Voyager Enters Final Frontier Of Solar System Options

[Mongo]

At the solar system's edge, more surprises from Voyager

Data from NASA's Voyager 1 spacecraft continues to provide new insight on the outskirts of our solar system, a frontier thought to be the last that Voyager will cross before becoming the first man-made object to reach interstellar space.

In papers published this week in the journal Science, scientists from the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md., and other Voyager partner institutions provide more clarity on the region they named the "magnetic highway" in December 2012. Cruising through what scientists describe as a curious, unexpected charged-particle environment, Voyager has detected, for the first time, low-energy galactic cosmic rays, now that particles of the same energy from inside the bubble around our Sun disappeared. As a result, Voyager now sees the highest level so far of particles from outside our solar bubble that originate from the death of other nearby stars.

"Voyager 1 may be months or years from leaving the solar system—we just don't know," says APL's Stamatios Krimigis, principal investigator for Voyager's Low-Energy Charged Particle (LECP) instrument. "But the wait itself is incredibly exciting, since Voyager continues to defy predictions and change the way we think about this mysterious and wonderful gateway region to the galaxy."

Voyager 1 and 2 were launched in 1977 and between them visited Jupiter, Saturn, Uranus and Neptune. Since 1990, the twin spacecraft have been on their Interstellar Mission, on track to leave the heliosphere, which is the bubble of magnetic field and charged particles the Sun blows around itself. On Aug. 25, 2012, when Voyager 1 was about 11 billion miles (18 billion kilometers) from the Sun, the spacecraft reached the so-called magnetic highway where charged particles from inside the heliosphere zoomed out along the magnetic field as cosmic rays from far outside zoomed in. The lack of a detectable change in the direction of that magnetic field, however, convinced scientists that Voyager remained within the Sun's influence.

The new Science papers focus on observations from the summer and fall of 2012 by LECP as well as Voyager 1's Cosmic Ray and Magnetometer instruments, with additional LECP data through April 2013.

"The most dramatic part was how quickly the solar-originating particles disappeared; they decreased in intensity by more than 1,000 times, as if there was a huge vacuum pump at the entrance ramp onto the magnetic highway," says Krimigis. "We have never witnessed such a decrease before, except when Voyager 1 exited the giant magnetosphere of Jupiter, some 34 years ago."

"Surprisingly, the traveling direction of the 'inside' charged particles in this region made a difference, with those moving straightest along the magnetic field lines decreasing most quickly. Those that moved perpendicular to the magnetic field did not change as quickly," adds LECP Co-investigator Robert Decker, also of APL. The cosmic rays from outside, moving along the field lines, were somewhat more intense than those moving perpendicular to the field, and this imbalance varied significantly with time during the eight months since "It is this time-varying behavior of the cosmic rays that tells us that we're still in a region controlled by our Sun," says APL's Edmond Roelof, also an LECP co-investigator.

The multidimensional measurements speak to the unique abilities of the LECP detector, designed at APL in the 1970s. It includes a stepper motor that rotates the instrument through 45-degree steps every 192 seconds, allowing it to gather data in all directions and pick up something as dynamic as the solar wind and galactic particles. The device, designed and tested to work for 500,000 steps and last four years, has been working for nearly 36 years and well past 6 million steps.

Magnetic Field Observations as Voyager 1 Entered the Heliosheath Depletion Region

Magnetic fields measured by Voyager 1 (V1) show that the spacecraft crossed the boundary of an unexpected region five times between days 210 and ~238 in 2012. The magnetic field strength B increased across this boundary from ≈0.2 nT to ≈0.4 nT, and B remained near 0.4 nT until at least day 270, 2012. The strong magnetic fields were associated with unusually low counting rates of >0.5 MeV/nuc particles. The direction of B did not change significantly across any of the 5 boundary crossings; it was very uniform and very close to the spiral magnetic field direction, which was observed throughout the heliosheath. The observations indicate that V1 entered a region of the heliosheath (“the heliosheath depletion region”), rather than the interstellar medium.

Search for the Exit: Voyager 1 at Heliosphere’s Border with the Galaxy

We report measurements of energetic (>40 keV) charged particles on Voyager 1 (V1) from the interface region between the heliosheath (HS), dominated by heated solar plasma, and the local interstellar medium (LISM) expected to contain cold nonsolar plasma and the galactic magnetic field. Particles of solar origin at V1, located at 18.5 billion km (123 AU) from the Sun, decreased by a factor >103 on 25 August 2012, while those of galactic origin (cosmic rays) increased by 9.3% at the same time. Intensity changes appeared first for particles moving in the azimuthal direction and were followed by those moving in the radial and antiradial directions with respect to the solar radius vector. This unexpected heliospheric "depletion region" may form part of the interface between solar plasma and the galaxy.

Voyager 1 Observes Low-Energy Galactic Cosmic Rays in a Region Depleted of Heliospheric Ions

On 25 August 2012, Voyager 1 was at 122 astronomical units when the steady intensity of low-energy ions it had observed for the last 6 years suddenly dropped for a third time and soon completely disappeared as the ions streamed away into interstellar space. Although the magnetic field observations indicate that Voyager 1 remained inside the heliosphere, the intensity of cosmic ray nuclei from outside the heliosphere abruptly increased. We report the spectra of galactic cosmic rays down to ~3 × 106 electron volts per nucleon, revealing H and He energy spectra with broad peaks from 10 × 106 to 40 × 106 electron volts per nucleon and an increasing galactic cosmic ray electron intensity down to ~10 × 106 electron volts.

[PDP8E]

Thanks for pointing out that update Mongo,

a little back-of-the-envelope math... V1 will have traveled 1% of the distance to the nearest star, on or about the year 2727 ( EDIT: not 2377 ... I sharpened my pencil)

BTW, its not pointing at the nearest star, it is heading towards the vicinity of the Solar Apex (the direction of the Sun's motion relative to nearby stars, or currently someplace southwest of the star Vega). Voyager 1 will leave the solar system aiming toward the constellation Ophiuchus.

From NASA:
In the year 40,272 AD, Voyager 1 will come within 1.7 light years of an obscure star in the constellation Ursa Minor (the Little Bear or Little Dipper) called AC+79 3888

V1 is only 17.18 light-hours from the Sun at the moment.

Voyager 2 is also escaping the solar system to the south toward the constellations of Sagitarrius and Pavo.
In about 40,000 years, Voyager 2 will come within about 1.7 light years of a star called Ross 248, a small star in the constellation of Andromeda

also see:

http://www.heavens-above.com/SolarEscape.aspx

[Mongo]

V1 is only 17.18 light-hours from the Sun at the moment.

That's 0.00196 light years from the Sun!

Well, it's a start...

[TheAnt]

Voyager 1 might indeed be close to the Interstellar boundary now.

Yet it's only a 2 degree shift in direction of the magnetic field, and if I read this right most cosmic rays are still moving along the magnetic fieldlines. Which suggest they have been affected by it for some duration while approaching our solar system.

So even though I got very enthusiastic about the magnetic highway and that it might be a herald of interstellar space close at hand. There might be some reason to not starting to yell 'Are we there yet?'

JPL update for V1.

[TheAnt]

Voyager 1 have now left the Solar system according to a study.

Univ of Maryland page

[TheAnt]

And another item on the question if Voyager 1 is in interstellar space or not.
Now described as 'competing models' it all is a sign of good science work on the matter.

The magnetic lines from the sun do connect to the galactic magnetic field as described
Is as far as I understand it the 'magnetic highway' that been noted.
In addition, IBEX have indeed shown that there's no bow shock, so that is consistent with the alternative hypothesis.

Science daily

[Explorer1]

Voyager press conference in 15 minutes! Regarding an article in Science embargoed until today.
Streaming here: http://www.youtube.com/watch?v=uBqYErSvi6A

EDIT: Interstellar space confirmed! http://www.jpl.nasa.gov/news/news.php?release=2013-277

[Paolo]

as Science titles: It's Official—Voyager Has Left the Solar System
for the lucky having full access here is the paper In Situ Observations of Interstellar Plasma With Voyager 1

[djellison]

Science (as well as the BBC, CNN, infact almost everyone) makes the wrong claim ( left the solar system) rather than the claim the paper that science is publishing ACTUALLY makes ( entered interstellar space )

The two are not one and the same - very important distinction to make.

In terms of the number of objects orbiting our Sun - Voyager will be passing them by for another 300 years.

[TheAnt]

Wonderful, even though those two items I posted in August did convince me, it did not take that long for the rest of the space science community jumped onto the bandwagon this time. =)

And djellison is right, news media is excused but a bit embarrassing to see AAAS stating V1 have left the solar system The Oort cometary region is still far ahead.

A NASA page has gone up now: NASA Spacecraft Embarks on Historic Journey Into Interstellar Space

[Explorer1]

Link already posted by me, Ant

And yes, dates for leaving the solar system are certainly subjective. Ask a heliophysicist and they'll say this past year, a comet scientist will say several centuries from now, a planetary scientist will say 1988/9, and a mathematician will say never.
Go figure....

[Paolo]

And djellison is right, news media is excused but a bit embarrassing to see AAAS stating V1 have left the solar system The Oort cometary region is still far ahead.

on the other hand, from a dynamical point of view, Voyager is no longer bound to the Sun (since 1979 in fact), so it can be considered to have left the solar system

[djellison]

Voyager is no longer bound to the Sun (since 1979 in fact), so it can be considered to have left the solar system

So you're saying that New Horizons left the solar system as its third stage burned out, a few hundred miles above the Earth?

I don't think anyone would agree that's a fair assessment. Speed is not location. "Where are you?" "Mach 30"

[dilo]

... Speed is not location. "Where are you?" "Mach 30"

Good point, Paolo/Doug! I always thought that space exploration lies in a six dimensions domain, a perfect mix of space and velocity or, better, distances and "delta-v". From this viewpoint, I think that you're both right!

[0101Morpheus]

Voyager finally made it! This is a historic moment, for real this time

OK but even if Voyager is currently drifting in interstellar plasma that does not change the fact that

1. Cosmic rays are still coming predominantly from one direction.

2. There has not been an significant field shift.

And Voyager 1 has about ten years of power to answer these questions. Plus who knows when Voyager 2 will enter the interstellar medium.

There is still a lot of work to be done here...