Interstellar: Voyager 2 goes where only one has gone before
NASA’s Voyager 2 spacecraft has become the second probe to enter interstellar space, as confirmed by data returned by several of the science instruments on board the spacecraft.
The probe’s Plasma Science Experiment (PLS), which studies the solar wind, a stream of charged particles that flow from the Sun, measured a significant decline in those particles starting on November 5 and has subsequently detected no solar wind in its environment.
Voyager 2‘s twin spacecraft, Voyager 1, crossed the heliosphere, the region of space under the influence of the solar wind, in 2012, but its PLS had long stopped working by that time.
Using the electrical current of the plasma flowing from the Sun, the PLS can measure the density, speed, pressure, temperature, and flux of the solar wind in its environment.
Three other instruments on board Voyager 2–its cosmic ray subsystem, low energy charged particle instrument, and magnetometer–also show evidence the probe has crossed the heliopause, or boundary of the solar wind’s influence, and is now in interstellar space.
Information traveling at the universal speed of light takes approximately 16.5 hours to travel home from Voyager 2, which is currently over 11 billion miles (18 billion km) from Earth. Signals are received via NASA’s Deep Space Network (DSN), which was built to communicate with distant spacecraft.
Launched in 1977, both Voyagers are powered by a radioisotope thermal generator (RTG). Since the RTGs have been losing power over time, some instruments on both probes, such as the cameras, have been turned off to prolong the spacecrafts’ lives.
Voyager 1 explored Jupiter, Saturn, and Saturn’s largest moon Titan while Voyager 2 flew by Jupiter, Saturn, Uranus, and Neptune. The latter remains the only spacecraft to have ever visited the solar system’s two ice giants planets. Over time, both spacecraft were upgraded remotely to broaden their capabilities.
“Working on Voyager makes me feel like an explorer, because everything we’re seeing is new. Even though Voyager 1 crossed the heliopause in 2012, it did so at a different place and a different time and without the PLS data. So we’re still seeing things that no one has seen before,” said PLS principal investigator John Richardson of the Massachusetts Institute of Technology (MIT) in Cambridge, MA.
Researchers are combining data returned by the Voyagers with that provided remotely by NASA’s Interstellar Boundary Explorer (IBEX) satellite to gain an in-depth understanding of the interaction between the heliosphere and the interstellar wind. IBEX was launched in 2008 and will be followed by a second satellite, the Interstellar Mapping and Acceleration (IMAP) probe, which is scheduled to launch in 2024.
“Voyager has a very special place for us in our heliophysics fleet. Our studies start at the Sun and extend out to everything the solar wind touches. To have the Voyagers sending back information about the edge of the Sun’s influence gives us an unprecedented glimpse of truly uncharted territory,” emphasized Nicola Fox, director of the Heliophysics Division at NASA Headquarters in Washington, DC.
The heliopause is not the boundary of the solar system, which extends into the Oort Cloud, a huge region that is the source of long-period comets and extends from 1,000 AU (astronomical units, with one AU equal to the average Earth-Sun distance or 93 million miles) to as far as 100,000 AU. Voyager 2 will not reach the inner Oort Cloud for another 300 years. It will exit the Oort Cloud in approximately 30,000 years.
Because they could last several billion years both Voyagers carry Golden Records containing images and sounds from Earth, which could someday convey information about the planet and human civilization to any intelligent alien life forms who find them.
Video courtesy of NASA’s Jet Propulsion Laboratory
Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.