- Steven J. Ostro
Steven J. Ostro is an American scientist specializing in
radar astronomy . He works atNASA 'sJet Propulsion Laboratory . Ostro has led radar observations of numerous asteroids, as well as the moons of Jupiter and Saturn, Saturn's rings, and Mars and its satellites. As of May 2008, Ostro and his collaborators have detected 222near-Earth asteroids (including 130 potentially hazardous objects and 24 binaries) and 118 main belt objects with radar [http://echo.jpl.nasa.gov/asteroids/asteroid_radar_highlights.txt] .Education and Employment
Ostro received an AB in liberal arts and a BS in ceramic science from
Rutgers University in 1969, a masters in engineering physics fromCornell in 1974, and his PhD inplanetary science fromMIT in 1978. At MIT, Ostro was advised byGordon Pettengill and studied the radar scattering properties ofSaturn's rings and theGalilean satellites using theArecibo Observatory .After completing his graduate work and a year as a
postdoc at MIT, Ostro served as anassistant professor of astronomy atCornell before moving toJPL in 1984.Currently, Ostro heads JPL's Asteroid Radar group, and is also a member of the
Cassini–Huygens RADAR team, studying the moons ofSaturn .Asteroid Radar Astronomy
Much of Ostro's career has focused on the development of asteroid
radar astronomy . In early experiments, such as the first radar detection ofCeres , radar observations of asteroids were restricted to measurements ofDoppler shift s andradar cross-sections [Ostro, S.J. et al. 1979. Radar observations of asteroid 1 Ceres. Icarus 40, 355-358] . Beginning in the early 1980's, Ostro led the development of radar imaging and shape-reconstruction techniques, first determining only outer limits of targets' shapes, then deriving three-dimensional shape models [Ostro, S.J. et al. 1988. Asteroid shapes from radar echo spectra: A new theoretical approach. Icarus 73, 15-24] . FromAugust 19 to 22 of1989 , Ostro andScott Hudson observed the contact binary4769 Castalia from theArecibo Observatory , producing the first resolved radar images of an asteroid, which they later used to construct a model of the object.Following the further development of imaging and shape reconstruction techniques by Ostro, Hudson, and
Christopher Magri and the upgrade of Arecibo in the mid-1990s, the number of radar observations has increased dramatically [echo.jpl.nasa.gov] .Notable asteroids observed by Ostro include:
*
216 Kleopatra - a large main-belt asteroid, the first asteroid confirmed to have a surface composition of nickel-iron.
*1986 DA - the first near-Earth asteroid confirmed to be metallic. The estimated amount ofplatinum -group metals in 1986 DA is comparable to that in theBushveld Igneous Complex , the largest source on Earth's surface.*
4769 Castalia - the first near-Earth asteroid imaged well enough to determine its shape, which is two distinct 0.9-km lobes in contact (a contact binary).
*4179 Toutatis - a contact binary asteroid that is in anon-principal axis rotation state.
*1998 JM8 - a large near-Earth asteroid that rotates very slowly.
*1998 KY26 - a very small (30 m wide) asteroid that spins so quickly that it has negativeeffective gravity .
*1999 KW4 - one of the first binary near-Earth asteroids known. The shape of the primary (alpha) has been determined by the orbital evolution of the secondary (beta), which is in turn coupled to the system's orbit around the Sun by radiation forces.
*6489 Golevka - the first asteroid for which theYarkovsky effect (radiation force changing the orbit) was measured.In these dynamical studies, Ostro has worked extensively with
Daniel J. Scheeres of the University of Colorado and his students.*
1950 DA - an approximately 1-km wide asteroid with a possible Earth impact in 2880 (initially studied by Ostro,Jon Giorgini ,Lance Benner , andScott Hudson ).
*99942 Apophis - a near-Earth asteroid that will pass withingeosynchronous orbit in 2029. Radar astrometry from observations by Ostro's group have been essential to predicting Apophis' trajectory.Radar provides extremely accurate measurement of the positions and velocities of target objects, and such
astrometry of near-Earth objects has been recognized as crucial to dealing with the impact hazard. In many cases, radar astrometry has excluded possible Earth impacts from trajectory predictions years before optical astrometry would have been able to do so.Work on other objects
Ostro has continued to work on radar observations of the icy satellites of Jupiter and Saturn, particularly with the
Cassini-Huygens RADAR instrument.Radar observations of Mars' moons,
Phobos andDeimos , have refined knowledge of their orbits and show that their surfaces are coated with very low density (~1 g/cm3) material, most likely fine-grain dust, to a depth of several meters.Asteroid impact hazardOstro was an early participant in discussion of the asteroid impact hazard, placing particular emphasis on the need to characterize asteroids before any deflection attempt. In a paper with
Carl Sagan , Ostro noted that while the asteroid impact hazard is a long-term risk to any civilization, the risk associated with maintaining an active deflection program is higher, because it is just as easy to deflect an asteroid to impact Earth as to prevent it from doing so [S.J. Ostro and Carl Sagan. 1994. Cosmic Collisions and Galactic Civilizations] . Ostro advocates for continued funding of the Arecibo Planetary Radar, on both hazard and scientific grounds.Awards and honors
Ostro received the
Gerard P. Kuiper Prize from theDivision for Planetary Sciences of theAmerican Astronomical Society in 2003.He was awarded NASA Medals for Exceptional Scientific Achievement in 1991 and 2004, in both cases for his leadership of asteroid radar astronomers as well as his scientific accomplishments.
The asteroid
3169 Ostro is named in his honor.References
External links
* [http://echo.jpl.nasa.gov NASA's Asteroid Radar Group]
* [http://www.aas.org/dps/MISC_NOTICES/030921_prizes2003.html Division for Planetary Sciences of the American Astronomical Society] : Ostro was the recipient of the 2003 DPS Kuiper Prize
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