Audouin Dollfus
Encyclopedia
Audouin Charles Dollfus was a French
astronomer
and aeronaut, specialist in studies of the solar system
and discoverer of Janus
, a moon of Saturn
.
, obtaining a doctorate in physical
sciences in 1955. Beginning in 1946, Dollfus worked as an astronomer at the Meudon
Observatory, following his advisor and mentor Bernard Lyot
. In particular, he
directed the Laboratory of Solar System Physics there. Today he is
currently an honorary astronomer at the Paris Observatory
. Most of his work was
carried out based on observations from the Pic du Midi Observatory, and his preferred research method
is the use of polarized light as a diagnostic of the properties of solar system objects.
Through patient and persistent research and the development of new observational techniques,
he was able to obtain many remarkable results.
Dollfus has published more than 300 scientific
publications, relating primarily to astrophysics of the solar system.
Before the Viking spacecraft
landed on Mars
, the composition of the
Martian surface was the subject of many debates.
Dollfus tried to determine the composition of the Martian desert, through
comparison with the appearance
in polarized light of
several hundred terrestrial minerals.
He found that only pulverized limonite
(Fe2O3) corresponded with the appearance of Mars, and concluded that the Martian surface could be
composed of iron oxide. However, another astronomer, Gerald Kuiper of the
University of Chicago
, disagreed with this conclusion, believing that fine-grained
igneous rocks were a better fit to the data, but subsequent observations proved
Dollfus correct.
By using the polarization of light, it is possible to detect an atmosphere
around a planet or natural satellite
. In 1950, most scientists thought that
Mercury
, because of its small size, had probably lost its atmosphere due to
molecular escape into space. Dollfus announced that he had detected a very
small atmosphere, again using polarization measurements made at the Pic du Midi
Observatory in the French Pyrenees
. His discovery contradicted the previous
theoretical predictions based on the kinetic theory of gases. Dollfus estimated
that the atmospheric pressure at the surface of Mercury was approximately 1 mm
of mercury
. The nature of gas composing this atmosphere was unknown but thought
to be a dense, heavy gas. It was however certain that the atmosphere of Mercury
must be less than 1/300th that of the Earth
. Currently, it is known that the
atmosphere of Mercury is very thin indeed: only 10-15 bar
, with the total mass
of the atmosphere not exceeding 1000 kg.
Mercury has dark zones which contrast with a brighter bottom; this was observed
first by Giovanni Schiaparelli
in 1889. By using the refracting
telescope of the Pic du Midi Observatory, Dollfus was able in 1959 to
clearly resolve surface features as small as 300 km.
Dollfus also studied the possible presence of an atmosphere around the Moon
.
The rate of dissipation into space of any gases on the Moon (except for certain
rare heavy elements) is so high that no substantial atmosphere is
possible. The presence of any atmosphere should be detectable by the
polarization of light; Bernard Lyot and later Dollfus showed that there was
no detectable polarization, thereby confirming the theoretical prediction that
the Moon lacks an atmosphere.
In 1966, Dollfus discovered Janus
, a small inner moon of
Saturn
. He made this discovery by observing at a time when
the rings, very close to Janus, were nearly edge-on to the Earth and thus
practically invisible. At this time he probably also observed Epimetheus
,
a smaller moon which shares the same orbit as Janus, but he did not realize
these were two separate objects and it is Richard Walker that holds
credit for this discovery.
several world records in ballooning
, including the first stratospheric flight
in France. He was the first to carry out astronomical observations from a
stratospheric balloon, in particular to study Mars in a detailed way.
2451 Dollfus
was named in his honour.
He was awarded the Prix Jules Janssen
of the French Astronomical Society in 1993.
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
astronomer
Astronomer
An astronomer is a scientist who studies celestial bodies such as planets, stars and galaxies.Historically, astronomy was more concerned with the classification and description of phenomena in the sky, while astrophysics attempted to explain these phenomena and the differences between them using...
and aeronaut, specialist in studies of the solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
and discoverer of Janus
Janus (moon)
Janus is an inner satellite of Saturn. It is also known as Saturn X . It is named after the mythological Janus.-Discovery and orbit:Janus occupies practically the same orbit as the moon Epimetheus...
, a moon of Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
.
Astronomical Career and Research
He studied at the University of ParisUniversity of Paris
The University of Paris was a university located in Paris, France and one of the earliest to be established in Europe. It was founded in the mid 12th century, and officially recognized as a university probably between 1160 and 1250...
, obtaining a doctorate in physical
sciences in 1955. Beginning in 1946, Dollfus worked as an astronomer at the Meudon
Observatory, following his advisor and mentor Bernard Lyot
Bernard Lyot
Bernard Ferdinand Lyot was a French astronomer.His interest in astronomy started in 1914. He soon acquired a telescope and soon upgraded to a . From graduation in 1918 until 1929, he worked as a demonstrator at the Ecole Polytechnique...
. In particular, he
directed the Laboratory of Solar System Physics there. Today he is
currently an honorary astronomer at the Paris Observatory
Paris Observatory
The Paris Observatory is the foremost astronomical observatory of France, and one of the largest astronomical centres in the world...
. Most of his work was
carried out based on observations from the Pic du Midi Observatory, and his preferred research method
is the use of polarized light as a diagnostic of the properties of solar system objects.
Through patient and persistent research and the development of new observational techniques,
he was able to obtain many remarkable results.
Dollfus has published more than 300 scientific
publications, relating primarily to astrophysics of the solar system.
Before the Viking spacecraft
Viking program
The Viking program consisted of a pair of American space probes sent to Mars, Viking 1 and Viking 2. Each spacecraft was composed of two main parts, an orbiter designed to photograph the surface of Mars from orbit, and a lander designed to study the planet from the surface...
landed on Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
, the composition of the
Martian surface was the subject of many debates.
Dollfus tried to determine the composition of the Martian desert, through
comparison with the appearance
in polarized light of
several hundred terrestrial minerals.
He found that only pulverized limonite
Limonite
Limonite is an ore consisting in a mixture of hydrated iron oxide-hydroxide of varying composition. The generic formula is frequently written as FeO·nH2O, although this is not entirely accurate as limonite often contains a varying amount of oxide compared to hydroxide.Together with hematite, it has...
(Fe2O3) corresponded with the appearance of Mars, and concluded that the Martian surface could be
composed of iron oxide. However, another astronomer, Gerald Kuiper of the
University of Chicago
University of Chicago
The University of Chicago is a private research university in Chicago, Illinois, USA. It was founded by the American Baptist Education Society with a donation from oil magnate and philanthropist John D. Rockefeller and incorporated in 1890...
, disagreed with this conclusion, believing that fine-grained
igneous rocks were a better fit to the data, but subsequent observations proved
Dollfus correct.
By using the polarization of light, it is possible to detect an atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
around a planet or natural satellite
Natural satellite
A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
. In 1950, most scientists thought that
Mercury
Mercury (planet)
Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 87.969 Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets, and it has the smallest axial tilt. It completes three rotations about its axis for every two orbits...
, because of its small size, had probably lost its atmosphere due to
molecular escape into space. Dollfus announced that he had detected a very
small atmosphere, again using polarization measurements made at the Pic du Midi
Observatory in the French Pyrenees
Pyrenees
The Pyrenees is a range of mountains in southwest Europe that forms a natural border between France and Spain...
. His discovery contradicted the previous
theoretical predictions based on the kinetic theory of gases. Dollfus estimated
that the atmospheric pressure at the surface of Mercury was approximately 1 mm
of mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
. The nature of gas composing this atmosphere was unknown but thought
to be a dense, heavy gas. It was however certain that the atmosphere of Mercury
must be less than 1/300th that of the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. Currently, it is known that the
atmosphere of Mercury is very thin indeed: only 10-15 bar
Bar (unit)
The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...
, with the total mass
of the atmosphere not exceeding 1000 kg.
Mercury has dark zones which contrast with a brighter bottom; this was observed
first by Giovanni Schiaparelli
Giovanni Schiaparelli
Giovanni Virginio Schiaparelli was an Italian astronomer and science historian. He studied at the University of Turin and Berlin Observatory. In 1859-1860 he worked in Pulkovo Observatory and then worked for over forty years at Brera Observatory...
in 1889. By using the refracting
telescope of the Pic du Midi Observatory, Dollfus was able in 1959 to
clearly resolve surface features as small as 300 km.
Dollfus also studied the possible presence of an atmosphere around the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
.
The rate of dissipation into space of any gases on the Moon (except for certain
rare heavy elements) is so high that no substantial atmosphere is
possible. The presence of any atmosphere should be detectable by the
polarization of light; Bernard Lyot and later Dollfus showed that there was
no detectable polarization, thereby confirming the theoretical prediction that
the Moon lacks an atmosphere.
In 1966, Dollfus discovered Janus
Janus (moon)
Janus is an inner satellite of Saturn. It is also known as Saturn X . It is named after the mythological Janus.-Discovery and orbit:Janus occupies practically the same orbit as the moon Epimetheus...
, a small inner moon of
Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
. He made this discovery by observing at a time when
the rings, very close to Janus, were nearly edge-on to the Earth and thus
practically invisible. At this time he probably also observed Epimetheus
Epimetheus (moon)
Epimetheus is an inner satellite of Saturn. It is also known as Saturn XI. It is named after the mythological Epimetheus, brother of Prometheus.-Discovery:Epimetheus occupies essentially the same orbit as the moon Janus...
,
a smaller moon which shares the same orbit as Janus, but he did not realize
these were two separate objects and it is Richard Walker that holds
credit for this discovery.
Aerospace and Ballooning Pioneer
With his father, the aeronautical pioneer Charles Dollfus, he holdsseveral world records in ballooning
Ballooning
Ballooning may refer to:* Hot air ballooning* Balloon * Ballooning * Ballooning degeneration...
, including the first stratospheric flight
in France. He was the first to carry out astronomical observations from a
stratospheric balloon, in particular to study Mars in a detailed way.
Honours and awards
The asteroidAsteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
2451 Dollfus
2451 Dollfus
2451 Dollfus is a main-belt asteroid discovered on September 2, 1980 by E. Bowell at the Anderson Mesa Station of the Lowell Observatory.- External links :*...
was named in his honour.
He was awarded the Prix Jules Janssen
Prix Jules Janssen
The Prix Jules Janssen is the highest award of the French Astronomical Society. Created in 1897 and awarded annually, it is usually given in alternate years to a French astronomer, and to an astronomer of another nationality. It is distinct from the Janssen Medal , which is awarded by the French...
of the French Astronomical Society in 1993.