Thursday, July 4, 2013

Is Voyager-1 leaving the solar system?

The Voyager Spacecraft on the edge of the Heliosphere  Image credit: NASA/JPL-Caltech

 Are there any space-program followers that are looking at the Voyager-1 news and scratching their heads?  When I first heard the ship was about to leave the solar system, I was very excited.  As I envisioned the spaceship diving into the deep expanse between the stars, not only did it conjure up images of a beautiful, bald woman demanding to be ‘one with the creator of V’GER[1], it also gave me a sense of pride that a ship from the seventies could last so long and somehow be gravity assisted to such an astonishing speed as to be ‘sling-shotted’ into interstellar space!
According to a NASA news release on June 27th, the spacecraft had reached 2 out of 3 criteria that would indicate it was in interstellar space.  The Suns charged solar particles have almost disappeared and cosmic rays have increased 10%, what remains is for the spacecraft to detect a switch from the sun’s magnetic field direction to the galactic magnetic field direction.  The particle shifting was expected due to that magnetic shift, but instruments on the spacecraft have not detected the field change, itself[2].  
I recently explored the concept of a human trip to the stars, a program promoted by the One-hundred Year Star Ship organization[3]. As I progressed through my writing exercise I thought something didn’t seem right about Voyager-1’s anticipated breakthrough. As of July 1st 2013, Voyager-1 was 18½ billion kilometers away from the sun (124 AU)[4]. It’s an astonishing distance when you realized that the earth’s distance from the sun, defining one Astronomical Unit (AU), is a less than 1% of the ship’s travel from its home star.  To further put it in perspective, Pluto’s average distance from the sun is 40 AU (5.9 billion kilometers), its aphelion (greatest orbital distance) is 52 AU (7.8 billion km) from the sun.  We now know Pluto lies in the heart of a region called the Kuiper belt, a region of icy asteroids and planetoids, similar to the asteroid belt, but comprised of rock, ice, and frozen nitrogen extending from 30 to 55 astronomical units.  Pluto was the first of, so far, 1300 Trans-Neptunian Objects (TNOs) detected in the Kuiper belt.  Past Pluto is the largest TNO, Eris, first detected in 2003 and situated in a region called the Scattered Disk, an area that stretches between 55 and 100 AU.  The furthest known plutoid is Sedna, detected in 2004, currently at 90 AU and having an an Aphelion of at least 542 AU. Some scientist place Sedna in the inner Oort cloud, an undefined region of space that is believed by many to be the home of the solar system’s long-period comets[5]As you see, our physical solar system has been extending further and further out from our traditional boundary of Pluto over the last couple of decades.
It was the knowledge of the Oort cloud that started me to question the statement that Voyager-1 is on the verge of exiting our solar system.  In 1950 Jan Hendrick Oort proposed that the comets came from a common region well beyond the known outer bodies of the solar system[6]. This region was later hypothesized to have two sub-regions, the inner Oort cloud, a donut shaped region that loosely follows the solar system’s ecliptic, and the outer Oort cloud, which is believed to be a spherical shape. Both ‘clouds’ are composed of the same icy materials very loosely tied to the sun’s gravitational influence.  Jan Oort, earlier in his career, was one of the very first people to discover an imbalance in the apparent universe and the gravitation effects it displayed.  This imbalance is now attributed to what we call dark matter. His Comet region theory attempted to partially explain the unaccounted for mass found in the galaxy. This cloud of scattered ice is believed to be the remaining proto-planetary material that made the solar system and its sister stars.   Due to its extreme remoteness and difficultly to verify observationally, the Oort cloud is still technically considered hypothetical. Still, most scientists accept its existence.

So far, only three Trans-Neptunium objects have been found that lie in the Oort region:

Peirhelion (AU)
Aphelion (AU)
90377 Sedna
2000 CR105
2006 SQ372

Only Sedna lies entirely outside the Kuiper belt region, the other TNOs start their highly elliptical orbits within the Kuiper Belt and extend well beyond the Scattered Disk Region.  The Inner or ‘Donut Oort’ is believed to be between 100 and 2,000 AU, the Outer or ‘Spheroid Oort’ is believed to range from 2,000 to 50,000 AU, some theorist put the outer shell as far out as 100,000 AU. That distance would put the Oort cloud nearly half way to Proxima Centauri, our closest stellar neighbor.  The extents of the Oort cloud will remain subject to interpretation having only three objects for a data set, and these extents cannot be defined until we have much more information and many more candidates.
So then, is the Voyager-1 leaving the solar system?  Under the definition of the sun’s magnetic field it appears that it is about to leave, but if the Oort cloud is part of the solar system, which seems to me it is, then Voyager-1 still has a long way to go. Even if we limit the solar system to the outer extents of the smaller, Donut Ort, then the spacecraft has only completed 6% of its journey to the edge of our system.
It is still an amazing accomplishment! It’s also coincidental that as Voyager treks on at 3.6 AU per year[8] our grasp of the solar system extends in conjunction with its reach.  In 2020 when the power supply of the ship is expected to be depleted, what will be our understanding of the extents of the solar system?
At 150 AU, will Voyager-1 still be within the realm of Sol? Or, has it already left us?

[1] Star Trek: the Motion Picture, Dir: Robert Wise, Wri: Gene Roddenberry and Alan Dean Foster, Perf: William Shatner, Leonard Nimoy, Persis Khambatta, Stephen Collins. Paramount Pictures, 1979. Film
[2] Philips, Tony “Voyager 1 approaches interstellar space”, NASA, NASA news services, 27 June 2013, WEB, retrieved 20 June 2013,
[3] “100 year Starship”,100 Year Starship, 100 Year Starship, n.d. WEB, retrieved 20 June 2013,
[4] Chang, Allicia “NASA’s Voyager 1 spacecraft encounters unknown Region of space at solar system’s edge”, Huffpost,, Inc.,28 June 2013,WEB, retrieved 30 June  2013,
[5] Brown, Mike “Sedna (2003 VB12)”,Caltech Division of Geology and Planetary sciences, California Institue of Technology, n.d. WEB, retrieved 1 July 2013,
[6] Erickson, Kristen “Kuiper Belt & Oort Cloud: Read More”, NASA Solar System Exploration, NASA Science Mission Directorate, 26 April 2013, WEB, Retrieved 3 July 3, 2013, 7/3/13 7:37 AM
[7] Yeomans, Donald K “JPL Small-Body Database Browser”, NASA Solar System Dynamics, NASA Jet Propulsion Laboratory, 2013-Jul-04 02:07 UT (server date/time),
[8] Angrum, Andrea, “Voyager the interstellar mission”, NASA Solar System, NASA Jet Propulsion Laboratory,  n.d., WEB, Retrieved 3 July 2013,

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