Probing Neptune

Astronomers know little about Neptune because it is so far from Earth. Neptune has been visited by only one spacecraft, Voyager 2, on 25 August 1989. Almost everything we know about Neptune has come from this encounter. Voyager had been travelling for about 12 years and had covered nearly 5 billion kilometres to reach Neptune. The space probe came to within 5000 km of the planet and it collected a wealth of information about this most distant gas giant and its moons. Voyager found Neptune to be...

Info

Later probes went into orbit around Mars and returned much more data. More recently, probes have successfully landed on the Martian surface, but to date no human has yet set foot on Mars. The first three space probes directed at Mars were launched by the USSR between 1960 and 1962, but failed to leave Earth orbit. Mars 1, launched by the USSR on 1 November 1962, was the first probe to fly past the planet, but it failed to return data. The USA attempted a fly-by of...

Introduction To Space Probes

The overwhelming importance of the solar system lies in the fact that we are part of it its origin and evolution are part of our own history. Astronomers have observed the solar system for the past few centuries via telescopes from the Earth's surface. Then, in 1957, a new method of exploration began with the launch of the first artificial satellite - humans had entered the Space Age. Since this time, humans have improved the technology of their spacecraft to the point where they can now send...

Did You Know

Astronomers use light years as a measure of distance in the universe. One light year is the distance that light travels in one Earth year. The speed of light is 300 000 kilometres per second, so in one year light travels a distance of 9.5 million million kilometres. The nearest star to our solar system (apart from the Sun) is Proxima Centauri, at a distance of about 4.2 light years. In a scale model with the Sun and Earth 30 cm apart, Proxima Centauri would be 82 km away. Because Proxima...

Diy

Figure 2.10 The Mars Odyssey space probe. 7 April 2001 via a Delta 2 launch vehicle from Cape Canaveral, Florida, and arrived at Mars in October of that year. The probe began orbiting the planet once every 25 hours, but this period was shortened to 2 hours as the craft's orbital path decreased bringing it closer and closer to Mars. One of the aims of the Odyssey mission was to find out more about the geology of Mars. A gamma-ray spectrometer was used to map the surface for elements like...

Density and composition

Earth has a slightly larger mass, diameter and average density than Venus. Because of this, the strength of gravity on Earth is slightly more than that of Venus. A 75 kg person on Earth weighs 735 N. Earth is also the densest planet in the solar system because it has a large nickel-iron core. Scientists know a lot about the interior of Earth from their study of earthquake (seismic) waves and volcanoes. Earthquakes release enormous amounts of energy that travel through Earth and along its...

Energy and luminosity

The Sun produces a hundred million times more energy than all the planets combined. Just over half this energy is in the form of visible light, with the rest being infrared (heat) radiation. Only about a billionth of the Sun's energy reaches us here on Earth. The Sun's energy comes from the 'burning' of its hydrogen gas via the process of nuclear fusion. In this process four hydrogen atoms combine to make one helium nucleus. During this process some mass is lost, and it is this mass that is...

Cloudy planet

Venus is the second planet from the Sun, orbiting on average at a distance of 108 million kilometres from the Sun. It is the sixth largest planet, with a diameter of 12 104 km. Venus is sometimes regarded as Earth's sister planet since it is similar in size and mass to Earth. Venus orbits the Sun between Mercury and Earth but it is twice as far as Mercury from the Sun. It comes closer to Earth than any other planet in the solar system. One of the strange things about Venus is that it spins on...

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Figure 2.5 Paths of Voyager 1 and Voyager 2 through the solar system. Both probes used the gravitational pull of Jupiter and Saturn to accelerate them further out into the solar system. This process is called gravity assist. Voyager 2 in August 1981. The probes discovered seven new moons and returned spectacular photographs of the planet's ring system. After passing Saturn, Voyager 1 left the solar system, but Voyager 2 was able to visit Uranus onJanuary 1986 and Neptune in August 1989. Voyager...

Probing the asteroids

In October 1991, the NASA space probe Galileo took the first detailed photograph of an asteroid while en route to Jupiter. The asteroid photographed, named Gaspra, is an irregularly shaped object measuring about 19 by 12 kilometres. The Galileo probe also passed by another asteroid, Ida, in August 1993. Both Gaspra and Ida are classified as S-type asteroids because they are composed of metal-rich silicates. Figure 8.4 Path of the Galileo space probe as it passed by the asteroid Gaspra. Figure...

Early views about Venus

Venus is the brightest planet as seen from Earth. At certain times of the year it can be seen in the evening sky just after sunset at other times of the year it appears to rise in the east just before sunrise. Venus was well known to the ancient Greeks and Romans because of its brightness in the night sky, but the Greeks believed Venus to be two different objects Phosphorus as the morning star, and Hesperos as the evening star. To the ancient Romans, Venus was the goddess of love and beauty....

Acknowledgements

Figure Solar System

The author and publisher are grateful to the following for the use of photographs in this publication. National Aeronautics and Space Administration (NASA) European Space Agency CSIRO Archives While every care has been taken to trace and acknowledge copyright, the author apologies in advance for any accidental infringement where copyright has proved untraceable. He will be pleased to come to a suitable arrangement with the rightful owner in each case. This chapter reviews our early and current...

Exploring the planets

This chapter reviews the significant space probes used to explore the solar system. Many probes were sent into space but were unsuccessful or made insignificant contributions. The probes examined here have added greatly to our knowledge of the planets in the solar system. Exploring space beyond Earth and the Moon Since the early space missions put humans into orbit around Earth, many advances have been made in space technology. It is now possible to send space probes deep into the solar system...

Position and orbit

Venus orbits the Sun in a nearly circular orbit, as shown by its small orbital eccentricity. Its mean orbital radius is just over 108 million kilometres, and it passes within 40 million kilometres of Earth, closer than any other planet. Figure 5.3 Orbital path of Venus (distance circles are in astronomical units, AU). Figure 5.3 Orbital path of Venus (distance circles are in astronomical units, AU). Observation of Venus is easy because of its close proximity to Earth, and it is the brightest...

Early views about the asteroids

The word 'asteroid' means 'star-like'. This name probably arose because, viewed through a small telescope from Earth, asteroids look like points of light. Ancient observers on Earth did not know the asteroids because they cannot be seen with the unaided eye. The idea that a planet-like body might exist between the orbits of Mars and Jupiter was suggested by Johann Elert Bode in 1768. In January 1801, the Sicilian astronomer Giuseppi Piazzi discovered a body in a position similar to that...

Early views about Mercury

Mercury has been known since the time of the Sumerians (3rd millennium BC). The planet was given two names by the ancient Greeks Apollo, for its apparition as a morning star, and Hermes as an evening star. Greek astronomers knew, however, that the two names referred to the same body. To the Greeks, Hermes was the messenger of the gods. In Roman mythology, Mercury was the god of commerce, travel and thievery. The planet probably received this name because it moves so quickly across the sky. The...

Soho

Another joint project of the ESA and NASA, the Solar Heliospheric Observatory, or SOHO, was launched in December 1995 via an Atlas Centaur rocket. SOHO has been keeping a watch on the Sun since April 1996 and is in orbit around the Sun in a region between the Earth and Sun where the gravitational pull of the two bodies are in balance (about 1.5 million km from Earth toward the Sun). SOHO contains instruments that are studying changes in the Sun's interior, corona, and solar wind. One of SOHO's...

Glossary

Asteroid number Astronomical unit (AU) One of three prominent rings encircling the planet Saturn. A measure of the proportion of light reflected from a planet, asteroid or satellite. The point in the elliptical orbit of a planet, comet or asteroid that is furthest from the Sun. The point in the orbit of the Moon or artificial satellite at which it is furthest from Earth. The visible brightness of a star or planet as seen from Earth. A small rocky and or metallic object, often irregular in...