All matter is made up of subatomic particles such as electrons and protons. Each particle has a counterpart with an opposite spin and charge; the counterpart of an electron, for example, is a positron. Those counterpart particles make up antimatter, and when they collide with their ordinary-matter twins, the particles annihilate each other, converting their mass into energy.

In the mid-1990s, physicist Gerald Smith led a research group at Penn State University dedicated to antimatter propulsion research. While there, he developed designs for antimatter-propelled aircraft and rockets. Antimatter is attractive because of its high specific impulse, which allows spacecraft to carry less fuel and reach higher speeds. “If you want to compare the launch of an antimatter rocket to the launch of the space shuttle, an antimatter rocket would burn right off the launch pad and be in the clouds in seconds,” Smith says. “Because you have all this energy in a very small amount of mass, you can really push the throttle forward and get it going fast.”

Because of its potential for high speeds, antimatter has often been discussed as an option for journeys to faraway stars. But Smith points out that its speed would also allow for safer trips within our solar system: “The principal danger to astronauts outside the Earth’s atmosphere is exposure to radiation. The less time you take to get to somewhere, the less radiation they will incur.”The possibility of antimatter propulsion allowed Smith and his colleagues to plan round-trips to Mars that would take just 90 days: 30 to get there, 30 on the surface, and 30 to travel back to Earth.

Smith and his colleagues never got as far as building an antimatter-propelled craft. Though he developed ways to contain antimatter particles in magnetic fields, Smith, who now works on other applications for antimatter at Positronics Research, an engineering company he founded, notes that the money for further research has dried up. “It would be hard to do in the current economic climate,”he says.

HOW AN ANTIMATTER CRAFT WOULD WORK

1. The ship carries a supply of antimatter in a magnetic field.

2. The antimatter and its ordinary-matter counterpart obliterate each other, releasing energy.

3. This energy propels the ship fast enough to get to Mars in a month.