Voyager 1 and 2: Now, we know a little better the fate of the probes!
Incredible Voyager 1 and 2!
Years and decades pass by, but not a month goes by that the two most popular interplanetary
probes in the world don't make people talk about them...
Astronomers seem literally unable to let them go, to resign themselves to losing them...
and so, even when the signals and the incoming data become more and more scarce, they continue
to chase them with their calculations, scrutinizing from afar the fate they are going to meet.
As in this case, where they even talk about the state of preservation of that message
in a bottle that the two probes carry within themselves, like a hope.
Predicting future events can be a very slippery topic to treat, but sometimes physics and
maths can help.
And while the future of each of us remains completely unpredictable, that of two interplanetary
probes seemingly destined to get lost in space can instead be anticipated with surprisingly
plausible details.
We can, for example, not only reconstruct the trajectory of two probes that are fleeing
from the Sun, accurately calculating their future encounters with other stars, but also
describe their gradual deterioration, including what precious things they carry inside, simply
by hypothesizing which region of our galaxy they will pass through.
The amount of interstellar dust they will encounter will in fact make a difference,
as will their dolphin-like sway above and below the equatorial plane of the galaxy.
And that's what he tried to do Nick Oberg, Ph.D. student at the Kapteyn Astronomical
Institute in the Netherlands, who wanted to try to improve the reliability and accuracy
of the next stellar encounters of the Voyager probes in his work recently presented at the
237th meeting of the American Astronomical Society.
But not only ... the Dutch astronomer also wanted to try to understand how long the famous
gold discs that the two spacecraft carry on board would be preserved so that they could
be read by some extraterrestrial civilization that had collected them.
You know what we are talking about, right?
NASA launched Voyager 1 and Voyager 2 in 1977 to trek across the Solar system.
On each was a 30 centimeters large gold-plated copper disk.
The brainchild of famed astronomer Carl Sagan, the Golden Records were engraved with music
and photographs meant to represent Earth and its humans to any intelligent beings the spacecraft
meet on their long journeys.
Both spacecraft visited Jupiter and Saturn, then the twins parted ways: Voyager 1 studied
Saturn's moon Titan while Voyager 2 swung past Uranus and Neptune.
In 2012, Voyager 1 passed through the heliopause that marks the edge of the sun's solar wind
and entered interstellar space; in 2018, Voyager 2 did so as well.
Now, the two spacecraft are chugging through the vast outer reaches of the Solar system.
They continue to send signals back to Earth, updating humans about their adventures far
beyond the planets, although those bulletins may cease in a few years, as the spacecraft
are both running low on power.
But their journeys are far from over.
Oberg combined tracking the Voyagers' trajectories forward with studying the environments the
spacecraft will fly through to estimate the odds of the Golden Records surviving their
adventures while remaining legible.
The result is a forecast that stretches beyond not just humanity's likely extinction, but
also beyond the collision of the Milky Way with the neighboring Andromeda galaxy - beyond
even the extinction of most stars.
Unsurprisingly, his research ambitions didn't start out quite so vast.
The new research was inspired by the release of the second batch of data from the European
Space Agency's spacecraft Gaia, which specializes in mapping more than a billion stars super
precisely.
"Our original goal was to determine with a very high precision which stars the Voyagers
might one day closely encounter using the at the time newly released Gaia catalog of
stars," Oberg said during his presentation.
So he and his co-author began by tracing the Voyagers' journeys to date and projecting
their trajectories out into the future.
But don't get excited for any upcoming milestones.
Not until about 20,000 years from now will the Voyagers pass through the Oort cloud — the
shell of comets and icy rubble that orbits the sun at a distance of up to 100,000 astronomical
units, or 100,000 times the average Earth-sun distance — finally waving goodbye to its
solar system of origin.
"At that point for the first time the craft will begin to feel the gravitational pull
of other stars more strongly than that of our own sun," Oberg said.
It's another 10,000 years before the spacecraft actually come near an alien star, specifically
a red dwarf star called Ross 248.
That flyby will occur about 30,000 years from now, Oberg said, although it might be a stretch
to say that the spacecraft will pass by that star.
"It's actually more like Ross 248 shooting past the nearly stationary Voyagers," he said.
These calculations are tricky, because as these spacecraft travel away from Earth, the
cosmos around them move, too.
Oberg and his colleague have found the spacecraft's destinations by using the 3D positions and
3D velocities of 7.2 million stars.
In the new study, Oberg calculated that the next star that Voyager 1 will pass will be
Earth's nearest stellar neighbor, Proxima Centauri, in 16,700 years.
However, this encounter will be unremarkable, as the craft's closest approach will be 3.6
light-years… very, very far away.
In fact, Voyager 1 is currently 4.24 light-years from the star, so this encounter won't be
much closer than the craft's current location is.
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These distant encounters might not generate excitement.
But Oberg predicts other future flybys in which the spacecraft will get remarkably close
to stars outside our solar system.
For example, Voyager 1 will get very close to the star TYC 3135-52-1, a star located
about 46.9 light-years from our sun, in 302,700 years.
The craft will pass within 0.9 light-year, so close that the spacecraft might penetrate
the star's Oort cloud, which is a shell of cosmic objects that surround a star past its
planets, if it has one...
Additionally, the researcher found that Voyager 1 will swing close, within 1.27 light-years,
of Gaia star that lies a whopping 520.22 light-years from the sun.
They predicted that the craft will pass close to this faraway star in 3.4 million years...
By 500 million years from now, the solar system and the Voyagers alike will complete a full
orbit through the Milky Way.
There's no way to predict what will have happened on Earth's surface by then, but it's a timespan
on the scale of the formation and destruction of Pangaea and other supercontinents, Oberg
said.
Throughout this galactic orbit, the Voyager spacecraft will oscillate up and down, with
Voyager 1 doing so more dramatically than its twin.
According to these models, Voyager 1 will travel so far above the main disk of the galaxy
that it will see stars at just half the density as we do.
The same difference in vertical motion will also shape the differing odds each spacecraft's
Golden Record has of survival.
The records were designed to last, meant to survive perhaps a billion years in space:
beneath the golden sheen is a protective aluminum casing and, below that, the engraved copper
disks themselves.
But to truly understand how long these objects may survive, you have to know what conditions
they'll experience, and that means knowing where they will be.
Specifically, Oberg and his colleague needed to know how much time the spacecraft would
spend swathed in the Milky Way's vast clouds of interstellar dust, which he called "one
of the few phenomena that could actually act to damage the spacecraft."
It's a grim scenario, dust pounding into the Voyagers at a speed of a few miles or kilometers
per second.
"The grains will act as a steady rain that slowly chips away at the skin of the spacecraft,"
Oberg said.
"A dust grain only one-thousandth of a millimeter across will still leave a small vaporized
crater when it impacts."
Voyager 1's vertical oscillations mean that spacecraft will spend more time above and
below the plane of the galaxy, where the clouds are thickest.
Oberg and his colleague simulated thousands of times over the paths of the two spacecraft
and their encounters with the dust clouds, modeling the damage the Golden Records would
incur along the way.
That work also requires taking into consideration the possibility that a cloud's gravity might
tug at one of the Voyagers' trajectories, Oberg said.
"The clouds have so much mass concentrated in one place that they actually may act to
bend the trajectory of the spacecraft and fling them into new orbits… sometimes much
farther out, sometimes even deeper toward the galactic core."
Both Golden Records have good odds of remaining legible since their engraved sides are tucked
away against the spacecraft bodies.
The outer surface of Voyager 1's record is more likely to erode away, but the information
on Voyager 2's record is more likely to become illegible, Oberg said.
"The main reason for this is because the orbit that Voyager 2 is flung into is more chaotic,
and it's significantly more difficult to predict with any certainty of exactly what sort of
environment it's going to be flying through," he said.
But despite the onslaught and potential detours, "Both Golden Records are highly likely to
survive at least partially intact for a span of over 5 billion years," Oberg said.
After those 5 billion years, modeling is quite impossible.
That's when the Milky Way is due to collide with its massive neighbor, the Andromeda galaxy,
and things get messy.
"The orderly spiral shape will be severely warped, and possibly destroyed entirely,"
Oberg said.
The Voyagers will be caught up in the merger, with the details difficult to predict so far
in advance.
Meanwhile, the vicarious sightseeing continues.
Oberg and his colleague calculated that in this 5-billion-year model-friendly period,
each of the Voyagers likely visits a star besides our sun within about 150 times the
distance between Earth and the sun, or three times the distance between the sun and Pluto
at the dwarf planet's most distant point.
Precisely which star that might be, however, very difficult.
It may not even be, infact, a star we know today.
"While neither Voyager is likely to get particularly close to any star before the galaxies collide,
the craft are likely to at least pass through the outskirts of some star system," Oberg
said.
"The very strange part is that that actually might be a system that does not yet exist,
of a star that has yet to be born."
Such are the perils of working on a scale of billions of years.
From here, the Voyagers' fate depends on the conditions of the galactic merger, Oberg said.
The collision itself might kick a spacecraft out of the newly monstrous galaxy - a one
in five chance, he said - although it would remain stuck in the neighborhood.
If that occurs, the biggest threat to the Golden Records would become collisions with
high-energy cosmic rays and the odd molecule of hot gas, Oberg said; these impacts would
be rarer than the dust that characterized their damage inside the Milky Way.
Inside the combined galaxy, the Voyagers' fate would depend on how much dust is left
behind by the merger; Oberg said that may well be minimal as star formation and explosion
both slow, reducing the amount of dust flung into the galaxy.
Depending on their luck with this dust, the Voyagers may be able to ride out trillions
of trillions of trillions of years, long enough to cruise through a truly alien cosmos, Oberg
said.
"Such a distant time is far beyond the point where stars have exhausted their fuel and
star formation has ceased in its entirety in the universe," he said.
"The Voyagers will be drifting through what would be, to us, a completely unrecognizable
galaxy, free of so-called main-sequence stars, populated almost exclusively by black holes
and stellar remnants such as white dwarfs and neutron stars."
It's a dark future, Oberg added.
"The only source of significant illumination in this epoch will be supernovas that results
from the once-in-a-trillion-year collision between these stellar remnants that still
populate the galaxy," he said.
"Our work, found on these records, thus may bear witness to these isolated flashes in
the dark."
Will the spacecraft ever collide with a star, thus ending their travels permanently?
Maybe.
But if so, it won’t likely be for a long, long, long time..like, nearly twice the current
age of the universe.
So, even if our species is gone, our spacecraft will wander on.
And maybe one of them will find its way into the “arms” of some other civilization,
who’ll unpack a Voyager Golden Record, marvel at the bizarre anatomies of us ancient aliens,
and get a kick out of Chuck Berry singing “Johnny B. Goode.”