STScI), and NASA.)

Impacts regularly occur on Jupiter, but 1994’s Shoemaker-Levy 9 revolutionized the game.

The impact site of fragment G of the nucleus of Comet Shoemaker-Levy 9, with an estimated size all on its own of approximately 1 km in diameter. This fragment left a lasting impact in Jupiter’s atmosphere. (Credit: Hubble Space Telescope Jupiter Imaging Team.)

A fragmented cometary nucleus impacted Jupiter, leaving 21 cumulative scars persisting for many months.

In 1994, the fragmented nucleus of Comet Shoemaker-Levy 9 struck Jupiter, with all 21 fragments impacting the giant planet. Cumulatively, these fragments left a number of scars and dark marks on Jupiter, whose net effects persisted for many months. (Credit: Hubble Space Telescope Comet Team and NASA.)

All told, the original body was about 2-5 km in diameter, comparable to Earth’s infamous K-Pg impactor (which killed off the dinosaurs).

Jupiter, as imaged by Ethan Chappel on August 7, 2019, displays a bright white, transient flash near its limb. This is consistent with either a comet or asteroid strike, the seventh one seen since the 1994 impact of Comet Shoemaker-Levy 9 with our solar system’s largest planet. 2020 and 2021 each have since brought forth another one. (Credit: Ethan Chappel /

Nine additional Jovian impacts were subsequently recorded.

As soon as it was possible, many of the same scientists who studied the Shoemaker-Levy 9 impact of Jupiter with the Hubble Space Telescope returned their sights to the Jovian world 15 years later, catching the aftermath of another large, ~300 meter diameter asteroid strike. This released more energy than any asteroid strike in recorded human history on Earth. (Credit: NASA, ESA, H. Hammel (Space Science Institute), and the Jupiter Impact team.)

One, from 2009, was also large: approximately 300-500 meters across.

The aftermath of the large impact on Jupiter left an enormous scar that could be seen as a black spot in visible light but as a bright spot in the infrared. The multi-wavelength professional measurements that were taken as a follow-up to the initial amateur discovery observations enabled scientists to reconstruct the magnitude of energy released by the impact. (Credit: P. Kalas, M. Fitzgerald, F. Marchis and J. Graham / W. M. Keck Observatories.)

The smallest, observed from Juno in 2020, likely occurs once every 22 minutes.

An ultraviolet view of Jupiter from NASA’s Juno spacecraft’s UVS instrument, revealing a bolide impact (yellow) on April 10, 2020. The ultraviolet data is shown in short wavelength green and long wavelength red, with the yellow spot indicating the emission of both sets of wavelengths. (Credit: R. S. Giles et al., Geophys. Res. Lett., 2021.)

Compared to Earth, strikes on Jupiter occur thousands of times more frequently.

A video of the impact seen on Jupiter on March 17, 2016, as recorded by John McKeon.

Physics predicts this, given Jupiter’s great size and mass advantages over Earth.

A to-scale size comparison of Earth and Jupiter. If we look at these two worlds in terms of cross-sectional area alone, Jupiter’s is 125 times as great, which should lead to a collision rate with asteroids and comets 125 times as large as Earth’s. But the actual rate is much, much larger, owing to Jupiter outmassing Earth by a factor of ~317. (Credit: NASA; brian0918 at English Wikipedia.)

Its gravitational effects will absorb potential impactors but also enhance Earth-crossing events.

The animation depicts a mapping of the positions of known near-Earth objects (NEOs) at points in time over the past 20 years and finishes with a map of all known asteroids as of January 2018. Although Jupiter absorbs many asteroids and comets, it can also redirect them, potentially further endangering the Earth. (Credit: NASA / JPL-Caltech.)

It’s unknown whether Jupiter’s net effects are protective or destructive.

Jupiter, although massive and large enough to draw many orbit-crossing objects into it, even the rapid ones, also redirects and perturbs the orbits of otherwise completely harmless spaceborne masses. Its net effect on the safety of Earth remains unquantified. (Credit: R. Munroe / xkcd / comic 681.)

Only improved simulations and observations will uncover a decisive answer.

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.


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