The latest observations of interstellar particles

Credit: NASA /Goddard /Adler /U. Chicago /Wesleyan

With all the news about Voyager 1 leaving the heliosphere and entering interstellar space you might think that the probe is the first spacecraft to detect interstellar particles.

That isn't entirely true, and the latest observations of interstellar particles has found some very interesting results.

The heliosphere is generated by the Sun's solar wind, a stream of charged (ionized) particles that flows outward from the Sun.

The solar wind interacts with the magnetic field of the sun, and together they create a kind of diffuse bubble of charged particles around the sun known as the heliosphere.

While this heliosphere prevents any interstellar charged particles from reaching us, it is less effective at preventing uncharged interstellar particles from reaching us.

Most of the interstellar wind is ionized like the solar wind, but there are some neutral particles (mostly hydrogen) that moves with the interstellar wind.

Since neutral particles don't interact strongly with the Sun's magnetic field, some of them can slip into the heliosphere, where we can detect them.

This neutral hydrogen comes from the local cloud, seen below, a very tenuous cloud of hydrogen that surrounds our stellar region.

The motion of this hydrogen relative to the Sun depends on the Sun's motion through the cloud and the motion of the cloud itself.

The Sun's motion through the galaxy is quite steady, and it was thought that the cloud's motion was also steady, but long term observations of the hydrogen flow through our solar system has found this is not the case.

In a recent paper in Science researchers compared hydrogen flow measurements from the IBEX satellite (taken during 2009-2010) with observations from Ulysses (1992-2002) and other observations (1972-1978).

What they found was that over the course of 30 years the direction has changed by about 6 degrees.

This may seem like a slow and gradual change, but on a cosmic scale it is huge. The local cloud is about 30 light years across, and the Sun moves through it at a speed of (only) about 50,000 mph (22 km/sec).

While variations in the hydrogen flow are expected as it interacts with variations in the solar wind, those variations average out.

Observing such a rapid change in flow (on a cosmic scale) means either there is turbulent flow within the cloud itself, or the interstellar wind is more dynamic than originally thought.

We've long known that the solar wind is quite dynamic due to the Sun's activity. Now we're finding the interstellar wind may be active as

More information: "Decades-long changes of the interstellar wind through our solar system." Frisch PC, et al. Science. 2013 Sep 6;341(6150):1080-2. DOI: 10.1126/science.1239925

Mozart, Bach and Beethoven leave solar system in Voyager-1 spacecraft

A selection of classical music travelling on the Voyager 1 spacecraft at 100,000mph has made it outside our solar system, and is now 11.6 billion miles away from Earth.

Launched in 1977, Voyager 1 is a remarkable piece of 70's technology but is an intergalactic relic by today's aerospace and communications standards.

Voyager 1 and 2 were originally launched to study the outer planets, and having successfully completed their missions, have now travelled further than anyone or anything in human history. 

Voyager 1 is so far away and has such poor broadcasting capability that it takes 17 hours for the weak radio signal sent from the craft to be picked up on Earth.

Along with greetings in 55 languages, music submitted by countries across the world was transferred onto a gold vinyl record to serve as a message to any life form that might someday stumble across the spacecraft. 

The out-of-this-world playlist includes jazz by Louis Armstrong, traditional tunes from different continents, and classical music by great composers including Bach, Stravinsky, Beethoven and Mozart.

The spacecraft will not approach another star for nearly 40,000 years. By this time, the plutonium power sources will have run out of power and the 20W transmitters will have stopped broadcasting a signal, so there's no way of knowing whether alien life forms will have discovered the music - or worked out how to play it.

Picture: NASA

See a Full list of music on the Voyager spacecraft here

NASA Voyager-1 has left the Solar System

An artist's concept shows the Voyager spacecraft traveling through space against a field of stars. 

Credit: NASA/JPL-Caltech.

University of Iowa space physicist Don Gurnett says there is solid evidence that NASA's Voyager 1 spacecraft has become the first man-made object to reach interstellar space, more than 11 billion miles distant and 36 years after it was launched.

The finding is reported in a paper published in the Sept. 12 online issue of the journal Science.

Don Gurnett

"On April 9, the Voyager 1 Plasma Wave instrument, built at the UI in the mid-1970s, began detecting locally generated waves, called electron plasma oscillations, at a frequency that corresponds to an electron density about 40 times greater than the density inside the heliosphere—the region of the sun's influence," says Gurnett.

"The increased electron density is very close to the value scientists expected to find in the interstellar medium.

"This is the first solid evidence that Voyager 1 has crossed the heliopause, the boundary between the heliosphere, and interstellar space," says Gurnett, principal investigator for the plasma wave instrument.

Bill Kurth

For several months, the relative position of Voyager 1 has stirred something of a scientific debate because there remains some lingering evidence of the nearby heliosphere beyond the heliopause.

Even though Voyager 1 has passed into interstellar space, it does not mean that its journey is over, says Bill Kurth, UI research scientist and co-author of the Science paper.

This is an artist's impression of Voyager 1's position on the sky when observed by the Very Long Baseline Array (VLBA) on Feb. 21, 2013, at which point -- according to NASA's Jet Propulsion Laboratory -- Voyager was already outside of our solar system. 

The actual image from the data (enlarged section) is 0.5 arcseconds across. 

The radio signal as shown is a mere 1 milliarcsecond across. 

Credit: Alexandra Angelich, NRAO/AUI/NSF.

"Now that we're on the outside, we are learning that interstellar space isn't a bland region," Kurth says.

"Rather, there are variations in some of Voyager's measurements that may be due to the nearby presence of the heliosphere. So, our attention is turning from crossing the boundary to understanding what is going on outside," he says.

At age 36, Voyager 1 is the most distant human-made object at more than 11.6 billion miles from the sun, or about 125 astronomical units.

"At that distance it takes more than 17 hours for a radio signal to travel from the spacecraft to one of NASA's Deep Space Network antennas. The signal strength is so incredibly weak that it takes both a 230-foot and a 110-foot-diameter antenna to receive our highest resolution data," Gurnett says.

Launched Sept. 5, 1977, Voyager 1 completed flybys of both Jupiter and Saturn and is currently moving outward from the sun at about 3.5 AU per year.

It's sister spacecraft, Voyager 2 was launched Aug. 20, 1977, on a flight path that took it to encounters with Jupiter, Saturn, Uranus, and Neptune.

At present, Voyager 2 is still inside the heliosphere about 103 AU from the sun and traveling outward at about 3.3 AU per year.

More information: The sounds of the electron plasma oscillations heralding Voyager's entry into interstellar space and other sounds of space can be heard by visiting Gurnett's website at: www-pw.physics.uiowa.edu/space-audio/

NASA Voyager-1: On the edge of the Solar System

Artist's concept of NASA's Voyager spacecraft. 

Credit: NASA/JPL-Caltech 

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."

This artist's concept shows NASA's Voyager 1 spacecraft exploring a region called the "depletion region" or "magnetic highway" at the outer limits of our heliosphere, the bubble the sun blows around itself. 

In this region, the magnetic field lines generated by our sun (yellow arcs) are piling up and intensifying and low-energy charged particles that are accelerated in the heliosphere's turbulent outer later (green dots) have disappeared. 

Scientists think the depletion region is the last region Voyager 1 has to cross before reaching interstellar space, which is the space between stars, Voyager 1 passed a shockwave known as the termination shock in 2004, where solar wind suddenly slowed down and became turbulent. 

In 2010, it then passed into an area called the "stagnation region" where the outward velocity of the solar wind slowed to zero and sporadically reversed direction. 

In the slow-down and stagnation regions, the prevalence of low-energy charged particles from our heliosphere jumped dramatically and is indicated by the green dots. 

On Aug. 25, 2012. Voyager 1 entered the depletion or magnetic highway region, where the magnetic field acts as a kind of "magnetic highway" allowing energetic ions from inside the heliosphere to escape out, and cosmic rays from interstellar space zoom in. 

Magnetic field lines form a spiral around the solar system because of the rotation of the sun, and at the edge of the heliosphere they form roughly parallel arcs. 

Because an interstellar wind outside is pushing back on the heliosphere, magnetic field lines pile up as the solar wind slows, like cars back up at a freeway off-ramp. 

The compression of field lines increases the strength of the magnetic field as Voyager approaches interstellar space. 

Since scientists don't know the exact location of the heliopause - which is the border to interstellar space - that area has been labeled with a question mark. 

Image credit: NASA/JPL-Caltech 

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.

More information: References:

* "Magnetic Field Observations as Voyager 1 Entered the Heliosheath Depletion Region," L. F. Burlaga, N. F. Ness, and E. C. Stone, Science, DOI: 10.1126/science.1235451; www.sciencemag.org/content/early/2013/06/26/science.1235451.abstract 
* "Search for the Exit: Voyager 1 at Heliosphere's Border with the Galaxy," S. M. Krimigis, R. B. Decker, E. C. Roelof, M. E. Hill, T. P. Armstrong, G. Gloeckler, D. C. Hamilton, and L. J. Lanzerotti, Science, DOI:10.1126/science.1235721; www.sciencemag.org/content/early/2013/06/26/science.1235721.abstract 
* "Voyager 1 Observes Low-Energy Galactic Cosmic Rays in a Region Depleted of Heliospheric Ions," E. C. Stone, A. C. Cummings, F. B. McDonald, B. C. Heikkila, N. Lal, and W. R. Webber, Science, DOI:10.1126/science.1236408; www.sciencemag.org/content/early/2013/06/26/science.1236408.abstract

NASA Voyager-1: Public Invited to Fly along

The public will be able to fly along with NASA's Voyager spacecraft as the twin probes head towards interstellar space, which is the space between stars. 

As indicated in this artist's concept, a regularly updated gauge using data from the two spacecraft will indicate the levels of particles that originate from far outside our solar system and those that originate from inside our solar bubble. 

Those are two of the three signs scientists expect to see in interstellar space. 

The other sign is a change in the direction of the magnetic field. 

Credit: NASA/JPL-Caltech

A gauge on the Voyager home page, tracks levels of two of the three key signs scientists believe will appear when the spacecraft leave our solar neighborhood and enter interstellar space.

When the three signs are verified, scientists will know that one of the Voyagers has hurtled beyond the magnetic bubble the sun blows around itself, which is known as the heliosphere.

The gauge indicates the level of fast-moving charged particles, mainly protons, originating from far outside the heliosphere, and the level of slower-moving charged particles, also mainly protons, from inside the heliosphere.

If the level of outside particles jumps dramatically and the level of inside particles drops precipitously, and these two levels hold steady, that means one of the spacecraft is closing in on the edge of interstellar space. These data are updated every six hours.

Scientists then need only see a change in the direction of the magnetic field to confirm that the spacecraft has sailed beyond the breath of the solar wind and finally arrived into the vast cosmic ocean between stars.

The direction of the magnetic field, however, requires periodic instrument calibrations and complicated analyses. These analyses typically take a few months to return after the charged particle data are received on Earth.

Voyager 1

VOYAGER-1
Voyager 1, the most distant human-made spacecraft, appears to have reached this last region before interstellar space, which scientists have called "the magnetic highway." Inside particles are zooming out and outside particles are zooming in.

However, Voyager 1 has not yet seen a change in the direction of the magnetic field, so the consensus among the Voyager team is that it has not yet left the heliosphere.

Voyager-2

VOYAGER-2
Voyager-2, the longest-operating spacecraft, but not as distant as Voyager 1, does not yet appear to have reached the magnetic highway, though it has recently seen some modest drops of the inside particle level.

NASA's Eyes on the Solar System program, a Web-based, video-game-like tool to journey with NASA's spacecraft through the solar system, has added a Voyager module that takes viewers along for a ride with Voyager 1 as it explores the outer limits of the heliosphere.

Time has been sped up to show one day per second. Rolls and other maneuvers are incorporated into the program, based on actual spacecraft navigation data. The charged particle data are also shown.

Visit that module HERE

The Voyager spacecraft were built and continue to be operated by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Caltech manages JPL for NASA.

The Voyager missions are a part of NASA's Heliophysics System Observatory, sponsored by the Heliophysics Division of the Science Mission Directorate at NASA Headquarters in Washington.

More information about the Voyager spacecraft here.