Termination Shock
Posted on Saturday 28 May 2005
Bow Shock (as in the bow of a ship) is a visible barrier just beyond the the heliopause of this distant star. The glow is caused by energetic cosmic rays being deflected by charged particles emanating from the star.
Cosmic radiation is prevented from entering our solar system by a structure known as the heliosphere, a protective shell formed from the continuous streaming of solar winds from our sun which pushes back against the pressure of interstellar space (and you thought space was a vacuum). The outer surface of this shell is known as the heliopause where the velocity of the solar wind drops to zero and this is technically what marks the edge of the solar system. The inner surface of this shell is known as the termination shock where the solar wind velocity drops to below supersonic levels.
Exploring the heliosphere at the edge of our solar system was the last remaining mission of the venerable Voyager I and II spacecraft. On the 17th of December 2004, after more than 27 years in space and having traveled an unprecedented distance of 14.5 billion kilometres from the Earth, Voyager I finally crossed the terminal shock. Suddenly the beams of charged particles detected by Voyager changed direction and stopped fluctuating. Also the magnetic field increased in strength and new radio sources were detected. From these changes in the spacecraft's environment, it was clear that Voyager I was now passing through the Sun's protective shell and on it way out of the solar system.
But just as scientists were readying the champagne for celebrations to mark this final stage in the journey of the first man-made object ever to enter interstellar space, news came through that the spacecraft had gone missing. Both of them, both Voyager I and Voyager II had suddenly and inexplicably vanished without a trace.
After that followed a frantic search. NASA scientists scrambled to study all the available data in a desperate effort to find some sign of the spacecraft.
But so far they have come up with nothing, not even the faintest indication of hope. All they found was empty space — a blank in the budget spreadsheet precisely at the point where the spacecraft were last seen.
UPDATE: This article from April gives more background to these astonishingly short sighted budget cuts (the Voyager program only costs NASA around $5 million per year). Yet another in a long line of examples of the Bush administration's retreat from science and science education. Fortunately it seems that there are plenty of privately funded faith-based initiatives that are ready to fill the breech.
