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Voyager 1: beyond the edge of the solar system at last?

The views expressed are those of the author and are not necessarily those of Scientific American.


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A Voyager launches in 1977. Credit: NASA

It was on my first birthday that the Voyager 1 spacecraft turned around and took a picture of the pale blue dot we call home. That picture was Voyager’s last glimpse of Earth before its camera was switched off and it began to sail, uninterrupted, towards interstellar space. Around the same time Voyager 2 finished its tour of the outer planets and joined Voyager 1 on its interstellar mission.

So by the time I came to learn about the Voyager spacecraft they were both well on their way to the edge of the solar system. Now one of them might have finally left.

I wrote about Voyager for my entry into this year’s Wellcome Trust Science Writing Prize, in association with the Guardian and the Observer. My entry – Beyond the edge of the solar system – was shortlisted and is up on the Wellcome Trust blog today.

And just in time! It looks as if, after all that waiting, Voyager 1 has finally broken through to the other side. It’s not quite official yet, but a huge drop in the number charged particles hitting Voyager 1 indicated that it passed through some kind of boundary around the start of September. Data from its magnetometer will be needed to confirm what exactly has happened, but I will be keeping my eyes peeled for an announcement soon.

Number of particles (mainly protons) from the sun hitting Voyager 1 against time. Notice the huge drop around September – that's one of the pieces of evidence that Voyager 1 is now in interstellar space. Credit: NASA

Kelly Oakes About the Author: Kelly Oakes has a master's in science communication and a physics degree, both from Imperial College London. Now she spends her days writing about science. Follow on Twitter @kahoakes.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. jtdwyer 6:11 pm 10/8/2012

    Unless something is shielding the detector (you never know) this data would appear to be pretty decisive.

    In fact, what could possibly be blocking the particles, preventing their continued propagation? It would seem that some opposing interstellar wind or media pressure would produce its own particle detections and affect spacecraft velocity…

    Link to this
  2. 2. Na g n o s t ic 6:15 pm 10/8/2012

    You are exceptional regarding your interest in a 1970′s spacecraft. Your youth makes it so. I was interested in Project Mercury and Gemini, which were active after I was born, not before. I have since become interested in the earliest days of powered flight, and the enormous advances made during its first five decades. People like you cause older people like me to hopeful that we may yet land on other moons and planets before I die.

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  3. 3. jtdwyer 7:05 pm 10/8/2012

    Nagnostic – A lot of astrophysicists are interested in these 1970′s era spacecraft, since they are our only probes of the outer Solar system.
    I was in elementary school when Sputnik orbited the Earth, not long before the Cuban Missile Crisis. I was then only interested in whether we would all soon be destroyed in a nuclear holocaust – it was not paranoia! Duck & cover!
    By now I’m just hope my grandchildren don’t suffer horribly from the consequences of overpopulation, including resource depletion and global warming.

    Link to this
  4. 4. sijodk 7:15 pm 10/8/2012

    Two thoughts…

    1: This is cool. I’m looking forward to hearing what the magnetometer data says.

    2: I know that if the magnetometer data agree it’s a safe bet to say that Voyager 1 has reached a region that is fundamentally different. Heck, even in the unlikely case that they don’t something is decidedly different (and there’ll be scientists working overtime to explain the data). But beyond the edge of the solar system? There are still scattered disk objects, detached objects and Oort cloud objects which are farther away, yet surely part of the solar system?

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  5. 5. syperdistic 7:43 pm 10/8/2012

    Has it possibly exited the Heliopause? If so, I would think this would constitute the exiting of the solar system. Voyager launched a couple of years before my existence started, so I do find them quite interesting.

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  6. 6. ErkkiRuohtula 1:36 am 10/9/2012

    I find talking about breaking to the other side a bit amusing. It is not like there is some kind of celestial sphere that the Voyager is banging into… I would imagine it is more like when your ship leaves port, at some point the murky waters of the harbour end, and you enter the chrystal-clear sea.

    Link to this
  7. 7. Kelly Oakes in reply to Kelly Oakes 3:51 am 10/9/2012

    I like that analogy, ErkkiRuohtula.

    syperdistic and sijodk: Yep, it’s the heliopause I’m really talking about when I say edge of the solar system here. There are objects outside that, sure. But as far as I (and I think others) are aware, that’s the best ‘edge’ we’re going to get – and is also where the sun’s influence ends, and interstellar cosmic rays pick up. So I think we’re justified in calling that the edge.

    jtdwyer: I’m not aware of anything that could be blocking particles, and it would be a bit of a coincidence that it happened now! Especially when the other two signs agree.

    Link to this
  8. 8. sijodk 6:55 am 10/9/2012

    But Kelly, logically if the heliopause marks the end of the solar system an object such as 90377 Sedna alternates periodically between being a solar system object and an interstellar one, and that does not make much sense.

    Link to this
  9. 9. Kelly Oakes in reply to Kelly Oakes 7:11 am 10/9/2012

    sijodk: Like I said, I think the heliopause is the best edge we’re going to get, even though the waters are a bit more murky than that in reality. But it’s not black and white and you’re free to think differently, as long as you can justify it.

    There is an argument that the solar system extends right out to the edge of the sun’s gravitational influence, at around two light years. But that’s half way to Proxima Centauri – it would take Voyager around 40,000 years to get there! So I hope you’ll forgive those of us who take this closer boundary as the edge, so that we know Voyager will leave us within our lifetimes.

    The main thing is that Voyager is now in or is about to reach a region of space where interstellar stuff has more influence than the solar wind, and that no human made spacecraft has ever been there before. Whether you think it’s out of the solar system or in, it is definitely uncharted.

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  10. 10. vinodkumarsehgal 8:31 am 10/9/2012

    On Sep 5, 2012, Nature had published an article ” Voyager long goodbye” by Ron Cowen http://www.nature.com/news/voyager-s-long-goodbye-1.11348. This article indicated that there still lack of unanimity and certainty amongst scientists regarding crossing of either of Voyager of heliopause which is considered as boundary of solar system. At the boundary, radial velocity of solar wind should cease to zero ( due to opposing velocity of wind from interstellar space) and re-appear along polar direction. Scientists have tested the velocity of solar wind in the vicinity of Voyager’s current location along both radial and polar direction. They have found velocity along both radial and polar direction as nil indicating that Voyager has not yet reached heliopause

    Link to this
  11. 11. sijodk 9:01 am 10/9/2012

    Kelly Oakes: Thank you for the link. Seems I’m not the only one arguing against the heliopause being seen as the edge. At any rate the debate is getting pointless as it’s only a matter of definition, kind of like the status of Pluto. And I wholeheartedly agree that the science that is being done is a lot more interesting.

    Disagreements about definitions aside I must commend you for actually following up on the comments posted. Many SciAm writers do not find the time to do this and that is a pity.

    Link to this
  12. 12. DaniEder 1:01 am 10/15/2012

    As you can see from this table by sorting on “Q” (maximum distance from the Sun):

    http://www.minorplanetcenter.net/iau/lists/t_centaurs.html

    There are 56 known Scattered Disk objects which reach farther from the Sun than Voyager is now. There are two selection effects happening. The first is distance bias. We only find these objects when they are close to the Sun, because their telescopic brightness falls as the 4th power of distance.

    Since these objects are in highly elliptical orbits (e=0.5 to 0.9+), they spend most of their time at the outer end of the ellipse, where we cannot see them. When you correct for observation bias, we expect there to be thousands of these objects in scattered orbits around the Sun.

    Voyager may be crossing the solar wind boundary, but I for one cannot describe it as “left the Solar System” when there are thousands of large objects which orbit up to 16 times farther out than it is now.

    Link to this
  13. 13. Quinn the Eskimo 8:51 pm 10/15/2012

    Kelly, the Voyager sensor might be blocked by debris. Like a NASCAR racer picking up a hot dog wrapper on the grill.

    It might have picked up a Taco Wrapper as it passed Saturn’s rings. Coulda.

    Link to this
  14. 14. SkyGuide 12:05 am 10/18/2012

    To extend ErkkiRuohtula’s excellent analogy of a ship leaving port, sailing initially thru murky water in the harbour until in the clear waters of the sea….

    sijodk rightfully points out that there are many (many!) Solar System objects beyond Voyager’s position. Yet, I think of those distant Kuiper Belt Objects and Oort Cloud comets as islands our ship passes after leaving the harbour lights far astern. Those islands are still “related” to the mainland, perhaps (to overextend the analogy) on the same continental shelf, but one must cross some of the interstellar sea to reach those distant points.

    And what of a star that has had a star pass very nearby, disrupting and scattering its comets – should that be sufficient to change the definition of the boundary of its solar system?

    Yes, I do think that the heliopause is a good place to mark the boundary of a stellar system, beyond which there is a real sea change of the environment.

    Link to this

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