The Voyager 1 is a space probe which was launched by NASA on September 5, 1977. It’s mission: study the outer Solar System and interstellar space beyond the Sun’s heliosphere. Its distance from earth is, at the time of writing, 14,288,282,585 mi (or about 22.994.761.848 KM) with a estimated Velocity (with respect to the Sun) of currently 38,026.77 mph.
After launch the probe made successful flybys of Jupiter, Saturn, and Saturn’s largest moon, Titan. Voyager 1 studied the weather, magnetic fields as well as the rings of the two planets and was the very first probe to provide detailed images of their moons. On February 14, 1990 it took the first portrait of the Solar System as seen from outside, which includes the famous “Pale Blue Dot” image of planet Earth. The mission continued far longer than expected and on August 25, 2012 Voyager 1 finally crossed the heliopause, making it the first man made object to reach interstellar space.
Now eight years into its interstellar journey, an analysis of Voyager 1’s data that it is still sending back to earth, is yielding new insights into what this new frontier is like. Stella Ocker, a Ph.D. student at Cornell University in Ithaca, New York published a new study in Nature Astronomy which reports what may be the first continuous measurement of the density of material out there in interstellar space. The Voyager 1 data samples used in this work were archived through the NASA Planetary Data System. This detection offers a new way to measure the density of interstellar space and opens up a new pathway to explore the structure of the very nearby interstellar medium.
“This detection offers us a new way to measure the density of interstellar space and opens up a new pathway for us to explore the structure of the very nearby interstellar medium.”
– Stella Ocker
Essentially like an ocean, interstellar space is full of turbulent waves. The biggest originate from our own galaxy’s rotation, while “smaller” waves come from supernova blasts, stretching billions of miles. The smallest ripples are normally produced by our Sun. These crashing waves give researchers clues about the density of the so called interstellar medium. It helps us to understand the shape of the heliosphere, or for example how stars form. As these waves travel through space, they constantly vibrate the electrons around them, which send out characteristic “ringing” frequencies depending how compressed they are. NASA explains that the higher the pitch of that ringing, the higher the electron density is. Voyager 1’s Plasma Wave Subsystem was designed to pick up that specific ringing.
When Voyager 1 left the heliosphere in November 2012, the probe heard these interstellar sounds for the first time after 3 months. Another 6 months later it recorded another, much louder and higher pitched signal, which means the interstellar medium appeared to be getting thicker. These short signals continue at irregular intervals in the probe’s data today. While they are rare and only appear about once a year, they are a great way for researchers to study the density of interstellar space. Stella Ocker calls the new signal “plasma wave emission”. When the signals appeared in the data, the tone of the emission rises and falls.
“This is really exciting, because we are able to regularly sample the density over a very long stretch of space, the longest stretch of space that we have so far,” said Ocker. “This provides us with the most complete map of the density and the interstellar medium as seen by Voyager.”