Flights of Fancy: Saving the Earth from its Future

We all know that in several billion years, our sun’s red giant stage will more or less incinerate the Earth. Nothing to do about it except move somewhere else, assuming that by then we still exist, and have mastered interstellar travel. But more immediately (relatively speaking), somewhere between 500M and 1B years from now, our Earth will not necessarily have burned, but will certainly become unfit for life as we know it.

Like all main sequence stars of its type, the sun emits gradually increasing levels of light over time, amounting to about a 10% increase in solar radiation every billion years. This slowly pushes the habitable zone farther out from the sun, which will eventually result in the Earth’s being too hot for life.

Earth will become like Venus.

When our oceans boil, that will be the end.

Or will it?

We’re roughly two centuries out from the industrial revolution. What might be our technological capabilities hundreds of millions of years from now? Although it’s difficult to imagine such a civilization, it’s conceivable that by then, our descendants might have found a solution to the sun’s onslaught.

One such solution might be what we could call a Dyson Shield.

There has been to date much discussion of the concept of a Dyson Sphere, including even one Star Trek episode. A Dyson Sphere is a hypothetical structure built by a highlyadvanced civilization to at least partially enclose and capture the energy of a star. Think of a big—really big—hollow sphere of solar arrays capturing our star’s energy and transforming it to a form which we can use—that’s an example of a Dyson Sphere. But what would a Dyson Shield be?

 Size:

Well, the first order of business is shielding our planet from the increasing energy of the sun. We don’t need to build a Dyson Sphere to do that.

We would just need to build something about the diameter of the Earth, which although a daunting proposal, is a far smaller project than building something large enough to encircle the entire sun from a distance of 1 astronomical unit (1 A.U. = the distance from the Earth to the sun).

How much smaller? Our shield would need a radius of roughly 6.3 thousand km, which is the radius of the Earth. So its surface area (assuming it’s flat) would be given by the formula πr 2 , in this case equating to roughly 130 million km 2 . That’s certainly big. But a full Dyson Sphere with a radius of 1 A.U. or 150M km, would in comparison have a surface area two billion times greater, or 2.8 x10 17 km 2 . Let’s leave that one for the next generation!

Orbit:

Geometry would dictate that the closer the shield is to the Earth (and the farther from the sun), the smaller it could be while still casting a shadow on the entire planet. So we would want to place our Earth-diameter size shield relatively close to the Earth. To protect the Earth all year, it would need to orbit the sun (and not the Earth!) just inside of the Earth’s orbit, and travel at Earth’s speed in parallel, i.e., a 365-day orbit.

The shield would need to be made of lightweight material, to minimize gravitational effects of its nearby mass on the Earth’s orbit. We wouldn’t want the shield’s gravity to tug the Earth closer to the sun! This could be avoided by also creating for example a counterweight—an object of equal mass, but smaller in size, orbiting the Sun on the opposite (night) side of the Earth. In any case it’s safe to assume that if our future selves are capable of building such a shield, then they should also be able to compensate for its gravitational effects.

Energy:

The shield would need to possess engines to maintain such an orbit. But as the shield could capture the energy of its entire surface facing the sun, it would have ample energy to power its engines and then some, also providing power for just about anything else we wish to do. That’s not bad as a secondary benefit!

The shield would also need to be semi-transparent. That is, we don’t want to cast the entire Earth into darkness, we just want to maintain the level of energy we get from the sun today (or maybe a bit less if we don’t solve global warming before then). We would want to make the amount of light passing through the shield adjustable over time, so that as the sun’s radiation continues to strengthen, we could ratchet up the opacity to maintain stable Earth temperatures. If the sun is 10% brighter, maybe we only need to block 10% of its light, which means the sun would still be visible through the shield, and similar in appearance to the sun of today.

Doing this could perhaps buy us billions of years of additional Earth habitability. As real estate improvements go, that’s certainly a worthwhile investment!

Feature image: Artist’s impression of a Dyson Shield; credit: Rori Baldari