On Sept. 12, NASA confirmed that Voyager 1 has become the first man-made object to leave the solar system and enter interstellar space. The probe, launched on Sept. 5, 1977, was at a distance of 18.752 billion kilometers from the Sun and 18.749 billion kilometers from Earth as of Sept. 6, 2013 and is traveling away from the Sun at 17 kilometers per second. At that distance, it takes approximately 17 hours for a signal from Voyager 1 to reach Earth.
According to a report published in the Sept. 12 edition of the journal Science on the analysis of new data from Voyager 1, the boundary between the solar system and interstellar space, known as the heliopause, is expected to be marked by a fifty-fold increase in plasma density. The Voyager 1 plasma wave instrument began detecting locally generated electron plasma oscillations at a frequency of about 2.6 kHz on April 9, 2013. This indicates an electron density of about 0.08 per cubic centimeter, which is close to the expected value of 0.1 electron per cubic centimeter in the interstellar medium. (Voyager 1 does not have a working plasma sensor, so it was necessary to measure the spacecraft's plasma environment in this way to make a definitive determination of its location.) As a result, the study finds that "[t]hese and other observations provide strong evidence that Voyager 1 has crossed the heliopause into the nearby interstellar plasma."
"We literally jumped out of our seats when we saw these oscillations in our data -- they showed us the spacecraft was in an entirely new region, comparable to what was expected in interstellar space, and totally different than in the solar bubble," said Dan Gurnett of the University of Iowa, one of the authors of the study. "Clearly we had passed through the heliopause, which is the long-hypothesized boundary between the solar plasma and the interstellar plasma."
"The team’s hard work to build durable spacecraft and carefully manage the Voyager spacecraft's limited resources paid off in another first for NASA and humanity," said Suzanne Dodd, Voyager project manager, based at NASA's Jet Propulsion Laboratory (JPL), Pasadena, Calif. "We expect the fields and particles science instruments on Voyager will continue to send back data through at least 2020. We can't wait to see what the Voyager instruments show us next about deep space."
Voyager 1 is expected to remain operational until sometime between 2020 and 2030. In about 40,000 years, Voyager 1 will drift within 1.6 light-years of AC+79 3888, a star in the constellation of Camelopardalis which is heading toward the constellation Ophiuchus.