The Voyager Spacecraft
Quite a long time ago two spacecraft called Voyager 1 and Voyager 2, and
weighing one ton each were launched on interplanetary expeditions. These two spacecraft were actually
launched way back in 1977 – 20th August (Voyager 2) and 5th September 1977
(Voyager 1) to be precise – and
between them they visited and photographed the outer planets (Jupiter, Saturn,
Uranus and Neptune) in incredible detail. At that time of my life I was living
in England, and I well remember the excellent BBC documentaries, "Encounter
with Uranus" and "Encounter with Neptune", which showed some of
the incredible images sent back from the far reaches of the solar system.
In the first twelve years of their lives, both spacecraft produced a wealth of
discoveries about the four gas giants, Jupiter, Saturn, Uranus and Neptune, and
their 48 moons which were then known.
Among their discoveries they revealed
that Jupiter's atmosphere has dozens of huge storms, that the hazy atmosphere of
Saturn's moon, Titan may hold the secrets of the origin of life, that Miranda, a
small moon of Uranus, has a jumble of old and new surfaces, and that Neptune's
moon Triton has active geysers.
As a result of their last planetary encounters, both these spacecraft were
ejected at great speed out of the plane of the solar system, Voyager 1 heading
"upwards" at an angle of 35 degrees to the ecliptic plane, and Voyager
2 heading "downwards" with respect to Earth’s orientation at an
angle of 48 degrees to the ecliptic. (The ecliptic is the horizontal plane of
the solar system and is basically the path which all the planets and the moon
follow as they move across the sky). The distances our two spacecraft have
now traveled is pretty significant. Voyager 1 currently (December 2010) is
the farthest human-made object, at a distance from the sun of about 18 billion
kilometers. Voyager 2 is currently about 14.7 billion
kilometers from the sun. This means that they are still only about half a light day away from us! Hard to believe,
isn’t it, that something traveling at 17 Km per second since
1977 can still only be 16.7 light hours away from us. Remember that the nearest
star is approximately 4 light YEARS away.
Both craft are powered by what is known as RTG’s, which stands for
Radioisotope Thermoelectric Generators. These are devices powered by the decay
of Plutonium, and at launch they generated 470 watts of 30 volt electrical
power. Due to the natural decay of the fuel source (which is how they work in
the first place), the power levels have been falling, and at the beginning of
1997 had fallen to about 335 watts for both spacecraft. However, this level of
power generation is still sufficient to run most of the on-board instruments
until perhaps the year 2020,
and so what had started as an interplanetary mission was converted by NASA to
the Voyager Interstellar Mission (VIM) in 1989.
The VIM objectives are to study the Termination Shock Boundary, the Heliosheath
through to the Heliopause, and finally the Interstellar Phase. So what exactly
do these terms mean? Well, I think we all know that the sun produces a
continuous stream of energetic particles, which we call the solar wind. This
plasma flow travels past the Earth and other planets at supersonic speeds as it
heads outwards from the sun. I think we also know that the sun and planets are
moving through space at a fair old speed, and the two Voyagers are racing ahead
of the sun in it's passage through space. Because of this
"forward" motion, the solar system creates a bow wave in the direction
of motion, at the point where the plasma stream comes into contact with the
interstellar "winds". This bow wave has the effect of slowing down the
solar wind particles, and a point is therefore reached where this slowing
becomes sufficient to reduce their speed to subsonic levels. This is the first
point for which the spacecraft will be looking, called the Termination Shock
Boundary. The exact location of this boundary is not known, but most current
estimates put it at between 82 and 93AU from the sun. So you can see that if
these calculations are correct, the boundary will be reached sometime between
the years 2003 and 2006. The next stage of the
mission will be when the spacecraft reach the limit of effect of the solar wind.
This will be the point beyond which they are subject only to the effects of the
interstellar winds, and is known as the Heliopause. Recent estimates are
that it will take Voyager 1 between 7 and 21 years to reach the Heliopause.
Until the Heliopause is
reached, the spacecraft are operating inside what is know as the Heliosheath,
which is the general area under the direct influence of the sun and the solar
wind. It is not known how extensive the Heliosheath is, but it could be
tens of astronomical units thick, taking several years for the spacecraft to
traverse. Once the Heliopause is reached, the spacecraft will enter the
true interstellar environment, and will be the first objects to completely
escape the influence of the sun. We have to hope that the craft and their
power supplies can endure until that point is reached.
How Long Will They Last?
So how long will the power last for the spacecraft systems? Well, as I said
earlier the power generated will gradually decrease as the fuel decays, and
plans are in place for gradually shutting down the various spacecraft systems to
eke out as far as possible the power which is available. First to be turned off
were the ultra-violet observation systems in year 2000, but now that this has
been done, the other instruments can be kept operating for several years. These
are the magnetic field instruments, the low energy charged particle
investigations, cosmic ray and plasma wave measurements. In about the year 2011,
gyro operations will be terminated. This will end the capability to rotate the
spacecraft, which could compromise our ability to maintain communication and
retrieve the data. Around the same time they will turn off the digital tape
recorder, which further compromises data playback and retrieval, but scientists
are confident they can maintain contact, and insist this is a necessary
compromise to maximise on the useful life for the two craft. Finally,
around the year 2018, power sharing between instruments will be initiated.
However, JPL plans to be able to continue to collect meaningful data at least
through 2020, after which point there will be insufficient power to run any of
the instruments, and our little messengers will finally be dead, nearly half a
century since they were launched.
Long after they fall silent, the
Voyager twins will keep speeding away from our solar system, each carrying a
disk of recorded images from Earth. Included are greetings from many Earth
languages, images of life on our planet and Man's achievements. Long after
our sun has swelled to become a red giant star, probably destroying the Earth in
the process, the Voyager craft will still be moving among the stars.
Perhaps long after mankind itself has disappeared from the cosmos they will
still be wandering. If they are ever found by another intelligence in the
farthest distant future, I wonder what they will make of the images of the
creatures who made it so long ago and so very far away.
Just a few more facts about the Voyagers before we leave them to their fate.
Each mission cost $865 million and a total of 11,000 people were involved with
the program through the encounter with Neptune. They carry with them special
time capsules, intended to communicate a story of our world to
extra-terrestrials. The Voyager message is carried on a 12-inch gold-plated
copper disk containing sounds and images which portray the diversity of life and
culture on Earth. The contents of the record were selected for NASA by a
committee chaired by Carl Sagan and it contains 115 images and a variety of
natural sounds, such as those made by surf, wind and thunder, birds, whales, and
other animals, musical selections from different cultures and eras, spoken
greetings from Earth-people in fifty-five languages, and printed messages from
President Carter and the then United Nations Secretary General, Kurt Waldheim.
Each record is encased in a protective aluminum jacket, together with a
cartridge and a needle. Instructions, in symbolic language, explain the origin
of the spacecraft and indicate how the record is to be played. The 115 images
are encoded in analog form. The remainder of the record is in audio, designed to
be played at 16-2/3 revolutions per second. It will be forty thousand years
before the spacecraft have any chance of making a close approach to any other
planetary system. As Carl Sagan noted, "The spacecraft will be encountered
and the record played only if there are advanced space faring civilizations in
interstellar space. But the launching of this bottle into the cosmic ocean says
something very hopeful about life on this planet."
Let’s hope he’s right!
(1st August, 2017)
spacecraft achieve 40 years of operation and exploration in August and September
2017. They continue to communicate
with NASA daily and have set numerous records. In
2012, Voyager 1, which launched on Sept. 5, 1977, became the only spacecraft to
have entered interstellar space. Voyager
2, launched on Aug. 20, 1977, is the only spacecraft to have flown by all four
outer planets - Jupiter, Saturn, Uranus and Neptune. Their
numerous planetary encounters include discovering the first active volcanoes
beyond Earth, on Jupiter's moon Io; first hints of a subsurface ocean on
Jupiter's moon Europa; the most Earth-like atmosphere in the solar system, on
Saturn's moon Titan; the jumbled-up, icy moon Miranda at Uranus; and icy-cold
geysers on Neptune's moon Triton. Though
the spacecraft have left the planets far behind - and neither will come remotely
close to another star for 40,000 years - they still send back observations about
conditions where our Sun's influence diminishes and interstellar space begins.
1, now almost 13 billion miles from Earth, travels through interstellar space
northward out of the plane of the planets. The probe has shown that cosmic rays
are as much as four times more abundant in interstellar space than in the
vicinity of Earth. This means the
heliosphere effectively acts as a radiation shield for the planets. Voyager 1
also hinted that the magnetic field of the local interstellar medium is wrapped
around the heliosphere.
2, now almost 11 billion miles from Earth, travels south and is expected to
enter interstellar space in the next few years. The different locations of the
two Voyagers allow scientists to compare right now two regions of space where
the heliosphere interacts with the surrounding interstellar medium using
instruments which measure charged particles, magnetic fields, low-frequency
radio waves and solar wind plasma. Once
Voyager 2 crosses into the interstellar medium they will also be able to sample
the medium from two different locations simultaneously.
twin Voyagers were well equipped for their journeys. Both carry redundant
systems which allow the spacecraft to switch to backup systems autonomously when
necessary, as well as long-lasting power supplies. Each
Voyager has three radioisotope thermoelectric generators using the decay of
plutonium-238 and only half of it will be gone after 88 years.
Space is almost empty, so the Voyagers are not at a significant level of
risk of bombardment by large objects. However, Voyager 1's environment is not a
complete void. It's filled with clouds of dilute material remaining from stars
which exploded as supernovae millions of years ago. This material doesn't pose a
danger to the spacecraft, but is a key part of the environment the Voyager
mission is helping scientists study and characterize.
Because the power decreases by four watts per year, engineers are
learning how to operate the spacecraft under ever-tighter power constraints. And
to maximize lifespan they also have to consult documents written decades
earlier, describing commands and software, in addition to the expertise of
former Voyager engineers.
Team members estimate they will have to turn off
the last science instrument by 2030. However, even after the spacecraft go silent,
they'll continue on their trajectories at their present speed of more than
30,000 mph (48,280 kilometers per hour), completing an orbit within the Milky
Way every 225 million years.
LATEST NEWS (16th
The Voyager 1 spacecraft has experienced three shock waves.
The most recent shock wave, first observed in February 2014, still appears to
be going on. The "tsunami wave" that the spacecraft began
experiencing earlier this year is still propagating outward, according to new
results. It is the longest-lasting shock wave that researchers have seen in
interstellar space. Most people thought the interstellar medium would be
smooth and quiet, but these shock waves seem to be more common than was
thought. A "tsunami wave" occurs when the sun emits a coronal
mass ejection, throwing out a magnetic cloud of plasma from its surface. This
generates a wave of pressure. When the wave runs into the interstellar plasma
-- the charged particles found in the space between the stars -- a shock wave
results that perturbs the plasma.
is the third shock wave that Voyager 1 has experienced. The first event was in
October to November of 2012, and the second wave in April to May of 2013
revealed an even higher plasma density. Voyager 1 detected the most recent
event in February, and it is still going on as of November data. The
spacecraft has moved outward 250 million miles (400 million kilometers) during
the third event. It is unclear to researchers what the unusual longevity
of this particular wave may mean. They are also uncertain as to how fast the
wave is moving or how broad a region it covers. The second tsunami wave helped
researchers determine in 2013 that Voyager 1 had left the heliosphere, the
bubble created by the solar wind encompassing the sun and the planets in our
solar system. Denser plasma "rings" at a higher frequency, and the
medium that Voyager flew through, was 40 times denser than what had been
previously measured. This was key to the conclusion that Voyager had entered a
frontier where no spacecraft had gone before: interstellar space.
seems that density of the plasma is higher the farther Voyager goes, but it is
not know if that is because the interstellar medium is denser as Voyager moves
away from the heliosphere, or if it is from the shock wave itself.
LATEST NEWS (6th December, 2011)
Voyager 1 has now entered a new ‘stagnation region’ in the outermost layer
of the bubble surrounding our solar system, and between the sun and interstellar
space. Data obtained over the last year (2011) reveal that in this new region
the “wind” of charged particles streaming out from the sun has calmed and
the solar system's magnetic field has piled up. Yet although the
spacecraft is about 11 billion miles (18 billion kilometers) from the sun, it is
not yet in true interstellar space. In the latest data, the direction of the
magnetic field lines has not changed, indicating Voyager is still within the
heliosphere, the bubble of charged particles the sun blows around itself. The
data do not reveal exactly when Voyager 1 will make it past the edge of the
solar atmosphere into interstellar space, but suggest it will be in a few months
to a few years.
The latest findings, come from Voyager's Low Energy Charged Particle instrument,
Cosmic Ray Subsystem and Magnetometer. Scientists previously reported the
outward speed of the solar wind had diminished to zero in April 2010, marking
the start of the new region.
managers rolled the spacecraft several times this spring and summer to help
scientists discern whether the solar wind was blowing strongly in another
direction. It was not. Voyager 1 is plying the celestial seas in a
region similar to Earth's doldrums, where there is very little wind.
During this past year, Voyager's magnetometer also detected a doubling in the
intensity of the magnetic field in the stagnation region, showing that inward
pressure from interstellar space is compacting it. Voyager has also been
measuring energetic particles that originate from inside and outside our solar
system. Until mid-2010, the intensity of particles originating from inside our
solar system had been holding steady. But during the past year, the intensity of
these energetic particles has been declining, as though they are leaking out
into interstellar space. The particles are now half as abundant as they were
during the previous five years. At the same time, a 100-fold increase has
been detected in the intensity of high-energy electrons from elsewhere in the
galaxy diffusing into our solar system from outside, which is another indication
of the approaching boundary. Scientists have been using the flow of
energetic charged particles at Voyager 1 as a kind of wind sock to estimate
the solar wind velocity. They have found that the wind speeds are low in this
region and gust erratically - for the first time, the wind even blows back at
us. Scientists had suggested previously that there might be a
stagnation layer, but now we have proof.
LATEST NEWS (15th June, 2012)
Data from Voyager 1 indicate that the spacecraft has encountered a region in
space where the intensity of charged particles from beyond our solar system has
markedly increased. Voyager scientists looking at this rapid rise draw closer to
an inevitable but historic conclusion – that humanity's first emissary to
interstellar space is on the edge of our solar system. The laws of physics say
that someday Voyager will become the first human-made object to enter
interstellar space, but we still do not know exactly when that someday will be.
This latest data indicate that the spacecraft is clearly in a new region where
things are changing more quickly. We are approaching the solar system's
frontier. The data making the 16-hour, 38 minute, 11.1-billion-mile
(17.8-billion-kilometer) journey from Voyager 1 to antennas of NASA's Deep Space
Network on Earth detail the number of charged particles measured by the two High
Energy telescopes aboard the 34-year-old spacecraft. These energetic particles
were generated when stars in our cosmic neighborhood went supernova. From
January 2009 to January 2012, there had been a gradual increase of about 25
percent in the amount of galactic cosmic rays Voyager was encountering. More
recently, there has been a very rapid escalation in that part of the energy
spectrum. Beginning on May 7, the cosmic ray hits have increased five percent in
a week and nine percent in a month. This marked increase is one of a triad of
data sets which need to make significant swings of the needle to indicate a new
era in space exploration. The second important measure from the spacecraft's two
telescopes is the intensity of energetic particles generated inside the
heliosphere, the bubble of charged particles the sun blows around itself. While
there has been a slow decline in the measurements of these energetic particles,
they have not dropped off precipitously, which could be expected when Voyager
breaks through the solar boundary. The final data set that Voyager scientists
believe will reveal a major change is the measurement in the direction of the
magnetic field lines surrounding the spacecraft. While Voyager is still within
the heliosphere, these field lines run east-west. When it passes into
interstellar space, the team expects Voyager will find that the magnetic field
lines orient in a more north-south direction. Such analysis will take weeks, and
the Voyager team is currently crunching the numbers of its latest data set.
Launched in 1977, Voyager 1 and 2 are in good health. Voyager 2 is more than 9.1
billion miles (14.7 billion kilometers) away from the sun. Both are operating as
part of the Voyager Interstellar Mission, an extended mission to explore the
solar system outside the neighborhood of the outer planets and beyond. NASA's
Voyagers are the two most distant active representatives of humanity and its
desire to explore.
NEWS (5th December, 2012)
1 has now entered a new region at the far reaches of our solar system that
scientists feel is the final area the spacecraft has to cross before reaching
interstellar space. They refer to this new region as a magnetic highway
for charged particles because our sun's magnetic field lines are connected to
interstellar magnetic field lines. This connection allows lower-energy
charged particles that originate from inside our heliosphere -- or the bubble of
charged particles the sun blows around itself -- to zoom out and allows
higher-energy particles from outside to stream in. Before entering this region,
the charged particles bounced around in all directions, as if trapped on local
roads inside the heliosphere. The Voyager team infers this region is still
inside our solar bubble because the direction of the magnetic field lines has
not changed. The direction of these magnetic field lines is predicted to change
when Voyager breaks through to interstellar space. and scientists believe this
is the last leg of the journey to interstellar space - possibly only a few
months to a couple of years away. The new region isn't what they had
expected, but they've come to expect the unexpected from Voyager.
Since December 2004, when Voyager 1 crossed a point in space called the
termination shock, the spacecraft has been exploring the heliosphere's outer
layer, called the heliosheath. In this region the solar wind abruptly
slowed down from supersonic speeds and became turbulent. Voyager 1's
environment was consistent for about five and a half years but the spacecraft
then detected that the outward speed of the solar wind had slowed to zero.
The intensity of the magnetic field also began to increase at that time.
Voyager data from two onboard instruments that measure charged particles showed
the spacecraft first entered this magnetic highway region on July 28,
2012. The region ebbed away and flowed toward Voyager 1 several times, the
spacecraft entering the region again on 25th August, and the environment has
been stable since.
LATEST NEWS (13th September, 2013)
Calif. -- NASA's Voyager 1 spacecraft officially is the first human-made object
to venture into interstellar space. The 36-year-old probe is about 12 billion
miles (19 billion kilometers) from our sun. New and unexpected data indicate
Voyager 1 has been traveling for about one year through plasma, or ionized gas,
present in the space between stars. Voyager is in a transitional region
immediately outside the solar bubble, where some effects from our sun are still
evident. A report on the analysis of this new data, an effort led by Don Gurnett
and the plasma wave science team at the University of Iowa, Iowa City, is
published in Thursday's edition of the journal Science. "Now that we have
new, key data, we believe this is mankind's historic leap into interstellar
space," said Ed Stone, Voyager project scientist based at the California
Institute of Technology, Pasadena. "The Voyager team needed time to analyze
those observations and make sense of them. But we can now answer the question
we've all been asking -- 'Are we there yet?' Yes, we are." Voyager 1 first
detected the increased pressure of interstellar space on the heliosphere, the
bubble of charged particles surrounding the sun that reaches far beyond the
outer planets, in 2004. Scientists then ramped up their search for evidence of
the spacecraft's interstellar arrival, knowing the data analysis and
interpretation could take months or years. Voyager 1 does not have a working
plasma sensor, so scientists needed a different way to measure the spacecraft's
plasma environment to make a definitive determination of its location. A coronal
mass ejection, or a massive burst of solar wind and magnetic fields, that
erupted from the sun in March 2012 provided scientists the data they needed.
When this unexpected gift from the sun eventually arrived at Voyager 1's
location 13 months later, in April 2013, the plasma around the spacecraft began
to vibrate like a violin string. On April 9, Voyager 1's plasma wave instrument
detected the movement. The pitch of the oscillations helped scientists determine
the density of the plasma. The particular oscillations meant the spacecraft was
bathed in plasma more than 40 times denser than what they had encountered in the
outer layer of the heliosphere. Density of this sort is to be expected in
interstellar space. The plasma wave science team reviewed its data and found an
earlier, fainter set of oscillations in October and November 2012. Through
extrapolation of measured plasma densities from both events, the team determined
Voyager 1 first entered interstellar space in August 2012.
new plasma data suggested a timeframe consistent with abrupt, durable changes in
the density of energetic particles that were first detected on Aug. 25, 2012.
The Voyager team generally accepts this date as the date of interstellar
arrival. The charged particle and plasma changes were what would have been
expected during a crossing of the heliopause.
mission controllers still talk to or receive data from Voyager 1 and Voyager 2
every day, though the emitted signals are currently very dim, at about 23 watts
-- the power of a refrigerator light bulb. By the time the signals get to Earth,
they are a fraction of a billion-billionth of a watt. Data from Voyager 1's
instruments are transmitted to Earth typically at 160 bits per second, and
captured by 34- and 70-meter NASA Deep Space Network stations. Traveling at the
speed of light, a signal from Voyager 1 takes about 17 hours to travel to Earth.
After the data are transmitted to JPL and processed by the science teams,
Voyager data are made publicly available. Scientists do not know when Voyager 1
will reach the undisturbed part of interstellar space where there is no
influence from our sun. They also are not certain when Voyager 2 is expected to
cross into interstellar space, but they believe it is not very far behind.
The cost of the Voyager 1 and Voyager 2 missions -- including launch, mission
operations and the spacecraft's nuclear batteries, which were provided by the
Department of Energy -- is about $988 million through September.
NEWS (7th July, 2014)
1 has experienced a new "tsunami wave" from the sun as it sails
through interstellar space. Such waves are what led scientists to the
conclusion, in the fall of 2013, that Voyager had indeed left our sun's bubble,
entering a new frontier. "Normally,
interstellar space is like a quiet lake," said Ed Stone of the California
Institute of Technology in Pasadena, California, the mission's project scientist
since 1972. "But when our sun has a burst, it sends a shock wave outward
that reaches Voyager about a year later. The wave causes the plasma surrounding
the spacecraft to sing." Data from this newest tsunami wave generated by
our sun confirm that Voyager is in interstellar space -- a region between the
stars filled with a thin soup of charged particles, also known as plasma. The
mission has not left the solar system -- it has yet to reach a final halo of
comets surrounding our sun -- but it broke through the wind-blown bubble, or
heliosphere, encasing our sun.
sun goes through periods of increased activity, where it explosively ejects
material from its surface, flinging it outward. These events, called coronal
mass ejections, generate shock, or pressure, waves. Three such waves have
reached Voyager 1 since it entered interstellar space in 2012. The first was
too small to be noticed when it occurred and was only discovered later, but
the second was clearly registered by the spacecraft's cosmic ray instrument in
March of 2013. Cosmic rays are energetic charged particles that come from
nearby stars in the Milky Way galaxy. The sun's shock waves push these
particles around and data from the cosmic ray instrument tell researchers that
a shock wave from the sun has hit.
another instrument on Voyager registers the shock waves, too. The plasma wave
instrument can detect oscillations of the plasma electrons. "The tsunami
wave rings the plasma like a bell," said Stone. "While the plasma
wave instrument lets us measure the frequency of this ringing, the cosmic ray
instrument reveals what struck the bell -- the shock wave from the sun."
This ringing of the plasma bell is what led to the key evidence showing
Voyager had entered interstellar space. Because denser plasma oscillates
faster, the team was able to figure out the density of the plasma. In 2013,
thanks to the second tsunami wave, the team acquired evidence that Voyager had
been flying for more than a year through plasma that was 40 times denser than
measured before -- a telltale indicator of interstellar space. Why is it
denser out there? The sun's winds blow a bubble around it, pushing out against
denser matter from other stars.
the team has new readings from a third wave from the sun, first registered in
March of this year. These data show that the density of the plasma is similar
to what was measured previously, confirming the spacecraft is in interstellar
space. Thanks to our sun's rumblings, Voyager has the opportunity to listen to
the singing of interstellar space -- an otherwise silent place.
1 and its twin, Voyager 2, were launched 16 days apart in 1977. Both
spacecraft flew by Jupiter and Saturn. Voyager 2 also flew by Uranus and
Neptune. Voyager 2, launched before Voyager 1, is the longest continuously
operated spacecraft and is expected to enter interstellar space in a few
LATEST NEWS (30th October, 2015)
Observations from the Voyager 1 after it left the heliosphere were puzzling
with regard to the magnetic field around it, as they differed from what
scientists derived from observations by other spacecraft. A
new study offers fresh insights into this mystery. Writing in the
Astrophysical Journal Letters, Nathan Schwadron of the University of New
Hampshire, Durham, and colleagues reanalyzed magnetic field data from Voyager
1 and found that the direction of the magnetic field has been slowly turning
ever since the spacecraft crossed into interstellar space. They believe this
is an effect of the nearby boundary of the solar wind. "This study
provides very strong evidence that Voyager 1 is in a region where the magnetic
field is being deflected by the solar wind," said Schwadron, lead author
of the study.
predict that in 10 years Voyager 1 will reach a more "pristine"
region of the interstellar medium where the solar wind does not significantly
influence the magnetic field. Observations
from Voyager's instruments have found that the particle density is 40 times
greater outside this boundary than inside, confirming that it had indeed left
the heliosphere. But so far, Voyager 1's observation of the direction of the
local interstellar magnetic field is more than 40 degrees off from what other
spacecraft have determined. The new study suggests this discrepancy exists
because Voyager 1 is in a more distorted magnetic field just outside the
heliopause, which is the boundary between the solar wind and the interstellar
you think of the magnetic field as a rubber band stretched around a beach
ball, that band is being deflected around the heliopause," Schwadron
2009, NASA's Interstellar Boundary Explorer (IBEX) discovered a
"ribbon" of energetic neutral atoms that is thought to hold clues to
the direction of the pristine interstellar magnetic field. The so-called
"IBEX ribbon," which forms a circular arc in the sky, remains
mysterious, but scientists believe it is produced by a flow of neutral
hydrogen atoms from the solar wind that were re-ionized in nearby interstellar
space and then picked up electrons to become neutral again. The new study uses
multiple data sets to confirm that the magnetic field direction at the center
of the IBEX ribbon is the same direction as the magnetic field in the pristine
interstellar medium. Observations from the NASA/ESA Ulysses and SOHO
spacecraft also support the new findings.
time, the study suggests, at increasing distances from the heliosphere, the
magnetic field will be oriented more and more toward "true north,"
as defined by the IBEX ribbon. By 2025, if the field around Voyager 1
continues to steadily turn, Voyager 1 will observe the same magnetic field
direction as IBEX. That would signal Voyager 1's arrival in a less distorted
region of the interstellar medium. "It's an interesting way to look at
the data. It gives a prediction of how long we'll have to go before Voyager 1
is in the medium that's no longer strongly perturbed," said Ed Stone,
Voyager project scientist, based at the California Institute of Technology in
Pasadena, who was not involved in this study.
Voyager 1 will continue delivering insights about interstellar space, its twin
probe Voyager 2 is also expected to cross into the interstellar medium within
the next few years. Voyager 2 will make additional observations of the
magnetic field in interstellar space and help scientists refine their