Planets

Jupiter Is Smashed by Over 6 Huge Fireballs per Year

The gas giant is known to be the target of some massive chunks of space debris, but now astronomers have a pretty good idea about how many big impacts can be seen from Earth.

Jupiter is walloped by impacting meteors and other bodies big enough to generate fireballs visible from Earth an average of 6.5 times per year, a new study shows.

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The estimate, based on observations from a group of about 60 amateur astronomers worldwide, is a bit lower than expectations, French astronomer and project coordinator Marc Delcroix said in a statement.

Since June 2010, amateur astronomers have serendipitously observed fireballs in Jupiter's atmosphere four times, including a March 2016 impact captured in telescope images by Austria's Gerrit Kernbauer and Ireland's John McKeon.

"In three years since our program started, amateur contributors from Europe, the United States and Australia have analyzed the equivalent of more than 56 days of videos - around 53,000 videos - without discovering an impact," Delcroix said.

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The group is working to improve software that would make it easier for more amateur astronomers to join the project.

Amateur astronomers capture an image of a fireball in Jupiter's atmosphere on March 17. | G. Kernbauer, J. McKeon, S. Voltmer

"This should help in refining the impact estimations for Jupiter, and hopefully discover new impacts," Delcroix said.

"Unfortunately, we are still dealing with the statistics of a very few number of impacts detected, but plans to improve our detection methods and perform systematic searches will help us to detect more of these objects," astronomer Ricardo Hueso, with the University of the Basque Country in Spain, said in a statement.

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"That will allow us to know more about the current architecture of the outer solar system and the role of Jupiter in protecting the Earth from comparable impacts," he added.

The estimate was presented Wednesday at an international workshop on Jupiter for professional and amateur astronomers at the Observatoire de la Côte d'Azur in Nice, France.

Jupiter looks badly bruised after fragments of Comet Shoemaker-Levy 9 collided into the giant planet in July 1994. The collision gave scientists worldwide a once-in-a-lifetime opportunity to watch comet pieces – traveling at 130,000 mph – slam into the planet and explode with 100 times the power of the world’s arsenal of nuclear warheads at the peak of the Cold War.

As NASA's Juno mission speeds towards a July 2016 date with Jupiter, the spacecraft is already racking up milestones in space. Just this month it became the furthest-flying solar spacecraft ever, even surpassing the feat of the Rosetta spacecraft that is still operating well at Comet 67P/Churyumov–Gerasimenko. As a preview of this amazing mission to the solar system's biggest planet, explore some of the science and engineering tasks Juno will focus on during its mission.

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We often speak about the water on the icy moons in the outer solar system, such as Jupiter's Europa. But what is not is well-known is Jupiter itself has quite a bit of water in it. The upper atmosphere is actually seeded with water from the Shoemaker-Levy 9 comet impact of 1994. The water was discovered in 2013 after the Herschel Space Observatory found water concentrated in areas close to where the comet fragments

slammed into the atmosphere

. Water in other parts of the atmosphere may have come about during Jupiter's formation, when icy planetesimals were abundant in the solar system. Looking at water and other elements within Jupiter will give us a sense of what the solar system used to look like, because Jupiter -- unlike our own planet -- is very close in composition to what it was when it was formed. (Earth gained a new atmosphere through plants and volcanic eruptions, among other factors.

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Image: Jupiter's water distribution in the stratosphere, mapped by the Herschel Space Observatory. White and cyan show high concentrations, and blue is lower concentrations. The map is overlaid on a visible-image picture of Jupiter taken by the Hubble Space Telescope.

Jupiter has an enormous and powerful magnetosphere, which is greatly apparent in the strength of its auroras. (This 2007 outburst is an example). The challenge is there are few long-term observations of faraway planets, which is where Juno will have an advantage over observatories such as the Hubble Space Telescope that can only check in from time to time. The key to Jupiter's strong auroras is hydrogen gas getting crushed in the planet's intense gravity. It becomes metallic hydrogen and this fluid is very conductive. Juno will look at Jupiter's charged particles and magnetic fields from up close, with the aim of making projections for other big planets in our solar system and other locations.

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Image: A 2007 X-ray view of auroras on Jupiter taken by the Chandra X-Ray Telescope (purple). The optical picture is from the Hubble Space Telescope.

Jupiter's immense gravity is a boon when we try to send spacecraft far out in the solar system. We've used the giant planet as a speed boost for missions such as Voyager and New Horizons. The bonus is during these maneuvers, investigators usually turn on the cameras and at least some instruments to add to our scientific knowledge of Jupiter. Juno's role will be to look at the gravity field in detail, to find out about any changes and how they may be caused. Fluctuations in gravity could point to changes in the planet's interior structure.

VIDEO: Juno's Epic Flyby View of the Earth and Moon

Image: A massive plume is visible on Io (foreground) in this montage picture of Jupiter based on New Horizons data obtained in 2007.

One of the atmospheric mysteries of Jupiter is why the Great Red Spot is shrinking. This feature has been a part of Jupiter for at least 400 years (as long as we have had telescopes), but it's getting smaller for reasons that are poorly understood. The rate of shrinking also changes from year to year. The Hubble image you see here also shows a rare wave structure that was only seen once before, in pictures from 1977 taken by the Voyager 2 mission. For its part, Juno will map how deep these colorful features in the atmosphere penetrate, and also track the motions of fluids below the cloud tops for the first time.

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Image: A 2015 map of Jupiter taken by the Hubble Space Telescope, including the Great Red Spot (lower right).

While Juno is focused on the science, the spacecraft itself will also be a useful point of study to plan future long-term missions. Juno is actually the furthest-operating spacecraft to use solar power, a milestone it just passed this month. Improvements in energy efficiency for the instruments and spacecraft, as well as better solar-cell performance, made this possible. As with all missions, scientists will be looking at how well the spacecraft does over time. When something breaks (as it inevitably will), the team will try to figure out a way to fix it. They will also try to design the next generation of that part better so that it doesn't break on the next spacecraft.

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