How It Works: Science and Technology - Vol. 15

By Wendy Horobin | Go to book overview

Solar System

A composite image of
the planets in the Solar
System, looking back
from Neptune (in the
foreground). As we
discover more about our
own system, we can begin
to understand how planets
form around other stars
and the conditions on
them that are necessary
for life.

The Solar System is a complex structure of planets, moons, asteroids, and comets orbiting a central star called the Sun. Together they sweep out a disk-shaped region of space that is 9 trillion miles (15 trillion km) in diameter. The Solar System is believed to have formed out of a huge cloud of spinning gas and dust called a solar nebula five billion years ago. The Sun, which contains more than 99 percent of the system’s mass, formed first, and planetary bodies gradually coalesced out of the remaining gas and debris over the next 500 million years to leave the nine planets in the positions we know them today.

The four planets nearest the Sun—Mercury, Venus, Earth, and Mars—are known as the terrestrial, or inner, planets. All are comparatively small and have rocky compositions and densities greater than 3 g/cm3. By contrast, the four outer planets—-Jupiter, Saturn, Uranus, and Neptune— are giant balls of gas and ice surrounding tiny rocky cores with densities less than 2 g/cm’. At the farthest reaches of the Solar System lies Pluto. Much debate has arisen over whether Pluto should in fact be classified as a planet. Smaller than the Moon, it is an icy, low-density body that resembles a satellite of one of the outer planets or the core of a comet.

Even before the advent of the space probe, a surprising amount was known about the physical and chemical characteristics of the planets. Earthbased observations of their orbital motions and relative distances enabled astronomers to calculate the diameter, mass, and degree and axis of spin. The introduction of the telescope revealed features such as rings, satellites, and large clouds on the large planets. New instruments, including spectroscopes and radio transmitters, followed, giving glimpses of the composition of planetary atmospheres and surface features such as craters, valleys, and mountains.

The space age transformed our knowledge of planets other than our own. With every new space probe sent deep into the Solar System, many questions have been solved, but entirely new questions have been raised. The exploration of space is a long-term business: spacecraft such as Voyager 2, launched in 1977 and containing technology that in any other field would be considered obsolete, was still able to return remarkable pictures of Neptune in 1989. Pioneer 10, sent out in 1973 to take pictures of Jupiter, was still sending signals back to Earth in 2001, as it traveled out of the Solar System.

Since the 1990s, in addition to spacecraft such as Galileo, targeted at Jupiter, and Magellan in orbit around Venus, the Earth-orbiting Hubble Space Telescope (HST) has proved itself capable of taking detailed planetary images. One of the most remarkable sights it has witnessed was the comet Shoemaker-Levy 9 crashing into Jupiter in July 1994. NASA and the European Space Agency (ESA) have plans for new probes to study some of the more unknown worlds in our Solar System in more detail, especially comets, asteroids, and the moons of Jupiter.


The Sun

As our nearest star, the Sun provides an excellent opportunity to study the processes that provide us with heat and light and gain insight into the workings of other stars in the cosmos. A number of probes were put into orbit around the Sun during the 1990s and have sent back spectacular pictures of the flares and eruptions that constantly shoot out from its surface. One of the probes,

-2118-

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How It Works: Science and Technology - Vol. 15
Table of contents

Table of contents

  • How It Works® Science and Technology 2017
  • Title Page 2019
  • Contents 2020
  • Salvage, Marine 2021
  • Satellite, Artificial 2024
  • Schlieren Techniques 2030
  • Screw Manufacture 2032
  • Seaplane and Amphibian 2035
  • Sea Rescue 2038
  • Security System 2042
  • Seismology 2046
  • Self-Righting Boat 2050
  • Semiconductor 2052
  • Servomechanism 2055
  • Sewing Machine 2058
  • Sextant 2062
  • Sheet Metal 2064
  • Ship 2067
  • Shutter 2074
  • Silicon 2076
  • Silicone 2078
  • Silver 2079
  • Sine Wave 2081
  • Siphon 2083
  • Ski and Snowboard 2084
  • Skin 2087
  • Skyscraper 2090
  • Slaughterhouse 2096
  • Sleep 2099
  • Smell and Taste 2103
  • Soap Manufacture 2107
  • Soft-Drink Dispenser 2109
  • Soil Research 2110
  • Solar Energy 2114
  • Solar System 2118
  • Solenoid 2124
  • Sonar 2126
  • Sorption 2129
  • Sound 2131
  • Sound Effects and Sampling 2136
  • Sound Mixing 2138
  • Soundproofing 2140
  • Sound Reproduction 2142
  • Soundtrack 2146
  • Space Debris 2150
  • Space Photography 2152
  • Space Probe 2156
  • Index i
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