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David SealJune 5, 2009

The Steven J. Ostro Memorial Symposium on Planetary Radar and Near-Earth Objects

by David Seal

he non e impresa da pigliare a gabbo
iscriver fondo a tutto l'universo,
e da lingua che chiami mamma o babbo.
a quelle donne aiutino il mio verso...
i che dal fatto il dir non sia diverso.

To talk about the bottom of the universe
he way it truly is, is no child's play,
o task for tongues that gurgle baby-talk.
ut may those heavenly ladies aid my verse...
hat my words may tell exactly what I saw.

I'm a fan of the movie "Joe Versus the Volcano". It slipped by sort of unnoticed, as just another fanciful romantic comedy (most of which I detest) way back yonder in 1990, despite starring Tom Hanks and Meg Ryan, and screenwriting by John Patrick Shanley. Shanley has won an Oscar (Moonstruck) and a Pulitzer (Doubt). There's a very short list of people who have won both a Pulitzer and an Academy Award. (Doubt has won just about everything else, as well.)

Anyway, there's a scene early in the movie which pretty much captures the spirit of the film, where Meg Ryan says to Tom Hanks:

y father says almost the whole world's asleep.
verybody you know, everybody you see, everybody you talk to.
e says only a few people are awake.
nd they live in a state of constant and total amazement.

It's quite a statement, and one that almost certainly put most people (myself included) on the defensive immediately. But this isn't my intention. I had the pleasure of attending part of the Steve Ostro symposium at JPL today, and based all of the testimonials mixed in with interesting science that his work enabled, and the fond stories shared during the meeting, I suspect Steve Ostro may have been awake most of the time. The meeting has certainly added to my happily long list of experiences in the field of science and engineering that have made me feel truly awake and alive, and privileged to be making a small contribution. I hope that Emily's blog helps engender a similar response in its readers, perhaps in small ways here and there. I certainly have memories of big thoughts being thunk (sic) at the eyepiece of my Dad's telescope years ago.

If you aren't familiar with Steve, you should pause for a moment and look at Emily's blog written back in December shortly after his death ( - or, the DPS in memorium ( He was the principal pioneer in the use of Earth-based radar to study bodies in the Solar System, notably asteroids, and his work has made significant contributions in the study of near-earth objects which Bruce Betts blogged about here just a few weeks ago. As one of the speakers pointed out, solar system evolution is collisional evolution. The study of the small bodies of the solar system, which shed so much light on collisional behavior and processes, contributes directly to our fundamantal understanding of the universe.

Steven J. Ostro, 1946-2008


Steven J. Ostro, 1946-2008

teve's family was in attendance, the talks were outstanding, and it was truly heartwarming to see so many of his friends and colleagues present and contributing their work, nearly all of which was enabled by Steve's contributions. Dan Scheeres said "Steve was a visionary, able to imagine what others could do with his science before they knew it." Erik Asphaug stated eloquently "Steve sent a lot of us on these trajectories in planetary science. And now we're alone." Don Yeomans, supervisor of JPL's Solar System Dynamics group and manager of NASA's Near-Earth Object program office also added, "He would have loved this symposium, surrounded by family, friends and colleagues.... One or two of us here taught Steve, but almost all of us were taught by Steve. He showed us worlds that we wouldn't otherwise have seen. And we were all very privileged to have known him."

Some of the current highlights and spinoffs from Steve's work that I don't think have been mentioned in detail in this blog are as follows.216 Kleopatra, perhaps the most bizarrely shaped asteroid ever imaged, has itself two satellites just recently discovered by one of Steve's colleagues Franck Marchis. Full article here. The many binary asteroids discovered so far - 16% of near-Earth asteroids are binaries - and the short lifetimes of their stability (compared to the age of the solar system) suggest that asteroids may become binaries (via collisional-induced "fission" or the collection of bodies through encounters) often during their lifetime. The evolution of asteroids seems to be far more complex and interesting than we ever thought - at least, before Steve came along.



steroid 216 Kleopatra. From Science, vol. 288, no. 5467, 5 May 2000.

steroid 2009 KK is the new naughty asteroid in the near-earth family, being only the second object to be currently listed above level zero on the Torino scale. The Torino scale is a very familiar approach to hazard assessment for mission planners such as myself, employing the product of probability and severity to rate an event. For example, we all wear seat belts when we get in the car, right? The probability of getting into an accident on any one day is quite small, but the severity of the event if we're NOT wearing a belt is high, and since the product of those two variables is not zero, we put our belts on dutifully. That's what the Torino scale tells you. For 2009 KK, there's a keyhole in about two weeks, and observations hopefully to take place shortly thereafter will help update the likelihood of impact in May 2022. Currently it's at 0.000096. (See The energy released from an earth impact would be about 1,000 megatons. (Perhaps Emily will blog on this in more detail in the near future.)1999 KW4 is an interesting example of a binary asteroid very well imaged by Steve's radar observations, and therefore, its shape and orbits are known pretty well. Dan Scheeres, one of the presenters, pointed me to a movie made here at JPL by the Digital Image Animation Laboratory which I'm happy to share.

David Seal David Seal is Cassini's Mission Planner at the Jet Propulsion Laboratory and has been involved with the Cassini mission to Saturn since 1992. Dave developed JPL's Solar System Simulator and has also worked on the Shuttle Radar Topography Mission. Outside of JPL, Dave enjoys acting in Caltech theater, disc golf, and the science of soap bubbles. Dave foolishly believes the universe is closed.

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David Seal

Cassini Mission Planner for Jet Propulsion Laboratory
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