Monday, June 07, 2010

Watch a falling star (on Jupiter)

Last week, the planet Jupiter was hit yet again again by a small asteroid.  This time, the impact was caught on video by amateur astronomer Anthony Wesley, and the impact was confirmed by a second observer, Christopher Go (see June 3), at a different site.  The different site confirms that the flash was not caused by something in the telescope, camera, or sky above Wesley's setup.  This is cool stuff, and many kudos are due to both amateurs.  Even more impressive is that this was Wesley's second impact on Jupiter; he was the first to report a dark spot on Jupiter last year that. Analysis of that spot, imaged by the newly-refurbished Hubble Space Telescope, found that the spot was almost certainly caused by an asteroid and not a comet.  Prior to these two events, the only known impact of which I'm aware was the spectacular crash of the comet Shoemaker-Levy 9.

So, why the recent activity on Jupiter?  Are we witnessing the vanguard of an approaching asteroid armada bent on raining destruction on the Solar System?

I think not.  In fact, I'm positive we are not.  Instead, I think we're witnessing a synergy of technology, of fantastic amateur astronomer abilities, and of our deeper understanding of Jupiter and impact events.  I also think that, if you want, you could personally contribute to our understanding of asteroid impacts on Jupiter, which could help us to better protect our home planet.  Let's look at each of these points.

Improving Technology. The tools that Wesley and Go used to detect the June 3 impact are not professional telescopes with million-dollar imaging systems, but modest-sized amateur telescopes with commercially-available cameras.   The software being used to analyze the images is widely available.  So I my guess is that incremental progress in these technologies and the rapidly increasing use of these technologies by amateurs has crossed a threshold where unambiguous detection of fireballs (very bright meteors) and impact scars on Jupiter is now possible. Further, computer control of telescopes, including robotic operation of telescopes and cameras when the observer has gone to bed, allow individual astronomers to make many more hours of observations than previously possible.

The Rise of the Citizen Scientist  Amateur astronomers have contributed to the science of astronomy as long as the science has existed.   For decades "citizen scientists" have discovered supernovae and comets and contributed to science through organizations like the American Association of Variable Star Observers and the International Occultation Timing Association.  In my own research, volunteers from the Central Texas Astronomical Society have donated their time, expertise, and use of their observatory to our white dwarf observing projects.  More recently, even armchair astronomers without telescopes have been able to contribute to science via projects like SETI@Home and Galaxy Zoo.

Amateur astronomers are eager and willing to do tasks that professional astronomers cannot do.  I'm lucky to get a couple of weeks of telescope time each year, but an amateur with their own telescope under robotic control can look every clear night.  The Hubble Space Telescope has so many projects that it cannot look at Jupiter for more than a few hours a year, while an amateur interested in planets can videotape Jupiter every night it is visible, resulting in over a thousand hours of observing time a year.  Perhaps only one or two professional astronomers could get financial support to look for meteor flashes in Jupiter's atmosphere, and so only one or two would have the resources and impetus to set up a Jupiter meteor watch. But dozens upon dozens of amateurs are willing to  dedicate their equipment to such a search, with the thrill coming in the hunt and the rare success as their reward.

Our better understanding of Jupiter. Prior to the Shoemaker-Levy 9 impact with Jupiter, we really didn't know what an impact would look like.  There have been reports of dark spots on Jupiter since the Giovanni Cassini reported such a spot in 1640.   Only since 1994 have we known that such a dark spot could be a sign of a comet or asteroid hit.  Further, spacecraft like the Galileo mission to Jupiter and the Hubble Space Telescope have been able to measure flashes on Jupiter due to lightning and aurorae.  Knowing the characteristics of other possible sources of bright flares on Jupiter makes us more confident in identifying flashes such as the one above as meteor impacts.

Also, we now understand that Jupiter, as the most massive thing in our Solar System besides the sun, throws its weight around.  Jupiter and the other large planets sculpt the asteroid belt, shepherd several families of asteroids, and shaped the early formation of the Solar System. The Earth, a much smaller target both in size and in gravity, has fireballs that would be bright enough to see from Jupiter relatively often.[1]  It is not surprising, then, that Jupiter should be hit quite regularly by fairly large objects.  Its gravity attracts them.  Therefore, we astronomers aren't as dubious now as we once were about the possibility and frequency of impacts on Jupiter.

How you can contribute to Jupiter science.  Now that Anthony Wesley has proven twice that backyard telescopes can detect impacts of objects on Jupiter, I think it's pretty clear that anyone with the right equipment can do the same.  And we can learn some interesting things from detecting more impacts.  A team of dedicated amateurs detecting many meteors on Jupiter could provide some extremely useful information.

The asteroids that are hitting Jupiter are too small for us to reliably detect from the Earth.  So we don't know how many of these small things there are, and we don't know the distribution of their sizes.  A project dedicated to detecting flashes on Jupiter and measuring their brightness and location on the planet could help planetary astronomers to deduce the numbers of asteroids of different sizes near Jupiter.  Such a project would probably need to detect dozens of flashes, and it would need to develop clever schemes of determining how good the team is at detecting flashes of various brightness, how long the team looked for these flashes, and how accurately they could measure the flashes.  We are probably talking about hundreds of hours of video of Jupiter, so either clever computer software able to detect flashes  or many eager volunteers willing to scrutinize the video would be needed. 

For the record, I am not volunteering to lead such an effort, nor do I know if such a program may already exist.  But if you are into planets, you have time and willpower, and you have or can get the right equipment, I have no doubt you could contribute to Solar System science.

[1] I'm guesstimating this.  A fireball as bright as the sun on Earth is seen from about 100 miles away.  Jupiter is, on average, about 500 million miles away, or 5 million times further.  Since brightness falls as the square of the distance, from Jupiter the fireball would appear 25 trillion times fainter.  But the sun is so bright that, even from Jupiter's distance, the fireball would be barely below the limits of the unaided eye (magnitude 7 for those who speak magnitudes).  This would be easily visible in a telescope, so even if I'm overestimating the brightness by a lot, I think it is still plausible.

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