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Almost Interstellar

March 22, 2013

So, has humanity become Earth’s first interstellar species?  It all depends on whether the Voyager 1 spacecraft has left our solar system or not.

Voyager

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NASA

First, some history.  The Voyager program actually consisted of two space probes, Voyager 1 and 2, launched September 5, 1977 and August 20, 1977, respectively.  The probes were launched in 1977 to take advantage of a once-every-177 year alignment of worlds in the outer solar system which would allow them to swing from planet to planet with minimal fuel.  Voyager 1 itself made it out to the Jupiterian and Saturnian systems, providing up close photographs of things like Jupiter’s Great Red Spot, the Galilean moons, Saturn’s rings, and Titan’s (Saturn’s major moon) atmosphere.  After last close fly-by of Titan, Voyager was directed on a course away from the Sun, to explore where the solar system officially ends.  Voyager 1 is now the most distant man-made object from Earth, approximately 18 billion kilometers away, traveling at a speed of 17.26 km/s.  Even though its original mission is long over, it has continued to send data back to scientists on Earth, and its nuclear power source is in fact estimated to last until 2025, meaning we’ll still be hearing from this intrepid spacefarer for years to come.

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NASA                                                                                         NASA

The current Voyager controversy, however, is whether or not it has actually left the solar system.  False alarms have been raised before, the most recent case being by NASA last October, so the debate isn’t new.  The answer, though, comes down mostly to semantics.  Voyager’s sensors have detected a drop in radiation and an increase in cosmic rays.  This is an indicator that it may have passed outside our solar system, because the area outside the solar system would also be outside the Sun’s heliosphere (the Sun’s protective magnetic bubble), and there would be an increase in the cosmic rays that are normally absorbed the the magnetic sphere.  However, until a dramatic change in magnetic field intensity is detected, NASA scientists believe the probe is in a transition zone within the outer part of the heliosphere.  Additionally, the Sun’s gravitational reach is distant, and the Oort cloud of comets 7.5 trillion km from the Sun should still be gravitationally bound to the star.  If that is considered the real edge of the solar system, Voyager still has a long way to go.

Here’s a video by NASA describing Voyager’s final journey.

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