H.G. Well's, science fiction classic, The Time Machine, described in 1895 the aging Sun swelling into a red giant, as the time traveller witnessed Earth's final days.
The Solar System's fate
Today's astronomers do not need a crude time machine to explore our Solar System's fate. In 5 billion years the Sun will expand into a red giant, the Sun's outer layers will escape into space, Earth will tend to migrate out to Mar's orbit and Mars will enter the present asteroid space. Unfortunately, the Sun will overcome Earth's orbital velocity and draw the Earth into a spiral towards the Sun. It is predicted that any gas giant planet within 500 million kilometres will fall into the dying star leaving trace amounts of lithium as evidence of its demise.
A new habitable zone
The inner planets would become uninhabitable yet the habitable zone will expand with the growing red giant. This habitable zone could extend from 1 billion kilometres to 3.5 billion kilometres with Saturn's Titan, a carbon rich moon, thawing out and incubating the first stages of life. Jupiter's ice bound moon Europa would become a lush marine environment supporting diverse forms of life.
New planets for old stars
Planets form around newborn stars with grains of interstellar dust whirling around the star's equator coalescing to form rocks eventually becoming asteroid sized bodies, some even becoming Jupiter sized worlds. The Cat's Eye Nebula, see attached image, is an excellent example of a dying star with concentric layers of planet forming dust. Slower forming embryos form like the Earth, Mars and Venus - familiar planets to Earth bound humanity. A dust disk around a star at the end of its life may also produce planets. Some planets may form in the aftermath of a supernova - the pulsar planets at PSR B1257+12 illustrate this planet forming mode.
Carbon planets
Red giant planets develop into white dwarfs, these second generation planets could be created from the merging of two white dwarfs, observational evidence for such a merger exists in GD 362. Earth sized carbon planets could form from shredded white dwarf debris. These planets could have an atmosphere of nitrogen, ammonia, carbon monoxide, methane and other hydocarbons. Their surfaces could contain oceans of ammonia mixed with metals, hardly conducive to mankind's existence.
The end of life on Earth
First and second generation planets ultimately face destruction. Civilisations based on these planets must escape or die. The Earth could transfer orbital energy from Jupiter moving Earth farther from the Sun. A main belt asteroid or even a Kuiper Belt object placed between the Earth and the Sun uses the same principle as a spacecraft passing near a planet thereby transferring energy from Jupiter to Earth. A surviving planet, far from an exploding star could leave beacons with documentary evidence of its civilisations for Earth explorers to discover. Earth's planetary paradise does not last forever.
Sources
- The Cat's Eye Nebula, Hubble Site, accessed 21/5/2011
- Astronomy Magazine, July 2009, Kalmbach Publishing
Michael Manning - ' The best lack all conviction while the worst are full of passionate intensity' W.B.Yeats
