Science@NASA: Fireballs Light Up Jupiter

[bystander]

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In a paper published today in the Astrophysical Journal Letters, a group of professional and amateur astronomers announced that Jupiter is getting hit surprisingly often by small asteroids, lighting up the giant planet's atmosphere with frequent fireballs.

"Jupiter is a big gravitational vacuum cleaner," says co-author and JPL astronomer Glenn Orton. "It is clear now that relatively small objects left over from the formation of the solar system 4.5 billion years ago still hit Jupiter frequently."

The impacts are bright enough to see through backyard telescopes on Earth. Indeed, amateur astronomers were the first to detect them, recording two fireballs in 2010 alone—one on June 3rd and another on August 20th.

Professional astronomers at NASA and elsewhere have followed up on the amateur observations, hoping to learn more about the impacting bodies. According to today's Letter, first-authored by Ricardo Hueso of the Universidad del País Vasco in Spain, the June 3rd fireball was caused by an object some 10 meters in diameter. When it hit Jupiter, the impact released about one thousand million million (10^15) Joules of energy. For comparison, that's five to ten times less energy than the "Tunguska event" of 1908, when a meteoroid exploded in Earth's atmosphere and leveled millions of trees in a remote area of Russia. Scientists continue to analyze the Aug. 20th fireball, but think it was comparable in scale to the June 3rd event.

Before amateurs spotted these fireballs, scientists were unaware collisions so small could be observed. The first hint of their easy visibility came in July 2009 when Anthony Wesley, an amateur astronomer from Australia, discovered a dark spot on Jupiter. It was clearly the swirling debris of an impact event that he had only just missed. Next time, however, his luck would improve. On June 3, 2010, he caught a fireball in action.

First Earth-based Detection of a Superbolide on Jupiter - R Hueso et al

• Astrophysical Journal Letters 721(2) L121 (01 Oct 2010) DOI: 10.1088/2041-8205/721/2/L129

[rstevenson]

What changed to so recently give amateurs the ability to spot these hits? Better optics more reasonably priced? Better digital image software? Jupiter being hit more often recently? What changed?

Rob

[Chris Peterson]

What changed to so recently give amateurs the ability to spot these hits? Better optics more reasonably priced? Better digital image software? Jupiter being hit more often recently? What changed?

Mainly, it's just that Jupiter is under more continual observation. The optics have not improved. But good quality digital video cameras have become more common, and cheaper. And since the best images of Jupiter are always made using video, an increasing number of people are watching the planet that way.

It is entirely unsurprising (at least in retrospect!) that fireballs are being imaged on Jupiter. They are pretty common on Earth, and Jupiter will have far more than Earth.

[Ann]

I'm the only one I know who prefers Jupiter over Saturn when it comes to visual appearance. And why? Because Jupiter has better colors, of course!

(But I'll say this... When I look at the planets through a 14-inch telescope, where you can't see many details and no color in Jupiter's cloud tops, but the rings of Saturn show up magnificently, then even I prefer Saturn!)

Ann

[Chris Peterson]

(But I'll say this... When I look at the planets through a 14-inch telescope, where you can't see many details and no color in Jupiter's cloud tops, but the rings of Saturn show up magnificently, then even I prefer Saturn!)

Am I misunderstanding what you are saying? Even a 2 or 3 inch scope will easily show Jupiter at 100X (giving about 3 times the apparent size of the Moon) and let you see excellent color- a range of browns, beiges, yellows, and pinks.

As far as detail... with my 12" scope on a night of good seeing, I can visually (at a few hundred power) make out structure in the bands, festoons, and lots of colorful features.

[Ann]

Well, when I have looked at it, I haven't been able to see much color at all. Of course our telescope is located right outside a city of 300,000 people and another city of a million people just some thirty miles away.

Bright stars, though, unlike planets, are always bright enough to make their colors known even in light-polluted surroundings.

Ann

[Chris Peterson]

Well, when I have looked at it, I haven't been able to see much color at all. Of course our telescope is located right outside a city of 300,000 people and another city of a million people just some thirty miles away.

Bright stars, though, unlike planets, are always bright enough to make their colors known even in light-polluted surroundings.

Interesting. I find that the colors of Jupiter, Mars, and Saturn are best seen in late twilight, when the sky isn't completely dark (I don't have any light pollution to use for this purpose <g>). With a really dark sky, the contrast between background and planet seems to make it a little harder to see subtle color. But I think star colors become more obvious under dark skies.

In any case, telescope aperture is not a factor in seeing color on planets. A telescope can never make a planet appear brighter than it does to the naked eye. It can make it appear dimmer, of course. Increased aperture will allow you to reach a higher magnification before the image becomes dimmer than it is unaided. But at low magnification, there is no advantage to a larger aperture at all.

[Ann]

All right, Chris. I realize that I didn't give you a good answer or a good reason for my failure to see color in Jupiter.

When I did some observing, I had already been interested in astronomy for many years without making an effort to actually see thigs through a telescope. For a long time I thought it wasn't worth it. And the reason for that was precisely that I knew that I wouldn't be able to see much color in the sky that way. What was the use of looking at a faint grey smudge in the sky and being told that now I had observed M51? I would much, much rather look at a glorious color image of that and other galaxies.

What made me finally decide to do some real observing with a telescope was that I had become convinced that it was possible, though not necessarily easy, to see blue color in the sky. I had become convinced that there were blue stars out there whose colors was detected by some people but not by others, and I really, really wanted to know if I was one of those who could "see blue" out there. But while the blue stars were my top priority hands down, I also needed to observe many non-blue stars of different hues to understand star colors in general.

As for Jupiter, it honestly never occurred to me that I could see color in it. And if someone had told me that I could, it wouldn't have been a priority with me. Of course the colors of Jupiter will be brought out much better by a good color photo than by making an effort to make out color details during an observing session with a telescope.

So while I have always been extremely concentrated when I had looked at stars and extremely focused on seeing their color, I never made any sort of an effort to see color in Jupiter. I was impressed that the planet was so obviously striped, and then I looked at the moons. And then I was done. I have observed stars all on my own, but when I have observed Jupiter I have always been in the company of others. And the other people have talked enthusiastically about the moons of Jupiter, but none of them have shown the least bit of interest in the colors of Jupiter.

Ann