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Unit 2 Day 3
Introduction to the Solar System
Our Solar System is a collection of planets, asteroids, satellites, comets, meteoroids, dust, and gas orbiting our sun, a
yellow star. The Sun contains about 99.9 percent of the mass of the system.
In the Beginning
The Solar System is believed to be about 5 billion years old and, presumably, formed at the same time as the Sun. To
understand the formation of the Solar System, we must first understand the formation of the Sun. For the sun to form
there was a solar nebula (a collection of gas and dust) which collapsed until the sun was several times larger than it is
now surrounded by a disk of dust and gas. The disk itself then broke off into the planets that we now know orbit our
sun.
Those closest to the sun were too warm and small to hold most of the original gases; most of the material escaped back
into the Solar nebula leaving only a residue upon which, in the case of the Earth, we live. These planets, Mercury,
Venus, Earth, and Mars are called the terrestrial planets. The rest of the planets, forming further from the Sun, were
cool and massive enough to keep most of their hydrogen. These massive, giant planets are called the jovian planets,
and are made up of mostly gas.
Much of the nebula was blown out of the solar system by the pressure of the Sun's radiation. Many fragments still
exist as meteoroids, asteroids, comets, and dust particles.
The Sun
At the heart of the Solar System is the Sun. Luckily for us, the Sun is quite an ordinary star, with no exciting changes
in brightness. Since the Sun is the primary source for almost all the energy on Earth, a stable environment makes the
Earth's ecosystem, and all the life within it, possible. The surface of the Sun has a temperature of about 5500 Kelvin.
The outer atmosphere of the Sun, the Corona, has a temperature of over a million degrees. The corona is visible during
the spectacular event of a total solar eclipse.
Mercury
The planet closest to the sun, Mercury is a rocky planet too close to the sun to maintain any detectable atmosphere.
Images taken of Mercury by space vehicles reveal a landscape very similar to that of the Earth's moon.
Venus
In many respects the twin of the Earth in size and, probably, initial circumstances, Venus is shrouded by a dense
atmosphere dominated by carbon dioxide. The pressure at the surface is about 30 times that of Earth and the
temperature is over 700 degrees K.
Earth
All of what we know of the Universe is deduced from our experiences on Earth. How unique are the characteristics of
the home planet? Of the four terrestrial planets, it seems to have been the only one to maintain a stable atmosphere,
accommodating to life, over the billions of years it took to evolve.
Mars
Just over 10% the mass of the Earth, Mars' respectful distance from the Sun permitted a slight atmosphere to form.
Long thought to be the planet with the best chance for life similar to that on Earth, the planet has revealed striking
evidence for ancient river valleys to space probes.
The Asteroids
Marking the boundary between the terrestrial planets and the massive gas giants is the asteroid belt. A jumble of
irregularly shaped boulders, one cannot help but wonder if they are debris left behind from a failed, or even exploded,
planet. If one is to make huge space stations or enormous space ships, the asteroid belt may be one of the easiest
places to find the raw materials needed to feed the smelters because the cost, in energy, of moving materials from the
surface of the Earth is enormous.
Jupiter
The dominant planet of the Solar System, Jupiter is the first of the jovian planets, a hydrogen-rich planet whose
multi-colored bands are constantly changing in color. Unlike the terrestrial planets, the gas giants have no rocky
surface but an ever increasing density of gas.
Saturn
The favorite of amateur astronomers, Saturn is surrounded by a thin, bright system of wide rings. The planet, a faded
version of Jupiter in appearance, seems to float inside this brilliant band of light. The Saturnian rings, composed of ice
particles in orbit around Saturn, are unique in planetary rings in their widths and narrow gaps. Saturn has more
satellites than Jupiter (18 vs. 16) but only one, Titan, is fairly large.
Uranus
Too far from Earth to be seen with an unaided eye, Uranus is the first of the discovered planets (William Herschel,
1781). The atmosphere is nearly featureless and the planet has a light blue appearance when viewed through a
telescope.
Neptune
Even further from Earth than Uranus, it seems a faint blue disk in Voyager 1 showed it to be a beautiful blue planet
with storm features slightly like those of Jupiter. Neptune seems to be the planet that defines the edge of the Solar
System for the clouds of comets that surround the Solar System.
Pluto
Pluto was discovered by Clyde Tombaugh in 1938. Its orbit is so eccentric that it crosses inside that of Neptune
(where it is now) leading some to speculate that it is an escaped satellite of that planet. In the last few years,
astronomers have come to think of Pluto as just an enormous comet nucleus, the largest example of a Kuiper Belt
object.
Planetary Satellites
All of the jovian planets are accompanied by satellites. Of the terrestrial planets, only Earth has a significant
companion: the Moon. The two moons of Mars are so small that they would appear to Martians as artificial satellites
seem to earthly observers. The largest satellite of the Solar system is Neptune's Triton, nearly four times the mass of
our Moon. Saturn's Titan, and the four moons of Jupiter are the other major satellites. Most of the rest, about 40 others
have been discovered so far, are small.
Comets and Meteors
The largest components of the solar system are the comets, whose tails sometimes reach between the orbits of planets.
The tails are gases evaporated from the icy cores and dust freed as the ices melt. Comets that stray into the inner
(planetary part) of the solar system are often gravitationally "captured" by a jovian planet causing them to have smaller
orbits and highly shortened periods. The resulting repeated passages by the Sun spells their doom as they quickly
evaporate. The smallest bodies in the Solar System are the meteoroids, floating along between planets until they crash
into the atmosphere of a planet, leaving a short, bright trail, a meteor. Some are left over from the formation of the
Solar System, some are the debris left behind by comets.
And in the End
Current theories predict that in about five billion years, the sun will become a red giant star, swelling to many times its
current size. This will destroy the terrestrial planets (certainly the Earth's atmosphere and water) and probably
massively change the characteristics of the jovian planets. Shortly thereafter it will shrink to a white dwarf, a faint star
barely brightening the remains of the Solar System for many more billions of years.
Unit 2 Day 3 Notes
1. A solar system is a collection of planets, satellites, asteroids, comets,
meteoroids, dust, and gas orbiting a star.
2. The sun contains 99.9 percent of the mass of our solar system.
3. Our solar system is about 5 billion years old.
4. Our solar system formed at the same time our sun formed.
5. A solar nebula is a collection of gas and dust.
6. Mercury, Venus, Earth, and Mars are called the Terrestrial planets.
7. Jupiter, Saturn, Uranus, and Neptune are called the Jovian planets.
8. The temperature of the surface of the sun is 5500 Kelvin.
9. The temperature of the corona of the sun is over a million degrees.
10. The landscape of Mercury is similar to our moon.
11. The main gas in the atmosphere of Venus is carbon dioxide.
12. The mass of Mars is a little over ten percent of the mass of Earth.
13. The asteroid belt between the Terrestrial planets and the Jovian planets
could be useful for mining.
14. One gas the makes up Jupiter is hydrogen.
15. The planet that has rings is Saturn.
16. Uranus appears to be a light blue when viewed through a telescope.
17. Neptune is the furthest true planet in our solar system.
18. Pluto is now considered to be a dwarf-planet.
19. All of the Jovian planets have moons (natural satellites).
20. The smallest bodies in the solar system are meteoroids.