Key concepts

• protected by the atmosphere and magnetosphere

• types of radiation – electromagnetic and corpuscular

• rems (radiation equivalents in man)

Introduction

Life on Earth has an over 3.5 billion year history. It had a beginning and it will have an end. The longest that life can possibly exist on Earth into the future is approximately 4 billion years, though a number of catastrophes can happen on much shorter timescales (some of these are discussed in Chapter 8). In approximately 4 billion years, our Sun will run out of nuclear fuel and enter what is called the Red Giant phase of stellar evolution. It will expand perhaps past the orbit of Earth, vaporizing Mercury, Venus, and Earth. If humans are to survive the end of Earth, we will have to develop the technological capability to move to another star system. Humans have made the first tentative steps off Earth. We routinely fly astronauts into low-Earth orbit, and the US and China plan to have a manned presence on the Moon and Mars in the relatively near future. However, the technological obstacles to space travel are daunting – some say even insurmountable.