Soapbox Science

Voyager 1 Reaches Interstellar Space

Bohle headshotShannon Bohle has experience with NASA, is a Fellow of the Royal Astronomical Society in the UK,  is a lifetime member of the Cambridge University Astronomical Society, and has held  professional memberships in the AAAS, the British Society for the History of Science, The National Space Society, The Planetary Society, and The Mars Society. She is  a registered consultant for the Science and Entertainment Exchange run by the National Academy of Sciences.

Boldly Traveling Where No Archival Recording has Gone Before

On 12 September 2013, following analysis of data from its Voyager 1 spacecraft, NASA confirmed that the spacecraft has now reached a new milestone; interstellar space. It seems fitting that Carl Sagan, astronomy popularizer and pioneer in the field of exobiology, wanted to send library materials. Inside the box-like portion of the spacecraft, called the satellite bus structure, is the first archival sound recording designed to be understood by non-human intelligent life. If intelligent life is out there, let’s just hope they enjoy our first publication so much that they visit Earth to request a library card.

SCI Space Craft International,

SCI Space Craft International, Click on the image to enlarge 

Infographic about the Voyager spacecraft showing the location of the image and sound recordings. “The SCI ‘Fact Sheet’ graphic products, for Voyager and other interplanetary spacecraft, have been seen in the hands of flight team members as well as enthusiasts among the public. The box structure is called the spacecraft bus. The circular, gold-plated information package is mounted to the outboard face of one of [the bus’s] ten bays.”

Voyager, A Look Back

Kicking the proverbial wheels and dipping the oil stick, on 5 September 1977 NASA launched Voyager 1 from Kennedy Space Flight Center. By 1979 it was whipping past Jupiter, and by 1980 it completed a flyby of Saturn and began a course that would take it out of the solar system:

Video credit: NASA JPL

pale blue dot

“This narrow-angle color image of the Earth, dubbed ‘Pale Blue Dot’, is a part of the first ever ‘portrait’ of the solar system taken by Voyager 1. The spacecraft acquired a total of 60 frames for a mosaic of the solar system from a distance of more than 4 billion miles from Earth and about 32 degrees above the ecliptic. From Voyager’s great distance Earth is a mere point of light, less than the size of a picture element even in the narrow-angle camera. Earth was a crescent only 0.12 pixel in size. Coincidentally, Earth lies right in the center of one of the scattered light rays resulting from taking the image so close to the sun. This blown-up image of the Earth was taken through three color filters — violet, blue and green — and recombined to produce the color image. The background features in the image are artifacts resulting from the magnification.”
(Description and image credit: NASA JPL).

In 1990, the spacecraft lost the ability to return photos to Earth. Its last image, Pale Blue Dot, has become a famous look back at our planet that shows just how small our world really is in the vastness of our solar system. It was also used in the title of and inspiration for science writer Carl Sagan’s book, Pale Blue Dot: A Vision of the Human Future in Space (1994).     

How Does NASA Know Voyager 1
Reached Interstellar Space?

There are some arguments about whether or not Voyager 1 has left the solar system. The term solar system is most commonly used to refer to the inner solar system which includes the sun and planets. So, yes, Voyager 1 left the inner solar system in 1990. On its journey, it continued towards the edge of the heliosphere. “The heliosphere is the immense magnetic bubble containing our [inner] solar system, solar wind, and the entire solar magnetic field.” In 2012, the probe passed the edge of the heliosphere, called the heliopause, which separates the heliosphere from the interstellar medium. The heliopause “traps” the stellar wind (which carries dust and particles) and does not let it escape into the interstellar medium. The term interstellar literally means “the space between stars,” the place where Voyager 1 is now located. (The plural of “interstellar medium” is “interstellar media,” from which is derived the title of this piece). The problem with saying that Voyager 1 is no longer in the solar system is that, technically speaking, the solar system (comprised of both the inner and outer solar system) is an area where any body is primarily influenced by the gravitational pull of a star, like our sun. Since the 1960s, scientists have agreed that the sun’s gravitational influence extends into the Oort Cloud, a very large region, but they are not sure how far into the Oort Cloud to draw the boundary of what could be considered our solar system. Clearly, then, Voyager is located in the interstellar medium but has not left the solar system.

v timeline

Voyager: The Grand Journey and Beyond.
(Image credit: NASA JPL)

As the sun “burns” it emits particles of light and heat released during nuclear reactions called hydrogen fusion. The energies from these reactions propel charged particles (called plasma) into space, sometimes through large bursts called prominences. Large prominences are called Coronal Mass Ejections (CMEs) while smaller ones are solar flares. Sometimes these particles hit the Earth in large doses, during space weather events, and are often referred to as solar storms or geomagnetic storms. Depending on their strength, which is measured and monitored by the US National Oceanic and Atmospheric Administration (NOAA) and other agencies, these particles can cause a variety of problems for communications satellites and the International Space Station orbiting the Earth as well as electronic equipment on Earth.

According to researchers at NASA’s Jet Propulsion Laboratory (JPL), when plasma passes through space within the heliosphere it would hit a detector “uniformly from all directions,” but particles that reached Voyager 1 as a result of the “St. Patrick’s Day Solar Storms” a year earlier showed different results. “Sunspot AR1429 unleashed a powerful X5-class solar flare detected by solar observing satellites and Earth on 7 March 2012, commencing the ‘St. Patrick’s Day storms’ of 2012.” Unusual readings continued to be detected from May through July 2012. According to NASA JPL, it took about 400 days (beginning 11 April 2013) for each solar outburst to have reached Voyager. See this video: Voyager 1 at the Final Frontier.

After the readings were taken it only took about 16 hours for Voyager’s radio waves to travel back to Earth. By 25 August 2012, scientists believed that Voyager had made it into interstellar space. Instead of normal readings, they said, “particles [were] hitting Voyager from some directions more than others” and sound recorded “oscillations increased in pitch,” like a shriek, indicating that the spacecraft had moved into a very different plasma environment, one that was nearly twice as dense as inside the heliosphere. Since this method for determining location had never been done before, they said, it took researchers at NASA over a year to be certain and to verify the data. See this video: Voyager Reaches Interstellar Space.

The heliopause boundary is created because in addition to plasma moving through space from the sun, so too is the solar magnetic field. The interstellar magnetic field, which is composed of ions like those found in hydronium, repels the adjacent solar magnetic field, creating a “bubble” of space called the heliopause which has previously been defined as the outer edge of the solar system. The magnetic field, while strong enough to create a barrier for radiation, is not strong enough to pose a problem for a metallic spacecraft passing through this boundary just as spacecraft are able to leave the Earth’s atmosphere.

Set a Course for the Oort Cloud–Engage!



Voyager still has a long way to go before leaving the solar system even though it is travelling at a rate of 37,000 miles per hour (60,000 km per hour). The spacecraft is presently 11.7 billion miles (18.8 billion kilometers) from Earth. Still, it will take an estimated “300 years for Voyager 1 to reach the inner edge of the Oort Cloud and possibly about 30,000 years to fly beyond it.” In 40,000 years it is expected to reach the constellation Camelopardalis. That’s long after you and I will live. To put it into perspective, should any intelligent life actually receive the message it is unlikely humanity (if it has managed to survive) will resemble anything like what is depicted in the recordings. If anything, it may serve as a record of our history, much like cave drawing of primitive humanoids 40,000 years ago during the Upper Paleolithic era (the “Later Stone Age”) does for us today. Interestingly, we are sending the message roughly at the midpoint of our communication technologies: analog stone tools, digital tools, and who knows what else 40,000 years from now.

Radio and television signals have long since left our solar system, so chances are that any non-human intelligent life in the universe would encounter those first, and view the Voyager 1 disk as an artifact. Nevertheless, unless faster than light transportation is turned from science fiction into science fact, Voyager 1’s “gold record” may be the first “Galactic hit” in terms of physical information objects from Earth held by an otherworldly civilization.


This blog post will be continued over on Shannon’s SciLogs blog


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