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article image35 years on, is Voyager 1 bidding farewell to the Solar System?

By Robert Myles     Mar 20, 2013 in Science
On September 5 1977, NASA’s Voyager 1 left Cape Canaveral. Thirty-five years later, Voyager continues to transmit data back to Earth and may now, finally, have stepped beyond the perimeter of the Solar System.
According to recently published data, more than a third of a century later, the Voyager 1 spacecraft may now be leaving our solar system in its wake and moving beyond the Sun’s influence into interstellar space.
When Voyager 1 left Space Launch Complex 41 at Cape Canaveral, Florida in 1977, atop a Titan IIIE-Centaur launch vehicle, no-one associated with the mission could have visualised that 35 years, 6 months, and 15 days into the mission as of today, (March 20) the first of the Voyager series would still be sending back meaningful data but that’s exactly what Voyager 1 is continuing to do according to a new study published by the American Geophysical Union.
The paper, entitled “Recent Voyager 1 Data Indicate that on August 25, 2012 at a Distance of 121.7 AU From the Sun, Sudden and Unprecedented Intensity Changes were Observed in Anomalous and Galactic Cosmic Rays” by W.R. Webber of New Mexico State University’s Department of Astronomy, Las Cruces, New Mexico, and the late F.B. McDonald of the University of Maryland’s Institute of Physical Science and Technology, College Park, Maryland, appeared in Geophysical Research Letters, the journal of the American Geophysical Union.
For the past of 35 years or so, Voyager 1 has been heading outwards into deep space but still within our Sun’s heliosphere. The heliosphere is the region of space dominated by the Sun encompassing our solar system far beyond the orbit of Pluto and its associated companions. Within the heliosphere, the solar wind of charged particles emanating from the Sun holds sway, with charged particles swirling out from the Sun under the influence of the Sun’s magnetic field, following a pattern that's sometimes been compared to a ballerina’s skirt. Beyond the heliosphere lies a theoretical boundary with interstellar space known as the heliopause where the influence of the Sun’s solar wind wanes, giving way to the stellar winds of surrounding stars — effectively where interstellar space begins.
The heliospheric current sheet results from the influence of the Sun s rotating magnetic field on th...
The heliospheric current sheet results from the influence of the Sun's rotating magnetic field on the plasma in the interplanetary medium (solar wind). The wavy spiral shape has been likened to a ballerina's skirt.
NASA - Werner Heil
Scientists have been closely monitoring data sent back by Voyager 1 since early 2009 when they began to detect a gradual increase in galactic cosmic rays. In May 2012, Voyager 1 detected a rapid increase in such cosmic rays — up 9% in the month compared with an increase of 25% over the three year period to January 2012. That suggested that Voyager 1 was approaching the heliopause. Readings taken by Voyager 1 on August 25, 2012 disclosed drastic changes in radiation levels at a distance of 11 billion miles from the Sun. It was these readings, taken when Voyager 1 was at a distance of 121.7 AU from the Sun, that peaked scientists’ interest.
At such distances, talk of millions and billions of miles starts to become meaningless and astronomers measure distance in terms of astronomical units, one astronomical unit (AU) being defined as the average distance between the Sun and the Earth. To put these distance into perspective, Pluto, now downgraded to a dwarf planet, has a highly elliptical orbit around the Sun at an average distance of around 39AU. Voyager 1 continues to plough its lonely furrow at over three times Pluto’s average distance from the Sun.
Towards the end of August 2012, scientists reported that anomalous cosmic rays, which are cosmic rays trapped in the outer heliosphere, all but disappeared, dropping to less than 1 percent of previous amounts. At the same time, a sharp increase was noted in galactic cosmic rays, that is, cosmic radiation originating from outwith the solar system. The difference in cosmic radiation was extremely marked with intensities noted at as much as twice previous levels.
One of the authors of the paper, Bill Webber, professor emeritus of astronomy at New Mexico State University, commented, “Within just a few days, the heliospheric intensity of trapped radiation decreased, and the cosmic ray intensity went up as you would expect if it exited the heliosphere."
Professor Webber coined a new phrase for the phenomenon traversed by Voyager 1, referring to the transition boundary as the “heliocliff”.
In the Geophysical Research Letter article, the joint authors state, "It appears that (Voyager 1) has exited the main solar modulation region, revealing (hydrogen) and (helium) spectra characteristic of those to be expected in the local interstellar medium."
As Webber notes, it remains to be seen whether Voyager 1 has truly reached interstellar space or a separate, as yet undefined, region of space beyond our solar system. He said, “It's outside the normal heliosphere... We're in a new region. And everything we're measuring is different and exciting."
Artist depiction of Voyager spacecraft
Artist depiction of Voyager spacecraft
NASA Images
Voyager 1 has long since exceeded the most optimistic of hopes for a mission originally conceived as a ‘Grand Tour’ of the Solar system. Funded by NASA's Jet Propulsion Laboratory in Pasadena, Calif., Voyager 1 set (and continues to set) the record for the most distant man-made object from Earth on November 17, 1998. Some of Voyager’s systems have already shut down but Voyager 1 is expected to continue returning data from its remaining functional instruments until 2020 and possibly beyond.
Ultimately, at some point between 2025 and 2030, Voyager 1 is expected to finally run out of power — but the spacecraft’s solitary eternal mission will continue. 40,000 years from now, (unless previously intercepted by a passing starship) Voyager 1 is expected to drift within 1.6 light years of AC+79 3888, a star in the constellation of Camelopardalis.
More about Space exploration, NASA, voyager missions, Voyager 1, Voyager spacecraft
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