Transcript Origin of the Earth and of the Solar System

Geophysics 01
Institute for Geophysics, Astrophysics,
and Meteorology (IGAM)
Introduction to Geophysics
and Planetary Physics
Lecture, winter term 2015
Ulrich Foelsche & Günter Kargl
[email protected]
http://www.uni-graz.at/~foelsche/
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The object of interest
Source: MPI Aeronomie
What‘s „Earth“? The Earth reaches up to the Magnetopause.
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Introduction to Geophysics and
Planetary Physics
(1) Origin of the Earth and of the
Solar System
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Star Formation (1) – Eagle Nebula
The Sombrero Galaxy seen from the edge – showing that spiral galaxies contain lots of dust – but in
very small concentrations (Source: R. Colombari).
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Star Formation (1) – Eagle Nebula
Dark clouds of dust and hydrogen gas in the
Eagle nebula M16 (~7000 light years away, in
the “Serpent” constellation), surrounded by
young, luminous stars (Source: HST).
Protostellar clouds at the edge of the dust and
gas pillars (each larger than our solar system) are
places of star formation – lust like our sun, ~4.6
billion years (Gyr) ago.
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Star Formation (2) – Collapse
The life of a star is a constant battle between radiation and gravitation. In the early phase of a star’s
live there are phases characterized by gravitational collapse (with a rapid increase in density), and
equilibrium phases, when a strong temperature-induced pressure increase counteracts gravitation (Ralf
Launhardt, SdW 08/2013).
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Star Formation (3) – Orion Nebula
IR
The Orion Nebula M42, 1500 light years away,
contains about 700 young stars (IR inset) and at
least 150 protostellar clouds. Several of the them
evaporate due to the intense UV radiation of four
young stars, building the „Trapeze“. Nr. 5 shows
the side view of an Accretion Disc. 1 AU
(Astronomical Unit) is 149.6 Mio. km, the mean
Earth – Sun distance. Source: HST
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Star Formation (4) – Star Clusters
Open Cluster of young stars: The Pleiades (Picture: R. Gendler)
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Star Formation (6) – Star Clusters
Open Cluster in NGC 602 (Source: HST)
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Star Formation (7) – Nuclear Fusion
In the center of a star energy is released by nuclear fusion. In sun-like stars the proton-proton chain
reaction is dominant: four hydrogen nuclei (protons) ultimately yield a Helium nucleus. Only when the
central temperature further increase, Helium nuclei can be fused to Carbon. In Red Supergiants, fusion
processes in concentric shells produce heavy elements – but only up to Iron.
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Star Formation (8) – Evolution
For another ~5 billion years our sun will remain a comparatively well-behaved main-sequence star.
Then hydrogen shell burning around a helium core will lead to the inflation to a red giant. But
habitability will end much earlier – the temperature increase in the sun’s center yields a (moderate)
luminosity increase of about 0.7 % in 100 million years. This is, however, enough create uncomfortable
conditions (for humans) about 500 million years from now (Ralf Launhardt, SdW 08/2013).
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Planet Formation (1) – Dying Stars
Planetary Nebulae (1)
Planetary Nebula NGC6543
„Egg Nebula“ CRL2688
All pictures: HST
„Eskimo Nebula“ NGC6392
At the end of the life of a red giant its outer layers are expelled, thereby enriching the interstellar
medium with heavy elements – a prerequisite for the formation of terrestrial planets. UV radiation from
the star “remainder” stimulates light emission in the expanding shell – which looks a bit like a planet in
small telescopes (therefore the name).
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Planet Formation (2) – Dying Stars
Planetary Nebulae (1)
All pictures: HST
„Helix Nebula“ NGC7293
„Ring Nebula“ M47
Planetary Nebula IC418
Planetary Nebula NGC6751
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Planet Formation (3) – Dying Stars
Supernovae
Crab Nebula M1
Supernova remnants in the
Cygnus constellation.
All pictures: HST
Supernova 1987A in the LMC
A Supernova is a gigantic explosion of a massive star after gravitational collapse (if no more energy can
be gained by nuclear fusion). At maximum a Supernova can be brighter than a whole galaxy. The outer
layers are expelled, while the center collapses to a Neutron Star or even to a Black Hole. All (naturally
occurring) elements heavier than iron have been formed during supernova eruptions (the heaviest ones
like Gold or Uranium maybe even during the collision of binary neutron stars) .
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Planet Formation (4) – Accretion Discs
The formation of Earth-like planets
could only happen after the interstellar
medium had been enriched by heavy
elements from dying stars.
Rotating gas and dust clouds contract
to accretion discs, since only in the
equatorial plane gravitation and
centrifugal force ban be in equilibrium.
The picture sequence (Source: Nature)
shows the (successful) simulation of
the formation of protoplanets in an
accretion disc.
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Planet Formation (5) – Accretion Discs
Left: Accretion disc around HL Tauri (ESO), above:
Planetesimals in an accretion disk (Artist impression, source:
GEO). The collision of planetesimals forms protoplanets.
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Planet Formation (6) – Discworld
Fomalhaut is a bright, young star in the constellation Piscis Australis (“Southern Fish”), 25 light years away.
Fomalhaut is surrounded by a debris disk (accretion disk). The prominent ring is shaped by “Fomalhaut b”, the
fist extrasolar planet detected at visible wavelengths (Source: HST).
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Planet Formation (7) – Synopsis
Credit: Nature
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The Solar System
Venus
Moon
Mercury
Earth
Earth
Mars
Terrestrial Planets
Gas planets, note different scale
www.solarviews.com
Saturn
Jupiter
Ganymede
Neptune
Mars
Venus
Erde
Titan
Mercury
Callisto
Uranus
Io
Moon
Europa
Triton
Pluto
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Moon Formation – Giant Impact
Giant impact (Source: GEO). For about one hour the Earth was brighter than the Sun.
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Moon Formation – Giant Impact
Simulation of the moon formation. Two (already differentiated)
protoplanets collide tangentially. During the second collision (9-16) the
iron core of the impactor (blue) merges with the larger body (the
Earth). Ejected mantle material (red) forms an accretion disk around
the Earth – and later the moon.
The composition of the
Moon’s is very similar the
Earth’s mantle, suggesting
that both formed in the same
region of the accretion disc.
The Moon’s Iron Core is,
however very small, and the
Moon is depleted in volatile
elements. Only the “Giant
Impact Hypotheses” can
(largely) explain all findings.
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Age of Formation
Source: Nature
Our actual stat of knowledge is, that the first planetesimals in our Solar system formed 4 567 million
years ago within the protosolar cloud (with an uncertainty of just 2 million years). Right: Ca/Al-rich
inclusion within Allende-Meteorite with a diameter of ~1 cm (the oldest material, which could be dated
so far). The first „Planetary-Embryos“ formed within just about 100 000 years. Roughly 10 million years
later the Proto-Earth was 2/3 „finished“. After another 20 million years. accretion was practically over,
Proto-Earth war completely differentiated. The collision with a Mar-size body (Theia – the mythical
mother of Selene, the Greek goddess of the moon) created the binary system Earth-Moon. All dates are
base on radiometric dating methods (see next chapter).
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Formation of the first Crust
The “Giant impact” resulted in melting of the outer The lava lake on Erta Ale (Ethiopia) as a „model“ for
layers of the Earth. The surface then cooled slowly and the formation of the primordial Earth’s crust.
crystallization resulted in the first crust – which was, Plate tectonics only developed on Earth.
however perforated by later impacts (Source: GEO).
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Scars from Planet Formation
Crater with ~ 80 km
diameter on the far side of
the Moon (Apollo 11).
Short after their formation, the young planets suffered a heavy bombardment by remaining
planetesimals (asteroids, meteorites and comets). Planets and moons without atmospheres (like the
Earth’s Moon – left, or Mercury – right) still show their scars. But these impacts also delivered the water
on Earth and organic compounds. Most Lunar Maria (“seas”) are remnants of the heaviest impacts
(Pictures: NASA).
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Scars from Planet Formation
Source: GEO
The South Pole
Aitken Basin
on the far side
of the Moon is
invisible for
observers on
Earth. It has a
diameter of
2 500 km.
Credit: NASA
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Scars from Planet Formation
Credit: NASA
Vesta (573 km × 557 km × 446 km) is the second largest asteroid in the asteroid belt between Mars and
Jupiter (Pallas is slightly larger but less dense (and massive). Vesta is differentiated and holds an iron
core. The south pole regions features a giant crater – Rheasilvia – with 505 km diameter (!) and a 23 km
high central peak (!).
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Remnants of Planet Formation
Credit: NASA
Ceres is even larger – but it counts as dwarf planet (the only one in the asteroid belt). Ceres is roughly
spherical with an equatorial diameter of 963 km). The nature of the bright spots in the Occator Crater
is still completely unknown and also Ahuna Mons looks very strange.
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Remnants of Planet Formation
Quelle: NASA
Asteroids and comets (above, composite: E. Lakdawalla) look
indeed similar to the ones is „Star Wars“, but they are way further
apart. Itokawa (right, length: ~500 m, credit: JAXA) seems to be a
combination of a compact (upper) part and a “pile of rubbish”.
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Remnants of Planet Formation
Churyumov–Gerasimenko (~4 km x 4.5 km, also known
as “Chury” or (German) “Tschuri”) is an (awaking) comet
nucleus with similar appearance as Itokawa. It is currently
visited by the European Rosetta mission and its lander
Philae ̶ Günter can (will) tell you more (credit: ESA).
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Planetesimals on Collision Course
On February 15, 2013 a mere 17 m diameter meteoroid exploded over the Ural mountains – with about
30 times the energy of Hiroshima atomic bomb (Credit: Alex Alishevskikh, Velentin Kazako, RMES).