The spot was first seen by an amateur Australian astronomer Anthony Wesley The spot was first seen by an amateur Australian astronomer Anthony Wesley
An object that hit Jupiter last year with a force equivalent to a few thousand nuclear bombs, which left it with a scar the size of Pacific Ocean was probably an asteroid, say astronomers.
Images of the "bruise" captured by the Hubble telescope show the aftermath of an asteroid striking a planet.
It could provide clues about what might happen if a similar object hit Earth.
The spot was first seen in 2009 by an Australian amateur astronomer.
The astronomer in question, Anthony Wesley, has recently taken another striking image of an bright fireball hitting the gas giant. Scientists believe it to be a meteoroid - a small particle of space debris.
A team of scientists described in the Astrophysical Journal Letters how they compared the 2009 Hubble images with those of scars left on Jupiter by a comet in 1994.
Jupiter impacts were thought to be quite rare. After the latest collision with a comet called P/Shoemaker-Levy 9, or SL9, astronomers didn't expect any other strikes for at least several hundred years.
'A surprise'
That is why some 500m-wide space rock plunging into the gas giant's atmosphere was rather unexpected, said astronomer Heidi Hammel of the Space Science Institute in Boulder, Colorado, who led the study.
"This solitary event caught us by surprise," she said.
"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."
Dr Hammel's team used the Hubble telescope's Wide Field Camera 3 to zoom in on the blemish near the Jupiter's southern pole and captured several sharp ultraviolet images.
Astronomers spotted a flash on Jupiter - possibly a meteoroid striking the planet Astronomers spotted a flash on Jupiter - possibly a meteoroid striking the planet
The scientists compared the pictures with those of the scars left by SL9 15 years earlier and saw important differences between the two impacts.
Most importantly, they found no "halo" around the latest collision site. A comet would have generated a halo of fine dust as it impacted the surface.
The clues helped them to conclude that the mystery object was probably not a dusty comet but a solid space rock that perhaps came from a nearby asteroid belt.
Agustin Sanchez-Lavega of the University of the Basque Country in Bilbao, Spain called Jupiter a "natural laboratory" to see what might happen to our planet in the event of a similar collision.
"It would be a catastrophe," he said.
"The Jupiter impact produced a pattern of debris some 5,000km long and 2,800 km wide - half the size of the Earth. And even if the response of the Earth atmosphere is different from that of Jupiter, entire continents could be destroyed."
Amateur astronomers
The scientist also commented on the latest flash spotted on Jupiter by Anthony Wesley and another amateur, Christopher Go from the Philippines.
It is believed to be the very first image of a meteoroid hitting a planet.
This also shows that amateur astronomers now have the necessary high quality technology to capture such events that only last a few seconds.
"We cannot devote the Hubble space telescope or other telescopes to observe Jupiter regularly, it is impossible," he said.
"And the amateurs make a very good survey of what is happening there, contributing to our database."
A similar impact occurred last July after a large asteroid collided into the planet.
A large object, possibly an  or a , hit the planet Jupiter Thursday, resulting in a large fireball.

The fireball was seen on June 3 at 2031  by two independent amateur astronomers, Christopher Go in the Philippines and Anthony Wesley in Australia. Wesley, who posted the news onto an , is known for having also spotted last July's . Go caught Thursday's impact on video, which showed a fireball the size of Earth after the object hit. It could be the first time someone has recorded a meteor crashing into a planet.

This latest strike came only hours after a team from the , led by astronomer , announced that last year's event was the result of an asteroid 1,640 feet (500 metres) wide. That asteroid caused a scar the size of the  when it hit Jupiter with the force of several thousand nuclear bombs on July 19, 2009.

The planet last experienced a major impact in July 1994, when it was hit by  (SL9), resulting in large scars as well. Scientists originally thought that there would not be any more Jupiter strikes for several centuries following SL9, but have now been proved wrong twice in as many years.

Now, astronomers around the world are trying to figure out what kind of mark Thursday's collision left on the planet, as well as determine exactly what hit it. Although the impact is believed to be relatively small, a dark debris field may soon appear in the clouds around Jupiter, which is what occurred in 2009.