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Voyager: Still Not Out of the Shockwave?

The recent Voyager news, reported from the American Geophysical Union conference in San Francisco and recently discussed here, has drawn attention to the apparent asymmetry of our Solar System. Voyager 1 crossed the termination shock — where the solar wind first encounters the thin gas of the interstellar medium — some three years ago. But that was a crossing with a difference. Voyager 1 went through the termination shock just once. Voyager 2 has apparently crossed it five times and may encounter it again. Ahead in a decade or so: The heliopause, where the Sun’s influence effectively ends.

Thus we have a glimpse of how the solar wind varies with changes in the Sun’s activity level, pulsating as the solar cycle swings from solar flares into quiet periods, pushing the shock area out a bit farther, then contracting it. And while Voyager 1’s plasma science instrument had stopped working when it encountered the termination shock, Voyager 2’s is working well and making detailed measurements.

John Richardson, principal investigator for the instrument, calls the area Voyager 2 is now in “…a different kind of shockwave than we’ve seen anywhere else.” Among the new Voyager findings is the existence of an unexpectedly strong magnetic field in the surrounding interstellar region, one that is distorting the bubble of outflowing gases from the Sun. A second surprise: The temperature just outside the termination shock, hotter than inside it, was nonetheless found to be fully ten times cooler than had been expected. This may be the result of limitations in the plasma instrument, though other ideas may emerge.

J. Randy Jokipii (University of Arizona) is already looking farther out:

“The Holy Grail for me will be when the spacecraft begin traveling in pure interstellar space. That’s maybe 10 years away. Scientists now can start thinking about what they want to look for when the Voyagers break through the last barriers to true interstellar space.”

Yes, providing we’re still getting good data from our doughty spacecraft, which will probably be the case. Our first look at actual interstellar space, the medium through which, let’s hope, our interstellar probes will one day fly, will come as a triumphant vindication for the Voyagers, both of them built for a five year mission. John Belcher and Mark Bessette at MIT have put together several nifty animations showing the solar wind interacting with the interstellar medium. Keep them in mind as the Voyagers push on through the heliosheath on the way to their final exit of the system.

Comments on this entry are closed.

  • Darnell Clayton December 11, 2007, 22:54

    It’s amazing how much we have learned about our solar system since these satellites first launched!

    If only we could travel with them, although we may have to wait another century before that happens.

  • Adam December 13, 2007, 4:07

    Hi Darnell

    Spaceflight takes will and a perceived need – something lacking amongst the “great and powerful”. Some of us hope that an Earth-like planet around Alpha Centauri A or B might stir things up, but such hope might be misplaced without a convincing FTL drive in our pockets.

    Things may change once there’s a sizable space-based population. Getting them out there is our present challenge. I hope a Bussard fusor breakthrough might make solar system travel feasibly inexpensive, but even if colonies on Mars become economical will they be desirable to those in power?

  • Darnell Clayton December 18, 2007, 23:48

    Hey Adam,

    The political powers that be are probably the most frustrating part about this. Ironically Bush seems to be the most interested in space, and most politicians are trying to find ways to distance themselves from all (or some) of his policies–with space taking collateral damage.

    As far as a habitable world around Alpha Centauri goes, if that did not energize the population, nothing on Earth ever will (although I think discovering worlds there would help jump start the pursuit of space again).

  • ljk March 20, 2008, 9:04

    Voyager spacecraft on the outer edge of the solar system

    (Science Show: 15/03/2008)

    The Voyager spacecraft are at the outer edge of the solar
    system. Voyager 1 is at 105 astronomical units. Neptune is
    only at 30 astronomical units. (One unit is the distance between
    the Earth and the Sun). Signals are received from the craft
    every day despite the transmitter on the craft being only 20

    The Voyager craft are expected to enter interstellar space in
    about five years time. Conditions outside the heliosphere are
    expected to be quite different from those within. Material floating
    around will be from other stars. The magnetic field will be different. Interstellar wind will be denser, and radio signals picked up by
    the craft should be stronger, with stronger cosmic rays. Energy
    for the craft, from the decay of plutonium will cool and power
    will run out some time after 2020.

    Full transcript here:


  • ljk March 22, 2008, 17:22

    Voyager Weekly reports to 02-15-2008 are available at:


    The spacecraft lifetime page has been updated to reflect the latest
    RTG power predictions: