The Solar System
One of the most difficult and controversial fields of astronomy is the study of the way in which the Solar System was formed, as well as its past and its future evolution.
The Solar System, or more particularly, its larger bodies - all the planets with their satellites, orbit in the Sun close to one plane known as the ecliptic which is defined as the plane in which the Earth orbits, and all move in the same direction. It is helpful to remember that an observer viewing this from a position above the plane of the ecliptic, or from the direction of the terrestrial north pole, would see the planets move around the Sun in an counter-clockwise direction, also referred to as prograde motion. All the planets and their major satellites rotate in an counter-clockwise direction on their axis, with the exception of Venus and Uranus which, because of the position of their axes shows that they experienced some cataclysmic event in their far-off past.
Sun
The Sun is an ordinary star that was born out of a
cloud of matter called the primordial nebula 4½ thousand million years ago (4.5
billion years), along with the 8 known planets in our corner of space called
the Solar System. The Sun is mainly
composed of Hydrogen, a much smaller amount of Helium together with other
chemical elements. It is a globe of intensely hot plasma, 1,391,785,000 Km in
diameter, more than a million times bigger than our Earth. It shines through an
atomic process called nuclear-fusion: four bits of Hydrogen join to 4 bits of
Helium; the Sun gives off heat and light, and loses solid material into space.
This all happens every second and our Sun loses 4 million tonnes of matter
during that brief time. The Sun's centre has a temperature of 15 million
degrees centigrade, cooling to 6 thousand degrees at its gaseous surface
Mercury
Mercury is the innermost and smallest planet in the Solar
System,[a]
orbiting the Sun once every 87.969
Earth days. The orbit of Mercury has the highest eccentricity of all the Solar System planets,
and it has the smallest axial tilt. It completes three rotations about its axis
for every two orbits. The perihelion of Mercury's orbit precesses around the Sun at an excess of
43 arcseconds per century, a phenomenon that was explained in the 20th
century by Albert Einstein's General Theory of Relativity.[11]
Mercury is bright when viewed from Earth, ranging from −2.3 to 5.7 in apparent magnitude, but is not easily seen as
its greatest angular separation from the Sun is only
28.3°
Venus
Venus is the second planet from the Sun, orbiting it every
224.7 Earth days.[9]
The planet is named after Venus,
the Roman goddess of love and beauty. After the Moon, it is the
brightest natural object in the night sky, reaching an apparent magnitude of −4.6, bright enough to
cast shadows. Because Venus is an inferior
planet from Earth,
it never appears to venture far from the Sun: its elongation reaches a maximum of 47.8°. Venus
reaches its maximum brightness shortly before sunrise or shortly after sunset,
for which reason it has been known as the Morning Star or Evening Star
Earth
Earth (or the Earth) is
the third planet from the Sun, and the densest and fifth-largest of the
eight planets in the Solar
System. It
is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the World, the Blue Planet,[20]
or by its Latin name, Terra.[note 6]
Earth formed 4.54 billion years ago, and life appeared on its surface within one
billion years.[21] The planet is home to
millions of species, including humans.[22] Earth's biosphere has significantly altered the atmosphere and other abiotic conditions on the planet,
enabling the proliferation of aerobic organisms as well as the formation of
the ozone
layer
which, together with Earth's magnetic field, blocks harmful solar radiation, permitting life on land.
Mars
Mars is the second smallest of the eight major planets in
the Solar System. Only Mercury is smaller. It is nearly 7,000 kilometres (km)
wide; just over half the width of the Earth. Its volume is about 15% of the
Earth. Since a lot of the Earth is covered by water, the total surface area of
the Mars is nearly as large as all of the land on the Earth. It is possible
that its size may eventually permit human colonies.
Jupiter
Jupiter is by far the largest planet within our Solar
System: two and a half times larger than all of the other planets put together.
It is the fifth planet from the Sun and one of the brightest planets. Jupiter,
along with Saturn, Neptune and Uranus, is sometimes called a "gas
giant" because most of this planet is made up of liquid and gas
Saturn
Saturn is the sixth planet from the Sun and the second
largest planet in the Solar System, after Jupiter. Saturn
is named after the Roman god Saturn, equated to the Greek
Cronus (the Titan
father of Zeus), the
Babylonian Ninurta and the Hindu
Shani. Saturn's astronomical symbol (♄)
represents the Roman god's sickle.
Uranus
Uranus
is the seventh planet
from the Sun. It has
the third-largest planetary radius and fourth-largest planetary mass in the Solar
System. It is named after the ancient Greek deity of the sky Uranus (Ancient
Greek: Οὐρανός),
the father of Cronus
(Saturn) and grandfather of Zeus (Jupiter). Though it is visible to the naked eye
like the five classical planets, it was never recognized as a
planet by ancient observers because of its dimness and slow orbit.
Neptune
Neptune
is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest
planet by diameter and the third largest by mass. Neptune is 17 times the mass
of Earth and is
slightly more massive than its near-twin Uranus, which is 15
times the mass of Earth but not as dense.[12]
On average, Neptune orbits the Sun at a distance of 30.1 AU,
approximately 30 times the Earth–Sun distance. Its astronomical symbol is ♆, a
stylized version of the god Neptune's trident
Earth's Moon
The Moon has no
atmosphere due to its weak gravity. It is composed of a 800 km thick
lithosphere, covering a core of thin magma.
The Moon has
two types of landscapes: bright, cratered highlands in the south, and
dark mare basins in the north. One side of the moon always faces the
earth; this side has many more mare basins.
Primary lunar
craters were caused by meteors. Secondary craters were caused by debris. Lunar
craters have rays around the edges. These are caused by the debris from
meteors: since the moon has weak gravity and no atmosphere, it sprays out for a
long distance.
Erosion is much
slower on the moon than on the Earth. It is estimated that Buzz Aldrin's
footprint will last 10 million years!
The maria
(plural of mare) were caused by big asteroids strikes which ruptured the Lunar
crust and released internal lava to flow up into the impact craters and
flood-fill the bottom of the crater out to the crater walls. The lava solidified
into basalt, creating the large, dark basins. This iron-rich basalt creates
tension in the maria basins. This sometimes causes the crust to crack, forming
graben.
Early in the
moon's history, meteoric impacts caused the surface to melt. The liquid lunar
surface underwent differentiation: the heavier iron sunk, while lighter
aluminum rose to the top. The core was kept liquid by radioactive heating from
uranium, potassium, and thorium.
Comet
About 4.5 billion years ago,
primordial comets were formed along with the Solar system from the collapse of
a giant, diffuse cloud of gas and dust. The cloud started to heat up and whirl
faster as it shrank. The material in the fast-spinning cloud spread out into a
flattened disk. The temperature in the dense, central core became so hot that
it ignited nuclear fusion creating the Sun, while low temperatures in the
disk's outer region allowed water to freeze onto dust grains, which grew in
size to make clumps. The clumps merged by collisions, eventually forming the
planets. But some of the matter did not merge into planets and came to reside
beyond Neptune in agglomerated bodies known as comets [1].
Comets moved randomly through the solar system. When a comet strayed too close
to a planet, the larger body's gravity pushed the comet into the inner solar
system. Then the comet grew a tail and became visible to observers on Earth [2].
It has been postulated that the chemical diversity observed in the population
of comets found in the Kuiper Belt (region extended after Neptune orbit) as
well as Oort cloud(spherical cloud lie roughly 50 000 AU from the Sun) is
primordial or due evolution effects since formation.
The chemical abundances of comets
were observed between both classes of comets: Oort cloud comets and the
Jupiter-Family comet (population consisting of short-period comets formed in
the Kuiper belt), and a difference was noted between the two groups. This can
be attributed to several factors including differences in the chemical and
physical environments in comet-forming regions, chemical evolution during their
long storage in the Oort cloud and Kuiper belt, and thermal processing by the
Sun when entering the inner Solar System. The chemical composition of comets is
investigated by remote sensing using spectroscopy. This investigation is
indirect, since only the gas and dust coma was observed after the nucleus ices
have sublimated from the nucleus.
Observations were made at millimeter/sub-millimeter
wavelengths with the IRAM 30-m, JCMT, CSO and SEST telescopes, which was based
on molecular abundances in comets by Biver et al. 2007. Six Jupiter-family,
three Halley-family, and fifteen long-period comet were observed from 1986 to
2001. The eight molecular species were HCN, HNC, CH3CN, CH3OH, H2CO, CO, CS,
and H2S. HCN were detected in all comets, while at least two molecules were
detected in nineteen comets. It was inferred that the HCN abundance relative to
water varies from 0.08% to 0.25% from the sub-sample of comets for which
contemporary H2O production rates are available. HCN is the molecule which
exhibits the lowest abundance variation from comet to comet with respect to
other species and was found in all the 24 Comets. HCN was found only in the 4
Comets and low CO abundances measured in Jupiter-family comets, while several
Oort cloud comets exhibit high CO abundances [3].
According to the observation 23% of CO molecule with respect to water was
observed in 5 comets. While 0.035% of HNC relative to water was observed in 5
comets.15 comets exhibits CH3CN up to maximum 6.2%.And H2CO, H2S and CS was
found in 13,11,9 comets respectively. They were found maximum up to 1.3%,1.5%
and 0.17% respectively relative to water.
Asteroids
Largest
bodies in the asteroid belt
|
|
Object
Name |
Maximum
Size |
1 Ceres
|
933 km
|
4 Vesta
|
530 km
|
2 Pallas
|
525 km
|
10 Hygiea
|
407 km
|
511 Davida
|
326 km
|
The asteroid
belt lies between the planets Mars and Jupiter. It contains lumps of rock and
metal much smaller than planets. These lumps are called asteroids or minor
planets. They are not visible from Earth with the naked eye, but many may be seen
through binoculars or small telescopes.
The largest
asteroid in the solar system is 2001 KX76. In the asteroid belt, the largest
body is a dwarf planet called Ceres, which is 933 kilometers across. The next
largest, which is called Vesta, is 530 kilometers across.
Some asteroids
are less than a kilometer across. Unofficially the limit has been set at 50
meters, and anything smaller than that is going to be simply called a
meteoroid. With advances in telescopes and particularly for objects that travel
close to the Earth, some objects smaller than 50 metres have indeed been seen
passing nearby the Earth.
There are probably several million asteroids in
the solar system. Over 96,000 asteroids have been given numbers. Almost 12,000
of them have names. But even though there are a lot of asteroids, the asteroid
belt is mostly empty space. Traveling through the asteroid belt in a space ship
would not be very much like what you see in a science fiction film.
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