Exoplanets Exoplanets - The Universe in my pocket - Jean Schneider Grażyna Stasińska
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The Universe in my pocket
Exoplanets
Exoplanets
Jean Schneider
Grażyna Stasińska
No. 8
ES-001
Paris Observatory
The idea that ‘other worlds’ can exist Why search for exoplanets ?
beyond our Solar System was suggested
by the Greek philosopher Epicure, 2,300 There are about 100,000,000,000
years ago. stars in our Galaxy, the Milky Way.
In 1584 the philosopher Giordano Bruno How many exoplanets – planets
argued that stars are suns, just like ours. outside of the Solar System – do we
In the XVIIth and XVIIIth centuries, many expect to exist? Why are some
scientists and philosophers, such as Charles stars surrounded by planets? How
Huygens and Immanuel Kant, further
developed the concept of other worlds. diverse are planetary systems?
Does this diversity tell us something
A drawing about the process of planet
representing ‘the
plurality of worlds’ as formation? These are some of the
imagined by the many questions that motivate the
French writer study of exoplanets.
Fontenelle in 1686.
A color version of an Some exoplanets may have the
engraving from a book necessary physical conditions
published in 1888 by Camille
Flammarion. It depicts a
(amount and quality of light from the
pilgrim discovering another star, temperature, atmospheric
world. composition) for the existence of
The first attempts by astronomers to
complex organic chemistry and
detect planets around other stars were in perhaps for the development of Life
the late1930s, but until 1989 there were (which may be quite different from
only false alarms. 2 Life on Earth). 3Dynamical methods :
Indirect methods of discovery
The planet and
the star orbit The first detections of exoplanets used
their common the effects of the planet on its star (see
center of mass. opposite page), allowing the derivation
The motion of of many planetary properties.
the star around the center of mass is
detected by the displacement of the lines • With dynamical methods, by
in its spectrum (see TUIMPs 2 and 10). studying the variations of the radial
velocity of the star, we obtain the
Transits: size and eccentricity of the orbit, the
If a planet period of revolution and a lower limit
passes in front on the mass of a planet. The true
of a star it
value of the mass and the orbit
produces a small
eclipse.
orientation are derived from the
change in position of the star with
Microlensing: respect to nearby stars (astrometry).
When a star F passes
in front of a star B, it • With the transit method, we obtain
B the size of the planet from the depth of
creates a
‘gravitational lens’ the light curve during the eclipse and the
P which magnifies the period of revolution from the time
F
light. If a planet P between eclipses.
orbits the star F, it • With microlensing we obtain the
too will lens the star
mass of the planet and its distance to
B, but for a shorter
4 time. the star. 5Two planets around
the star HR 8799,
Direct methods of discovery
discovered in 2008
using coronography
Direct detection of an exoplanet is
in infrared light with difficult because planets are small
the Gemini North and dim and lie very close to their
telescope in Hawaii. stars, which are at least 10 million
times brighter. Thus, we need to
Sequence of
images taken at carefully mask the star by a
the ESO Very technique called coronography.
Large Telescope Direct detection, when possible, is
in Chile. It shows very fruitful, because with several
the motion of
the planet
images we can determine the full orbit.
Beta Pictoris b as Spectroscopy of the planet reveals
it orbits its star. the molecular composition of its
Credit: Lagrange et al. atmosphere as well as its climate
The first image of an and weather.
exoplanet, taken at Photometric monitoring of the
the ESO VLT in 2004.
It orbits the ‘brown
planet gives its rotation period, that
dwarf’ star 2M1207, a is, the length of its day.
faint, low-mass star The size and mass of the planet,
shown here in white. however, can only be obtained by
Credit: Chauvin et al.
indirect methods.
6 7The satellite CoRoT A brief history of discoveries
discovered 36
exoplanets. 600 The first discoveries of exoplanets were
candidates are still made from the ground with the radial
being examined. velocity method using high-precision
spectrographs. HD114762b was the
The Kepler mission first planet discovered, in1989. In
observed 530,000 1992, 3 planets were found around a
stars, finding pulsar. Then the number of detections
2500 exoplanets
so far. Another
skyrocketed. As of 2019, over 800
2500 candidates
planets and 600 multi-planet systems
await analysis. have been found using this method.
The European satellite In 2006 the French-ESA satellite
Gaia, launched in 2013, CoRoT was launched, followed in 2009
will operate until 2022. by the NASA Space Telescope Kepler.
It will study the position Both used the transit method. CoRoT
and motion of over one was the first to detect a rocky planet.
billion stars with Kepler discovered thousands of planets.
exquisite precision.
The masses (with
90 planets were found by microlensing,
respect to the Earth) and 100 planets were found by direct
versus the year length imaging from Earth.
(in terrestrial days) for Gaia will provide astrometry and
all known exoplanets as transit
velocity
proper motions for over 1 billion
of February 2019. (data imaging stars. It should detect thousands of
from exoplanets.eu).
8 new planets. 9An imaginary
view (not to The diversity of worlds
scale) of the
very hot As of 2019, more than 4000 planets
Super-Earth have been confirmed while more than
CoRoT-7 b 3000 await confirmation.
Many strange planets have been
An artistic discovered that do not exist in the
representation by Solar System:
G. Thimm of the
planet
• Planets with temperatures of
Kepler-432b, with more than 1000°C that orbit their
its highly eccentric star in only a few days (as compared
orbit which to one year for the Earth)
produces extreme
• Evaporating planets
seasons.
• Planets twice as big as the Earth,
The planet called Super-Earths, with extreme
Kepler-413b, seasons (-100°C in winter, +100°C in
which revolves summer).
around two
• Planets with two suns
stars: an
orange one and a • Systems of planets very tightly
red one. packed around their sun.
10 11Plato, the future
European exoplanet The future
hunter, to be launched
in 2026. It will Within the next 10 years, 30 to 40m
observe hundreds of diameter telescopes will operate
thousands of stars, from the Earth to detect exoplanets
looking for planets by imaging and velocity variations
using the transit technique.
of the stars. Satellite telecopes
An artist’s impression including Cheops, JWST, Plato and
of the future European Ariel, will be launched to detect
Extremely Large planets by the transit method. The
Telescope, which will
begin operation in Chile
JWST will also do direct imaging.
in 2025. It will gather Large Space telescopes 8 to18m
13 times more light in diameter (LUVOIR, Habex) are
than the largest existing telescopes and being designed at NASA to detect
produce images 16 times sharper than signs of life on exoplanets by 2050.
those from the Hubble Space Telescope.
In the more distant future, huge
The hypertelescope space interferometers will make
project by A. Labeyrie. detailed maps of planets. And
A future, very large possibly, interstellar probes will be
interferometer in launched towards the nearest
Space, for the exoplanets to take close-up images.
cartography of Engineers are already working on propul-
exoplanets with a resolution of 100 m.
sion techniques to reach such distant
12 targets. 13An artist’s view of
51 Pegasi b
a giant planet with a
‘year’ of only 4 days.
An artist’s view of
HD 114762 b,
the first
exoplanet to be
Quiz discovered, in
1989.
An image of Jupiter
Which of these taken by the orbiter
images Juno and processed
represents a by citizen scientist
planet of the David Marriott.
NASA / JPL-Caltech / SwRI /
Solar System? MSSS / Marriott
An artist’s view
of Kepler-16b, a
Answers on overleaf planet orbiting
two stars.The Universe in my pocket No. 8
This booklet was written in 2019 by Jean
Schneider and Grażyna Stasińska from
Paris Observatory (France).
Nr 1
Cover image: This picture illustrates the
idea that rocky worlds may be both plentiful
and highly diverse in the Universe (credit
JPL). All the images of exoplanets and of
satellites in this booklet are artist’s
depictions . Credits: NASA, ESA and ESO.
To learn more about this
series and about the topics
presented in this booklet,
please visit
http://www.tuimp.org
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