Histoire de la cosmologie

Histoire de la cosmologie
Un cours offert aux étudiants
de la Faculté des Lettres,
de la Faculté de Biologie et de médecine,
de la Faculté des Hautes études commerciales,
de la Faculté de Géosciences et environnement,
de la Faculté des Sciences sociales et politiques et
de la Faculté de Théologie et de sciences des religions
de l’Université de Lausanne
dans le cadre de « Sciences au carré »
Histoire de la cosmologie
Prof. Georges Meylan
Laboratoire d’astrophysique
Ecole Polytechnique Fédérale de Lausanne
Site web du laboratoire et du cours :!
http://lastro.epfl.ch
Histoire de la cosmologie
03 – Le système solaire - B
03.B.1 Météores et météorites
03.B.2 Comètes
03.B.3 La formation du système solaire
03.B.4 Astéroïdes, astroblèmes et les dangers des NEOs
03.B.5 L’explosion de la Tunguska du 30 juin 1908
03.B.6 Les canaux de Mars : histoire d’un mythe oublié
Voir le fichier 03-Systèmesolaire-B.pdf sur le site web !
du laboratoire et du cours : http://lastro.epfl.ch

Histoire de la cosmologie
03 – Le système solaire – B
Bibliographie succincte
• GOUNELLE, Matthieu. Les Météorites. Paris : PUF, 2009.
• LEVASSEUR-REGOURD A.-C. et de la COTARDIERE P. Les comètes et les as-
téorïdes. Paris : Editions du Seuil, 1997.
• LUMINET, Jean-Pierre. Le rendez-vous de Vénus. Paris : JC Lattès, 1999.
• LUMINET, Jean-Pierre. Le feu du ciel : Météores et astéroïdes tueurs. Paris : Le
Cherche-midi Editeur, 2002.
• LUMINET, Jean-Pierre. Astéroïdes : La Terre en danger. Paris : Le Cherche-midi
Editeur, 2012.
• YEOMANS, Donald K. Comets : A Chronological History of Observation, Science,
Myth and Folklore. New York : Wiley Science Editions, John Wiley & Sons, 1991.
03.B.1
Météores et météorites
Météore et météorite
Définition du Petit Robert Edition 2004
• Météore : n. m. v. 1270, du latin médiéval meteora, du
grec meteôros « élevé dans les airs »
Tout phénomène qui se produit dans l’atmosphère.
Corps céleste qui traverse l’atmosphère terrestre (visible
la nuit par une traînée lumineuse).
• Météorite : n. m. ou f. V. 1830
Fragment de corps céleste qui traverse l’atmosphère et
tombe sur la Terre
Gravure du XIXe siècle représentant les Perséïdes

Du météore au météorite
Ensisheim, Alsace, le 7 novembre 1492 vers 11:30
Gravure de l'époque dépeignant la pluie de météores au-dessus de Ensisheim,
en Alsace, le 7 novembre 1492 vers 11h30.
Il s’agit de la première chute de météores bien observée en Europe et documentée.
On a récupéré 127 kg de fragments
dont un, pesant 53 kg, est toujours exposé au musée de la ville.
Le météorite de Peekskill – 9 octobre 1992
Russian Asteroid Impact : ESA Update and Assessment
(19 February 2013) The first firm details of the 15 February asteroid impact in Russia, the
largest in more than a century, are becoming clear. ESA is carefully assessing the
information as crucial input for developing the Agency’s asteroid-hunting effort. At 03:20
GMT on 15 February, a natural object entered the atmosphere and disintegrated in the skies
over Chelyabinsk, Russia. Extensive video records indicate a northeast to southwest path at a
shallow angle of 30° above the horizontal. The entry speed is estimated at around 18 km/s –
more than 64 000 km/h. According to calculations by Peter Brown at the University of
Western Ontario, Canada, drawing on extremely low-frequency sound waves detected by a
global network, the object is estimated to have been about 17 m across with a mass of
7000–10 000 tonnes when it hit atmosphere. It exploded with a force of nearly 500 kilotons
of TNT – some 30 times the energy released by the Hiroshima atomic bomb – around
15–20 km above the ground. With our current understanding of near-Earth objects, events
of this magnitude are expected once every several of tens to 100 years.
Questions and answers with ESA's near-Earth object team
Nicolas Bobrinsky, Head of ESA’s Space Situational Awareness (SSA) programme, and
Detlef V. Koschny, responsible for the programme’s Near-Earth Object activity, responded
to questions about the event.
Was this event related to the predicted flyby of asteroid 2012 DA14, which passed Earth at
19:27 GMT that same day at just 28 000 km?
DVK: The trajectory, the location of entry into the atmosphere and the large time separation
between the two events indicate that the Russian object was unrelated to 2012 DA14.

What caused the damage on the ground? Did pieces hit people or buildings?
DVK: Many media reported that an airburst caused window breakage and some structural
damage in downtown Chelyabinsk. Normally, some damage begins to occur at around five
times normal air pressure at sea level. Widespread window damage is expected around 10–
20 times this value. As the explosion and fireball progressed along a shallow trajectory, the
cylindrical blast wave would have propagated directly to the ground and would have been
intense. The terminal part of the explosion probably likely occurred almost directly over
Chelyabinsk. This was perhaps the single greatest contributor to the blast damage. We are
waiting for confirmation from the Russian authorities that pieces of the object – bits of
meteorite – have been found in the region. We’re unaware of any media reports of anyone or
any structure being hit by any debris from the object itself.
Have there been similar events in the past?
DVK: Yes. Perhaps the most famous recent one is the 1908 Tunguska event, in which a
large meteoroid or comet fragment, thought to be in the order of 40 m in size, exploded at an
altitude of 5–10 km. It’s the largest in recorded history, although many, many larger impacts
are known from geological history. On 12 February 1947, the Sikhote-Alin event in the
former Soviet Union involved an iron object, which meant that much of its 10 kilotons TNT
of energy was deposited in the ground rather than in the air like last week. On 8 October
2009, a body generated an atmospheric fireball blast similar to last week's event over an
island region of Indonesia. Its energy was about 5 kilotons.
What are the risks of a similar event happening in the future?
DVK: Near-Earth Objects (NEOs) are asteroids or comets with sizes ranging from metres
to tens of kilometres that orbit the Sun and with orbits that come close to Earth’s. Currently,
there are over 600 000 asteroids known in our Solar System; more than 9000 of these are
NEOs. Once an object is discovered, its orbit can be calculated and an individual risk profile
developed for that object.
How is ESA's SSA team receiving information?
DVK: Like NASA and other national space agencies, ESA maintains close contact with
government-level technical and scientific information-sharing bodies. The information is
also discussed within government-level bodies. We also work closely with NEO teams at
NASA and European national space agencies.
What is a possible scenario for an asteroid warning?
DVK: A very good example is the case of 2008 TC3, an 80-tonne, 2–5 m object that hit the
desert in Sudan on 7 October 2008. It was very small and was spotted by chance only 20
hours before it hit. Initial, rough observations gave a possible impact zone over 2000 km
long. Within hours, this had been refined to an area of just the Sudan desert. In a similar case
in the future, civil authorities would be able to tell the population in the narrowed-down area
to stay away from windows, glass or other structures and stay indoors. The risk that an
airburst and resulting over-pressure would cause personal injury by fractured glass or a
flimsy structure would be significantly reduced.
How is ESA helping to find asteroids that may hit Earth?
NB: Our SSA programme is already supporting astronomical teams around Europe in a
continuing sky search. While complex and requiring very good equipment and trained
astronomers, it really comes down to a simple process: acquire images of the sky and then
check these for pinpoints of light that move. In the past couple of years, ESA-supported
teams working at various observatories have found several previously unknown objects,
including asteroid 2012 DA14 that also passed by on Friday at the extraordinarily close
distance of just 28 000 km. This effort, however, is just a start, and we really have to place
the search on a long-term effective footing by increasing our observational capabilities.
In the future, ESA’s SSA programme aims to establish a ‘wide survey’ based on a network
of automated 1 m-diameter telescopes. This system would scan the complete sky once per
night for moving objects. It would be capable of detecting objects of the size of last week’s
Russian event a few days before they enter the atmosphere, provided they are seen
approaching from the dark sky. It will also take advantage of space-based observations
performed through ESA missions such as Gaia.
ESA’s SSA programme has already secured funding and a mandate from ESA Member
States to develop a first prototype telescope. A total of four to six such telescopes would be
needed for the complete survey.
Summary
On 15 February, a large fireball was reported over Chelyabinsk, Russia.
Time of impact : 03:20:26 GMT
Location : 55° 10' N, 61° 25' E
Entry angle : 20º above horizontalº
Entry speed : below 20 km/s
Trajectory : northeast to southwest
Asteroid diameter before entry : about 17 m
Kinetic energy : 500 kt TNT equivalent, corresponding to 30 times the energy of
the Hiroshima bomb
Explosion altitude : 15–25 km
(source: ESA)

Nature
14 Nov. 2013, Vol.
503, No. 7475
The trajectory,
origin, and airburst
behaviour
of the Chelyabinsk
fireball
Nature, 14 Nov. 2013, Vol. 503, No. 7475
Nature, 14 Nov. 2013, Vol. 503, No. 7475
Sonde spatiale visitant la comète Wild 2 et ramenant un échantillon sur Terre
Comète Wild 2 photographiée le 2 janvier 2004 par la caméra du système
de navigation de Stardust, au moment de l’approche maximale à environ 500 km.