For the second time in history, a human-made object has reached the space between the stars. NASA’s Voyager 2 probe now has exited the heliosphere – the protective bubble of particles and magnetic fields created by the Sun.
The story of Voyager II Probe
During the summer 1965, calculations reveal it possible for a spacecraft launched in the late 1970s to visit all four giant outer planets, using the gravity of each planet to swing the spacecraft on to the next. This alignment occurs one every 176 years.
12 years later, Voyager 2 launches from NASA’s Kennedy Space Center. It is named Voyager 2 because, even though it launches first, Voyager 2 planned to reach Jupiter and Saturn after Voyager 1.
On July 9, 1979, Voyager 2 makes its closest approach to Jupiter. Highlights of this encounter include the first images of Jupiter’s ring system; discovery of a third moon (Adrastea); and a close approach to the moon Europa.
On August 25, 1981, the spacecraft makes its closest approach to Saturn. It met several of Saturn’s icy moons and took images of the half-young, half-old terrain of Enceladus, which suggests it might be geologically active.
On January 24, 1986, Voyager 2 approaches Uranus, it is the first time the seventh planet from the Sun has been seen up-close. Upon approach, Voyager 2 images reveal 11 new moons.
On August 25, 1989, the spacecraft encounters Neptune, making it the first spacecraft to observe Neptune up close and the first to visit four planets beyond Earth. 6 new moons were discovered as well as the first images of Neptune’s rings taken.On October 10 and December 5, 1989, Voyager 2’s Cameras Turn Off.
On August 30, 2007, Voyager 2 crosses the termination shock into the heliosheath, the outer layer of the bubble the Sun blows around itself and all of the planets. This time, antennas at Earth are listening for the spacecraft data transmissions and scientists are able to analyze the first measurements of the passage through the termination shock.
On August 13, 2012, the mission becomes the longest-operating one, breaking the previous record for continuous operation by Pioneer 6.
Finally, on December 10, 2018, Voyager 2 Probe enters Interstellar Space for the second time in history! It has reached the space between the stars.
Comparing data from different instruments aboard the trailblazing spacecraft, mission scientists determined the probe crossed the outer edge of the heliosphere on November 5. Thus boundary, called the heliopause, is where the tenuous, hot solar wind meets the cold, dense interstellar medium. Voyager 2 carries a working instrument that will provide first-of-its-kind observations of the nature of this gateway into interstellar space.
Voyager 2 now is slightly more than 18 billion kilometers from Earth. Missions operators still can communicate with Voyager 2 as it enters this new phase of its journey, but information – moving at the speed of light – takes about 16.5 hours to travel from the spacecraft to Earth.
The most compelling evidence of Voyager 2’s exit from the heliosphere came from its onboard Plasma Science Experiment (PLS), an instrument that stopped working on Voyager 1 in 1980. Until recently, the space surrounding Voyager 2 was filled predominantly with plasma flowing out from our Sun. This outflow, called the Solar wind, creates a bubble – the heliosphere – that envelopes the planets in the Solar System. The PLS uses electrical current of the plasma to detect the speed, density, temperature, pressure and flux of the solar wind. The PLS aboard Voyager 2 observed a steep decline in the speed of the solar wind particles on November 5. Since that date, the plasma instrument has observed no solar wind flow in the environment around Voyager 2, which makes mission scientists confident the probe has left the heliosphere.
"Working on Voyager makes me feel like an explorer, because everything we're seeing is new" - John Richardson, principal investigator for the PLS instrument and a principal research scientist at the Massachusetts Institute of Technology in Cambridge.
Is there a future for those probes?
While the probes have left the heliosphere, Voyager 1 and Voyager 2 have not yet left the solar system, and won’t be leaving anytime soon. The boundary of the Solar System is considered to be beyond the outer edge of the Oort cloud, a collection of small objects that are still under the influence of the Sun’s gravity. The width of the Oort cloud is not known precisely, but it is estimated to begin at 1,000 astronomical units from the Sun and to extend to about 100,000 AU. It will take about 300 years for Voyager 2 to reach the inner edge of the Oort cloud and possibly 30,000 years to fly beyond it.
Moreover, electrical power is supplied by three Radioisotope Thermoelectric Generators (RTGs). The current power levels are about 249 watts for each spacecraft. As the electrical power decreases, power loads on the spacecraft must be turned off in order to avoid having demand exceed supply. As loads are turned off, some spacecraft capabilities are eliminated.
Instruments on Voyager 2- Cosmic Ray Subsystem (CRS) – ON - Low-energy Charged Particles (LECP) – ON - Magnetometer (MAG) – ON - Plasma Wave Subsystem (PWS) – ON - Plasma Science (PLS) – ON - Imaging Science Subsystem (ISS) – OFF - Infrared Interferometer Spectrometer and Radiometer (IRIS) – OFF - Photopolarimeter Subsystem (PPS) – OFF - Planetary Radio Astronomy (PRA) – OFF - Ultraviolet Spectrometer (UVS) – OFF
The Golden Record
Pioneers 10 and 11, which preceded Voyager, both carried small metal plaques identifying their time and place of origin for the benefit of any other spacefarers that might find them in the distant future. With this example before them, NASA placed a more ambitious message aboard Voyager 1 and 2, a kind of capsule, intended to communicate a story of our world to extraterrestrials. The Voyager message is carried by a phonograph record, a 12-inch gold-plated copper disk containing sound and images selected to portray the diversity of life and culture on Earth.Reference: Voyager Mission – JPL NASA, California Institute of Technology