There’s no two-ways about it, the Universe is an extremely big place! And thanks to the limitations placed upon us by Special Relativity, traveling to even the closest star systems could take millennia. As we addressed in a previous article, the estimated travel time to the nearest star system (Alpha Centauri) could take anywhere from 19,000 to 81,000 years using conventional methods.
For this reason, many theorists have recommended that humanity rely on generation ships to spread the seed of humanity among the stars. Naturally, such a project presents many challenges, not the least of which is how large a spacecraft would need to be to sustain a multi-generational crew. In a new study, of international scientists addressed this very question and determined that a lot of interior space would be needed!
On August 25th, 2012, the Voyager 1 spacecraft accomplished something no human-made object ever had before. After exploring the Uranus, Neptune, and the outer reaches of the Solar System, the spacecraft entered interstellar space. In so doing, it effectively became the most distant object from Earth and traveled further than anyone, or anything, in history.
Well, buckle up, because according to NASA mission scientists, the Voyager 2 spacecraft recently crossed the outer edge of the heliopause – the boundary between our Solar System and the interstellar medium – and has joined Voyager 1 in interstellar space. But unlike its sibling, the Voyager 2 spacecraft carries a working instrument that will provide the first-ever observations of the boundary that exists between the Solar System and interstellar space.
Over the course of many centuries, scientists learned a great deal about the types of conditions and elements that make life possible here on Earth. Thanks to the advent of modern astronomy, scientists have since learned that these elements are not only abundant in other star systems and parts of the galaxy, but also in the medium known as interstellar space.
Consider carbon, the element that is essential to all organic matter and life as we know it. This life-bearing element is also present in interstellar dust, though astronomers are not sure how abundant it is. According to new research by a team of astronomers from Australia and Turkey, much of the carbon in our galaxy exists in the form of grease-like molecules.
Their study, “Aliphatic Hydrocarbon Content of Interstellar Dust“, recently appeared in the Monthly Notices of the Royal Astronomical Society. The study was led by Gunay Banihan, a professor from the Department of Astronomy and Space Sciences of Erge University in Turkey, and included members from multiple departments from the University of New South Wales in Sydney (UNSW).
For the sake of their study, the team sought to determine exactly how much of our galaxy’s carbon is bound up in grease-like molecules. At present, it is believed that half of the interstellar carbon exists in pure form, whereas the rest in bound up in either grease-like aliphatic molecules (carbon atoms that form open chains) and mothball-like aromatic molecules (carbon atoms that form planar unsaturated rings).
To determine how plentiful grease-like molecules are compared to aromatic ones, the team created material with the same properties as interstellar dust in a laboratory. This consisted of recreating the process where aliphatic compounds are synthesized in the outflows of carbon stars. They then followed up on this by expanding the carbon-containing plasma into a vacuum at low temperatures to simulate interstellar space.
“Combining our lab results with observations from astronomical observatories allows us to measure the amount of aliphatic carbon between us and the stars.”
Using magnetic resonance and spectroscopy, they were then able to determine how strongly the material absorbed light with a certain infrared wavelength. From this, the team found that there are about 100 greasy carbon atoms for every million hydrogen atoms, which works out to about half of the available carbon between stars. Expanding that to include all of the Milky Way, they determined that about 10 billion trillion trillion tonnes of greasy matter exists.
To put that in perspective, that’s enough grease to fill about 40 trillion trillion trillion packs of butter. But as Schmidt indicated, this grease is far from being edible.
“This space grease is not the kind of thing you’d want to spread on a slice of toast! It’s dirty, likely toxic and only forms in the environment of interstellar space (and our laboratory). It’s also intriguing that organic material of this kind – material that gets incorporated into planetary systems – is so abundant.”
Looking ahead, the team now wants to determine the abundance of the other type of non-pure carbon, which is the mothball-like aromatic molecules. Here too, the team will be recreating the molecules in a laboratory environment using simulations. By establishing the amount of each type of carbon in interstellar dust, they will be able to place constraints on how much of this elements is available in our galaxy.
This in turn will allow astronomers to determine exactly how much of this life-giving element is available, and could also help shed light on how and where life can take hold!
The Milky Way is an extremely big place. Measured from end to end, our galaxy in an estimated 100,000 to 180,000 light years (31,000 – 55,000 parsecs) in diameter. And it is extremely well-populated, with an estimated 100 to 400 million stars contained within. And according to recent estimates, it is believed that there are as many as 100 billion planets in the Milky Way. And our galaxy is merely one of trillions within the Universe.
So if we were to break it down, just how much matter would we find out there? Estimating how much there is overall would involve some serious math and incredible figures. But what about a single light year? As the most commonly-used unit for measuring the distances between stars and galaxies, determining how much stuff can be found within a single light year (on average) is a good way to get an idea of how stuff is out there.
Even though the name is a little confusing, you probably already know that a light year is the distance that light travels in the space of a year. Given that the speed of light has been measured to 299,792, 458 m/s (1080 million km/h; 671 million mph), the distance light travels in a single year is quite immense. All told, a single light year works out to 9,460,730,472,580.8 kilometers (5,878,625,373,183.6 mi).
So to determine how much stuff is in a light year, we need to take that distance and turn it into a cube, with each side measuring one light year in length. Imagine that giant volume of space (a little challenging for some of us to get our heads around) and imagine just how much “stuff” would be in there. And not just “stuff”, in the sense of dust, gas, stars or planets, either. How much nothing is in there, as in, the empty vacuum of space?
There is an answer, but it all depends on where you put your giant cube. Measure it at the core of the galaxy, and there are stars buzzing around all over the place. Perhaps in the heart of a globular cluster? In a star forming nebula? Or maybe out in the suburbs of the Milky Way? There’s also great voids that exist between galaxies, where there’s almost nothing.
Density of the Milky Way:
There’s no getting around the math in this one. First, let’s figure out an average density for the Milky Way and then go from there. Its about 100,000 to 180,000 light-years across and 1000 light-years thick. According to my buddy and famed astronomer Phil Plait (of Bad Astronomy), the total volume of the Milky Way is about 8 trillion cubic light-years.
And the total mass of the Milky Way is 6 x 1042 kilograms (that’s 6,000 trillion trillion trillion metric tons or 6,610 trillion trillion trillion US tons). Divide those together and you get 8 x 1029 kilograms (800 trillion trillion metric tons or 881.85 trillion trillion US tons) per light year. That’s an 8 followed by 29 zeros. This sounds like a lot, but its actually the equivalent of 0.4 Solar Masses – 40% of the mass of our Sun.
In other words, on average, across the Milky Way, there’s about 40% the mass of the Sun in every cubic light year. But in an average cubic meter, there’s only about 950 attograms, which is almost one femtogram (a quadrillionth of a gram of matter), which is pretty close to nothing. Compare this to air, which has more than a kilogram of mass per cubic meter.
To be fair, in the densest regions of the Milky Way – like inside globular clusters – you can get densities of stars with 100, or even 1000 times greater than our region of the galaxy. Stars can get as close together as the radius of the Solar System. But out in the vast interstellar gulfs between stars, the density drops significantly. There are only a few hundred individual atoms per cubic meter in interstellar space.
And in the intergalactic voids; the gulfs between galaxies, there are just a handful of atoms per meter. Like it or not, much of the Universe is pretty close to being empty space, with just trace amounts of dust or gas particles to be found between all the stars, galaxies, clusters and super clusters.
So how much stuff is there in a light year? It all depends on where you look, but if you spread all the matter around by shaking the Universe up like a snow globe, the answer is very close to nothing.
Given that our Solar System sits inside the Milky Way Galaxy, getting a clear picture of what it looks like as a whole can be quite tricky. In fact, it was not until 1852 that astronomer Stephen Alexander first postulated that the galaxy was spiral in shape. And since that time, numerous discoveries have come along that have altered how we picture it.
For decades astronomers have thought the Milky Way consists of four arms — made up of stars and clouds of star-forming gas — that extend outwards in a spiral fashion. Then in 2008, data from the Spitzer Space Telescope seemed to indicate that our Milky Way has just two arms, but a larger central bar. But now, according to a team of astronomers from China, one of our galaxy’s arms may stretch farther than previously thought, reaching all the way around the galaxy.
This arm is known as Scutum–Centaurus, which emanates from one end of the Milky Way bar, passes between us and Galactic Center, and extends to the other side of the galaxy. For many decades, it was believed that was where this arm terminated.
However, back in 2011, astronomers Thomas Dame and Patrick Thaddeus from the Harvard–Smithsonian Center for Astrophysics spotted what appeared to be an extension of this arm on the other side of the galaxy.
But according to astronomer Yan Sun and colleagues from the Purple Mountain Observatory in Nanjing, China, the Scutum–Centaurus Arm may extend even farther than that. Using a novel approach to study gas clouds located between 46,000 to 67,000 light-years beyond the center of our galaxy, they detected 48 new clouds of interstellar gas, as well as 24 previously-observed ones.
For the sake of their study, Sun and his colleagues relied on radio telescope data provided by the Milky Way Imaging Scroll Painting project, which scans interstellar dust clouds for radio waves emitted by carbon monoxide gas. Next to hydrogen, this gas is the most abundant element to be found in interstellar space – but is easier for radio telescopes to detect.
Combining this information with data obtained by the Canadian Galactic Plane Survey (which looks for hydrogen gas), they concluded that these 72 clouds line up along a spiral-arm segment that is 30,000 light-years in length. What’s more, they claim in their report that: “The new arm appears to be the extension of the distant arm recently discovered by Dame & Thaddeus (2011) as well as the Scutum-Centaurus Arm into the outer second quadrant.”
This would mean the arm is not only the single largest in our galaxy, but is also the only one to effectively reach 360° around the Milky Way. Such a find would be unprecedented given the fact that nothing of the sort has been observed with other spiral galaxies in our local universe.
Thomas Dame, one of the astronomers who discovered the possible extension of the Scutum-Centaurus Arm in 2011, was quoted by Scientific American as saying: “It’s rare. I bet that you would have to look through dozens of face-on spiral galaxy images to find one where you could convince yourself you could track one arm 360 degrees around.”
Naturally, the prospect presents some problems. For one, there is an apparent gap between the segment that Dame and Thaddeus discovered in 2011 and the start of the one discovered by the Chinese team – a 40,000 light-year gap to be exact. This could mean that the clouds that Sun and his colleagues discovered may not be part of the Scutum-Centaurus Arm after all, but an entirely new spiral-arm segment.
If this is true, than it would mean that our Galaxy has several “outer” arm segments. On the other hand, additional research may close that gap (so to speak) and prove that the Milky Way is as beautiful when seen afar as any of the spirals we often observe from the comfort of our own Solar System.
Wow! Even from interstellar space, the plucky Voyager 1 can still listen in to activities from our Sun. Whenever the Sun has a large amount of activity, the waves of energy it sends out bashes into the charged gas particles or plasma surrounding the NASA spacecraft, which has been sailing away from Earth since 1977.
There have been three events so far from our Sun (which is in solar maximum), with each one confirming scientists’ findings that interstellar space is where the spacecraft is, NASA said.
“Normally, interstellar space is like a quiet lake,” stated Voyager project scientist Ed Stone of the California Institute of Technology. “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.”
“The tsunami wave rings the plasma like a bell,” added 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.”
The discovery of this wave front confirms the previous assertion that Voyager 1 is indeed in interstellar space, NASA added. Winds from the sun push against the plasma at the edge of interstellar space, making it denser (40 times denser than what was measured before Voyager reached the milestone in 2012, in fact.)
NASA’s announcement in 2013 that Voyager 1 is in interstellar space was accompanied by intense discussion about whether it is in or out of the Solar System (it still hasn’t reached the shell of the Oort Cloud that hosts comets, a milestone that won’t be possible for 300 years). Prior to the announcement, several scientific papers had also weighed in on Voyager 1’s status, with some saying it was interstellar space and some not.
Yesterday, NASA announced that as of August 2012, Voyager 1 is in a new frontier to humanity: interstellar space. Our most distant spacecraft is now in a region where the plasma (really hot gas) environment comes more from between the stars than from the sun itself. (There’s still debate as to whether it’s in or out of the solar system, as this article explains.)
The plucky spacecraft is close to 12 billion miles (19 million kilometers) from home, and in its 36 years of voyaging has taught us a lot about the planets, their moons and other parts of space. Here are 10 of some of its most historic moments. Did we miss any? Let us know in the comments.
10. The launch: Aug. 20, 1977
Voyager 1 blasted off from Cape Canaveral on Sept. 5, 1977. Its twin, Voyager 2, departed Earth 16 days earlier. Each spacecraft carried various scientific instruments on board as well as a “Golden Record” that had sounds of Earth on it, as well as a diagram showing where Earth is in the universe.
9. Capturing the Earth and Moon together for the first time
About two weeks after launching, Voyager 1 turned back towards Earth and took three images, which were combined into this single view of the Earth and Moon together in space. This was the first time both bodies were pictured together, NASA said.
8. The ‘Pale Blue Dot’ image
On February 14, 1990, Voyager 1 was about 3.7 billion miles (6 billion kilometers) away from Earth. Scientists commanded the spacecraft to turn its face towards the solar system and snap some pictures of the planets. Among them was this famous image of Earth, which astronomer Carl Sagan called the Pale Blue Dot. “Look again at that dot. That’s here. That’s home. That’s us,” wrote Sagan in his 1997 book of the same name. In 2013, the spacecraft Cassini also took a picture of Earth, and NASA encouraged everyone to wave back.
7. Finding moons “shepherding” Saturn’s F ring
Voyager 1 spotted Prometheus and Pandora, two moons of Saturn that keep the F ring separate from the rest of the debris, as well as Atlas, which “shepherds” the A ring. More recently, astronomers have found even more interesting things in Saturn’s rings — such as rain.
6. Spotting what appeared to be a LOT of water ice on Saturn’s moons
After many years of seeing Saturn’s moons as mere points of light, Voyager 1 buzzed several of them in its quick flyby through the system: Dione, Enceladus, Mimas, Rhea, Tethys and Titan among them. Many of these moons appeared to be icy, which was a surprising find since astronomers previously thought water was pretty rare in the Solar System. We know better now.
5. Imaging Titan’s orange haze
Voyager 1 pictures such as this tortured astronomers for decades — what lies beneath this mysterious haze surrounding Titan, Saturn’s moon? That mystery, in fact, inspired the European Space Agency to send a lander to the moon, called Huygens, which successfully reached the surface in 2005.
4. Finding active volcanoes on Io
Voyager 1 helped show us that the Solar System is full of very interesting moons. At Io — a moon of Jupiter — it turns out the moon flexes during its 42-hour orbit of massive Jupiter, which powers a lot of volcanic activity.
3. Voyager 1 becomes the most distant human object
On Feb. 17, 1998, Voyager 1’s distance surpassed that of another long-flying probe, Pioneer 10. This made Voyager 1 the farthest-flung human object in space.
2. Riding the “magnetic highway”
In December, NASA said Voyager 1 had reached an area (as of July 28, 2012) where high-energy magnetic particles were starting to bleed through the bubble of lower-energy particles from our sun. “Voyager’s discovered a new region of the heliosphere that we had not realized was there. It’s a magnetic highway where the magnetic field of the Sun is connected to the outside. So it’s like a highway, letting particles in and out,” said project scientist Ed Stone at the time. After that point, as more measurements were analyzed by different teams, there was a lot of debate as to whether Voyager had reached interstellar space.
1. Reaching interstellar space
With Voyager 1 now known to be in interstellar space, we’re lucky enough to have a few years left to communicate with it before it runs out of power. All of the instruments will be turned off by 2025, and then engineering data will be available for about 10 years beyond that. The silent emissary from humanity will then come within 1.7 light years of an obscure star in the constellation Ursa Minor (the Little Bear) called AC+79 3888 in the year 40,272 AD and then orbit the center of the Milky Way for millions of years.
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.
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.”
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.”
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.”
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.