WASHINGTON (UPI) -- Life on Earth as we know it will come to an end in 1,500 million years and the planet will look more like its dusty, volcanic sister Venus in 2,500 million years, scientists said Wednesday. But mirrors or shades potentially could shield Earth from increasing heat from the sun and delay the catastrophic consequences, they said. A collision with a comet or other major change in the atmosphere could speed up the end of life. Ken Caldeira and James Kasting of Pennsylvania State University calculated the doomsday estimates using computer models of temperature and atmosphere changes and projections of the sun's increasing heat. As the sun continues to brighten and warm over time, the amount of carbon dioxide in the atmosphere drops -- eventually to a point too low for plants to survive, the scientists said in the British journal Nature.
After 2 1/2 billion years, all of Earth's water would have been lost to space. That's a pretty strong barrier to life,'' said Caldeira, an Earth systems scientist.
Tyler Volk, an applied science professor at New York University, suggested there may be ways to delay or prevent the eventual demise of life.
``Our descendants or descendant species would not have to run from the devolution...they could fight,'' said Volk. ``Shades in space or mirrors on the Earth that keep out a small fraction of the elevated future (heat from the sun) would be an option.''
Other possible solutions include constructing closed environments such as the Biosphere 2 project in Arizona, in which cycling of carbon dioxide, water and other essential matter would be controlled. Establishing controlled Earth-like environments in space also could be considered, Volk said.
(Is it really true that mainly doom-seekers become Earth systems scientists, and mainly problem-solvers become applied science professors?)
The most straightforward way to avoid the death of the earth from the overheating predicted by Caldeira and Kasting is to move the earth farther from the sun on whatever schedule seems appropriate to our descendants.
Here's the best way to do it that I have been able to think of. It is along the same line as what Thomas Clarke offhandedly suggested in a reply to my original post. The present post contains only a qualitative discussion with a few numbers taken from calculations I made for a slightly different project - moving Mars closer to the sun in order to improve its climate. I need to work on the formulas and the numbers some more before giving them.
The method involves no new science and only predictable improvement in present technology.
Our object is to transfer energy from the orbit of Venus to the orbit of the earth so that Venus will move closer to the sun and the earth farther away. Jupiter could also be used. Unfortunately, it seems that the matter is a bit more complicated than this, because the process must not only conserve energy, but it must also conserve angular momentum of the earth and Venus about the sun. Maybe this can be done at the cost of giving Venus a more eccentric orbit, but maybe it requires a third planet. (This is analogous to processes in atomic physics that require a third body in order to satisfy all the conservation laws.)
The problem is to arrange for a coupling between the orbits of the earth and Venus and possibly another planet as well.
Our tool for doing this is what I shall call a *tame asteroid*. A tame asteroid is one that has repeated encounters with planets. A small deflection of the asteroid's orbit before an encounter is magnified by the encounter. The asteroid is always controlled so that it never stops having encounters. The deflections (delta-v s) are accomplished as many encounters in advance as the noise in the system will permit.
[This process is analogous to the trajectory of the spacecraft Galileo, but apparently the plan with Galileo is to give up the close encounters when it enters the Jovian system. If JPL were to keep control of it by a sequence of encounters, it could be returned to the vicinity of the earth after spending sufficient time in the Jovian system. I have no idea what use this might be.]
The asteroid, say Ceres, has repeated encounters with the earth and Venus. It passes in front of the earth and behind Venus on each encounter. Thus it adds energy to the earth's orbit and takes it from Venus's orbit.
When I was thinking about moving Mars, I made some calculations involving the masses of Ceres, Mars and Venus and the ratio between the escape velocity from Mars and the delta-v s needed to move Mars to the more salubrious distance of the earth's orbit. I got a figure of at least 330 encounters taking at least about two years each. This assumed that each encounter with Mars transferred the maximum possible amount of energy. Therefore, the computation is optimistic by some small factor, say 5.
Since the earth is 9 times as massive as Mars, about 9 times as many encounters would be required. At least at first, the encounters would take less time, because the earth and Venus are closer to the sun.
The problem with conserving angular momentum is one I only encountered recently, so I haven't figured out what additional encounters might be needed.
Keeping a Tame Asteroid Tame
Ceres has a mass of 10^21 kilograms, so it would be important to make its deflections as much in advance as possible. I assume that the gravitational fields of the bodies involved will have been measured accurately long before the project is attempted, i.e. the high order harmonics of the gravitational potentials will be accurately known. What I don't know is this: What is the largest source of noise, i.e. unpredictable deflections, in the system? I speculate that it is weather in the sun causing unpredictable fluctuations in the sun's gravitational field. I don't know if this is right, and I hope someone else can shed light on how large they are likely to be.
Continued in part 2
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