Recalculating the Pulsar Map for the 21st Century

The design embedded in the terrazzo floor of the Boeing Milestones of Flight Hall is based on a famous illustration from the 1970s that shows, without using any words, the location of Earth’s solar system in relation to a known set of pulsars (simply put, blinky collapsed stars). The original map was included on four different spacecraft, Pioneer 10 & 11 and Voyager 1 & 2, all launched on trajectories heading out of this solar system. The Museum’s version celebrates the 50th anniversary of the building on the National Mall and the 250th birthday of the United States. 

Communicating Without Words

In the 1970s, as scientists began to send spacecraft to fly past the inner and outer planets, they started to think about these probes’ long lives, flying endlessly through space. Could you include messages on them—without using words or any assumption of universally understood symbols? Some scientists, including Frank Drake and Carl Sagan, started experimenting with sending each other messages without any key for decoding them. Could they communicate without relying on any pre-existing understanding? The pulsar map is one version of that kind of message. It’s not a map to Earth so much as to Earth’s solar system, and it works from any direction.   

Francis “Frank” Drake is the author of the Drake equation by which one can calculate the likely number of active radio-capable alien civilizations in our galaxy (any result better than zero is encouraging). He sketched out the original idea for the pulsar map in 1961.

N = R_* × f_p × n_e × f_l × f_i × f_c × L

The Drake equation.

Linda Salzman Sagan included the pulsar map on the plaque design prepared for the Pioneer 10 and 11 planetary probes launched in 1972 and 1973. These were the first spacecraft launched on trajectories that would take them out of our solar system. 

The pulsar map was also inscribed on the covers of the golden records included on the two Voyager spacecraft launched in 1977. Even though the Voyager spacecraft were launched after two Pioneer probes, they traveled faster and left the solar system sooner. 

Drawing Your Own “Pulsar Map” 

Imagine that you needed to give someone directions to your house (or your hometown), but you didn’t know from what direction they would be traveling—so you couldn’t send them turn-by-turn directions. You could just send your location, latitude and longitude that could be turned into directions. But what if the location was a whole planet or solar system, not just a house or a town? That was the thought experiment that scientists were having in the 1970s when they started designing planetary probes that they knew would eventually leave our solar system. How could they show that this came from Earth? That Earth had joined the universe of spaceflight-capable worlds? One answer was a pulsar map. 

Let’s use the National Air and Space Museum as an example location. How might you direct someone to the Museum’s building on the National Mall without using words? You could draw a map of Washington, DC landmarks: the Pentagon, the Washington Monument, the National Cathedral, and the Capitol building, for instance. A simple map could show how far and in what direction the Museum’s National Mall building is from each of those guideposts. No matter where visitors started, they should be able to figure out how to get close to the Museum’s building. The more landmarks, the easier it would be. And, presumably, once they got close, our imagined visitors could figure out that the National Air and Space Museum is the building with aircraft and spacecraft displayed behind giant glass windows. 

Drake chose pulsars as the landmarks in the galactic neighborhood. Jocelyn Bell first detected radio pulsars in 1967. So, the map’s creators were using some of the newest science as the guideposts of their nonverbal directions. When stars go supernova, they don’t disappear. Their cores collapse into neutron stars. These spinning remains send out energy, much as a lighthouse sends out rotating beams of light. From Earth (or any fixed point in space), pulsars are detectable as pulses (hence the name). Specific pulsars have distinctive timing of their electromagnetic pulses. 

The pulsar map locates Earth’s solar system in relation to 14 different local pulsars. Each line on the map shows the relative distance to between a pulsar and Earth’s solar system. The cross hatches show (in binary) the interval of the pulsar’s pulses. Technically, once you have three reference points, you should be able to triangulate a location. But more information should make that easier. The assumption is that the map contained enough scientific information—14 galactic guideposts, if you will—to determine which solar system created this. And then Earth is the planet in that system with the lights on, the radio/television playing, and satellites orbiting it. The larger design also included a key that indicated how to calculate the actual distances. 

The end result is as much a signature as a working map: This came from Earth. We made this.

Updating the Pulsar Map

What’s really cool about the pulsar map included on the Pioneer and Voyager spacecraft is that it is not only a map in space but also in time. Because pulsars slow over time, the map identifies not only the location of Earth’s solar system, but also the point in time at which the message was sent: the 1970s. The National Air and Space Museum’s building on the National Mall was constructed around that same time, the mid 1970s, opening on July 1, 1976. 

The exhibit team working on the Boeing Milestones of Flight Hall first talked about doing something with the pulsar map design in 2013, when we were redesigning Milestones for the building’s 40th anniversary in 2016, but it did not become a part of the final plan. The current Transformation of the Museum’s downtown building included terrazzo floors. Andrew Johnston, formerly of the Museum’s Center for Earth and Planetary Studies (CEPS), now at the Adler Planetarium, did the calculations to adjust the 1970s map to one that dates from 2026, the 50th anniversary of the Museum’s building on the National Mall. Ultimately, the positions of the pulsars are not changed but the binary information indicated on the spokes has been updated. 

We owe a debt of gratitude to the brilliant crews who managed to construct this complex pattern in the Museum’s floor even while a construction wall bisected the Hall. The lines run from end to end across the building, inviting visitors to locate themselves at the Museum’s updated seal. It’s now a new kind of signature, marking the renovated Museum in relation to the 50th anniversary of the building and the United States’s 250th birthday. Come find us!