The Interplanetary Superhighway

The Solar System might have been made for our convenience. The Sun, for example, is a placid star at the right distance from us. We have been in a benign region of space for the past 100,000 years and will continue to be for tens of thousands of years to come. The space through which we have passed has been clean of the destructive debris that fills most of the Galaxy's spiral arms.   Our most massive planet, Jupiter, is at the right distance from us to protect Earth from the impact of incoming comets. In some stellar systems, the most massive planet is as close or closer to its star as Mercury is to ours, taking up the mass that might otherwise have been left over for a habitable planet.

Most important, we have a Moon much larger than the moon of any other planet in the system, whose gravity keeps the axial tilt of our world constant and makes our seasons stable. Without it, our climate would change constantly and unpredictably.  Another little known asset is going to make travel between the planets much easier than is generally imagined. There is an invisible network of ``tubes'', made of gravity, that interconnect many of the planets. NASA engineers are already calling it the ``interplanetary Superhighway.'' The idea is based on the discovery made two centuries ago by Joseph-Louis Lagrange, one of the greatest mathematicians of the eighteenth century, that every pair of bodies in the Solar System have five points between them, regions in space that are forever stable. The Earth and Moon, for example, have five Lagrangian points between them. A spacecraft parked at one of these points need never move. Many of these points are interconnected, and hence the aims of the L5 Society, a group that wanted to establish a space colony at this position. Suppose one wishes to send a cargo ship from Earth to Mars. The cheapest way to go––the way that requires the least energy––is to send the ship to the outermost Lagrangian point of the Earth‑Sun system. Then, only a little nudge of rocket power will be enough to send it on in turn to the outermost point of the Mars‑Sun system. All the planets (except perhaps for Pluto) are interconnected by Lagrangian points in this fashion, and a ship could wind its way through the Solar System by means of these invisible tubes. But this means of travel is very slow. It is for cargo, not for passengers. It is not a way of saving time but of saving fuel. A trip from Earth to Venus, if carried out with maximum rocket power, would take about 150 days. With the use of tubes this would be increased to some 650 days, but the amount of fuel needed would be reduced by two thirds. This system will be a boon for the industrial development of the Solar System. Nor is the existence of these tubes wholly an accident. As the mathematician Ian Stewart points out in a recent article in the New Scientist, in the ``landscape'' created by the formation of the Sun and Jupiter there were preferred locations where other planets, with their tube connections, were likely to form.