Today’s Sun is 40 percent brighter than it was when it was born 4.6 billion years ago! In 1 billion years the Sun will release 10 percent more energy than it does now! What does that mean for civilization on Earth? It means the Sun’s heat output will result in complete chaos here on Earth, and at one point the Sun will consume the Earth! First, as the Sun heats up the moist greenhouse effect begins to kick in. The moist greenhouse is when oceans begin to evaporate into the atmosphere and eventually off into space. In the atmosphere water acts as a greenhouse gas which causes Earth to trap more heat, which causes even more water to rise to the atmosphere, thus ending surface life on Earth. Why are the oceans so important? According to scientist every living organism thrives on water with the exception of very few prokaryotic organisms. During this moist greenhouse effect temperatures on Earth will soar to a whopping 700 degrees Fahrenheit! Earth’s beautiful landscape will be that of a Venusian inferno. Thick clouds of sulfur and carbon dioxide will fill the air because the greenhouse effect will be so intense.
As time progresses and the Sun brightens, the habitable zone ( or HZ for short) moves further out into the solar system. The habitable zone is the region some distance from the Sun where water on a planet can stay in its liquid form. The inner boundary of the HZ is defined by the point where water would boil and evaporate, and the outer boundary of the HZ is defined by the point where water would freeze. What happens to Earth when it is no longer in the HZ? Before Earth is consumed by the Sun, proactive Earthlings will have figured out ways to colonize Mars. But why Mars you might ask? I’ll tell you.
The graph below from Guo, Zhang, & Han (2010) shows how the habitable zone changes with time. The green shaded area on the graph shows the habitable zone (the top of the green area is the outer boundary of the HZ, the bottom is the inner boundary). The y-axis on this graph is the logarithm of the distance of various planets (represented by horizontal lines) in AU from the Sun (Note: one AU is the distance between Earth and Sun). Finally, the x-axis is the age of Sun in Gyrs ( 1 Gyr=1 billion years) starting from the point when the Earth first becomes inhabitable. Anytime a planet’s horizontal line crosses the green area it means that planet is in the HZ!The graph above shows how the habitable zone (or HZ) changes with time. The green shaded area on the graph shows the habitable zone. On the x- axis lies time in Gyrs (= one billion years). The y- axis is the logarithm of the distance expressed in astronomical units. The four lines show the location of different planets Mars (Pink), Jupiter (Purple), Saturn (Black), and Uranus (Red).
Since the Sun will have a greater heat output, Mars will be in the habitable zone, and according to the graph Mars will remain in the HZ for 1.5 billion years! That’s 10x longer than the amount of time people have been around for! A closer HZ means Mars polar ice caps will melt into an ocean. If proactive Earthlings release carbon dioxide, plant plants (which produces oxygen), and distribute water on Mars it will make the martian planet habitable. Mars natural greenhouse effect will make its atmosphere thick as it once was. When Earthlings accomplish this process they have successfully colonized Mars. Remember though, Earthlings will have only 1.5 billion years until the Sun undergoes another evolution where it becomes much brighter. When this occurs, the Sun will consume Mercury, Venus, Earth, and make even Mars inhabitable. Earthlings will be forced to colonize elsewhere. But where?
As Zachary mentioned in his Europa post, Jupiter’s moon has the resources to host life but one key element is missing and that is heat. Europa, according to leading theories , has a tremendous ocean under an icy crust. According to the graph below, Jupiter and all its moon will remain in the HZ for approximately 325 Myrs (Million Years). Heated by the Sun, Europa has the possibility of becoming a oceanic planet! The Sun will continue to age and increase in size. Eventually the Sun will consume Jupiter and its moons, thus leaving Earthlings with two options; to perish in an inferno-like moon or continue advancing as a civilization. I dont know about you all but I prefer the advancement of civilization.
Earthlings will have no choice but to move to the beautiful moon of Saturn, Titan. Titan is the second- largest moon in the Solar System, and is 80% more massive and 50% larger than Earth’s moon. Earthlings, according to the graph, will have approximately 130 Myrs (Million years) to inhabit Saturns moon, Titan. Titan has an organic- rich atmosphere and surface. Its atmosphere has approximately the correct temperature and composition to support the existence on liquid! But unfortunately, data from the Hubble Telescope and observations suggest existence of liquid methane found in oceanic areas around Titan.
Finally, fast-forwarding 4-5 billion years from now, the Sun will exhaust its hydrogen. The Sun will eventually eject its plasma into space, forming a vast planetary nebula. What’s left behind is a White Dwarf and the remaning planets, Jupiter, Saturn, Uranus, and Neptune. The remaning planets will be inhabitable because of the cooling White Dwarf and gaseous, hazardous space. What will become of civilization in 5 billion years? Will our civilization solar-system hop to the nearest star? We may never know…