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When amateur astronomer Anthony Wesley from Australia saw a dark spot the size of the Pacific Ocean appear on Jupiter through his telescope on July 19, 2009, this started a flurry of astronomic activity, with other telescopes quickly slewing to take a look. It didn’t take long for other astronomers to confirm Jupiter had been hit by an object, either an asteroid or a comet. Of course, the world’s most famous telescope, Hubble, zeroed in on this unexpected activity on Jupiter, and luckily, the telescope had been recently updated with a new Wide Field Camera 3 and newly repaired Advanced Camera for Surveys. Astronomers have now released a series of images from Hubble which may show for the first time the immediate aftermath of an asteroid striking another planet.
Astronomers have witnessed this kind of cosmic event before, but from a comet. Similar scars had been left behind during the course of a week in July 1994, when more than 20 pieces of Comet P/Shoemaker-Levy 9 (SL9) plunged into Jupiter’s atmosphere. The 2009 impact occurred during the same week, 15 years later.
But comparing Hubble images of both collisions, astronomers say the culprit was likely an asteroid about 1,600 feet (500 meters) wide.
Source: Hubblesite.org
“This solitary event caught us by surprise, and we can only see the aftermath of the impact, but fortunately we do have the 1994 Hubble observations that captured the full range of impact phenomena, including the nature of the objects from pre-impact observations” says astronomer Heidi Hammel of the Space Science Institute in Boulder, Colo., leader of the Jupiter impact study.
The analysis revealed key differences between the two collisions (in 1994 and 2009), providing clues to the 2009 event. Astronomers saw a distinct halo around the 1994 impact sites in Hubble ultraviolet (UV) images, evidence of fine dust arising from a comet-fragment strike. The UV images also showed a strong contrast between impact-generated debris and Jupiter’s clouds.
Hubble ultraviolet images of the 2009 impact showed no halo and also revealed that the site’s contrast faded rapidly. Both clues suggest a lack of lightweight particles, providing circumstantial evidence for an impact by a solid asteroid rather than a dusty comet.
The elongated shape of the recent asteroid impact site also differs from the 1994 strike, indicating that the 2009 object descended from a shallower angle than the SL9 fragments. The 2009 body also came from a different direction than the SL9 pieces.
Source: Hubblesite.org
Team member Agustin Sanchez-Lavega of the University of the Basque Country in Bilbao, Spain, and colleagues performed an analysis of possible orbits that the 2009 impacting body could have taken to collide with Jupiter. Their work indicates the object probably came from the Hilda family of bodies, a secondary asteroid belt consisting of more than 1,100 asteroids orbiting near Jupiter.
The 2009 strike was equal to a few thousand standard nuclear bombs exploding, comparable to the blasts from the medium-sized fragments of SL9. The largest of those fragments created explosions that were many times more powerful than the world’s entire nuclear arsenal blowing up at once.
The recent impact underscores the important work performed by amateur astronomers. “This event beautifully illustrates how amateur and professional astronomers can work together,” said Hammel.
The Jupiter bombardments reveal that the solar system is a rambunctious place, where unpredictable events may occur more frequently than first thought. Jupiter impacts were expected to occur every few hundred to few thousand years. Although there are surveys to catalogue asteroids, many small bodies may still go unnoticed and show up anytime to wreak havoc.
The study by Hammel’s team appeared in the June 1 issue of The Astrophysical Journal Letters.
Science Paper by: Hammel et al. (PDF document)
Source: HubbleSite
@brundall – Just like when a meteoroid hits Earth’s atmosphere and is heated by friction until it either vaporizes and leaves a bright trail across the (night) sky and/or explodes. If any part of it survives and hits/lands on the Earth, it becomes a meteorite. Meteors are traveling through space at speeds somewhere between 25,000 mph (~7 miles per second) and 160,000 mph (~45 miles per second) when they enter the Earth’s atmosphere. That’s much faster than a re-entering shuttle and most spacecraft. Because of Jupiter’s mass, those speeds can be much higher as the object falls into its massive gravity well. You are right that Jupiter is mostly gas with a solid core. “At its center, Jupiter is thought to have solid metal-rock core, similar in composition to Earth, with a diameter of about 24,000 km and a mass of 10 to 15 Earth-masses. Surrounding this, out to a diameter of about 100,000 km, is a metallic mixture of hydrogen and helium. On Earth we know these two as gases; in Jupiter’s interior the pressure is so high that the hydrogen takes up a state in which it behaves like a metal.” quote from The Encyclopedia of Science
I saw C. Shoemaker/Levy 9 in 4″, 8″ and 10″ telescopes when it hit… I found it hard to believe that my little 4″ scope was able to see some of the details of those impacts! It was quite the memorable night! We were clouded out here and I was unable to see Anthony Wesley’s remarkable find… dzzz.. Maybe next time?
So what exactly does an asteroid or comet impact with on Jupiter to explode in such a way? Isn’t Jupiter mostly gas with a solid core?
@brundall Massive shock-waves of the very high entry speed.
So they do actually explode then and not just punch holes in the gas layer?
Aqua, is incorrect in stating, above, that a meteoroid “is heated by friction until it either vaporizes and leaves a bright trail across the (night) sky and/or explodes.”
Actually, a meteoriod/asteroid impacting a planet’s atmosphere produces a shock wave generated by the extremely rapid compression of gas in front of the meteoroid/asteroid. It is primarily this ram pressure (rather than friction) that heats the gas in front of the meteoroid/asteroid, which then heats up the object as the hot gas (plasma) flows around it — at this point, the object is called a “meteor”/”fireball” as the resulting plasma glows brightly.
Think of it this way: the ceramic tiles on the Space Shuttle are extremely delicate; they crumble easily in your hand. If they were heated by friction as the shuttle de-orbits and enters the atmosphere at Mach 25, the tiles would disintegrate — which would not be a very good design characteristic for a spacecraft’s heat-shield if friction were the governing factor.
AFAIU, the reason why some large objects, such as “rubble pile” asteroids or comets, explode upon entering the atmosphere (as did happen at Tunguska on 30th June 1908) is that when the pressure differential between the high ram pressure at the front and the low pressure at the rear of the object exceeds the weak van der Waals cohesion force that holds such objects together, the object quickly disintegrates and the smaller particles, each with less momentum, are slowed down abruptly by the atmosphere; consequently, the extremely high total kinetic energy of the individual particles of the original object are subsequently converted into thermal energy, which results in them almost instantly vaporizing into gas and then the rapidly expanding hot gas causes the explosion — conventional explosives rapidly convert chemical energy into thermal energy that transforms a solid (or liquid) into an expanding hot gas to create an explosion.
of course, the observed gravitational fragmentation of the comet but not the putative asteroid object add to the observational difference.
First, I like IVAN3MAN_AT_LARGE’s description.
With excuses if I mess this up, but: anything above ~ 3 km/s or roughly the sound of speed in crystalline materials is defined as hypervelocity. The stress on the material from the resulting shock waves make the strain exceed material deformation limits.
That explains why such objects that aren’t compressively slowed down or disintegrated will make a huge crater out of anything it meets.
Second, to make comparison here, think of it in terms of energy and momenta from escape and orbital velocities. The Earth-Moon system has an escape velocity of ~ 11 km/s; only artifacts such as the Apollo capsule achieve the corresponding speeds from the energy gained when falling down the gravity well.
Add Earth orbital velocity, ~ 30 km/s, to that to get the potential asteroid velocity. Asteroids typically strikes Earth at ~ 20 km/s I believe; enough momentum that some few percent ejecta may in turn exceed escape velocity in large impacts!
For comets, add solar system escape velocity, ~ 40 km/s for tumbling down the larger well, to orbital velocity. AFAIU, comets typically hits us at ~ 60 km/s. That gives some ram pressure, I would say.
Interesting people agreeing with Aqua for once.
But I also agree with the explanation of Aqua. If he is right then he is right.
OK Incorrectly read the first sentence of IVAN3MAN_AT_LARGE.
Incorrect instead of correct, I missed the “in”
But in defence of Aqua this time, he was trying to explain it to brundall in a simple way, even though technically it is not perfect. For brundall, this was more than enough.
I just did a quick calculation, 1 kg mass entry at 45km/s would be about 1 Giga joule kinetic energy.
A 4000 ton mass at 45km/s would have the equivalent of an 1 Megaton atomic bomb.
Apophis has 2.7 × 10^10 kg mass
2.7 × 10^10 kg/ 4000 tons which is equivalent of a 6,750,000 Megaton bomb energy if it entered Jupiter at 45 km/s
One Tsar bomb, the biggest atom bomb ever was 100 Mega Tons. Imagine that Apophis would be the equivalent of 67,500 Tsar bombs.
I guess that Jupiter would have a big hole. LOL
Anyone know of any estimates of how far below the visible surface of Jupiter (define it however you like) the asteroid got before coming to rest?
By that I mean that if it vaporized, where did the vapor stop. Of course, the shock wave will have traveled through the whole planet!
I imagine, but do not know, that the distance for a comparable-sized comet would be considerably less.
How long would it take to get there?