The Voyager 2 space probe has entered interstellar space, according to NASA, 42 years after it and the Voyager 1, its nearly identical sibling, were launched. Voyager 1 first passed across the edge of the magnetic bubble generated by the sun in 2013, as it took a different path, and the bubble is elliptical. The probes’ original missions were slated for five years.
This latest transition provided NASA with more confirmation about the separation between the interior of the magnetic bubble, called the heliosphere, and what lies outside it: a medium full of galactic cosmic rays. Measurements taken by Voyager 2 on Nov. 5 showed the same pattern of differences measured five years ago by Voyager 1.
While the Voyager probes have both left the sun’s magnetic pull, they decidedly have not left the solar system, even though NASA occasionally slips up and uses that term. The heliosphere defines the sun’s magnetic reach, but astronomers largely agree that the gravitational pull of the sun encompasses the solar system.
At the time Voyager 1 left the heliosphere, NASA and many astronomers believed that it would measure a 90-degree rotation in the orientation of detected magnetic fields, like rotating a bar magnet a quarter turn. However, that magnetic effect didn’t appear. Instead, Voyager 1 and now 2 found a distinct difference in the kinds of particles detected.
Inside the heliosphere, the solar wind prevails, a high-energy plasma that streams from the sun’s corona into space, and which is made up of stripped bits of atoms, like electrons, protons, and alpha particles. But outside the bubble, galactic cosmic rays predominate. These rays comprise full atomic nuclei, the core of atoms, with all the electrons shorn away and accelerated to nearly the speed of light.
Despite their advanced age and long space journeys, the probes have active scientific instruments, which provided the data necessary to detect differences in the kinds of particles and energy detected.
The ships’ power comes from generators that produce heat from the decay of radioactive elements. Because the decay reduces the amount of material over time, ever less heat and power is generated, and NASA has gradually shut down less critical instruments and functions. Cameras stop being used after successful flybys of Jupiter and Saturn by both probes, and of Uranus and Neptune by Voyager 2.
Voyager 1 and 2 should continue to provide scientific data through at least 2020, and perhaps for a few years thereafter, at which point it will continue to travel indefinitely.
The solar system extends to the Oort Cloud, a ring of objects that may stretch as far as 100,000 times the distance of the Earth to the sun (a measure known as an astronomical unit or AU). Voyager 1 and 2, currently at 145 and 120 AU from Earth, respectively, will take about 300 more years before the probes reach the anticipated closest edge of the cloud at 1,000 AU, and potentially 30,000 years before they pass beyond it entirely and finally exit the solar system.
The next nearest active craft is New Horizons, which delivered unprecedented photos and data about Pluto and its moon, Charon, and is en route to an object in the Kuiper Belt, a mere four billion miles or 40-odd AU from Earth.