Anton M.J. "Tom" Gehrels (February 21, 1925 – July 11, 2011) was a Dutch–American

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, natural satellite, moons, comets and galaxy, g ...

, Professor of Planetary Sciences, and Astronomer at the

University of Arizona The University of Arizona (Arizona, U of A, UArizona, or UA) is a public land-grant research university in Tucson, Arizona. Founded in 1885 by the 13th Arizona Territorial Legislature, it was the first university in the Arizona Territory. T ...

, Tucson.

Biography

Youth and education

Gehrels was born at

Haarlemmermeer Haarlemmermeer () is a municipality in the west of the Netherlands, in the province of North Holland. Haarlemmermeer is a polder, consisting of land reclaimed from water. The name Haarlemmermeer means ' Haarlem's lake', referring to the body of w ...

the Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...

on February 21, 1925. He was born in bible-belt Netherlands, and was forced to attend church regularly, an act he despised. When he was older he rejoiced when he found out his childhood church had been destroyed. During

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

he was, as a teenager, active in the Dutch Resistance. After he escaped to

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

, he was sent back by parachute as an organizer for

Special Operations Executive The Special Operations Executive (SOE) was a secret British World War II organisation. It was officially formed on 22 July 1940 under Minister of Economic Warfare Hugh Dalton, from the amalgamation of three existing secret organisations. Its pu ...

SOE committing sabotage against the German forces. After the war, he attended the

University of Leiden Leiden University (abbreviated as ''LEI''; nl, Universiteit Leiden) is a public research university in Leiden, Netherlands. The university was founded as a Protestant university in 1575 by William, Prince of Orange, as a reward to the city of Le ...

where he graduated with a degree in physics and astronomy in 1951. He continued his education at the

University of Chicago The University of Chicago (UChicago, Chicago, U of C, or UChi) is a private research university in Chicago, Illinois. Its main campus is located in Chicago's Hyde Park neighborhood. The University of Chicago is consistently ranked among the b ...

where he obtained his doctorate in astronomy and astrophysics in 1956 under Professor

Gerard P. Kuiper Gerard Peter Kuiper (; ; born Gerrit Pieter Kuiper; 7 December 1905 – 23 December 1973) was a Dutch astronomer, planetary scientist, selenographer, author and professor. He is the eponymous namesake of the Kuiper belt. Kuiper is co ...

. In 1960, he moved to the University of Arizona along with

Gerard Kuiper Gerard Peter Kuiper (; ; born Gerrit Pieter Kuiper; 7 December 1905 – 23 December 1973) was a Dutch astronomer, planetary scientist, selenographer, author and professor. He is the eponymous namesake of the Kuiper belt. Kuiper is c ...

where he would remain for the next 50 years.

Astronomical work

Gehrels pioneered the first photometric system of

asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...

s in the 1950s, and wavelength dependence of polarization of

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

s and

planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...

s in the 1960s, each resulting in an extended sequence of papers in the

Astronomical Journal ''The Astronomical Journal'' (often abbreviated ''AJ'' in scientific papers and references) is a peer-reviewed monthly scientific journal owned by the American Astronomical Society (AAS) and currently published by IOP Publishing. It is one of the p ...

. He discovered, jointly with the husband and wife team of

Cornelis Johannes van Houten Cornelis Johannes van Houten (18 February 1920 – 24 August 2002) was a Dutch astronomer, sometimes referred to as Kees van Houten. Early life and education Born in The Hague, he spent his entire career at Leiden University except for a brief pe ...

and

Ingrid van Houten-Groeneveld Ingrid van Houten-Groeneveld (; 21 October 1921 – 30 March 2015) was a Dutch astronomer. Background In a jointly credited trio with Tom Gehrels and her husband Cornelis Johannes van Houten, she was the discoverer of many thousands of aster ...

, over 4000

s, including

Apollo asteroid The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, discovered by German astronomer Karl Reinmuth in the 1930s. They are Earth-crossing asteroids that have an orbital semi-major axis greater than that of the Earth ...

Amor asteroid The Amor asteroids are a group of near-Earth asteroids named after the archetype object 1221 Amor . The orbital perihelion of these objects is close to, but greater than, the orbital aphelion of Earth (i.e., the objects do not cross Earth's orb ...

s, as well as dozens of

Trojan asteroid In astronomy, a trojan is a small celestial body (mostly asteroids) that shares the orbit of a larger body, remaining in a stable orbit approximately 60° ahead of or behind the main body near one of its Lagrangian points and . Trojans can sha ...

s. That was done in a sky survey using the 48-inch Schmidt telescope at

Palomar Observatory Palomar Observatory is an astronomical research observatory in San Diego County, California, United States, in the Palomar Mountain Range. It is owned and operated by the California Institute of Technology (Caltech). Research time at the observat ...

and shipping the plates to the two Dutch astronomers at

Leiden Observatory Leiden Observatory ( nl, Sterrewacht Leiden) is an astronomical institute of Leiden University, in the Netherlands. Established in 1633 to house the quadrant of Rudolph Snellius, it is the oldest operating university observatory in the world, with ...

, who analyzed them for new asteroids. The trio are jointly credited with several thousand discoveries. Gehrels also discovered a number of

comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ar ...

s. He was Principal Investigator for the Imaging Photopolarimeter experiment on the

Pioneer 10 ''Pioneer 10'' (originally designated Pioneer F) is an American space probe, launched in 1972 and weighing , that completed the first mission to the planet Jupiter. Thereafter, ''Pioneer 10'' became the first of five artificial objects to ach ...

and

Pioneer 11 ''Pioneer 11'' (also known as ''Pioneer G'') is a robotic space probe launched by NASA on April 5, 1973, to study the asteroid belt, the environment around Jupiter and Saturn, solar winds, and cosmic rays. It was the first probe to encounter ...

first flybys of Jupiter and Saturn in the 1970s. Gehrels initiated the

Space Science Space is the boundless three-dimensional extent in which objects and events have relative position and direction. In classical physics, physical space is often conceived in three linear dimensions, although modern physicists usually consider ...

Series of textbooks, was General Editor for the first 30 volumes of the University of Arizona Press, and set the style by participating in the editing of six of them. He also initiated the

Spacewatch The Spacewatch Project is an astronomical survey that specializes in the study of minor planets, including various types of asteroids and comets at University of Arizona telescopes on Kitt Peak near Tucson, Arizona, in the United States. The Sp ...

program in 1980 and was its Principal Investigator (PI) for electronic surveying to obtain statistics of asteroids and comets, including

near-Earth asteroid 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). ...

s. Bob McMillan was co-investigator and manager, and became the PI in 1997. Gehrels taught an undergraduate course for non-science majors in Tucson in the Fall, and lectured a brief version of that in the Spring at the Physical Research Laboratory in

Ahmedabad Ahmedabad ( ; Gujarati: Amdavad ) is the most populous city in the Indian state of Gujarat. It is the administrative headquarters of the Ahmedabad district and the seat of the Gujarat High Court. Ahmedabad's population of 5,570,585 (per t ...

, India. His recent research was on

cosmology Cosmology () is a branch of physics and metaphysics dealing with the nature of the universe. The term ''cosmology'' was first used in English in 1656 in Thomas Blount (lexicographer), Thomas Blount's ''Glossographia'', and in 1731 taken up in ...

and evolution of the universe, which was woven in as the guiding thread through these courses. He was the named winner of the 2007

Harold Masursky Award The Harold Masursky Award for Meritorious Service to Planetary Science, usually called the Masursky Award, is awarded annually by the Division for Planetary Sciences (DPS) of the American Astronomical Society. The award for Meritorious Service to P ...

for his outstanding service to planetary science. Gehrels was requested by the Journal ''

Nature Nature, in the broadest sense, is the physics, physical world or universe. "Nature" can refer to the phenomenon, phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. ...

'' to write a review on a book regarding

Wernher von Braun Wernher Magnus Maximilian Freiherr von Braun ( , ; 23 March 191216 June 1977) was a German and American aerospace engineer and space architect. He was a member of the Nazi Party and Allgemeine SS, as well as the leading figure in the develop ...

, in which he quotes inmates of concentration camp Dora. He has therefore charged that von Braun was there regularly and much in charge, and that von Braun bears greater responsibility and guilt than his official biography would imply.''Of Truth and Consequences'', Tom Gehrels (1994). Nature 372, 511-512 Towards the end of the book review it reads: ''Von Braun needs no phony defense, for he was a great man in his own scientific specialization... What is needed is a more sophisticated historical perspective...''. Tom Gehrels was the husband of Aleida J. Gehrels (née de Stoppelaar) and father of

Neil Gehrels Cornelis A. "Neil" Gehrels (October 3, 1952 – February 6, 2017) was an American astrophysicist specializing in the field of gamma-ray astronomy. He was Chief of the Astroparticle Physics Laboratory at NASA's Goddard Space Flight Center (GS ...

, George Gehrels and Jo-Ann Gehrels. He died in Tucson, Arizona. The minor planet 1777 Gehrels was named in his honour. Th
professional and personal papers of Tom Gehrels
are held at the University of Arizona.

Career

* Special airborne services in Europe and Far East, 1944–1948. * B.Sc. astronomy and physics, Leiden University 1951. * Ph.D. astronomy and astrophysics, Univ. of Chicago, 1956. * Professor of Planetary Sciences and Astronomy, Univ. of Arizona, 1961–2011.

Books

* ''Physical Studies of Minor Planets'', edited by Tom Gehrels (1971), NASA SP-267 * ''Planets Stars and Nebulae Studied With Photopolarimetry'', edited by Tom Gehrels (1974) Tucson:

University of Arizona Press The University of Arizona Press, a publishing house founded in 1959 as a department of the University of Arizona, is a nonprofit publisher of scholarly and regional books. As a delegate of the University of Arizona to the larger world, the Press p ...

* ''Jupiter: Studies of the Interior, Atmosphere, Magnetosphere, and Satellites'', edited by Tom Gehrels and Mildred Shapley Matthews (1976) Tucson: University of Arizona Press * ''Protostars & Planets: Studies of Star Formation and of the Origin of the Solar System'', edited by Tom Gehrels and Mildred Shapley Matthews (1978) Tucson:

* ''Asteroids'', edited by Tom Gehrels and Mildred Shapley Matthews (1979), * ''Saturn'', edited by Tom Gehrels and Mildred Shapley Matthews (1984) Tucson:

* ''Asteroids II'', edited by Richard P. Binzel, Tom Gehrels, and Mildred Shapely Matthews (1989)Tucson:

* ''Hazards Due to Comets and Asteroids'', edited by Tom Gehrels, Mildred Shapley Matthews, and A. M. Schumann (1994) Tucson:

* ''On the Glassy Sea, in Search of a Worldview'', Tom Gehrels (2007, originally published in 1988), * ''Survival Through Evolution: From Multiverse to Modern Society'', Tom Gehrels (2007), * "The Chandra Multiverse", in From Big Bang to Galactic Civilizations: A Big History Anthology, Volume 3, The Ways that Big History Works: Cosmos, Life, Society, and our Future, eds. Barry Rodrigue, Leonid Grinin, Andrey Korotayev, Delhi: Primus Books, 2017, pp. 45-70.

References

External links

Tom Gehrels
- Astronomy Tree

– university page
Obituary
– obituary from University of Arizona
Memorial
– university page {{DEFAULTSORT:Gehrels, Tom 20th-century American astronomers 20th-century Dutch astronomers 1925 births 2011 deaths Discoverers of asteroids Discoverers of comets Dutch emigrants to the United States People from Haarlemmermeer Special Operations Executive personnel University of Arizona faculty 21st-century American astronomers Dutch resistance members