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First astrometric attempts
In 1943, Dirk Reuyl and Erik Holmberg, two
astronomers from McCormick Observatory (Virginia),
deduced,
from
ten
years
of photographic
measurements, that the double system 70 Ophiuci
probably contains a planet with a mass of about ten
times Jupiter's mass (MJ ).
Two months later, Kaj Aage Strand, from Sproul
Observatory
http://daily.swarthmore.edu
(Pennsylvania), announced that the star 61 Cygni has
a planet with a mass equal to 16 M J .
Unfortunately, these measurements are not
confirmed, therefore, the existence of these planets
has been called into question.
In 1944, Piet Van de Kamp thought that he had
Sproul Observatory - Swarthmore College in Pennsylvania :
detected an object of 60 M J around the Barnard star
"Students walk along a path leading from Wharton to the
(a red-dwarf star with a record of proper movement). Sproul Observatory"
Copyright : Daily journal of Swarthmore College in Pennsylvania With the number of images increasing, the
Casey Reed
characteristics of this body became more refined and
in 1963, Van de Kamp was sure that it was a planet with a mass 1,6 M J and a period of 24 years. Six years
later, the measurements indicated that the Barnard star actually had two planets, with masses of 0.8 and
1.1 M J , and periods of 12 and 26 years, respectively.
Sadly, a study by John Hershey in 1973 led to the conclusion that these planets are only an illusion due to
a problem with the Sproul telescope. Independent observations of the Barnard star by George Gatewood and
Heinrich Eichhorn confirmed this fact
Gamma Cep and Epsilon Eri, exoplanets or
illusions ?
In 1988, the Canadians Bruce Campbell, Gordon
Walker and Stephensen Yang published their results
on 6 years of spectroscopic observations of 23 solar
stars with the Canada-France-Hawaii telescope (site
mirror of CFHT).
Mauna Kea, in Hawaii. The Canada-France-Hawaii
telescope (CFHT) enabled the study of lots of astrophysical
phenomena.
Some of these stars, in particular
Cephei and
Copyright : Jean-Charles Cuillandre (CFHT)
Eridani, were then suspected to contain planets. In
1992, one showed that in actuality, the variations observed were due to the chromospheric activity of the
stars.
Out of pique, Bruce Campbell decided to quit working in astronomy and work in the private sector.
But this is not the end of the story....
In 2000, Artie Hatzes, from McDonald Observatory (Texas), and his colleagues finally argued that the
variations of Eridani are probably due to the presence of a planet of 0,86 M J and a period of 7 years!
Their study was based on the analysis of six sets of data from four different telescopes.
Then in 2002, Hatzes et al. claimed that
mass of 1,7 M J ).
Cephei also had a planet (with a period of 2.5 years and a
HD 114672 b, a possible brown dwarf?
In 1989, David Latham, from the Center for
Astrophysics (Massachusetts), and Michel Mayor et
al., from the Geneva Observatory, published the
discovery of a planet of 11 M J and a period of 84 days
around the star HD 114672.
Careful, the authors prefer to talk about a possible
brown dwarf rather than a giant planet .
Artistic reproduction of a brown dwarf (between 10 and 20
M J).
Copyright : Paris Observatory / UFE
Exotic exoplanets
In 1970, David Richards noticed an anomaly in the
periodicity of a signal from the Crab pulsar,
discovered one year before. He proposed three
explanations :
A precession effect,
A vibration of the pulsar
or a perturbation due to the presence of a
planet with a period of 11 days.
The vibration hypothesis was considered to be the
correct one. On the other hand, in 1991, Andrew
Lyne published the discovery of a planet around PSR
1829-10, from observations with the radiotelescope
of Jodrell Bank.
In January 1992, the same day Lyne retracted his
discovery (he didn't take into account the eccentricity
of the orbit of the Earth), Alexander Wolszczan
announced the discovery of two planets (with a
period of 67 days and a mass of 3,4 M J for the first
one, and a period of 90 days and a mass of 2,8 M J for
the second one) around PSR 1257+12 !
Artistic reproduction of an extrasolar planet around a pulsar.
Copyright : Paris Observatory / UFE
This time, the observations of Wolszczan at Arecibo were confirmed by Dale Frail in VLA. Moreover, the
study of the system enabled us to highlight a 3:2 gravitational resonance between the two planets.
The existence of these strange planets seemed to be truly real, since in 1994 a second pulsar, PSR B162026, was found to have a planet of mass 2,5 M J .
The three first giant exoplanets
51 Peg b, 47 Uma b and 70 Vir b
In 1995, Michel Mayor and Didier Queloz, from
Geneva Observatory, detected a planet around 51
Pegasi using the radial velocity spectroscopy method.
This object, with a mass of 0,5 M J , was so close to
its star (0,05 AU, period 4,2 days) that the Swiss
researchers were very careful before annoucing their
discovery, considered today to be the first
detection of an exoplanet around a solartype star .
The Americans Geoffrey Marcy and Paul Butler,
who were running a program similar to the Swiss' one,
confirmed the appearance of 51 Pegasi b, and the
year after announced two new exoplanets, 47 Ursae
Majoris b (3,4 M J , period 3 years) and 70 Virginis b
(6,6 M J , period 117 days). The orbit of the third
planet is very elliptic (eccentricity of 0,4).
Artistic reproduction of a hot-Jupiter type extrasolar planet
The highly elliptic orbits, such as those of giant
planets close to their stars like 51 Pegasi b, were not
predicted by the theories of the formation of the Solar System.
Copyright : Paris Observatory / UFE
These discoveries motivate an important theoretical work. In particular, the Migration Phenomenon,
proposed in 1980 by Peter Goldreich and Scott Tremaine, is used to explain the presence of 51 Peg b on its
current orbit, at a location where it couldn't have formed.
The return of Lalande 21185
Galvanized by the discovery of 51 Pegasi b, George
Gatewood announced in June 1996 at the conference
of the American Astronomical Society that Lalande
21185 had a planet, contrary to his denial, in 1974,
of Sarah Lippincott's 1960 discovery.
This discovery remains unconfirmed today.
Lalande 21185
Copyright : Rutherford Appleton Laboratory http://ast.star.rl.ac.uk
Shades and lights with HD 209458
In 1999, David Charbonneau et al., and then
Gregory
Henry
and
collaborators,
observed
independently HD 209458 b (discovered with the
radial velocity method), and showed that it was
occulting its star at each rotation.
They deduced, from the weak decrease of the
star's brightness during the event, that the planet has
1,3 times Jupiter's radius and a density of 0.4, thus
demonstrating that HD 209458 b can only be a
gazeous giant planet.
In 2000, the same observations were made with the
Hubble Space telescope. The excellent photometric
precision of the measurements allowed us to highlight
the presence of sodium in the atmosphere of the
planet.
Artistic reproduction of Spitzer, a space telescope of NASA,
on a bright background of the Milky Way in the infrared.
In 2001, other observations with the HST led Alfred
Copyright : NASA
Vidal-Madjar and his collaborators to conclude that
hydrogen was escaping from HD 209458 b, thus forming a kind of cometary tail. In 2003, carbon and oxygen
were also detected.
In 2005, Drake Deming et al. observed in infrared the passage of HD 209458 b behind its star ("secondary"
transit) with the space telescope Spitzer. Thus, they could deduce the temperature of the planet to be
1130K.