I found this on my laptop just now. Apparently I wrote it in 2003, but I can’t remember what it was for. Still, when you’ve got a hungry blog to feed, who cares about a little recycling?
It seems to be part of our nature for we humans to feel the urge to understand our relationship to the Universe. In ancient times, attempts to cope with the vastness and complexity of the world were usually in terms of myth or legend, but even the most primitive civilizations knew the value of careful observation. Astronomy, the science of the heavens, began with attempts to understand the regular motions of the Sun, planets and stars across the sky. Astronomy also aided the first human explorations of own Earth, providing accurate clocks and navigation aids. But during this age the heavens remained remote and inaccessible, their nature far from understood, and the idea that they themselves could some day be explored was unthinkable. Difficult frontiers may have been crossed on Earth, but that of space seemed impassable.
The invention of the telescope ushered in a new era of cosmic discovery, during which we learned for the first time precisely how distant the heavenly bodies were and what they were made of. Galileo saw that Jupiter had moons going around it, just like the Earth. Why, then, should the Earth be thought of as the centre of the Universe? The later discovery, made in the 19th Century using spectroscopy, that the Sun and planets were even made of the same type of material as commonly found on Earth made it entirely reasonable to speculate that there could be other worlds just like our own. Was there any theoretical reason why we might not be able to visit them?
No theoretical reason, perhaps, but certainly practical ones. For a start, there’s the small matter of getting “up there”. Powered flying machines came on the scene about one hundred years ago, but conventional aircraft simply can’t travel fast enough to escape the pull of Earth’s gravity. This problem was eventually solved by adapting technology developed during World War II to produce rockets of increasingly large size and thrusting power. Cold-war rivalry between the USA and the USSR led to the space race of the 1960s culminating in the Apollo missions to the Moon in the late 60s and early 70s. These missions were enormously expensive and have never been repeated, although both NASA and the European Space Agency are currently attempting to gather sufficient funds to (eventually) send manned missions to Mars.
But manned spaceflights have been responsible for only a small fraction of the scientific exploration of space. Robotic probes have been dispatched all over the Solar System. Some have failed, but at tiny fraction of the cost of manned missions. Landings have been made on the solid surfaces of Venus, Mars and Titan and probes have flown past the beautiful gas giants Jupiter, Saturn, Uranus and Neptune taking beautiful images of these bizarre frozen worlds.
Space is also a superb vantage point for astronomical observation. Above the Earth’s atmosphere there is no twinkling of star images, so even a relatively small telescope like the Hubble Space Telescope (HST) can resolve details that are blurred when seen from the ground. Telescopes in space can also view the entire sky, which is not possible from a point on the Earth’s surface. From space we can see different kinds of light that do not reach the ground: from gamma rays and X-rays produced by very energetic objects such as black holes, down to the microwave background which bathes the Universe in a faint afterglow of its creation in the Big Bang. Recently the Wilkinson Microwave Anisotropy Probe (WMAP) charted the properties of this cosmic radiation across the entire sky, yielding precise measurements of the size and age of the Universe. Planck and Herschel are pushing back the cosmic frontier as I write, and many more missions are planned for the future.
Over the last decade, the use of dedicated space observatories, such as HST and WMAP, in tandem with conventional terrestrial facilities, has led to a revolution in our understanding of how the Universe works. We are now convinced that the Universe began with a Big Bang, about 14 billion years ago. We know that our galaxy, the Milky Way, is just one of billions of similar objects that condensed out of the cosmic fireball as it expanded and cooled. We know that most galaxies have a black hole in their centre which gobbles up everything falling into it, even light. We know that the Universe contains a great deal of mysterious dark matter and that empty space is filled with a form of dark energy, known in the trade as the cosmological constant. We know that our own star the Sun is a few billion years old and that the planets formed from a disk of dusty debris that accompanied the infant star during its birth. We also know that planets are by no means rare: nearly two hundred exoplanets (that is, planets outside our Solar System) have so far been discovered. Most of these are giants, some even larger than Jupiter which is itself about 300 times more massive than Earth, but this may simply because big objects are easier to find than small ones.
But there is still a lot we still don’t know, especially about the details. The formation of stars and planets is a process so complicated that it makes weather forecasting look simple. We simply have no way of knowing what determines how many stars have solid planets, how many have gas giants, how many have both and how many have neither. In order to support life, a planet must be in an orbit which is neither too close to its parent star (where it would be too hot for life to exist) nor too far aware (where it would be too cold). We also know very little about how life evolves from simple molecules or how robust it is to the extreme environments that might be found elsewhere in our Universe. It is safe to say that we have no absolutely idea how common life is within our own Galaxy or the Universe at large.
Within the next century it seems likely that we will whether there is life elsewhere in our Solar System. We will probably also be able to figure out how many earth-like exoplanets there are “out there”. But the unimaginable distances between stars in our galaxy make it very unlikely that crude rocket technology will ever enable us to physically explore anything beyond our own backyard for the foreseeable future.
So will space forever remain the final frontier? Will we ever explore our Galaxy in person, rather than through remote observation? The answer to these questions is that we don’t know for sure, but the laws of nature may have legal loopholes (called “wormholes”) that just might allow us to travel faster than light if we ever figure out how to exploit them. If we can do it then we could travel across our Galaxy in hours rather than aeons. This will require a revolution in our understanding not just of space, but also of time. The scientific advances of the past few years would have been unimaginable only a century ago, so who is to say that it will never happen?
Ten Facts about Space Exploration
- The human exploration of space began on October 4th 1957 when the Soviet Union launched Sputnik the first man-made satellite. The first man in space was also a Russian, Yuri Gagarin, who completed one orbit of the Earth in the Vostok spacecraft in 1961. Apparently he was violently sick during the entire flight.
- The first man to set foot on the Moon was Neil Armstrong, on July 20th 1969. As he descended to the lunar surface, he said “That’s one small step for a man, one giant leap for mankind.”
- In all, six manned missions landed on the Moon (Apollo 11, 12, 14, 15, 16 and 17; Apollo 13 aborted its landing and returned to Earth after an explosion seriously damaged the spacecraft). Apollo 17 landed on December 14th 1972, since when no human has set foot on the lunar surface.
- The first reusable space vehicle was the Space Shuttle, four of which were originally built. Columbia was the first, launched in 1981, followed by Challenger in 1983, Discovery in 1984 and Atlantis in 1985. Challenger was destroyed by an explosion shortly after takeoff in 1992, and was replaced by Endeavour. Columbia disintegrated over Texas while attempting to land in 2003.
- Viking 1 and Viking 2 missions landed on surface of Mars in 1976; they sent back detailed information about the Martian soil. Tests for the presence of life proved inconclusive, but there is strong evidence that Mars once had running water on its surface.
- The outer planets (Jupiter, Saturn, Uranus and Neptune) have been studied by numerous fly-by probes, starting with Pioneer 10 (1973) and Pioneer 11 (1974) . Voyager 1 and Voyager 2 flew past Jupiter in 1979; Voyager 2 went on to visit Uranus (1986) and Neptune (1989) after receiving a gravity assist from a close approach to Jupiter. These missions revealed, among other things, that all these planets have spectacular ring systems – not just Saturn. More recently, in 2004, the Cassini spacecraft launched the Huygens probe into the atmosphere of Titan. It survived the descent and sent back amazing images of the surface of Saturn’s largest moon.
- Sending a vehicle into deep space requires enough energy to escape the gravitational pull of the Earth. This means exceeding the escape velocity of our planet, which is about 11 kilometres per second (nearly 40,000 kilometres per hour). Even travelling at this speed, a spacecraft will take many months to reach Mars, and years to escape the Solar System.
- The nearest star to our Sun is Proxima Centauri, about 4.5 light years away. This means that, even travelling at the speed of light (300,000 kilometres per second) which is as fast as anything can do according to known physics, a spacecraft would take 4.5 years to get there. At the Earth’s escape velocity (11 kilometres per second), it would take over a hundred thousand years.
- Our Sun orbits within our own galaxy – the Milky Way – at a distance of about 30,000 light years from the centre at a speed of about 200 kilometres per second, taking about a billion years to go around. The Milky Way contains about a hundred billion stars.
- The observable Universe has a radius of about 14 billion light years, and it contains about as many galaxies as there are stars in the Milky Way. If every star in every galaxy has just one planet then there are approximately ten thousand million million million other places where life could exist.
In the Dark 