Planetary securitySun's growing brightness a threat to Earth

Published 24 October 2008

The Sun is slowly getting brighter and warmer; in seven billion years it will engulf Earth — but much sooner, in 1.1 billion years, the Sun will grow 11 percent brighter, raising average terrestrial temperatures to around 50 °C, causing oceans to evaporate; the solution: move Earth away from the Sun

Yes, John Maynard Keynes said that “In the long run we are all dead,” but this does not mean that we should not be concerned with the state of the world even when we are no longer around. Here is an issue which gives new meaning to the term “long run”: The Australian writer Robert Jungk (1913-94) wrote an early history of the atomic age, giving it the title Brighter than a Thousand Suns: A Personal History of the Atomic Scientists (1958). The “Brighter” in the title referred to the flash created by an explosion of a hydrogen bombs, but, alas, the Sun itself is getting brighter and warmer, and this poses a problem for Earth. New Scientist’s Jeff Hecht writes that the clock is ticking inexorably toward doomsday even if we do not kill ourselves by poisoning the environment or overheating the planet.

The Sun is slowly getting warmer as it burns the hydrogen in its core. In about five billion years the Sun will begin evolving into a bloated red giant. Scientists calculate that as the Sun’s outer gas shell swell up, it will, seven billion years from now, engulf the Earth. The troubles will begin much sooner: In 1.1 billion years the Sun will grow 11 percent brighter, raising average terrestrial temperatures to around 50 °C (120 °F). This will warm the oceans so much that they will evaporate without boiling, like a pan of water left on a sunny kitchen counter.

What is to be done? Scientists say that we cannot keep the Sun smaller and cooler, but we can increase the distance between Sun and Earth by moving Earth away. Colin McInnes, a mechanical engineer at the University of Strathclyde, says we can do that by using a giant solar sail. Solar sails are thin, mirror-like films that are propelled by the weak pressure of the sunlight that falls on them. Hecht writes that McInnes’s idea is to put a free-floating solar sail at a point near the Earth where the pressure of solar radiation essentially balances the Earth’s gravitational pull. His analysis shows that the reflection of sunlight from the sail will pull the Earth outward along with the sail (to use physics terminology: there is a need to increase the Earth’s orbital energy and accelerating the center of mass of the system outward, away from the Sun).