Origin of earth

• It is a assemblage consisting of the Sun—an average star in the Milky Way Galaxy
and those bodies orbiting around it: 8 (formerly 9) planets with about 210 known
planetary satellites (moons); countless asteroids, some with their own satellites;
comets and other icy bodies; and vast reaches of highly tenuous gas and dust known
as the interplanetary medium.
• Located at the centre of the solar system and influencing the motion of all the other
bodies through its gravitational force is the Sun, which in itself contains more than 99
percent of the mass of the system. The planets, in order of their distance outward from
the Sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
Solar system

Pluto had been officially listed among the planets since it was discovered in 1930
orbiting beyond Neptune, but in 1992 an icy object was discovered still farther from the
Sun than Pluto. Many other such discoveries followed, including an object named Eris
that appears to be at least as large as Pluto. It became apparent that Pluto was simply
one of the larger members of this new group of objects, collectively known as the
Kuiper belt.
History of Pluto
Size comparison between
earth and Pluto

 Accordingly, in August 2006 the International Astronomical Union (IAU),
the organization charged by the scientific community with classifying
astronomical objects, voted to revoke Pluto’s planetary status and place it
under a new classification called dwarf planet.
 Any natural solar system object other than the Sun, a planet, a dwarf planet, or
a moon is called a small body; these include asteroids, meteoroids, and comets.
Most of the several hundred thousand asteroids, or minor planets, orbit
between Mars and Jupiter in a nearly flat ring called the asteroid belt.
 One astronomical unit is the average distance from Earth to the Sun—about
150 million km [93 million miles].

ORBIT
 The shape of an object’s orbit is defined in terms of its eccentricity. For a perfectly
circular orbit, the eccentricity is 0; with increasing elongation of the orbit’s shape,
the eccentricity increases toward a value of 1.
 Of the eight major planets, Venus and Neptune have the most circular orbits
around the Sun, with eccentricities of 0.007 and 0.009, respectively. Mercury, the
closest planet, has the highest eccentricity, with 0.21; the dwarf planet Pluto, with
0.25, is even more eccentric.

Classification of Eight Planets
• Jovian, or giant, planets (Jupiter,
Saturn, Uranus, and Neptune)
• Composed primarily of hydrogen
and helium (Jupiter and Saturn)
or of ice, rock, hydrogen, and
helium (Uranus and Neptune)
• Inner, or terrestrial, planets
(Mercury, Venus, Earth, and
Mars)
• Rocky compositions and
densities greater than 3 grams
per cubic cm
based on densities (mass
per unit volume)
Planets and their moons

Differentiation between terrestrial and Jovian planets

• The asteroid belt is home to rocky bodies ranging in size from the largest known
asteroid, Ceres (also classified by the IAU as a dwarf planet), with a diameter of roughly
940 km (585 miles), to microscopic dust particles that are dispersed throughout the belt.
Asteroids and comets

 Some asteroids travel in paths that cross the orbit of Earth, providing opportunities for
collisions with the planet.
 The rare collisions of relatively large objects (those with diameters greater than about
1 km [0.6 mile]) with Earth can be devastating, as in the case of the asteroid impact
that is thought to have been responsible for the massive extinction of species at the end
of the Cretaceous Period 65 million years ago (see dinosaur: Extinction; Earth impact
hazard).

Gaspra, an asteroid of the main belt, in a
composite of two images taken by the Galileo
spacecraft during its flyby on October 29,
1991. Pocked with numerous small craters, Its
irregular shape and groovelike linear
markings suggest that it was once part of a
larger body that experienced one or more
shattering collisions.
Image: NASA/JPL/Caltech
Gaspra
The icy nucleus of Comet Wild 2, in a composite
image taken by the U.S. Stardust spacecraft during
its close approach to the comet on January 2, 2004.
The image consists of a short exposure to resolve
fine details of the surface and a longer exposure to
capture the faint jets of gas and dust streaming into
space.
NASA/JPL/Stardust/University of Washington, Seattle
Comet Wild

Origin Of The Solar System The Kant-Laplace nebular
hypothesis
 Kant’s central idea was that the solar system
began as a cloud of dispersed particles.
 assumed that the mutual gravitational attractions
of the particles caused them to start moving and
colliding, at which point chemical forces kept
them bonded together.
 As some of these aggregates became larger than
others, they grew still more rapidly, ultimately
forming the planets.

 Laplace’s model begins with the Sun already formed and
rotating and its atmosphere extending beyond the distance
at which the farthest planet would be created. Laplace
assumed that the Sun would start to cool as it radiated
away its heat. In response to this cooling, as the pressure
exerted by its gases declined, the Sun would contract.
 Centrifugal acceleration would push the material in the
atmosphere outward, while gravitational attraction would
pull it toward the central mass.
 This process would have continued through the formation
of several concentric rings, each of which then would have
coalesced to form a planet.

Dis Advantages
 Kant did not recognize the intrinsic limitations of his approach. His model does not account for
planets moving around the Sun in the same direction and in the same plane, as they are observed
to do, nor does it explain the revolution of planetary satellites.
 the Sun contains 99.9 percent of the mass of the solar system, the planets (principally the four
giant outer planets) carry more than 99 percent of the system’s angular momentum. For the solar
system to conform to this theory, either the Sun should be rotating more rapidly or the planets
should be revolving around it more slowly.
 Laplace’s model led naturally to the observed result of planets revolving around the Sun in
the same plane and in the same direction as the Sun rotates. Because the theory of Laplace
incorporated Kant’s idea of planets coalescing from dispersed material, their two approaches
are often combined in a single model called the Kant-Laplace nebular hypothesis. This model
for solar system formation was widely accepted for about 100 years.

Modern theories – Big Bang theory
 Big Bang Theory is about the origin of Universe. It suggests that about 1370 crore
(13.7 billion) years ago, all matter and energy in the universe was concentrated into an
area smaller than an atom.
 At this instant, matter, energy, space and time were not existent. Then suddenly with a
bang, the Universe began to expand at an incredible rate and matter, energy, space and
time came into being.
 As the Universe expanded, matter began to coalesce into gas clouds and the stars and
planets. Some scientists believe that this expansion is finite and will done day cease.
 After this point in time, the Universe will begin to collapse until a Big Crunch occurs.

PROOFS OF BIG BANG
 Expanding galaxies: Hubble in 1929, noted that galaxies outside our own Milky
Way were all moving away from us, each at a speed proportional to its distance
from us. He quickly realized what this meant that there must have been an instant
in time (now known to be about 14 billion years ago) when the entire Universe
was contained in a single point in space. The Universe must have been born in
this single violent event which came to be known as the “Big Bang.”
 Cosmic Background radiation: Those early photons – the afterglow of the Big
Bang known as cosmic background radiation – can be observed today.

Origin of earth

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Origin of earth