It’s Official: Voyager 1 Is Now In Interstellar Space

This artist's concept shows the Voyager 1 spacecraft entering the space between stars. Interstellar space is dominated by plasma, ionized gas (illustrated here as brownish haze), that was thrown off by giant stars millions of years ago.Credit: NASA.

In a cosmically historic announcement, NASA says the most distant human made object — the Voyager 1 spacecraft — is in interstellar space, the space between the stars. It actually made the transition about a year ago.

“We made it!” said a smiling Dr. Ed Stone, Voyager’s Project Scientist for over 40 years, speaking at a briefing today. “And we did it while we still had enough power to send back data from this new region of space.”

While there is a bit of an argument on the semantics of whether Voyager 1 is still inside or outside of our Solar System (it is not farther out than the Oort Cloud — it will take 300 more years reach the Oort cloud and the spacecraft is closer to our Sun than any other star) the plasma environment Voyager 1 now travels through has definitely changed from what comes from our Sun to the plasma that is present in the space between stars.

There’s also been a recent debate on if Voyager was really in or out of the Solar System – a debate between the latest various science papers and their authors. (More on that later…)

But Stone now says the evidence in clear: Voyager 1 has made the transition.

“This conclusion is possible from the space craft’s plasma wave instrument,” Stone said. “The 36-year old probe is now sailing through uncharted waters of a new cosmic sea and it has brought us along for the journey.”

Voyager 1’s 36-year, 13 billion mile journey began in 1977.

Scientists thought that when the spacecraft had crossed over into interstellar space, the magnetic field direction would change. However, it turned out that didn’t happen, and scientists determined they needed to look at the properties of the plasma instead.

The Sun’s heliosphere is filled with ionized plasma from the Sun. Outside that bubble, the plasma comes from the explosions of other stars millions of years ago. The main tell-tail difference is the interstellar plasma is denser.

Unfortunately, the real instrument that was designed to make the measurements on the plasma quit working in the 1980’s, so scientists needed a different way to measure the spacecraft’s plasma environment to make a definitive determination of its location.

Instead they used the plasma wave instrument, located on the 10-meter long antennas on Voyager 1 and an unexpected “gift” from the Sun, a massive Coronal Mass Ejection.

The antennas have radio receivers at the ends – “like the rabbit ears on old television sets,” said Don Gurnett, who led the plasma wave science team at the University of Iowa. The CME erupted from the Sun in March 2012, and eventually arrived at Voyager 1’s location 13 months later, in April 2013. Because of the CME, the plasma around the spacecraft began to vibrate like a violin string.

The pitch of the oscillations helped scientists determine the density of the plasma. Stone said 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.

“Now that we have new, key data, we believe this is mankind’s historic leap into interstellar space,” said Stone, “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.”

Artist's impression of Voyager 1's position on the sky when observed by the Very Long Baseline Array (VLBA) on February 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.
Artist’s impression of Voyager 1’s position on the sky when observed by the Very Long Baseline Array (VLBA) on February 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.

The plasma wave science team reviewed its data and found an earlier, fainter set of oscillations in October and November 2012 from other CMEs. Through extrapolation of measured plasma densities from both events, the team determined Voyager 1 first entered interstellar space in August 2012.

“We literally jumped out of our seats when we saw these oscillations in our data — they showed us the spacecraft was in an entirely new region, comparable to what was expected in interstellar space, and totally different than in the solar bubble,” Gurnett said. “Clearly we had passed through the heliopause, which is the long-hypothesized boundary between the solar plasma and the interstellar plasma.”

The 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.

At that time, Stone said, “We are certainly in a new region at the edge of the solar system where things are changing rapidly. But we are not yet able to say that Voyager 1 has entered interstellar space,” adding that the data are changing in ways that the team didn’t expect, “but Voyager has always surprised us with new discoveries.”

Now, after further review, the Voyager team generally accepts the August 2012 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. This reinforces that definitive science results don’t always come fast.

“The team’s hard work to build durable spacecraft and carefully manage the Voyager spacecraft’s limited resources paid off in another first for NASA and humanity,” said Suzanne Dodd, Voyager project manager, based at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “We expect the fields and particles science instruments on Voyager will continue to send back data through at least 2020. We can’t wait to see what the Voyager instruments show us next about deep space.”

There has been some back and forth about whether Voyager 1 was in or out of the Solar System. As we said, it was first questioned in August of 2012, with more speculation in December 2012, then in March of 2013 a paper by William Webber and F.B. McDonald claimed Voyager 1 had exited the Solar System the previous December, but Stone insisted the data wasn’t positive yet. Then about a month ago a paper came out by Marc Swisdak from the University of Maryland saying Voyager 1 was out of the solar system, but at that point Ed Stone and the Voyager team put out a statement saying they were still making that determination.

Today, Gurnett revealed that the timing of all scientists being in “official” agreement was off due to the timing of the review process for scientific papers. “Our paper was submitted a month before theirs, they just got through the review cycle before ours,” he said. “But theirs was basically a theory paper.”

Voyager 1 and its twin, Voyager 2, were launched 16 days apart in 1977. A fortuitous planetary alignment that only happens every 176 years enabled the two spacecraft to join together to reach all the outer planets in a 12 year time period. 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. It is about 9.5 billion miles (15 billion kilometers) away from our Sun.

Voyager 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.

“Voyager has boldly gone where no probe has gone before, marking one of the most significant technological achievements in the annals of the history of science, and adding a new chapter in human scientific dreams and endeavors,” said John Grunsfeld, NASA’s associate administrator for science in Washington. “Perhaps some future deep space explorers will catch up with Voyager, our first interstellar envoy, and reflect on how this intrepid spacecraft helped enable their journey.”

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.

“In a sense this is only really the beginning. We’re now going into a completely alien environment and what Voyager is going to discover truly unknown,” said Gary Zank, from the Department of Space Sciences at the University of Alabama, Huntsville, speaking at today’s press conference.

While Voyager 1 will keep going, we will not always be able to communicate with it, as we do now. In 2025 all instruments will be turned off, and the science team will be able to operate the spacecraft for about 10 years after that to just get engineering data. Voyager 1 is aiming toward the constellation Ophiuchus. 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. It will swing around the star and orbit about the center of the Milky Way, likely for millions of years.

Read more: NASA, JPL

Winds of Change at the Edge of the Solar System

As the venerable Voyager 1 spacecraft hurtles ever outward, breaking through the very borders of our solar system at staggering speeds upwards of 35,000 mph, it’s sending back information about the curious region of space where the Sun’s outward flow of energetic particles meets the more intense cosmic radiation beyond — a boundary called the heliosheath.

Voyager 1 has been traveling through this region for the past seven years, all the while its instruments registering gradually increasing levels of cosmic ray particles. But recently the levels have been jumping up and down, indicating something new is going on… perhaps Voyager 1 is finally busting through the breakers of our Sun’s cosmic bay into the open ocean of interstellar space?

Data sent from Voyager 1 — a trip that currently takes the information nearly 17 hours to make — have shown steadily increasing levels of cosmic radiation as the spacecraft moves farther from the Sun. But on July 28, the levels of high-energy cosmic particles detected by Voyager jumped by 5 percent, with levels of lower-energy radiation from the Sun dropping by nearly half later the same day. Within three days both levels had returned to their previous states.

The last time such a jump in levels occurred was in May — and that spike took a week to happen.

“The increase and the decrease are sharper than we’ve seen before, but that’s also what we said about the May data,” said Edward Stone, the Voyager project scientist based at the California Institute of Technology. “The data are changing in ways that we didn’t expect, but Voyager has always surprised us with new discoveries.”

The graph below shows the jump in cosmic particles detected starting May 2012.

Over 11 billion miles (18 billion km) from home, Voyager 1 has been cruising through space since its launch on September 5, 1977. Its twin, Voyager 2, was launched two weeks earlier and is currently 9.3 billion miles (15 billion km) away. Both spacecraft are healthy and continue to communicate with Earth, and will both eventually break through the borders of our solar system and enter true interstellar space. If they are still operational when that happens — and there’s no reason that they shouldn’t be — we will finally get a sense of what conditions are like “out there”.

Although Voyager 1 is registering intriguing fluctuations in radiation from both inside and outside the Solar System, it’s not quite there yet.

“Our two veteran Voyager spacecraft are hale and healthy as they near the 35th anniversary of their launch,” said Suzanne Dodd, Voyager project manager based at JPL in Pasadena. “We know they will cross into interstellar space. It’s just a question of when.”

Read more about Voyager’s ongoing breakout here.

“We are certainly in a new region at the edge of the solar system where things are changing rapidly. But we are not yet able to say that Voyager 1 has entered interstellar space.”

–  Edward Stone, Voyager project scientist, Caltech

Images: NASA/JPL-Caltech

Voyager 1 Breaking Through the Borders of the Solar System

After almost 35 years traveling at over 35,000 mph, the venerable (and still operational!) Voyager 1 spacecraft is truly breaking through to the other side, crossing the outermost boundaries of our solar system into interstellar space — over 11 billion miles from home.

Data received from Voyager 1 — a trip that currently takes the information 16 hours and 38 minutes to make — reveal steadily increasing levels of cosmic radiation, indicating that the spacecraft is leaving the relatively protected bubble of the Sun’s influence and venturing into the wild and wooly space beyond.

From the JPL press release:

“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,” said Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena. “The latest data indicate that we are clearly in a new region where things are changing more quickly. It is very exciting. 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,” said Stone. “More recently, we have seen 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.

“When the Voyagers launched in 1977, the space age was all of 20 years old. Many of us on the team dreamed of reaching interstellar space, but we really had no way of knowing how long a journey it would be — or if these two vehicles that we invested so much time and energy in would operate long enough to reach it.”

– Ed Stone, Voyager project scientist, Caltech

Read more on the JPL site here.

Addition: Check out the accompanying video from [email protected] below:

Top image: Artist’s concept showing NASA’s two Voyager spacecraft exploring a turbulent region of space known as the heliosheath, the outer shell of the bubble of charged particles around our sun. Credit: NASA/JPL-Caltech. Secondary image: Artist’s concept of NASA’s Voyager spacecraft. Credit: NASA/JPL-Caltech.


What is Interstellar Space?

Glittering Metropolis of Stars


The boundary of what is known, that place known as the great frontier, has always intrigued and enticed us. The mystery of the unknown, the potential for discovery, the fear, the uncertainty; that place that exists just beyond the edge has got it all! At one time, planet Earth contained many such places for explorers, vagabonds and conquerors. But unfortunately, we’ve run out of spaces to label “here be dragons” here at home. Now, humanity must look to the stars to find such places again. These areas, the vast stretches of space that fall between the illuminated regions where stars sit, is what is known as Interstellar Space. It can be the space between stars but also can refer to the space between galaxies.

On the whole, this area of space is defined by its emptiness. That is, there are no stars or planetary bodies in these regions that we know of. That does not mean, however, that there is absolutely nothing there. In fact, interstellar areas do contain quantities of gas, dust, and radiation. In the first two cases, this is what is known as interstellar medium (or ISM), the matter that fills interstellar space and blends smoothly into the surrounding intergalactic space. The energy that occupies the same volume, in the form of electromagnetic radiation, is known as the interstellar radiation field. On the whole, the ISM is thought to be made up primarily of plasma (aka. ionized hydrogen gas) because its temperature appears to be high by terrestrial standards.

The nature of the interstellar medium has received the attention of astronomers and scientists over the centuries. The term first appeared in print in the 17th century in the works of Sir Francis Bacon and Robert Boyle, both of whom were referring to the spaces that fell between stars. Before the development of electromagnetic theory, early physicists believed that space must be filled with an invisible “aether” in order for light to pass through it. It was not until the 20th century though that deep photographic imaging and spectroscopy that scientists were able to postulate that matter and gas existed in these regions. The discovery of cosmic waves in 1912 was a further boon, leading to the theory that interstellar space was pervaded by them. With the advent of ultraviolet, x-ray, microwave, and gamma ray detectors, scientists have been able to “see” these kinds of energy at work in interstellar space and confirm their existence.

Many satellites have been launched with the intention of sending back information from interstellar space. These include the Voyager 1 and 2 spacecraft which have cleared the known boundaries of the Solar System and passed into the heliopause. They are expected to continue to operate for the next 25 to 30 years, sending back data on magnetic fields and interstellar particles.

We have written many articles about interstellar space for Universe Today. Here’s an article about deep space, and here’s an article about interstellar space travel.

If you’d like more information on the Interstellar Space, here’s a link to Voyager’s Interstellar Mission Page, and here’s the homepage for Interstellar Science.

We’ve recorded an episode of Astronomy Cast all about Interstellar Travel. Listen here, Episode 145: Interstellar Travel.


Probing Exoplanets

Sometimes topics segue perfectly. With the recent buzz about habitable planets, followed by the raining on the parade articles we’ve had about the not insignificant errors in the detections of planets around Gliese 581 as well as finding molecules in exoplanet atmospheres, it’s not been the best of times for finding life. But in a comment on my last article, Lawrence Crowell noted: “You can’t really know for sure whether a planet has life until you actually go there and look on the ground. This is not at all easy, and probably it is at best possible to send a probe within a 25 to 50 light year radius.”

This is right on the mark and happens to be another topic that’s been under some discussion on arXiv recently in a short series of paper and responses. The first paper, accepted to the journal Astrobiology and led by Jean Schneider of the Observatory of Paris-Meudon, seeks to describe “the far future of exoplanet direct characterization”. In general, this paper discusses where the study of exoplanets could go from our current knowledge base. It proposes two main directions: Finding more planets to better survey the parameter space planets inhabit, or more in depth, long-term studying of the planets we do know.

But perhaps the more interesting aspect of the paper, and the one that’s generated a rare response, is what can be done should we detect a planet with promising characteristics relatively nearby. They first propose trying to directly image the planet’s surface and calculate the diameter of a telescope capable of doing so would be roughly half as large as the sun. Instead, if we truly wish to get a direct image, the best bet would be to go there. They quickly address a few of the potential challenges.

The first is that of cosmic rays. These high energy particles can wreak havoc on electronics. The second is simple dust grains. The team calculates that an impact with “a 100 micron interstellar grain at 0.3 the speed of light has the same kinetic energy than a 100 ton body at 100 km/hour”. With present technology, any spacecraft equipped with sufficient shielding would be prohibitively massive and difficult to accelerate to the velocities necessary to make the trip worthwhile.

But Ian Crawford, of the University of London, thinks that the risk posed by such grains may be overstated. Firstly, Crawford believes Schneider’s requirement of 30% of the speed of light is somewhat overzealous. Instead, most proposals of interstellar travel by probes generally use a value of 10% of the speed of light. In particular, the most exhaustive proposal yet created, (the Daedalus project) only attempted to achieve a velocity of 0.12c. However, the ability to produce such a craft was well beyond the means at the time. But with the advent of miniaturization of many electronic components, the prospect may need to be reevaluated.

Aside from the overestimate on necessary velocities, Crawford suggests that Schneider’s team overstated the size of dust grains. In the solar neighborhood, dust grains are estimated to be nearly 100 times smaller than reported by Schneider’s team. The combination of the change in size estimation and that of velocity takes the energy released on collision from a whopping 4 x 107 Joules, to a mere 4.5 Joules. At absolute largest, recent studies have shown that the upper limit for dust particles is more in the range of 4.5 micrometers.

Lastly, Crawford suggests that there may be alternative ways to offer shielding than the brute force wall of mass. If a spacecraft were able to detect incoming particles using radar or another technique, it is possible that it could destroy the incoming particles using lasers, or deflect it using a electromagnetic field.

But Schneider wasn’t finished. He issued a response to Crawford’s response. In it, he criticizes Crawford’s optimistic vision of using nuclear or anti-matter propulsion systems. He notes that, thus far, nuclear propulsion has only been able to produce short impulses instead of continuous thrust and that, although some electronics have been miniaturized, the best analogue yet developed, the National Ignition Facility, is, “with all its control and cooling systems, is presently quite a non-miniaturized building.”

Anti-matter propulsion may be even more difficult. Currently, our ability to produce anti-matter is severely limited. Schneider estimates that it would take 200 terrawatts of energy to produce the required amounts. Meanwhile, the overall energy of the entire Earth is only 20 terrawatts.

In response to the charge of overestimation, Schneider notes that, although such large dust grains would be rare, but “even two lethal or severe collisions are prohibitory”, but does not go on to make any honest estimations of what the actual probability of such a collision would be.

Ultimately, Schneider concludes that all discussion is, at best, extremely preliminary. Before any such undertaking would be seriously considered, it would require “a precursor mission to secure the technological concept, including shielding mechanisms, at say 500 to 1000 Astronomical Units.” Ultimately, Schneider and his team seems to remind us that the technology is not yet there and that there are legitimate threats we must address. Crawford, on the other hand suggests that some of these challenges are ones that we may already be well on the road to addressing and constraining.