The first spacecraft to leave the solar system carry roadmaps. Plaques on Pioneer 10 and 11 include a diagram that points the way to the Sun. The landmarks for that roadmap are 14 pulsars — the tiny, rapidly spinning corpses of once-mighty stars. If another civilization finds either probe, it should be able to use the map to navigate to the solar system.

Scientists and engineers here on Earth are looking at ways to use pulsars to navigate through the solar system. In particular, they’re using millisecond pulsars, which spin from dozens to hundreds of times per second. Like a lighthouse, such a pulsar sends out a beam of radio waves, X-rays, or other forms of energy. If Earth happens to line up with such a beam, we see “pulses” of light.

Pulsars are small but heavy. Their great density and high-speed rotation make them extremely stable. So their pulses of energy serve as excellent clocks. Comparing the timing from several pulsars — such as the four depicted here — should allow a spacecraft to triangulate its position anywhere in the solar system.

A test in 2018 used an X-ray telescope aboard the International Space Station. It was able to plot its position with an accuracy of three miles. And today, the European Space Agency is using pulsars to double check its GPS satellites.

In the future, probes to the planets and beyond might be guided by pulsars — landmarks on a galactic roadmap.

Script by Damond Benningfield