Voyager 2 – astroengine.com

How Gaia Is Already Shaping Our Interstellar Adventures

The space telescope has refined the stellar flybys of the Voyager and Pioneer probes—how might it help us chart our way to the stars in the future?

When looking up on a starry night, it can be difficult to comprehend that those stars are not fixed in the sky. Sure, on timescales of a human lifetime, or even the entirety of human history, the stars don’t appear to move too much. But look over longer timescales—tens of thousands, to millions of years—and it becomes clear that the stars in the sky are in motion. This means the constellations we see today will be misshapen (or even non-existent!) in a few hundred thousand years’ time.

This poses an interesting question: If humanity were to send a spacecraft on an interstellar mission—an endeavor that could take thousands of years, depending on how ambitious the target—aiming it directly at a distant star would be a mistake. Depending on how far away that star is, by the time the spacecraft reaches its target, the star could have moved a few light-years away. This is why precision astrometry—the astronomical measurement of a star’s position, speed and direction of motion—will be needed to predict where a target star will be, and not where it currently is, when our future interstellar mission gets there.

To test this, we don’t need to wait until humanity has the means to build a starship, however. We have a bunch of interstellar probes that have already started their epic sojourns into the galaxy.

Interstellar Interlopers

Earlier this year, NASA’s Voyager 2 spacecraft departed the Sun’s sphere of influence and became humanity’s second interstellar mission, six years after its twin, Voyager 1, made history to become the first human-made object to drift into the space between the stars. Both Voyagers are still transmitting telemetry to this day, over 40 years since their launch. Another two spacecraft, the older Pioneer 10 and 11 missions, are also on their way to interstellar space, but they stopped transmitting decades ago. A newcomer, NASA’s New Horizons mission, will also become an interstellar mission in the future, but it has yet to finish its Kuiper belt explorations and still has fuel to make course corrections, so predictions of its stellar encounters will remain unknown for some time.

Both Voyager 1 and 2 have left the Sun’s heliosphere to become humanity’s first interstellar missions [NASA]

Having explored the outer planets in the 1970’s and 80’s, the Voyagers and Pioneers barreled on, revealing stunning science from the outer solar system. In the case of Voyager 1 and 2, when each breached the heliopause (the invisible boundary that demarks the limit of the Sun’s magnetic bubble, between the heliosphere and interstellar medium), they gave us a profound opportunity to experience this distant alien environment, using their dwindling number of instruments to measure particle counts and magnetic orientation.

But where are our intrepid interstellar interlopers going now? With the help of precision astrometry of local stars observed by the European Space Agency’s Gaia space telescope, two researchers have taken a peek into the future, seeing which star systems the spacecraft will drift past in the next few hundred thousand to millions of years.

Previously, astronomers have been able to combine the spacecrafts’ trajectory with stellar data to see which stars they will fly past, but in the wake of the Gaia Data Release 2 (GDR2) last year, an unprecedented trove of information has been made available for millions of stars in the local galaxy, providing the most precise “road map” yet of those stars the Voyagers and Pioneers will encounter.

“[Gaia has measured] the positions and space velocities of nearby stars more precisely than before and so has more precisely characterized the encounters with stars we already knew about,” says astronomer Coryn Bailer-Jones, of the Max Planck Institute for Astronomy in Heidelberg, Germany.

Close Encounters of the Voyager Kind

Bailer-Jones and colleague Davide Farnocchia of NASA’s Jet Propulsion Laboratory in Pasadena, Calif., published their study in Research Notes of the American Astronomical Society, adding another layer of understanding about where our spacecraft, and the stars they’ll encounter, are going. Although their work confirms previous estimates of some stellar close encounters, Bailer-Jones tells Astroengine.com that there have been some surprises in their calculations—including encounters that have not been identified before.

For example, the star Gliese 445 (in the constellation of Camelopardalis, close to Polaris) is often quoted as being the closest encounter for Voyager 1, in approximately 40,000 years. But with the help of Gaia, which is giving an extra layer of precision for stars further afield, the researchers found that the spacecraft will come much closer to another star, called TYC 3135-52-1, in 302,700 years.

“Voyager 1 will pass just 0.30 parsecs [nearly one light-year] from that star and thus may penetrate its Oort cloud, if it has one,” he says.

This is interesting. Keep in mind that the Voyager and Pioneer spacecraft include the famous Golden Records and plaques (respectively), revealing the location, form, and culture of a civilization living on a planet called “Earth.” For an alien intelligence to stumble across one of our long-dead spacecraft in the distant future, the closer the stellar encounter the better (after all, the likelihood of stumbling across a tiny spacecraft in the vast interstellar expanse would be infinitesimally small). Passing within one light-year of TYC 3135-52-1 is still quite distant (for instance, we currently have no way of detecting something as dinky as a Voyager-size probe zooming through the solar system’s Oort Cloud), but who knows what the hypothetical aliens in TYC 3135-52-1 are capable of detecting from their home world?

The Pioneer plaque is attached to the spacecrafts’ antenna support struts, behind Pioneer 10 and 11’s dish antennae, shielding the plaques from erosion by interstellar dust [NASA]

Another interesting thought is that these Gaia observations can help astronomers find stars that are currently very far away, but now we know their speed and direction of travel, some of those stars will be in our cosmic backyard in the distant future.

“What our study also found, for the first time, is some stars that are currently quite distant from the Sun will nonetheless come very close to one of the spacecraft within the next few million years,” says Bailer-Jones. “For example, the star Gaia DR2 2091429484365218432 is currently 159.5 parsecs [520 light-years] from the Sun (and thus from Voyager 1), but Voyager 1 will pass within 0.39 parsecs [1.3 light-years] of it in 3.4 million years from now.”

In some cases, given unlimited time, you may not have to go to a star, the star will come to you!

Our Interstellar Future?

While pinpointing the various stellar encounters for our first interstellar probes is interesting, the observations being made by Gaia will be important for when humanity develops the technology to make a dedicated effort to travel to the stars.

“It will be essential to have extremely precise astrometry of any target star,” explains Bailer-Jones. “We must also measure its velocity and its acceleration precisely, because these affect where the star will be when the spacecraft arrives.”

Although this scenario may seem a long way off, any precision astrometry we do now will build our knowledge of the local stellar population and boost the “legacy value” of Gaia’s observations, he adds.

“Once a target star has been selected, we would want to make a dedicated campaign to measure its position and velocity even more precisely, but to determine the accelerations we need data measured at many time points over long periods (at least tens of years), so Gaia data will continue to be invaluable in the future,” Bailer-Jones concludes.

“Even now, astrometry from the previous Hipparcos mission—or even from surveys from decades ago or photometric plates 100 years ago!—are important for this.”

An artist’s impression of the Icarus Interstellar probe, a concept for a fusion-powered, un-crewed starship that may be used to travel to the stars [Icarus Interstellar/Adrian Mann]

Update (May 23): One of the reasons why I focused on the Voyager missions and not the Pioneers is because the latter stopped transmitting a long time ago. Another reason is because we already know Pioneer 10 doesn’t make it very far into interstellar space:

For more on how Gaia observations are being used, see my previous interview with Coryn on how these data were used to find the possible origins of ‘Oumuamua, the interstellar comet.

Voyager 2 Has Left the (Interplanetary) Building

The NASA probe was launched in 1977 and has now joined its twin, Voyager 1, to begin a new chapter of interstellar discovery

Both Voyager 1 and 2 are sampling particles from the interstellar medium, becoming humanity’s furthest-flung missions into deep space [NASA/JPL-Caltech]

Carolyn Porco, planetary scientist and lead of the NASA Cassini mission imaging team, probably said it best:

Voyager 1 made us an interstellar species; 6 yrs later, Voyager 2 makes it look easy. While these are historic, soul-stirring achievements, I am most happy right now that Ed Stone, the best Project Scientist who ever lived, lived to see this moment.
via Twitter

It can be easy to lump today’s announcement about Voyager 2 entering interstellar space as “simply” another magnificent science achievement for NASA — but that would be too narrow; the Voyager spacecraft have become so much more. They represent humanity at our best; our will to explore, our need to push boundaries, our excitement for expanding the human experience far beyond terrestrial shores. They also act as a means to understand the sheer scale of our solar system. And what better way to measure that scale than with a human life.

Ed Stone started working on the Voyager Program in 1972 as a project scientist. Now, at 82 years old, he’s still working on the Voyagers nearly half a century later as they continue to send back data from the frontier beyond our solar system. When we start measuring space missions in half-centuries, or missions that have lasted entire careers, it becomes clear how far we’ve come. Not only does NASA build really tough space robots that surpass expectations routinely, returning new discoveries and revelations about the universe that surrounds us, the Voyagers have become a monument to the essence of being human, something with which Stone would probably agree.

Although most of the instruments aboard the Voyagers are no longer functional, both missions are still returning data from the shores of the interstellar ocean and, on Nov. 5, mission controllers noticed that one of Voyager 2’s instruments, the Plasma Science Experiment (PSE), had detected a rapid change in its surrounding environment. Used to being immersed the comparatively warm and tenuous solar wind flowing past it, its plasma measurements detected a change. The spacecraft had passed into a region of space where the plasma was now denser and cooler. Three other particle experiments also detected a dramatic change; solar wind particle counts were down, but cosmic ray counts precipitously increased. Voyager 1’s PSE failed in 1980, so couldn’t measure this boundary when it entered interstellar space in 2012, so Voyager 2 is adding more detail about what we can expect happens when a spacecraft travels from the heliosphere, through the heliopause and into interstellar space.

“There is still a lot to learn about the region of interstellar space immediately beyond the heliopause,” said Stone in a NASA statement.

The heliosphere can be imagined as a vast magnetized bubble that is generated by the Sun. This bubble is inflated by the solar wind, a persistent stream of solar particles that ebb and flow with the Sun’s 11-year cycle. When the Sun is at its most active, the bubble expands; at its least active, it contracts. This dynamic solar sphere of influence affects the flux of high-energy cosmic rays entering the inner solar system, but the physics at this enigmatic boundary is poorly understood. With the help of the Voyagers, however, we’re getting an in-situ feel for the plasma environment at the boundary of where the Sun’s magnetism hits the interstellar medium.

To achieve this, however, we had to rely on two spacecraft that were launched before I was born, in 1977. Voyager 2 is now 11 billion miles away (Voyager 1 is further away, at nearly 14 billion miles) and it took the probe 41 years just to reach our interstellar doorstep. Neither Voyagers have “left” the solar system, not by a long shot. The gravitational boundary of the solar system is thought to lie some 100,000 AU (astronomical units, where one AU is the average distance from the Earth to the Sun), the outermost limit to the Oort Cloud — a region surrounding the solar system that contains countless billions of icy objects, some of which become the long-period comets that intermittently careen through the inner solar system. Voyager 2 is barely 120 AU from Earth, so as you can see, it has a long way to go (probably another 30,000 years) before it really leaves the solar system — despite what the BBC tells us.

So, tonight, as we ponder our existence on this tiny pale blue dot, look up and think of the two space robot pioneers that are still returning valuable data despite being in deep space for over four decades. I hope their legacy lives on well beyond the life of their radioactive generators, and that the next interstellar spacecraft (no pressure, New Horizons) lives as long, if not longer, than the Voyagers.

Was Voyager 2 Hijacked by Aliens? No.

The interstellar probes are still operational (NASA)

The Voyager 2 spacecraft has been speeding through the Solar System since 1977 and it’s seen a lot. Besides scooting past Jupiter, Saturn, Uranus and Neptune, the probe is now passing through the very limit of the heliosphere (called the heliopause) where it has begun to detect a magnetic field beyond the Solar System. The fact we have man-made objects exiting our star system is something that makes me goosebumpily.

For some perspective, Voyager 2 is so far away from Earth that it takes nearly 13 hours for commands sent from Earth to reach the probe.

After decades of travel, the NASA spacecraft continues to relay data back to us, making it one of the most profound and exciting space missions ever launched. Perhaps unsurprisingly, the aging explorer recently experienced a glitch and the data received by NASA was rather garbled.

Naturally, the conspiracy theorists were out in force quickly pointing their sticky fingers at a possible encounter of the 3rd kind. How these ‘aliens’ found the probe in the first place and reprogrammed the transmission for it to appear corrupt Earth-side is beyond me, but according to an ‘expert’ in Germany, aliens (with an aptitude for reprogramming 30 year old Earth hardware, presumably) were obviously to blame.

One of the alien implication articles came from yet another classic ‘science’ post thrown together by the UK’s Telegraph where they decided to take the word of a UFO expert (obviously a viable source) without any kind of counter-argument from a real expert of real science. (But this is the same publication that brought us other classics such as the skull on Mars and the Doomsday Turkey, so it’s not too surprising.)

As I discussed in a recent CRI English radio debate with Beyond Beijing hosts Chris Gelken and Xu Qinduo, the Voyager-alien implication is beyond funny; an entertaining sideline to poke fun at while NASA worked out what actually went wrong. But the big difference was that Chris and Xu had invited Seth Shostak (from the SETI Institute) and Douglas C. Lin (from the Kavli Institute for Astronomy and Astrophysics at Peking University) to join the fun. No UFO expert in sight, so the discussion was biased toward science and logic, not crazy talk.

(It was an awesome show by the way, and you can check out the recording via my Discovery News article.)

So what did happen to Voyager 2? It turns out that aliens are not required to answer this cosmic mystery.

On Tuesday, NASA announced that Voyager 2 had flipped one of its bits of memory the wrong way. “A value in a single memory location was changed from a 0 to a 1,” said JPL’s Veronia McGregor.

This glitch was thought to occur in the flight data system, which formats information for transmission to Earth. Should something go wonky in its memory allocation, the stuff it transmits can be turned into gibberish.

Although it isn’t known how this single bit was flipped (and we may never know, as Voyager 2 is an awful long way from home), it sounds very much like a cosmic ray event interfering with the onboard electronics. As cosmic rays are highly energetic charged particles, they can penetrate deep into computer systems, causing an error in calculations.

And this situation isn’t without precedent either. Recently, NASA’s Mars Reconnaissance Orbiter (MRO) was hit by a cosmic ray event, causing the onboard computer to switch to “safe mode.” Also, Voyager 2 is beginning to exit the Sun’s outermost sphere of influence, where turbulence and confused magnetic fields rule. If I had to guess, I’d say — statistically-speaking — the probe might have a greater chance of being hit by the most energetic cosmic rays from deep space.

Just because something “mysterious” happens in space doesn’t mean aliens, the Illuminati or some half-baked doomsday phenomenon caused it. Before jumping to conclusions it would be nice if certain newspapers and UFO experts alike could look at the most likely explanation before pulling the alien card.

Alas, I suspect that some things will never change.