SOLAR SYSTEM
Our solar system is made up of the sun
and everything that travels around it. This includes eight planets and their
natural satellites such as Earth's moon; dwarf planets such as Pluto and Ceres;
asteroids; comets and meteoroids.
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- The sun is the center of our solar system.
- It contains almost all of
the mass in our solar system and exerts a tremendous gravitational pull on
planets and other bodies.
- Our solar system formed about 4.6 billion years ago.
- The four planets closest to the sun -- Mercury, Venus, Earth, and
Mars -- are called the terrestrial planets because they have solid, rocky
surfaces.
- Two of the outer planets beyond the orbit of Mars -- Jupiter and
Saturn -- are known as gas giants; the more distant Uranus and Neptune are
called ice giants.
- Most of the known dwarf planets exist in an icy zone beyond Neptune
called the Kuiper Belt, which is also the point of origin for many comets.
- Many objects in our solar system have atmospheres, including
planets, some dwarf planets and even a couple moons.
- Our solar system is located in the Orion Arm of the Milky Way
Galaxy. There are most likely billions of other solar systems in our
galaxy. And there are billions of galaxies in the Universe.
- We measure distances in our solar system by Astronomical Units
(AU). One AU is equal to the distance between the sun and the Earth, which
is about 150 million km (93 million miles).
HISTORY
People
believed Earth to be stationary at the center of the universe and categorically
different from the divine or ethereal objects that moved through the sky.
Although the Greek philosopher Aristarchus had speculated on a heliocentric
reordering of the cosmos, Nicolas Copernicus was the first to develop a mathematically predictive heliocentric system. In the
17th-century, Galileo Galileo, Johannes Kepler and Isaac Newton, developed an understanding of physics that led to the
gradual acceptance of the idea that Earth moves around the Sun and that the
planets are governed by the same physical laws that governed Earth. The
invention of the telescope led to the discovery of further planets and moons.
Improvements in the telescope and the use of unmanned spacecraft have enabled the investigation of geological phenomena, such as mountains, craters, seasonal meteorological phenomena, such as clouds, dust storms and ice caps on the other planets.
Formation
The Solar
System formed 4.568 billion years ago from the gravitational collapse of a
region within a large molecular cloud. This
initial cloud was likely several light-years across and probably birthed
several stars. As is typical of
molecular clouds, this one consisted mostly of hydrogen, with some helium, and
small amounts of heavier elements fused by previous generations of stars. As
the region that would become the Solar System, known as the pre-solar nebula, collapsed, conservation of angular momentum caused it to rotate faster. The centre, where most of the mass
collected, became increasingly hotter than the surrounding disc. As the contracting nebula rotated
faster, it began to flatten into a protoplanetary disc with a diameter of roughly 200 AU and a hot, dense protostar at the centre. The planets formed by accretion from this disc, in
which dust and gas gravitationally attracted each other, coalescing to form
ever larger bodies. Hundreds of protoplanets may have existed in the early
Solar System, but they either merged or were destroyed, leaving the planets,
dwarf planets, and leftover minor bodies.
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