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Voyager – the journey continues

AFTER 33 YEARS, NASA’s twin Voyager spacecraft are still going strong and still sending home information. This video features highlights of the Voyager journeys to the outer planets, and looks at their current status, at the edge of our Solar System, poised to cross over into interstellar space.

Adapted from information issued by NASA / JPL.

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Voyager sees solar wind run out of puff

Artist's impression of the heliosphere

Artist's impression of the bubble—the heliosphere—blown in interstellar space by the solar wind. The Voyager 1 spacecraft is soon to cross the boundary into interstellar space.

  • Voyager 1 launched on September 5, 1977
  • The most distant spacecraft from Earth – 17.4 billion km
  • Now exploring the boundary between Solar System and interstellar space

The 33-year-long odyssey of NASA’s Voyager 1 spacecraft has reached a new milestone…a distant point at the edge of our Solar System where there is no outward motion of solar wind.

The solar wind is a stream of hot ionised gas, or plasma, emanating directly outward from the Sun. It forms a bubble—known as the heliosphere—around our Solar System. The solar wind travels at supersonic speed until it crosses a shockwave called the termination shock. At this point, the wind dramatically slows down and heats up in the heliosheath.

Outside the bubble lies true interstellar space, through which blows a gentle “interstellar wind”.

Now hurtling toward that interstellar space some 17.4 billion kilometres from the Sun, Voyager 1 has crossed into an area where the solar wind speed has slowed to zero.

Scientists suspect the solar wind has been turned sideways by the pressure from the interstellar wind.

The event is a major landmark in Voyager 1’s passage through the heliosheath, the turbulent outer shell of the Sun’s sphere of influence, and the spacecraft’s upcoming departure from our Solar System.

Voyager spacecraft

The twin Voyager spacecraft were launched in 1977 to investigate the outer planets of the Solar System.

“The solar wind has turned the corner,” said Ed Stone, Voyager project scientist based at the California Institute of Technology. “Voyager 1 is getting close to interstellar space.”

Voyager shows us something new

Launched on September 5, 1977, Voyager 1 crossed a region called the termination shock in December 2004 into the heliosheath. Scientists have used data from Voyager 1’s Low-Energy Charged Particle Instrument to deduce the solar wind’s velocity.

When the speed of the charged particles hitting the outward face of Voyager 1 matched the spacecraft’s speed, researchers knew that the net outward speed of the solar wind was zero. This occurred in June, when Voyager 1 was about 17 billion kilometres from the Sun.

Because the velocities can fluctuate, scientists gathered four more monthly readings before they were convinced the solar wind’s outward speed actually had slowed to zero.

Analysis of the data shows the velocity of the solar wind has steadily slowed at a rate of about 72,400 kph each year since August 2007, when the solar wind was speeding outward at about 209,000 kph. The outward speed has remained at zero since June.

The results were presented at the American Geophysical Union meeting in San Francisco.

“When I realised that we were getting solid zeroes, I was amazed,” said Rob Decker, a Voyager Low-Energy Charged Particle Instrument co-investigator and senior staff scientist at the Johns Hopkins University Applied Physics Laboratory.

“Here was Voyager, a spacecraft that has been a workhorse for 33 years, showing us something completely new again.”

Entering a new frontier

Scientists think Voyager 1 has not crossed the heliosheath into interstellar space. Crossing into interstellar space would mean a sudden drop in the density of hot particles and an increase in the density of cold particles.

Researchers are putting the data into their models of the heliosphere’s structure and should be able to better estimate when Voyager 1 will reach interstellar space.

They currently estimate Voyager 1 will cross that frontier in about four years.

Diagram of Voyager and Pioneer spacecraft positions

Where are they now? Positions of the two Voyager spacecraft, and Pioneers 10 and 11. Voyager 1 (bottom right corner) is the most distant.

“In science, there is nothing like a reality check to shake things up, and Voyager 1 provided that with hard facts,” said Tom Krimigis, principal investigator on the Low-Energy Charged Particle Instrument, who is based at the Applied Physics Laboratory and the Academy of Athens, Greece.

“Once again, we face the predicament of redoing our models.”

A sister spacecraft, Voyager 2, was launched in August 20, 1977 and has reached a position 14.2 billion kilometres from the Sun.

Both spacecraft have been travelling along different trajectories and at different speeds. Voyager 1 is travelling faster, at a speed of about 61,100 kph, compared to Voyager 2’s velocity of 56,300 kph.

In the next few years, scientists expect Voyager 2 to encounter the same kind of phenomenon as Voyager 1.

The Voyagers were built by NASA’s Jet Propulsion Laboratory, which continues to operate both spacecraft.

Adapted from information issued by NASA / JPL.

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Life on Titan: up in the air?

Titan, Epimetheus and Saturn's rings

Saturn's moon Titan looms large behind the planet's rings. (A smaller moon, Epimetheus, is in the foreground.) Chemical reactions in Titan's upper atmosphere could form molecules that are the precursor of life.

  • Titan’s atmosphere simulated in the lab
  • Chemical reactions produce amino acids
  • Key ingredients for life as we know it

While simulating possible chemical processes that could occur in the hazy atmosphere of Titan, Saturn’s largest moon, a University of Arizona-led planetary research team found amino acids and nucleotide bases in the mix—the most important ingredients of life on Earth.

“Our team is the first to be able to do this in an atmosphere without liquid water. Our results show that it is possible to make very complex molecules in the outer parts of an atmosphere,” said Sarah Hörst, a graduate student in the University of Arizona’s (UA) Lunar and Planetary Lab, who led the international research effort together with her adviser, planetary science professor Roger Yelle.

The molecules discovered include the five nucleotide bases used by life on Earth to build the genetic materials DNA and RNA: cytosine, adenine, thymine, guanine and uracil, and the two smallest amino acids, glycine and alanine. Amino acids are the building blocks of proteins.

Reaction chamber

A window into Titan’s atmosphere: Energised by microwaves, the gas mix inside the reaction chamber lights up like a pink neon sign. Thousands of complex organic molecules accumulated on the bottom of the chamber during this experiment.

The results suggest not only that Titan’s atmosphere could be a reservoir of pre-biotic molecules that serve as the springboard to life, but they offer a new perspective on the emergence of terrestrial life as well: Instead of coalescing in a primordial soup, the first ingredients of life on our planet may have rained down from a primordial haze high in the atmosphere.

Oddball of the Solar System

Titan has fascinated—and puzzled—scientists for a long time.

“It’s is the only moon in our Solar System that has a substantial atmosphere,” Hörst said. “Its atmosphere stretches out much further into space than Earth’s. The moon is smaller so it has less gravity pulling it back down.”

Titan’s atmosphere is much denser, too—on the surface, atmospheric pressure equals that at the bottom of a 5-metre-deep pool on Earth.

“At the same time, Titan’s atmosphere is more similar to ours than any other atmosphere in the Solar System,” Hörst said. “In fact, Titan has been called ‘Earth frozen in time’ because some believe this is what Earth could have looked like early in time.”

Saturn's moon Titan

Saturn's moon Titan has a thick, hazy atmosphere.

When the Voyager I spacecraft flew by Titan in the 1970s, the pictures transmitted back to Earth showed a blurry, orange ball.

“For a long time, that was all we knew about Titan,” Hörst said. “All it saw were the outer reaches of the atmosphere, not the moon’s body itself. We knew it has a an atmosphere and that it contains methane and other small organic molecules, but that was it.”

In the meantime, scientists learned that Titan’s haze consists of aerosols, just like the smog that cloaks many metropolitan areas on Earth. Aerosols, tiny particles about a quarter millionth of an inch across, resemble little snowballs when viewed with a high-powered electron microscope.

The exact nature of Titan’s aerosols remains a mystery. What makes them so interesting to planetary scientists is that they consist of organic molecules—potential ingredients for life.

“We want to know what kinds of chemistry can happen in the atmosphere and how far it can go.” Hörst said. “Are we talking small molecules that can go on to becoming more interesting things? Could proteins form in that atmosphere?”

What it takes to make life’s molecules

For that to happen, though, energy is needed to break apart the simple atmospheric molecules—nitrogen, methane and carbon monoxide—and rearrange the fragments into more complex compounds such as pre-biotic molecules.

“There is no way this could happen on Titan’s surface,” Hörst said. “The haze is so thick that the moon is shrouded in a perpetual dusky twilight. Plus, at -124 degrees Celsius, the water ice that we think covers the moon’s surface is as hard as granite.”

However, the atmosphere’s upper reaches are exposed to a constant bombardment of ultraviolet radiation and charged particles coming from the sun and deflected by Saturn’s magnetic field, which could spark the necessary chemical reactions.

Smog-like particles

Tiny particles are thought to create the smog-like haze that enshrouds Saturn's moon Titan.

To study Titan’s atmosphere, scientists have to rely on data collected by the spacecraft Cassini, which has been exploring the Saturn system since 2004 and flies by Titan every few weeks on average.

“With Voyager, we only got to look,” says Hörst. “With Cassini, we get to touch the moon a little bit.”

During fly-by manoeuvres, Cassini has gobbled up some of the molecules in the outermost stretches of Titan’s atmosphere and analysed them with its on-board mass spectrometer. Unfortunately, the instrument was not designed to unravel the identity of larger molecules—precisely the kind that were found floating in great numbers in Titan’s mysterious haze.

“Cassini can’t get very close to the surface because the atmosphere gets in the way and causes drag on the spacecraft,” Hörst said. “The deepest it went was 900 kilometres (560 miles) from the surface. It can’t go any closer than that.”

To find answers, Hörst and her co-workers had to recreate Titan’s atmosphere here on Earth. More precisely, in a lab in Paris, France.

“Fundamentally, we cannot reproduce Titan’s atmosphere in the lab, but our hope was that by doing these simulations, we can start to understand the chemistry that leads to aerosol formation,” Hörst said. “We can then use what we learn in the lab and apply it to what we already know about Titan.”

Like a spy in a movie

Hörst and her collaborators mixed the gases found in Titan’s atmosphere in a stainless-steel reaction chamber and subjected the mixture to microwaves causing a gas discharge—the same process that makes neon signs glow—to simulate the energy hitting the outer fringes of the moon’s atmosphere.

The electrical discharge caused some of the gaseous raw materials to bond together into solid matter, similar to the way UV sunlight creates haze on Titan. The synthesis chamber, constructed by a collaborating group in Paris, is unique because it uses electrical fields to keep the aerosols in a levitated state.

“The aerosols form while they’re floating there,” Hörst explains. “As soon as they grow heavy enough, they fall onto the bottom of the reaction vessel and we scrape them out.”

“And then,” she added, “the samples went on an adventure.”

To analyse the aerosols, Hörst had to use a high-resolution mass spectrometer in a lab in Grenoble, about a three-hour ride from Paris on the TGV, France’s high-speed train.

“I always joke that I felt like [I was in ] a spy in a movie because I would take our samples, put them into little vials, seal them all up and then I’d get on the TGV, and every 5 minutes I’d open the briefcase, ‘Are they still there? Are they still there?’ Those samples were really, really precious.”

Analysing the reaction products with a mass spectrometer, the researchers identified about 5,000 different molecular formulas.

Sarah Hörst

“When I came back and looked at the screen, I thought: That can’t be right,” said graduate student Sarah Hörst.

“We really have no idea how many molecules are in these samples other than it’s a lot,” Hörst said. “Assuming there are at least three or four structural variations of each, we are talking up to 20,000 molecules that could be in there. So in some way, we are not surprised that we made the nucleotide bases and the amino acids.”

“The mass spectrometer tells us what atoms the aerosols are made of, but it doesn’t tell us the structure of those molecules,” Hörst said. “What we really wanted to find out was, what are all the formulas in this mass spectrum?”

“On a whim, we said, ‘Hey, it would be really easy to write a list of the molecular formulas of all the amino acids and nucleotide bases used by life on Earth and have the computer go through them.’”

“I was sitting in front of my computer one day—I had just written up the list—and I put the file in, hit ‘Enter’ and went to go do something,” she said. “When I came back and looked at the screen, it was printing a list of all the things it had found and I sat there and stared at it for a while. I thought: That can’t be right.”

“I ran upstairs to find Roger, my adviser, and he wasn’t there,” Hörst said with a laugh. “I went back to my office, and then upstairs again to find him and he wasn’t there. It was very stressful.”

“We never started out saying, ‘we want to make these things,’ it was more like ‘hey, let’s see if they’re there.’ You have all those little pieces flying around in the plasma, and so we would expect them to form all sorts of things.”

In addition to the nucleotides, the elements of the genetic code of all life on Earth, Hörst identified more than half of the molecular formulas for the 22 amino acids that life uses to make proteins.

Titan: A window into Earth’s past?

In some way, Hörst said, the discovery of Earth’s life molecules in an alien atmosphere experiment is ironic.

Here is why: The chemistry occurring on Titan might be similar to that occurring on the young Earth that produced biological material and eventually led to the evolution of life. These processes no longer occur in the Earth’s atmosphere because of the large abundance of oxygen cutting short the chemical cycles before large molecules have a chance to form. On the other hand, some oxygen is needed to create biological molecules. Titan’s atmosphere appears to provide just enough oxygen to supply the raw material for biological molecules, but not enough to quench their formation.

“There are a lot of reasons why life on Titan would probably be based on completely different chemistry than life on Earth,” Hörst added, “one of them being that there is liquid water on Earth. The interesting part for us is that we now know you can make pretty much anything you want in an atmosphere. Who knows this kind of chemistry isn’t happening on planets outside our Solar System?”

Adapted from information issued by UA / S. Hörst / NASA.

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Voyager: the Greatest Journey of Discovery

  • Twin missions visited the outer planets
  • Discovered new moons and planetary rings
  • Voyager 1 is now the farthest manmade object

A “meditation on the nature and meaning of exploration itself, disguised as a chronicle of the life and times of a space mission,” is what the New York Times says of Arizona State University Professor Stephen Pyne’s new book, Voyager: Seeking Newer Worlds in the Third Great Age of Discovery.

It adds that Pyne’s book takes readers on the roller-coaster ride through time and space, offering “a rich mix of history, science and fine writing. Sometimes it seems as if Captain Cook and Prince Henry the Navigator themselves are aboard the busy spacecraft.”

Cover of Voyager: Seeking Newer Worlds in the Third Great Age of Discovery

Voyager: Seeking Newer Worlds in the Third Great Age of Discovery, traces the history and impact of the twin Voyager spacecraft.

The expeditions of the twin Voyager spacecraft, rank among the most amazing achievements of the space age…indeed, among any age. Launched in August and September 1977 respectively, Voyager 2 and Voyager 1 journeyed to the outer reaches of the Solar System. Voyager 1 flew past Jupiter and Saturn; Voyager 2 encountered Jupiter, Saturn, Uranus and Neptune.

Along the way they discovered numerous new moons, rings around Jupiter, Uranus and Neptune, volcanoes on Jupiter’s moon Io, lightning in Saturn’s atmosphere, as well as many more accomplishments.

Both spacecraft are now way out beyond the edge of the Solar System, slowly drifting through the region where the Sun’s influence ends and true interstellar space begins. In 1998, Voyager 1 overtook Pioneer 10 as the most distant manmade object from Earth—almost 70 times further from the Sun than Earth is.

Today, Voyager 1 is almost 114 times further than the Earth. Voyager 2, travelling in a different direction, is 93 times the Earth-Sun distance.

Voyager: a modern-day Magellan

Why Pyne’s focus on the Voyager mission? While discovery is a uniquely human activity, the Voyager missions stand as iconic testaments, “grand gestures.” Moments of exploring, Pyne says, “that more than any other capture the general imagination, that fuse place, time, discovery and yearning in ways that seem to speak to an era’s sense of itself.”

Artist's impression of Voyager 2 flying past Jupiter

Artist's impression of Voyager 2 flying past Jupiter.

Voyager, he argues, was of the same ilk as Magellan’s journey in the First Age of Discovery and Alexander von Humboldt’s cross-continental trek across South America in the Second Age of Discovery.

Voyager was a defining symbol of the Third Age of Discovery, the exploratory tale of which transcends time and weaves the thread of all human endeavour into the distant future.

Pyne’s work raises “fascinating questions about the human impulses embedded in the space program and about how Voyager’s journey may change our sense of who we are.”

Time Magazine says of Voyager: Seeking Newer Worlds in the Third Great Age of Discovery, “For space geeks, a sweet read; for everyone else, an eye-opener.”

Pyne is an award-winning environmental historian, and the author of three previous books: “Year of the Fires,” “The Ice,” and “How the Canyon Became Grand.”

You can get more details of Voyager: Seeking Newer Worlds in the Third Great Age of Discovery at the SpaceInfo shop.

Adapted from information issued by ASU / NASA / Wikipedia.

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