Transcript Document

The solar system
• Earth and Moon
• Telluric planets
• Jovian planets…
• … and their moons
• Small bodies
Earth and Moon
A unique couple
RMoon = 0.27 REarth
MMoon = 1/81 MEarth
Special case in the solar system
RTitan = 0.043 RSaturn
MTitan = 1/4400 MSaturn
RTriton = 0.056 RNeptune
MTriton = 1/4700 MNeptune
Le couple Terre – Lune vu par Galileo
Earth and Moon - 2
Tides
Gravitational attraction of Moon FA > FC > FB → bulges on Moon
side and opposite side (same for Sun with a 46% strength)
• ocean tides (up to 15 m) and continental tides (30 cm)
B
C
A
Moon
Earth
gravitational attraction
centrifugal force
Earth and Moon - 3
Effects of tides on the Earth – Moon system (1)
Earth rotation carries the tidal bulges
Moon attraction on the bulges slows down Earth rotation
Conversely, the orbital motion of the Moon is accelerated
A
C
B
Moon
Earth
Earth
rotation
Earth and Moon - 4
Effects of tides on the Earth – Moon system(2)
Lunar tides caused by Earth attraction (stronger)
→ slowing down of Moon rotation, until synchronisation with orbital
motion → always the same side towards Earth
Visible side and hidden side of the Moon
Earth and Moon - 5
Effects of tides on the Earth – Moon system (3)
Now:
• day’s length increased by 1 minute every 4 millions years
• Moon gets 3.7 cm further each year
400 millions years ago, length of day was 20 h
When rotation of Earth will be synchrone (in a
few dozen billion years) it will rotate in 47
present days
Earth and Moon - 6
Peculiarities of the Earth – Moon system
Earth is the only telluric planet with a genuine satellite
Among all solar system satellites, our Moon is unique because:
• its orbit does not coincide with the planet’s equatorial plane
• its large size compared to the planet
Moreover, the Moon was closer to the Earth in
the past
→ suggests a formation
scenario different from
the other satellites
Neptune
Earth
Triton
Moon
Earth and Moon - 7
Formation scenario for the Earth – Moon system
100 million yeras after its formation, the proto-Earth would have
collided with another proto-planet, of size similar to Mars
→ debris ring around proto-Earth
→ debris start to stick together
→ formation of a big moon close
to the planet
Then, gradually, the two bodies
move further away
Earth and Moon - 8
Internal structure of the Earth (1)
Mean density ≈ 5.5 (5500 kg/m3) – Density earth crust ≈ 3
→ cannot be made of the same rocks in its whole volume
Earthquakes
→ seismic waves
Propagation:
depends on the medium crossed
→ allow to model the Earth
interior
Earth and Moon - 9
Internal structure of the Earth (2)
Continental crust (granite) – oceanic crust (basalt)
Mantle (olivine = heavy silicate)
• rigid in upper layers
• viscous below
Metallic core (iron, nickel,…)
• external
(liquid, T ≈ 3800 – 4200 K)
• internal
(solid, T ≈ 4200 – 4300 K)
Earth and Moon - 10
Plate tectonics
Convection in mantle
→ displacement of the crust
→ continental drift
→ volcanism
Earth and Moon - 11
Dating rocks
Time elapsed since rock solidification:
Measured by radioactive clocks
Half-life: T½ = time for half of the nuclei to disintegrate
The proportion of children / parents nuclei increases with time
Child
T½ (109 yrs)
40K
40Ar
1.3
238U
206Pb
4.5
232Th
208Pb
14.0
87Sr
48.8
Parent
87Rb
Earth and Moon - 12
Earth’s age
Age of oldest • terrestrial rocks: 4.0 billion years
• lunar rocks:
4.4
• meteorites:
4.6
Most solar system bodies probably
formed at the same time
→ Earth’s age = meteorites age
Terrestrial rocks: appear younger
because they experienced fusion
phases during the first hundred billion
years
Earth and Moon - 13
Terrestrial magnetism
North Magnetic Pole (NMP) 20° from North Geographic Pole
Continuously moves, on average 40 m per day
Analysis of different age rocks → displacement of NMP during
geological eras (polarity inversions)
Cause of magnetism:
Rotation of the outer metallic
core (partly ionized) faster than
crust
→ `dynamo effect´
Earth and Moon - 14
Magnetosphere
Earth’s magnetic field extends through space
`Shield´ which deflects solar wind charged particles
→ essential for life on Earth
vent solaire
Capture of charged particles
→ Van Hallen belts
Particle overflow
→ enter the atmosphere close to the
magnetic poles
→ polar auroras
Earth and Moon - 15
Polar auroras (1)
Collision of charged particles with
atoms of upper atmosphere
→ excitation of atoms
The excited e– falls back to the
fundamental level while emitting a
photon
e–
E
hν
Earth and Moon - 16
Polar auroras(2)
Green color:
atomic oxygen (577.7 nm)
(altitude ~100 km)
Purple-red color: nitrogen
molecules N2
Earth and Moon - 17
Earth’s atmosphere (1)
75 % of its mass
in a 10 km layer
Composition:
N2
78 %
O2
21 %
Ar
0.9 %
CO2
0.04 %
H2O
0–4%
Earth and Moon - 18
Earth’s atmosphere (2)
Compared to those of Venus (96% CO2) and Mars (95% CO2) Earth’s
atmosphere has a very peculiar composition
That peculiarity is related to:
• oceans (dissolve CO2)
• life:
Plants photosynthesis converts
CO2 in O2
→ close link between life and
atmospheric composition
Earth and Moon - 19
Earth’s orbit
Sidereal period: 365.26 days
Angle equator – orbit: 23.5°
Mean orbital radius: 149.6 ×106 km = 1 astronomical unit (AU)
orbital eccentricity: e = 0.0167
Excentricity:
f
e
a
b2
e  1 2
a
b
a
f
Earth and Moon - 20
Moon’s orbit
Mean orbital radius: 384 000 km
Angle equator – orbit: 2.6°
Sidereal period: 27.3 days
Angle orbit – ecliptic: 5.1°
Synodic period: 29.5 days
(٪ Sun → phases → month)
Orbital eccentricity: e = 0.0549
Elliptical orbit
+ angle equator – orbit
→ apparent oscillation (libration)
→ 59% of Moon’s surface is visible
Earth and Moon - 21
Characteristics of Moon
• No atmosphere → no erosion
• meteoritic impacts → craters
• `marias´ and `highlands´
• Fully cooled
→ no tectonic activity
• Mean albedo: 7 %
The telluric planets
Planet
M
R
g
D
e
Tyr
Tday
Mercury
0.056
0.38
0.38
0.39
0.21
88j
59j
Venus
0.82
0.95
0.90
0.72
0.007
225j –243d
Earth
1.00
1.00
1.00
1.00
0.017
365j
23h56
Mars
0.11
0.53
0.38
1.52
0.093
687j
23h37
M = mass
R = radius
D = mean distance to Sun
g = acceleration of gravity(surface)
(all with respect to Earth)
e = orbital eccentricity
Tyr = revolution period
Tday = rotation period (sidereal day)
The telluric planets - 2
Mercury
No atmosphere, except H et He captured from solar wind, P ~ 10–12 bar
Orbital eccentricity: e = 0.206
Rotation : 59 d = 2/3 of year
→ gravitational resonance
1 rotation ½ over itself between
2 perihelion passages
→ always a tidal bulge towards
the Sun at perihelion
→ faces alternatively hot and
cold
Mercury imaged by Mariner 10
The telluric planets - 3
Venus (1)
Thick atmosphere, P ~ 90 bar, density ρ ~ 0.1, Tsurface ~ 480°C
CO2 (96%) –
N2 (3.5%)
H2O – SO2 – H2SO4 (traces)
Greenhouse effect increases T by
500 K
SO2 → volcanic activity
Retrograde rotation
→ collision with another planet?
(but, then, why e ≈ 0?)
Resonance with earth (5 orbits of
Venus between each alignement)
Venus in visible light (Galileo)
The telluric planets - 4
Venus (2)
Opaque atmosphere → reconstruction of surface relief by radar
measurements from probes orbiting Venus (Magellan, 1990)
Reconstruction of Venus surface by radar measurements (Magellan)
The telluric planets - 5
Mars
Tiny atmosphere, P ~ 0.008 bar, Tsurface ~ –140 (night) to +20°C (day)
CO2 (95%) – N2 (3%) – Ar (2%)
H2O – O2 (traces)
g too low to effectively retain the
atmosphere
Polar axis inclined (25°)
→ seasons
Polar caps : H2O + CO2
Weather: sandstorms
Mars seen from Earth (HST)
The telluric planets - 6
Martians
1877 : Schiaparelli sees straight lines on Mars surface
1894 : Lowell builds an observatory and observes the same lines
Channels built by
Martians to
irrigate dry lands
with water from
the polar caps!
1970:
Mariner probes
→ channels don’t
exist
`Channels´ on Mars and a recent picture
The telluric planets - 7
Other martian fantasmagories
1976 (Viking 1) : structure resembling a human face
2001 (Mars Global Surveyor): where is it gone?…
`Face´ on Mars…
… at better resolution
The telluric planets - 8
Mars landscapes
Since 2002, `Spirit´ and `Opportunity´rovers (and `Curiosity´ since
2012) explore Mars → harvest of pictures
Mars = arid desert, with sandstorms from time to time
Martian landscape
Mars or Southern Morocco?
The telluric planets - 9
Water on Mars?
No surface liquid water in present conditions
Numerous gullies:
depth ~ few m
width ~ few 10 m
length ~ few km
(much too narrow to
account for Sciaparelli
observations)
+ remains of river systems
→ water must have flown
on Mars in the past, when
the atmosphere was thicker
Gullies observed by MGS
The telluric planets - 10
Life on Mars (1)
1976: 2 Viking probes land on Mars at median latitudes
(température from –170 to +few °C)
Soil samples → 4 experiences to detect
signs of life
• no organic molecules (< 1/109)
• search for chemical changes due to
living organisms (soil samples placed in
nutritive environments) : slight changes
observed not due to life according to
specialists
Viking mission
The telluric planets - 11
Life on Mars (2)
1996: analysis of a meteorite found in Antarctica in 1984
• fragment of Mars crust ejected by a big meteorite impact some ~15
millions years ago, fallen on Earth some ~15000 years ago
• some scientists claim that microscopic
structures in the meteoritewould be
remains from a primitive life form
• it could have appeared some 3.5
billion years ago, under a thicker
atmosphere plus dense and with liquid
water
→ life on Mars: controversial subject
Meteorite ALH84001
The telluric planets - 12
Mars satellites
Phobos and Deimos (sons of Ares): 2 captured asteroids (27 and13 km)
TPhobos < Trot(Mars) → tidal effects reverse from Earth – Moon system
→ Rorbit decreases → Phobos will crash on Mars (in ~108 years)
Phobos (MGS)
Deimos (Viking)
Jovian planets
Planet
M
R
g
D
e
Tyear
Tday
Jupiter
318
11.2
2.5
5.2
0.048
11.9yr
9h55
Saturn
95
9.3
1.1
9.5
0.056
29.5yr 10h39
Uranus
15
4.0
0.9
19.2
0.046
84.0yr 17h
Neptune
17
3.9
1.1
30.1
0.010 164.8yr 16h
M = mass
R = radius
g = acceleration of gravity (surface)
D = mean distance from Sun
(all with respect to Earth)
e = orbital eccentricity
Tyear = revolution period
Tday = internal rotation period
The jovian planets - 2
General properties
• Made of a fluid, which density increases with depth (gradual
transition gas → liquid)
• Probably small core made of rocks and metals
• Differential rotation
of atmosphere
(vequator > vpole)
• Strong magnetic
field → allows to
measure internal
rotation
The jovian planets - 3
Jupiter
Upper layers:
H2 (78%) + He (20%) + CH4
+ clouds of NH3, NH4SH, H2O
Cloud color: solid particles
(sulfur, methane compounds)
Great red spot:
huge storm (2 × Earth size)
discovered by Robert Hooke (1664)
= high pressure zone
Jupiter emits more energy than it
receives from the Sun (gravitational
contraction)
Jupiter (Cassini)
The jovian planets - 4
Dive into Jupiter’s interior
Gradual increase of pressure and temperature
(1) gaseous H2 et He + clouds
(2) gradual transition to liquid H2 +
He (~0.75 RJ)
(3) dissociation of H2 followed b y
ionization of H
→ metallic hydrogen
→ strong magnetic field
(17000 × terrestrial field)
(4) Core of H2O, NH4, rocks,
metals (1% of total mass)
Region of the Great Red Spot
… and their moons - 5
The moons of Jupiter
16 moons including 12 captured asteroids
4 largest: discovered by Galileo in 1610
Moon
M(MM) R(RM)
T(d)
g(ms-2)
Io
1.2
1.05
1.8
1.8
Europe
0.7
0.9
3.6
1.4
Ganymede
2.0
1.5
7.2
1.5
Callisto
1.5
1.4
16.7
1.2
All in synchroneous rotation (tidal effects)
T° ~ –150 °C
The 4 galilean moons
… and their moons - 6
Io (1)
D = 420000 km from Jupiter
Most active volcanism in the
solar system
Eruptions of S and SO2 and
not H2O and CO2 as on Earth
(probably exhausted)
Volcanism caused by tidal
effects (perturbations from
other moons → oscillations
around the equilibrium
position → frictions → heat)
Io (Galileo)
… and their moons - 7
Io (2)
Surface constantly renewed by volcanic ashes
Gas ejected at v > 1 km/s,
part of it escapes and forms a
ring around Jupiter
Volcanic eruption on Io
Io in April and September 1997
… and their moons - 8
Europa (1)
D = 670000 km from Jupiter
Very smooth surface (features <
1 km) composed of ices
(mainly H2O, with NH3, CO2)
Model:
• Metallic core
• Rocky mantle
• Ocean of water or mud (life?)
• Ice crust (thickness ~100 km)
Europa (Galileo)
… and their moons - 9
Europa (2)
Few craters → surface rapidly regenerates → crust not too thinck, nor
too rigid
Covered with cracks 10 to 80 km broad, up to 1000 km long
Impact on Europa
Surface of Europa
… and their moons - 10
Ganymede (1)
D = 1070000 km from
Jupiter
Biggest moon in solar
system
Density: ρ ~ 0.5 ρMoon
→ ± 50% ice
→ prototype of
`ganymedian´ objects (as
all giant planet moons,
except Io and Europa)
Ganymede (Galileo)
… and their moons - 11
Ganymede (2)
Surface partly coverded by
grooves a few hundred meters
deep
Current explanation:
Ganymede still cooling
→ phase transition:
water → ice
→ increase of volume
→ cracks filled up by new ice
Surface of Ganymede
… and their moons - 12
Callisto
D = 1840000 km from
Jupiter
Ganymede `little brother´
No big cracks
→ thicker crust
Craters
→ `Icy´version of our moon
Callisto (Galileo)
The jovian planets - 13
Saturn
Chemical composition similar to Jupiter
(1) density ρ < 1
(2) fast rotation
→ flattening ~10 %
Emission of energy more
efficient than Jupiter :
lower temperature
→ helium droplets falling
towards the core
→ energy from phase
transition + gravity
Saturn (Voyager 2)
The jovian planets - 14
Seasons on Saturn
Contrary to Jupiter,
Saturn’s equator is
significantly inclined
with respect to orbit
(27°)
→ seasons
→ rings seen under
different angles from
year to year
→ seen by Galileo but
not by Huygens, who
found the correct
explanation
Saturn (HST)
The jovian planets - 15
Saturn rings
Rings present around all jovian planets, but by far the most massive
and bright around Saturn
Composed of rock and ice
blocks of various sizes (from
a dust grain to a few meters)
Estimated thickness ~ 10 m
Distance: 70000 to 140000
km from Saturn center
High albedo (~ 0.6)
Total mass ~ 1020 kg
Saturn rings (Cassini)
The jovian planets - 16
The Roche limit (1)
dmin for a satellite whose cohesion is due to its own gravity
Tidal force:
(on a mass element)
1
1

F  FC  FA  GM P  2 
2
d
(
d

R
)


2GM P R
R  d  F 
d3
GM S
Gravitational force (cohesion) :
FG 
R2
F  FG
1
 d min
  
  2 P  RP
 S 
A C
MP
3
R
d
RP
The jovian planets - 17
The Roche limit (2)
This simple calculation
neglects:
– the satellite rotation
– its tidal deformation
These 2 factors weaken
cohesion
A more sophisticated
computation gives:
1
d min
 P  3
 2.45  RP
 S 
Backlighting of Saturn’s rings (Cassini)
The jovian planets - 18
Planetary rings
No massive satellites under Roche limit → rings composed of dust and
small rocks
Rings = transient or stable structures? >Opinions diverge...
The rings of Jupiter, Uranus and
Neptune are:
– much less massive (J, U, N)
– less reflective (U, N):
CH4 ice adds to H2O
→ albedo ~0.05 instead of 0.60
Jupiter ring (Galileo)
… and their moons - 19
Titan (1)
Moon
M(ML) R(RL)
T(j)
g(ms-2)
Titan
1.8
16
1.4
1.48
Main satellite of Saturn
Dense atmosphere
→ awakened scientists interest
Visited by space mission
Cassini – Huygens in 2005
Orbital probe + lander
Methane sea on Titan (Cassini)
… and their moons - 20
Titan (2)
Psurf ~ 1.5 bar, T ~ –170°C
N2 (98%) + CH4 (2%)
+ organic compounds
Ground covered by organic
precipitates + ice pebbles
Best candidate for life in our
Solar System?
However temperature is
very low…
River Ground
system and
coast(Huygens)
onTitan (Huygens)
of Titan
… and their moons - 21
Other moons of Saturn
Hyperion:
Diameter ~ 250 km
Too small for gravity to
dominate → no spherical
shape
`Sponge´ aspect
Very low density
→ inner caves?
Hyperion (Cassini, false colours)
… and their moons - 22
Other moons of Saturn
Dione:
Diameter ~ 1100 km
… and many others…
Dione, Saturn and rings (Cassini)
The jovian planets - 23
Uranus
Discovered by William Herschel in 1781, first named `George´
Atmosphere : H + He
+ CH4 → blueish colour
Density higher than Jupiter and
Saturn → less H et He, core
probably more important
Equateur at 98° from orbital
plane → collision with another
planet soon after its formation?
Rings and moons align with the
equatorial bulge
Uranus (HST, increased contrast)
The jovian planets - 24
Neptune (1)
Existence predicted in 1843 by
J.C. Adams on the basis of
perturbations of Uranus orbit
(nobody took him seriously)
Independant prediction in 1846 by
Urbain Le Verrier (already wellknown → taken seriously)
Discovered by J.G. Galle at the
predicted position
→ triumph of Newtonian theory
of gravitation
Neptune (Voyager 2)
The jovian planets - 25
Neptune (2)
Slightly more massive and
denser than Uranus
Atmosphere: H + He + CH4
Stronger meteorological
phenomena despite less solar
energy received
Lower T° → lower viscosity
→ less energy needed to
activate motion
Spots = high pressure zones
Neptune (Voyager 2)
… and their moons - 26
Triton
Diameter: 2760 km
T° ~ –236°C
Retrograde orbit with
20° inclination with
respect to Neptune’s
equator
→ captured TNO?
(Trans-Neptunian
Object, see below)
Triton (Voyager 2)
The small bodies
The Titius – Bode law (1)
1741: mathématicien Max Wolf discovers that distances of planets to
the Sun obey a simple law
1766: Johann Daniel Titius rediscovers ans fomalizes this law
1778: Johann Elert Bode publishes the law
d  0.4  0.3  k
(k  0,1,2,4,8,16,32)
Titius
Bode
The small bodies - 2
Titius – Bode law (2)
Precision ~ 3 %
+ predictive power!
(discovery of Uranus)
But:
a planet is missing
Where is that 5th
planet?
→ searching!
Planet
k
dcalc
dobs
Mercury 0
Venus
1
Earth
2
Mars
4
?
8
Jupiter 16
Saturn 32
Uranus 64
0.4
0.7
1.0
1.6
2.8
5.2
10.0
19.6
0.39
0.72
1.00
1.52
?
5.20
9.54
19.2
δd
(%)
2.6
2.8
0.0
5.3
?
0.0
4.8
2.1
The small bodies - 3
Asteroids (1)
1801 : Giuseppe Piazzi, founder of Palermo observatory, discovers a
body at 2.77 UA from the Sun and names it Ceres (tutelary goddess of
Sicily)
• at the predicted distance
→ new triumph of Titius – Bode law
(but failure for Neptune)
• diameter ≈ 940 km
• M ≈ 1021 kg ≈ 1/6000 ME
Later, discovery of more bodies:
Pallas, Juno, Vesta…
→ more than 100000 at present time
Ceres (Dawn)
The small bodies - 4
Asteroids (2)
Total mass ~ 1/1000 ME
Most orbiting in main belt, from 2.2
to 3.3 AU
(in between orbits of Mars – 1.5 AU
and Jupiter – 5.2 AU)
Asteroids Ida et dactyl (Galileo)
Nearly circular orbits
A dozen with size > 250 km
Large range in size
Examples:
Ida (60 km)
Itokawa (500 m)
Asteroid Itokawa (Hayabusa)
The small bodies - 5
Asteroids (3)
A minority do not belong to the main belt
Some have rather eccentric orbits which bring them close to Earth (as
Eros) or even cross its orbit
They were probably deflected by
Jupiter’s gravitational attraction
Other effect of Jupiter : Kirkwood
gaps (at 2.50, 2.82, 2.96, 3.27 AU):
orbits with periods T = 1/3, 2/5, 3/7
and 1/2 TJupiter
→ gravitational resonances
Asteroid Eros (NEAR)
The small bodies - 6
Pluto
1915: from perturbations of Neptune’s orbit, Percival Lowell computes
that a planet of 6.5 ME should be found at 42 AU
Searches around the ecliptic, no success
1930: Clyde Tombaugh discovers Pluto
• eccentric orbit: e = 0.25, a = 39 UA
• inclination of 17° onto the ecliptic
• R ≈ 0.18 RE ,
M ≈ 0.002 ME
1978: discovery of moon Charon
• d = 19400 km from Pluto
• MCharon ≈ 0.17 MPluto
Pluto (New Horizons)
The small bodies - 7
Trans Neptunian Objects (TNOs)
Since 1992: discovery of numerous objects further away than Neptune,
some with sizes comparable to Pluto
→ International Astronomical Union, 2006 : new definition.
A planet is a celestial body:
• is in orbit around the Sun
• has sufficient mass to assume hydrostatic equilibrium (a nearly round
shape)
• has `cleared the neighborhood´ around its orbit
→ Pluto is no more considered as a planet, but as a dwarf planet (new
class of celestial bodies)
The small bodies - 8
Oort cloud and Kuiper belt
TNOs are located in a ring from the orbit of Neptune
(30 UA) up to ~50 AU: the Kuiper belt
A multitude of small bodies probably orbit even much
further away, in a spherical shell at about
100000 AU (a light-year) from the
Sun
Gerard Kuiper
Its existence has been postulated in
1932 by Öpik, then in 1950 by Oort
to explain the origin of long period
comets
Short period comets come from
Kuiper belt
Ernst Öpik
Jan Oort
The small bodies - 9
Comet nuclei
Comet nucleus = agregate of rocks and ices (size: a few km)
Gravitational perturbation
→ leaves Oort cloud
→ hyperbolic or high
eccentricity elliptical orbit
(→ periodic or not)
→ enters the inner solar
system
When d < 3 UA → ices
start to sublimate
Nucleus of comet Tempel 1 (Deep Impact)
The small bodies - 10
Comet nuclei & Rosetta
2014: the Rosetta mission reaches comet 67P/ChuryumovGerasimenko and the Philea module lands on the nucleus
Nucleus of comet P67 (Rosetta)
The small bodies - 11
Comets
Sublimation of ices
→ `coma´ composed of gas and dust
Solar wind and radiation pressure
→ drag particles
→ tail (direction opposite to the Sun,
length up to 0.5 AU)
Orbital motion of comet
→ the tail `trails´
Effect is stronger for dust, which moves
slower → 2 tails
Light emission: fluorescence (gas) or
diffusion of sunlight (dust)
Comet Hale-Bopp
The small bodies - 12
Halley’s comet
In 1705, Edmund Halley realizes that the comets of 1531, 1607 and
1682 are the same object, seen at succesive orbits
→ predicts it will return in 1759
Most famous of short
period comets
(76 years)
Last appearance to
date: 1986
Visited by several
space probes
Edmund Halley
Halley’s nucleus (Giotto)
The small bodies - 13
Comets: astronomical fossils, sources of life?
• Stayed in the outskirts of the solar system until recently
→ not modified by physicochemical processes
→ chemical and isotopic
composition unchanged since
formation of the solar system
• Contain many simple
organic molecules
→ did they have some
influence on the emergence
of life on Earth?
Comet Swan
The small bodies - 14
Shooting stars
Brief luminous flash produced by aerodynamic heating of a small
body entering the atmosphere (typical size ~ 1 cm ; altitude ~ 100 km)
Total ~ 10 tons / day
Often cometary debris
→ more numerous when
Earth crosses the orbit of
a (past) comet
Perseids (~11 August)
Leonids (~11 November)
…
Perseids 2004 (F. Bruenjes)
The small bodies - 15
Meteors and fireballs (1)
Larger size bodies which burn (partially
or completely) in the atmosphere
Speed ~ 30 km/s ~ 10000 km/h
Pieces of comets or asteroids
If they reach the ground → danger
1911, Egypt: dog killed by a 40 kg
meteorite
1954, Alabama: woman leg hurt by a
meteorite which went through the roof of
her house
Meteor Perseid 2004 (C. Mouri)
The small bodies - 16
Meteors and fireballs (2)
1972: a bolide ~ 1000 tons flies
60 km over North America and
bounces back to space
1992, New York State: car
damaged by 12 kg meteorite
No record of human being killed
by meteorite in last millenium
Luckily, most recent major
impacts happened in uninhabited
locations
Car damaged by meteorite (1992)
The small bodies - 17
The Tunguska impact (Siberia)
30 June 1908: asteroid or comet nucleus (mass ~ 10000 tons)
explodes in Siberia
Seismic wave recorded
1000 km away
Trees lying down in a 30
km radius
No crater
→ the meteor exploded
several km before
touching ground
(power ~ 1000 times the
Hiroshima bomb)
The Tunguska impact
The small bodies - 18
Major impacts
Frequency of Tunguska-like imapcts: ~ one every few centuries
Meteor Crater, Arizona: diameter 1.2 km; depth 200 m,
happened ± 25000 years ago
Iron meteorite ~ 109 kg
(60 m diameter)
Largest known crater:
Chixculub, Yucatán :
diameter 200 km,
dated 65 millions years
= extinction of dinosaurs
Meteor Crater, Arizona