Steven Jeffrey Ostro (March 9, 1946 – December 15, 2008) was an American scientist specializing in

radar astronomy Radar astronomy is a technique of observing nearby astronomical objects by reflecting radio waves or microwaves off target objects and analyzing their reflections. Radar astronomy differs from ''radio astronomy'' in that the latter is a passive ob ...

. He worked at

NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeedi ...

Jet Propulsion Laboratory The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, United States. Founded in the 1930s by Caltech researchers, JPL is owned by NASA ...

. Ostro 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 had detected 222

near-Earth asteroids A near-Earth object (NEO) is any small Solar System body whose orbit brings it into proximity with Earth. By convention, a Solar System body is a NEO if its closest approach to the Sun (perihelion) is less than 1.3 astronomical units (AU). ...

(including 130

potentially hazardous objects A potentially hazardous object (PHO) is a near-Earth object – either an asteroid or a comet – with an orbit that can make close approaches to the Earth and is large enough to cause significant regional damage in the event of impact. They are ...

and 24

binaries A binary file is a computer file that is not a text file. The term "binary file" is often used as a term meaning "non-text file". Many binary file formats contain parts that can be interpreted as text; for example, some computer document file ...

) and 118 main belt objects with radar. He died December 15, 2008, due to complications related to cancer. He has been remembered fondly by his colleagues for both his personal and professional contributions.

Education and employment

Ostro received an

A.B. Bachelor of arts (BA or AB; from the Latin ', ', or ') is a bachelor's degree awarded for an undergraduate program in the arts, or, in some cases, other disciplines. A Bachelor of Arts degree course is generally completed in three or four ye ...

liberal arts Liberal arts education (from Latin "free" and "art or principled practice") is the traditional academic course in Western higher education. ''Liberal arts'' takes the term '' art'' in the sense of a learned skill rather than specifically th ...

and a

B.S. A Bachelor of Science (BS, BSc, SB, or ScB; from the Latin ') is a bachelor's degree awarded for programs that generally last three to five years. The first university to admit a student to the degree of Bachelor of Science was the University of ...

in ceramic science from

Rutgers University Rutgers University (; RU), officially Rutgers, The State University of New Jersey, is a public land-grant research university consisting of four campuses in New Jersey. Chartered in 1766, Rutgers was originally called Queen's College, and wa ...

in 1969, a

Master's A master's degree (from Latin ) is an academic degree awarded by universities or colleges upon completion of a course of study demonstrating mastery or a high-order overview of a specific field of study or area of professional practice.

engineering physics Engineering physics, or engineering science, refers to the study of the combined disciplines of physics, mathematics, chemistry, biology, and engineering, particularly computer, nuclear, electrical, electronic, aerospace, materials or mechanical en ...

from

Cornell University Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to ...

in 1974, and his

Ph.D A Doctor of Philosophy (PhD, Ph.D., or DPhil; Latin: or ') is the most common degree at the highest academic level awarded following a course of study. PhDs are awarded for programs across the whole breadth of academic fields. Because it is a ...

planetary science Planetary science (or more rarely, planetology) is the scientific study of planets (including Earth), celestial bodies (such as moons, asteroids, comets) and planetary systems (in particular those of the Solar System) and the processes of the ...

from the

Massachusetts Institute of Technology The Massachusetts Institute of Technology (MIT) is a Private university, private Land-grant university, land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern t ...

in 1978. At MIT, Ostro was advised by

Gordon Pettengill Gordon Hemenway Pettengill (February 10, 1926 – May 8, 2021) was an American radio astronomer and planetary physicist. He was one of the first to take radar from its original military application to its use as a tool for astronomy. He was pro ...

and

Irwin I. Shapiro Irwin Ira Shapiro is an American astrophysicist and Timken University Professor at Harvard University. He has been a professor at Harvard since 1982. He was the director of the Center for Astrophysics Harvard & Smithsonian from 1982 to 20 ...

and studied the radar scattering properties of

Saturn's rings The rings of Saturn are the most extensive ring system of any planet in the Solar System. They consist of countless small particles, ranging in size from micrometers to meters, that orbit around Saturn. The ring particles are made almost entir ...

and the

Galilean satellites The Galilean moons (), or Galilean satellites, are the four largest moons of Jupiter: Io, Europa, Ganymede, and Callisto. They were first seen by Galileo Galilei in December 1609 or January 1610, and recognized by him as satellites of Jupiter ...

using the

Arecibo Observatory The Arecibo Observatory, also known as the National Astronomy and Ionosphere Center (NAIC) and formerly known as the Arecibo Ionosphere Observatory, is an observatory in Barrio Esperanza, Arecibo, Puerto Rico owned by the US National Science ...

. After completing his graduate work and a year in

postdoctoral research A postdoctoral fellow, postdoctoral researcher, or simply postdoc, is a person professionally conducting research after the completion of their doctoral studies (typically a PhD). The ultimate goal of a postdoctoral research position is to pu ...

at MIT, Ostro served as an

assistant professor Assistant Professor is an academic rank just below the rank of an associate professor used in universities or colleges, mainly in the United States and Canada. Overview This position is generally taken after earning a doctoral degree and gene ...

of astronomy at

Cornell Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to teac ...

before moving to

JPL The Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center in the City of La Cañada Flintridge, California, United States. Founded in the 1930s by Caltech researchers, JPL is owned by NASA a ...

in 1984. Ostro headed JPL's Asteroid Radar group, and was a member of the

Cassini–Huygens ''Cassini–Huygens'' ( ), commonly called ''Cassini'', was a space-research mission by NASA, the European Space Agency (ESA), and the Italian Space Agency (ASI) to send a space probe to study the planet Saturn and its system, including its ri ...

RADAR team, studying the moons of

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; ...

. In 2008, Ostro was elected a Fellow of the

American Geophysical Union The American Geophysical Union (AGU) is a 501(c)(3) nonprofit organization of Earth, atmospheric, ocean, hydrologic, space, and planetary scientists and enthusiasts that according to their website includes 130,000 people (not members). AGU's ...

, awarded for acknowledged eminence in the Earth and Space sciences.

Asteroid radar astronomy

Much of Ostro's career focused on the development of asteroid

. In early experiments, such as the first radar detection of Ceres, radar observations of asteroids were restricted to measurements of

Doppler shift The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who ...

s and

radar cross-sections Radar cross-section (RCS), also called radar signature, is a measure of how detectable an object is by radar. A larger RCS indicates that an object is more easily detected. An object reflects a limited amount of radar energy back to the source. ...

. Beginning in the early 1980s, 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. From August 19 to 22 of 1989, Ostro and Scott Hudson observed the contact binary

4769 Castalia 4769 Castalia (; '' prov. designation:'' ) is a near-Earth object and potentially hazardous asteroid of the Apollo group, approximately in diameter and was the first asteroid to be modeled by radar imaging. It was discovered on 9 August 1989, b ...

from the

, 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 Arecibo (; ) is a city and municipality on the northern coast of Puerto Rico, on the shores of the Atlantic Ocean, located north of Utuado and Ciales; east of Hatillo; and west of Barceloneta and Florida. It is about west of San Juan, the c ...

in the mid-1990s, the number of radar observations increased dramatically.

Asteroid impact hazard

Ostro 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 Carl Edward Sagan (; ; November 9, 1934December 20, 1996) was an American astronomer, planetary scientist, cosmologist, astrophysicist, astrobiologist, author, and science communicator. His best known scientific contribution is research on ...

, 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. Ostro advocated for continued funding of the Arecibo Planetary Radar, on both hazard and scientific grounds.

Notable asteroids observed by Ostro include

216 Kleopatra 216 Kleopatra is a large M-type asteroid with a mean diameter of and is noted for its elongate bone or dumbbell shape. It was discovered on 10 April 1880 by Austrian astronomer Johann Palisa at the Austrian Naval Pola Observatory, in what is now ...

– a large main-belt asteroid, the first asteroid confirmed to have a surface composition of nickel-iron. *

1986 DA is a metallic asteroid, classified as near-Earth object of the Amor group, approximately 3 kilometers in diameter. It was discovered on 16 February 1986, by Japanese astronomer Minoru Kizawa at Shizuoka Observatory, Japan. 1986 DA was the first ...

– the first near-Earth asteroid confirmed to be metallic. The estimated amount of

platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Pla ...

-group metals in 1986 DA is comparable to that in the

Bushveld Igneous Complex The Bushveld Igneous Complex (BIC) is the largest layered igneous intrusion within the Earth's crust. It has been tilted and eroded forming the outcrops around what appears to be the edge of a great geological basin: the Transvaal Basin. It is ...

, the largest source on Earth's surface. *

– 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 4179 Toutatis, provisional designation , is an elongated, stony asteroid and slow rotator, classified as a near-Earth object and potentially hazardous asteroid of the Apollo asteroid and Alinda asteroid groups, approximately 2.5 kilometers in d ...

– a contact binary asteroid that is in a non-principal axis rotation state. * – a large near-Earth asteroid that rotates exceptionally slowly. * – a very small (30 m wide) asteroid that spins so quickly that it has negative

effective gravity Effectiveness is the capability of producing a desired result or the ability to produce desired output. When something is deemed effective, it means it has an intended or expected outcome, or produces a deep, vivid impression. Etymology The ori ...

. *

66391 Moshup 66391 Moshup , provisional designation , is a binary asteroid, classified as a near-Earth object and potentially hazardous asteroid of the Aten group, approximately 1.3 kilometers in diameter. It was discovered on 20 May 1999, by Lincoln Near-Ea ...

– one of the first binary near-Earth asteroids known. The shape of the primary (alpha) has been determined by inversion of radar images. This enabled studies of 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 6489 Golevka is an Apollo, Mars-crosser, and Alinda asteroid discovered in 1991 by Eleanor F. Helin. Its name has a complicated origin. In 1995, Golevka was studied simultaneously by three radar observatories across the world: Goldstone in Ca ...

– the first asteroid for which the

Yarkovsky effect The Yarkovsky effect is a force acting on a rotating body in space caused by the anisotropic emission of thermal photons, which carry momentum. It is usually considered in relation to meteoroids or small asteroids (about 10 cm to 10 km ...

(radiation force changing the orbit) was measured. *

1950 DA , provisional designation ', is a risk–listed asteroid, classified as a near-Earth object and potentially hazardous asteroid of the Apollo group, approximately in diameter. It once had the highest known probability of impacting Earth. In 2002 ...

– an approximately 1 km wide asteroid with a possible Earth impact in 2880. *

99942 Apophis 99942 Apophis is a near-Earth asteroid and potentially hazardous asteroid with a diameter of that caused a brief period of concern in December 2004 when initial observations indicated a probability up to 2.7% that it would hit Earth on April&nbs ...

– a near-Earth asteroid that will pass within

geosynchronous orbit A geosynchronous orbit (sometimes abbreviated GSO) is an Earth-centered orbit with an orbital period that matches Earth's rotation on its axis, 23 hours, 56 minutes, and 4 seconds (one sidereal day). The synchronization of rotation and orbit ...

in 2029. Radar astrometry from observations by Ostro's group have been essential to predicting Apophis' trajectory. To explore the dynamical implications of these observations in detail, Ostro collaborated with

Steven Chesley Stephen or Steven is a common English first name. It is particularly significant to Christians, as it belonged to Saint Stephen ( grc-gre, Στέφανος ), an early disciple and deacon who, according to the Book of Acts, was stoned to death; h ...

Jon D. Giorgini Jon is a shortened form of the common given name Jonathan, derived from "YHWH has given", and an alternate spelling of John, derived from "YHWH has pardoned".Scott Hudson,

Jean-Luc Margot Jean-Luc Margot (born 1969) is a Belgian-born astronomer and a UCLA professor who specializes in planetary sciences. Career Margot has discovered and studied several binary asteroids with radar and optical telescopes. His discoveries include ( ...

, and Daniel J. Scheeres. Radar provides extremely accurate measurement of the positions and velocities of target objects, and such

astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. Histor ...

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 worked on radar observations of the icy satellites of Jupiter and Saturn, particularly with the Cassini-Huygens RADAR instrument. Radar observations of Mars' moons,

Phobos Phobos (Greek for "fear") most commonly refers to: * Phobos (moon), a moon of Mars * Phobos (mythology), the Greek god and personification of fear and panic Phobos may also refer to: Comics * Phobos (Marvel Comics) * Phobos (''W.I.T.C.H.''), a ...

and

Deimos Deimos, a Greek word for ''dread'', may refer to: * Deimos (deity), one of the sons of Ares and Aphrodite in Greek mythology * Deimos (moon), the smaller and outermost of Mars' two natural satellites * Elecnor Deimos, a Spanish aerospace company * ...

, 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.

Honors

Awards

Gerard P. Kuiper Prize The Gerard P. Kuiper Prize is awarded annually by the Division for Planetary Sciences of the American Astronomical Society for outstanding lifetime achievement in the field of planetary science. The prize is named for Gerard P. Kuiper. Kuiper Pri ...

from the American Astronomical Society's

Division for Planetary Sciences Division or divider may refer to: Mathematics *Division (mathematics), the inverse of multiplication *Division algorithm, a method for computing the result of mathematical division Military * Division (military), a formation typically consisting ...

(2003) *

NASA Distinguished Service Medal The NASA Distinguished Service Medal is the highest award that can be bestowed by the National Aeronautics and Space Administration of the United States. The medal may be presented to any member of the federal government, including both militar ...

, posthumous (2010) * NASA Medals for Exceptional Scientific Achievement (1991 and 2004)

Eponym

3169 Ostro 3169 Ostro, provisional designation , is a Hungaria family asteroid from the innermost regions of the asteroid belt, approximately 5 kilometers in diameter. The asteroid was discovered on 4 June 1981, by American astronomer Edward Bowell at Lowel ...

, asteroid named after Ostro in 1981

Erdős Number The Erdős number () describes the "collaborative distance" between mathematician Paul Erdős and another person, as measured by authorship of mathematical papers. The same principle has been applied in other fields where a particular individua ...

Three, through

Robert Connelly Robert Connelly (born July 15, 1942) is a mathematician specializing in discrete geometry and rigidity theory. Connelly received his Ph.D. from University of Michigan in 1969. He is currently a professor at Cornell University. Connelly is best ...

and Peter J. Cameron

References

External links

* {{DEFAULTSORT:Ostro, Steven J. 1946 births 2008 deaths People from Somerville, New Jersey American astronomers Rutgers University alumni Cornell University College of Engineering alumni Massachusetts Institute of Technology School of Science alumni Cornell University faculty People associated with radar NASA people Fellows of the American Geophysical Union