Is Voyager's magnetic field direction data wrong?

[celeste]

You may be familiar with this surprising data: http://www.nasa.gov/mission_pages/voyag ... a3_prt.htm
It seems Voyager sees no change in magnetic field direction as it flies through and out of our solar system, but are they even measuring solar system/galactic magnetic field directions?

Here is what they have done: They put magnetometers on a boom, fixed to Voyager's axis (see page 51 here http://ntrs.nasa.gov/archive/nasa/casi. ... 013181.pdf). They keep Voyager's attitude fixed (as discussed in the third paragraph here http://en.wikipedia.org/wiki/Attitude_control ). Then they hurl Voyager out of the solar system, making it into an electric comet. Only they don't believe in electric comets.

Here is my question: If Voyager's attitude is fixed on us in the inner solar system, and it's boom is fixed to Voyager,and Voyager's cometary tail also points away from the sun (inner solar system), does that not mean that we are always measuring the magnetic field at a fixed point compared to that tail? Keeping in mind, the magnetometers are seven and thirteen meters from this charging/discharging spacecraft? (boom itself obviously a point of discharge too). Can we be measuring the local field of the discharging comet,or it's Birkeland like tail,rather than the larger scale magnetic field direction?

Either way,one design parameter that may be blown is this (from page 51 of that NASA pdf): "Boom and spacecraft combined must produce a magnetic field no greater than 0.2 nT at the outboard sensor" So we have a discharging spacecraft, with a boom sticking out,but we want no magnetic field around/between boom and craft. Good luck!

[Sparky]

That is an interesting perspective!

I think you are on to something. What other data may be affected by such a scenario ?

[celeste]

Sparky, good question. Their interpretation of particle detection data is wrong too.
First, let's look at what happens with a comet: A comet comes in towards the sun,and a tail forms. We may see a sudden brightening as the comet discharges (particle exchange),and then a brighter comet tail. The tail will have a sudden increase in magnetic strength (more particles in the tail means more current), but the tail continues to stream in the same direction (away from the sun).
Now we can understand the Voyager data. They see a sudden increase in charged particle detection, accompanied by changes in magnetic field strength, but no change in field direction. Again, they are not merely measuring the background magnetic field, nor are they merely measuring the number of charged particles their "neutral" Voyager is encountering. They are measuring the charge exchange at Voyager,the magnetic field of this charge flow, and the direction of the magnetic field in Voyager's coma or tail.

[viscount aero]

Sparky, good question. Their interpretation of particle detection data is wrong too.
First, let's look at what happens with a comet: A comet comes in towards the sun,and a tail forms. We may see a sudden brightening as the comet discharges (particle exchange),and then a brighter comet tail. The tail will have a sudden increase in magnetic strength (more particles in the tail means more current), but the tail continues to stream in the same direction (away from the sun).
Now we can understand the Voyager data. They see a sudden increase in charged particle detection, accompanied by changes in magnetic field strength, but no change in field direction. Again, they are not merely measuring the background magnetic field, nor are they merely measuring the number of charged particles their "neutral" Voyager is encountering. They are measuring the charge exchange at Voyager,the magnetic field of this charge flow, and the direction of the magnetic field in Voyager's coma or tail.

That's a very brilliant observation/hypothesis.

Of course Voyager scientists would never consider that, and if they did they would not consider it seriously. Their beliefs disallow for it.

[Sparky]

They are measuring the charge exchange at Voyager,the magnetic field of this charge flow, and the direction of the magnetic field in Voyager's coma or tail.

How could we get around that problem?

[viscount aero]

They are measuring the charge exchange at Voyager,the magnetic field of this charge flow, and the direction of the magnetic field in Voyager's coma or tail.

How could we get around that problem?

Perhaps we cannot. This appears to be a case of limitation by the instruments. We cannot know the actual structure as the measuring tool is subject to its own environmental conditions that it cannot escape assuming that celeste's idea is factual.

[Solar]

Hmmm...

The most sensitive magnetometer instruments are mounted on long booms, deployed away from the craft (e.g., the Voyagers, Cassini). Many contaminant fields then decrease strongly with distance, while background fields appear unchanged. Two magnetometers may be mounted, one only partially down the boom. The vehicle body's fields will then appear different at the two distances, while background fields may or may not change significantly over such scales. Magnetometer booms for vector instruments must be rigid, to prevent additional flexing motions from appearing in the data. – Wiki

I don't much like Wiki and rarely use it so here is a paper about that:

The magnetic field experiment to be carried on the voyager 1 and 2 missions consist of dual low field (LFM) and high field Magnetometer (HFM) systems. The dual systems provide greater reliability and, in the case of the LFM’s, permit the separation of the spacecraft magnetic fields from the ambient fields.

(…)

The low field magnetometers are located remotely from the spacecraft on a 13m boom, with sufficient separation to permit analytic removal of spacecraft fields from simultaneous measurements– Magnetic field experiment for Voyagers 1 and 2

[celeste]

Hmmm...

The most sensitive magnetometer instruments are mounted on long booms, deployed away from the craft (e.g., the Voyagers, Cassini). Many contaminant fields then decrease strongly with distance, while background fields appear unchanged. Two magnetometers may be mounted, one only partially down the boom. The vehicle body's fields will then appear different at the two distances, while background fields may or may not change significantly over such scales. Magnetometer booms for vector instruments must be rigid, to prevent additional flexing motions from appearing in the data. – Wiki

I don't much like Wiki and rarely use it so here is a paper about that:

The magnetic field experiment to be carried on the voyager 1 and 2 missions consist of dual low field (LFM) and high field Magnetometer (HFM) systems. The dual systems provide greater reliability and, in the case of the LFM’s, permit the separation of the spacecraft magnetic fields from the ambient fields.

(…)

The low field magnetometers are located remotely from the spacecraft on a 13m boom, with sufficient separation to permit analytic removal of spacecraft fields from simultaneous measurements– Magnetic field experiment for Voyagers 1 and 2

Ah, the 13m boom is farther from the body of the craft (if that was where the field was coming from). But the boom itself is a point of discharge, and hence not outside but INSIDE the coma or tail of charged particles coming off or to the craft. In other words, they can correct for magnetic fields in other parts of the craft, but not for the magnetic field of the whole craft and boom discharging together into space. Again to use the comet example: could we have any area on a comet sticking out so far that it is clear of the coma? No! The coma would surround that raised point too.

[Solar]

Ah, the 13m boom is farther from the body of the craft (if that was where the field was coming from). But the boom itself is a point of discharge, and hence not outside but INSIDE the coma or tail of charged particles coming off or to the craft. In other words, they can correct for magnetic fields in other parts of the craft, but not for the magnetic field of the whole craft and boom discharging together into space. Again to use the comet example: could we have any area on a comet sticking out so far that it is clear of the coma? No! The coma would surround that raised point too.

I like the approach considering these satellites as manmade comets because; its correct. Even NASA knows this but they couch it in a variety of terms depending on who’s articles one is reading:

Wake and Sheath Generation: As it travels through space, the Shuttle affects the density, temperature, and electrical properties of the surrounding plasma. An electric field sheath develops around the vehicle and, like a boat, the Shuttle creates a wake in the plasma. The wake is depleted of plasma as the Shuttle collides with and displaces the gas, and various instabilities occur as the wake region is refilled with plasma. – Using Space as a laboratory: Space Plasma Physics

Here is NASA’s website for the Technical Working Group on this issue:
TECHNICAL WORKING GROUP - Electromagnetic Effects & Spacecraft Charging

That is a nice resource. You are making me worry about the interpretive veracity of the swirls and eddies creating my precious "Magnetic Bubbles" because the overall shape of the plasmasheath of the Voyager, or any other celestial body, is idealized. The sheaths actually waft around to fro, change intensities etc. I'm guessing off hand that MHD "frozen in" analysis was utilized as opposed to a dynamic magnetic field that would present 'peaks and valleys' and that these could have been misinterpreted?

[celeste]

Solar, If we use the comet analogy again, we see that as a comet leaves the solar system, it is PRECEEDED by the tail of charged particles that stream off of the comet. The comet clearly is not moving in to an undisturbed plasma, where the plasma merely "fills in again behind it" . Their "wake" is broken long before the comet ever gets there. As long as the mainstream does not believe there is any electric field out there in our solar system, there is no reason to suspect anything disturbing the plasma in front of the spacecraft. They are very wrong.

[Solar]

Solar, If we use the comet analogy again, we see that as a comet leaves the solar system, it is PRECEEDED by the tail of charged particles that stream off of the comet. The comet clearly is not moving in to an undisturbed plasma, where the plasma merely "fills in again behind it" . Their "wake" is broken long before the comet ever gets there. As long as the mainstream does not believe there is any electric field out there in our solar system, there is no reason to suspect anything disturbing the plasma in front of the spacecraft. They are very wrong.

Thank you for clearing up my misunderstanding of that (preceded) relationship Celeste. I wasn't seeing that for some reason.

[Osmosis]

Anyone know what type of total-field magnetometers are on Voyagers? Proton precession? Helium? Alkalai vapor?
Is there a calibration test they can run, to ensure the maggies are still working?

BTW, Happy Turkey Day!

Osmosis

[Solar]

Anyone know what type of total-field magnetometers are on Voyagers? Proton precession? Helium? Alkalai vapor?
Is there a calibration test they can run, to ensure the maggies are still working?

BTW, Happy Turkey Day!

Osmosis

Happy Thanksgiving!

TRIAXIAL FLUXGATE MAGNETOMETER

Fluxgate magnetometer

[Osmosis]

Thanks, Solar!

Osmosis

[seasmith]

just one more possible scenario:

However, that boundary seems to be more complicated than they thought as Voyager sends back information which doesn't completely match these expectations. Resolving the differences could help improve the understanding of what's happening at the edge, about 100 times farther from the sun than the Earth.

Astrophysicists looking at recent Voyager data saw that starting around August of 2012, the spacecraft detected a big jump in the number of particles from outside the solar system and a simultaneous decrease in the particles that originated from the sun. This change led NASA to announce that the spacecraft had passed through the heliopause and entered interstellar space.

However Nathan Schwadron, an astrophysicist at the University of New Hampshire in Durham, disagrees. There was a third signal that scientists expected to see but didn't: a change in the surrounding magnetic field direction as the craft passed from the sun's magnetic field into the Milky Way galaxy's magnetic field.

"This is a pretty important signature and if we don't see that, maybe something else is going on," Schwadron said. "The direction of the magnetic field is more or less the same."


He theorized that instead of passing through the heliopause, Voyager 1 instead entered a "flux transfer event." These are long, rope-shaped magnetic eddies that sometimes form for brief periods of time where two large magnetic fields meet.
Astronomers have observed them inside the magnetic fields of all the solar system's planets where they meet the sun's magnetic field. These disturbances can last for a few minutes around planets, but at the inside edge of the solar system's much larger field, they could last for many months and be big enough to take Voyager up to years to traverse.

These magnetic eddies open up a channel that lets in outside particles. If Voyager was inside of one of these flux transfer events between the sun and the galaxy's magnetic fields, Schwadron said it would explain why Voyager detected a sudden increase in galactic particles and a dropoff in the sun's particles without the magnetic field changing its direction.

"It accounts for all of the observations that we've seen," Schwadron said. His research appears in the December 1 issue of the journal Astrophysical Journal Letters.

It comes down to a question as to whether the edge of the solar system is a smooth boundary like Gurnett believes, or turbulent, as Schwadron's model implies … New readings of Voyager's onboard magnetic field detector will be released at the American Geophysical Union meeting later in December, which should include new readings over the last year.

Gurnett pointed to recent research indicating that the galactic magnetic field might bend around the sun's. It would make the transition through the heliopause difficult to detect because the two magnetic fields would align just past the interstellar boundary, and only start to unwind farther out.

"The interstellar magnetic field gets twisted as it approaches the heliopause, so its angle is not very different from the magnetic field inside," said the University of Maryland's James Drake, who led a team that published a separate paper in the December 1 Astrophysical Journal Letters.

http://iopscience.iop.org/2041-8205/778/2/L33/article

http://iopscience.iop.org/2041-8205/778/2/L26/article

Because Voyager is the first craft to approach the edge of the solar system, and many of its instruments no longer work, it's difficult for any scientist to say definitively when it is at the edge. Voyager 2 has more functioning instruments and is expected to reach the solar system's edge around 2016. It should be able to take more measurements and offer a better picture of the boundary.

http://www.insidescience.org/content/vo ... ystem/1504