The more we learn about the abundance of planets around nearby stars, the more we want to go there. Sending humans is a distant dream, but launching spacecraft that could reach these stars in decades is almost within our grasp. We still need to work out how to slow such missions down, however, if we want much data. One scientist may have the answer.
We've found so many fascinating worlds astronomers recently held the ExoCup to choose people's favorite. (Congratulations Kepler-10b; the original, and apparently still the best). The next generation of telescopes will help us learn a little more about these worlds, but will barely scratch the surface of what we want to know.
Thus the enthusiasm to send spacecraft; nevertheless, to get results in the life of anyone alive today will require travel at a significant portion of the speed of light. Yet if a probe passed through our Solar system at, say, a tenth of the speed of light, it would spend at most 26 hours inside the orbit of Saturn – a long voyage for such a short mission.
The fuel required to slow a craft down through rockets would be far too heavy for such a mission. However, Professor Claudius Gros of Goethe University has proposed an alternative. In the Journal of Physics Communications Gros outlines a proposal to slow spacecraft down sufficiently as they approach a star that they could collect plenty of useful data, or even go into permanent orbit.
"Slow would mean in this case a travel velocity of 1,000 kilometers per second, which is only 0.3 percent of the speed of light but nevertheless about 50 times faster than the Voyager spacecraft," Gros explained in a statement.
Gros proposes fitting the craft with magnetic sails that, once deployed, interact with interstellar gas to decelerate the craft. Rather than being solid physical sails, with all the required weight, these would involve an enormous loop of superconducting material. The chilly conditions of space are ideal for superconduction, so the 1.5 million Amp current Gros proposes will circulate endlessly, producing a powerful magnetic field.
There are up to 100,000 charged particles per cubic meter (3,000 per cubic foot) of interstellar space, and even more where stellar winds are felt. The field would repel charged particles it approaches, transferring its momentum to them and slowing itself down.
Gros has proposed using the same approach to distribute seeds to habitable but sterile planets. In the shorter term, however, he calculates a craft could orbit Proxima Centauri just 58 years after launch. Unfortunately, this would require a loop with a 1,600 kilometers (1,000 miles) radius, which would need a spacecraft whose 1,500-ton (1,400-tonne) weight Gros calls “daunting” to build and launch.