FIND a clear, dark sky and look for a constellation shaped like a giraffe, and you may see the future resting place of Voyager 1.
After years of repeated but unconfirmed rumours that the spacecraft had broken free of the sun's protection,
Voyager 1 has enough nuclear fuel to keep doing science through to 2025, and then it will be dead, adrift. On its current trajectory, the probe should eventually end up within 1.5 light years of a star in Camelopardalis, a northern constellation that looks like a cross between a giraffe and a camel. No one knows if there are any planets around that star, nor if aliens will be in residence by the time the probe arrives.
"But if they are there, maybe they will capture Voyager 1," says mission scientist
Since 2004 Voyager 1 had been travelling through a border zone in the heliosphere, the magnetic bubble blown by charged particles streaming from the sun. The motions of objects beyond the heliosphere showed that the charged gas, or plasma, that fills the space between stars should be much denser outside the border than within, and the Voyager team was at last convinced of an exit from the heliosphere thanks to a sudden increase in plasma density.
Oscillations in the plasma surrounding the probe seen in late 2012 and early 2013 showed that its density has been on the rise and is now about 40 times higher than it was before. Extrapolating backwards, the increase must have started on
This corresponds to readings from another of Voyager 1's instruments, also taken in August last year, that showed a drop in solar cosmic rays hitting the probe. Instead, the craft saw an excess of galactic cosmic rays, which come from sources outside the heliosphere. Together, the lines of evidence suggest that Voyager 1 has truly crossed over.
The probe may no longer be bathed in solar particles, but the galactic cosmic rays show that its surroundings are still being tugged on by solar magnetic field lines. This suggests Voyager 1 is in a final transition zone.
Premature reports of the probe's "exits" from the heliosphere show how little we know about the solar outskirts. So what will Voyager 1 tell us about them? "I'm very reticent to make predictions when our track record is so poor," says Krimigis. "But I do anticipate surprises."
As the craft ploughs deeper into the galaxy, the
Drift long and prosper
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