The big science news of the week has been the announcement that the Voyager I spacecraft, launched on September 5, 1977, is on the verge of exiting the Solar System:
For nearly 35 years, NASA’s Voyager 1 probe has been hurtling toward the edge of the solar system, flying through the dark void on a mission unlike anything attempted before. One day, mission controllers hope, Voyager 1 will leave the solar system behind and enter the realm of the stars—interstellar space.
That day may be upon us.
“The latest data from Voyager 1 indicate that we are clearly in a new region where things are changing quickly,” says Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena. This is very exciting. We are approaching the solar system’s final frontier.”
The “frontier” he’s referring to is the edge of the heliosphere, a great magnetic bubble that surrounds the sun and planets. The heliosphere is the sun’s own magnetic field inflated to gargantuan proportions by the solar wind. Inside lies the solar system—“home.” Outside lies interstellar space, where no spacecraft has gone before.
A telltale sign of the frontier’s approach is the number of cosmic rays hitting Voyager 1. Cosmic rays are high energy particles such as protons and helium nuclei accelerated to near-light speed by distant supernovas and black holes. The heliosphere protects the solar system from these subatomic bullets, deflecting and slowing many of them before they can reach the inner planets.
As Voyager approaches the frontier, the number of cosmic rays has gone up.
“From January 2009 to January 2012, there had been a gradual increase of about 25 percent in the amount of galactic cosmic rays Voyager was encountering,” says Stone.
“More recently, however, we have seen a very rapid escalation in that part of the energy spectrum. Beginning on May 7, 2012, the cosmic ray hits have increased five percent in a week and nine percent in a month.”
The sharp increase means that Voyager 1 could be on the verge of a breakthrough 18 billion kilometers from Earth.
When Voyager 1 actually exits the heliosphere, researchers expect to see other changes as well. For one thing, energetic particles from the sun will become scarce as the spacecraft leaves the heliosphere behind. Also, the magnetic field around Voyager 1 will change direction from that of the sun’s magnetic field to that of the new and unexplored magnetism of interstellar space.
So far, neither of these things has happened. Nevertheless, the sudden increase incosmic rays suggests it might not be long.
It’s an amazing accomplishment, made all the more so by the fact that nobody really thought that Voyager would remain operational this long when the probe was first launched nearly 35 years ago. However, some at NASA are pointing out the fact that, technically, it will be many more thousands of years before Voyager I officially leaves the confines of our Solar System:
In that sense, it can be said that the spacecraft will be able to sample what space is like beyond our solar system. (If we define the solar system as the Sun and everything that primarily orbits the Sun, however, Voyager 1 will remain within the confines of the solar system until it emerges from the Oort cloud in another 14,000 to 28,000 years).
Voyager 2 isn’t far behind its sister ship, but neither are expected to last the thousands of years it will take to traverse the Oort Cloud in terms of being able to transmit data or make course corrections. Nonetheless, they will continue traveling, and Voyager 2 should be passing by the star Sirius in about 296,000 years.
Illustration via NASA
