A recent upsurge in planet-warming methane may not be caused by increasing emissions, as previously thought, but by methane lingering longer in the atmosphere.

That’s the conclusion of two independent studies that indirectly tracked concentrations of hydroxyl, a highly reactive chemical that rips methane molecules apart. Hydroxyl levels in the atmosphere decreased roughly 7 or 8 percent starting in the early 2000s, the studies estimate.

The two teams propose that the hydroxyl decline slowed the breakdown of atmospheric methane, boosting levels of the greenhouse gas. Concentrations in the atmosphere have crept up since 2007, but during the same period, methane emissions from human activities and natural sources have remained stable or even fallen slightly, both studies suggest. The research groups report their findings online April 17 in Proceedings of the National Academy of Sciences.
“If hydroxyl were to decline long-term, then it would be bad news,” says Matt Rigby, an atmospheric scientist at the University of Bristol in England who coauthored one of the studies. Less methane would be removed from the atmosphere, he says, so the gas would hang around longer and cause more warming.

The stability of methane emissions might also vindicate previous studies that found no rise in emissions. The Environmental Protection Agency, for instance, has reported that U.S. emissions remained largely unchanged from 2004 to 2014 (SN Online: 4/14/16).

Methane enters the atmosphere from a range of sources, from decomposing biological material in wetlands to leaks in natural gas pipelines. Ton for ton, that methane causes 28 to 36 times as much warming as carbon dioxide over a century.

Since the start of the Industrial Revolution, atmospheric methane concentrations have more than doubled. By the early 2000s, though, levels of the greenhouse gas inexplicably flatlined. In 2007, methane levels just as mysteriously began rising again. The lull and subsequent upswing puzzled scientists, with explanations ranging from the abundance of methane-producing microbes to the collapse of the Soviet Union.

Those proposals didn’t account for what happens once methane enters the atmosphere. Most methane molecules in the air last around a decade before being broken apart during chemical reactions with hydroxyl. Monitoring methane-destroying hydroxyl is tricky, though, because the molecules are so reactive that they survive for less than a second after formation before undergoing a chemical reaction.
Neither study can show conclusively that hydroxyl levels changed, notes Stefan Schwietzke, an atmospheric scientist at the National Oceanic and Atmospheric Administration’s Earth System Research Laboratory in Boulder, Colo. The papers nevertheless add a new twist in explaining the mysterious methane rise, he says. “Basically these studies are opening a new can of worms, and there was no shortage of worms.”

Despite being conducted by two separate teams — one headed by Rigby and the other by atmospheric scientist Alex Turner of Harvard University — the new studies used the same roundabout approach to tracking hydroxyl concentrations over time.

Both teams followed methyl chloroform, an ozone-depleting substance used as a solvent before being banned by the Montreal Protocol. Like methane, methyl chloroform also breaks apart in reactions with hydroxyl. Unlike methane, though, emission rates of methyl chloroform are fairly easy to track because the chemical is entirely human-made.

Examining methyl chloroform measurements gathered since the 1980s revealed that hydroxyl concentrations have probably wobbled over time, contributing to the odd pause and rise in atmospheric methane concentrations. But to know for sure whether hydroxyl levels varied or remained steady, scientists will need to take a more detailed look at regional emissions of methane and methyl chloroform, Rigby says.

Why hydroxyl levels might have fallen also remains unclear. Turner and colleagues note that the ban on ozone-depleting substances like methyl chloroform might be the cause. The now-recovering ozone layer (SN: 12/24/16, p. 28) blocks some ultraviolet light, an important ingredient in the formation of hydroxyl. Identifying the cause of the hydroxyl changes could help climate scientists better predict how methane levels will behave in the future.

NEW ORLEANS — A relatively small brain can pack a big evolutionary punch. Consider Homo naledi, a famously puzzling fossil species in the human genus. Despite having a brain only slightly larger than a chimpanzee’s, H. naledi displays key humanlike neural features, two anthropologists reported April 20 at the annual meeting of the American Association of Physical Anthropologists.

Those brain characteristics include a region corresponding to Broca’s area, which spans parts of the right and left sides of the brain in present-day people. The left side is typically involved in speech and language.
“It looks like Homo naledi’s brain evolved a huge amount of shape change that supported social emotions and advanced communication of some type,” said Shawn Hurst of Indiana University Bloomington, who presented the new findings. “We can’t say for sure whether that included language.” Frontal brain locations near Broca’s area contribute to social emotions such as empathy, pride and shame. As interactions within groups became more complex in ancient Homo species, neural capacities for experiencing social emotions and communicating verbally blossomed, Hurst suspects.

Scientists don’t know how long ago H. naledi inhabited Africa’s southern tip. If H. naledi lived 2 million or even 900,000 years ago, as some researchers have suggested (SN: 8/6/16, p. 12), humanlike brains with a language-related area would be shocking. A capacity for language is thought to have emerged in Homo over the last few hundred thousand years at most.

Discoverers of H. naledi, led by anthropologist Lee Berger of the University of the Witwatersrand in Johannesburg, will announce an estimated age for the species and describe new fossil finds within the next few weeks, Hurst said.

Hurst and Ralph Holloway of Columbia University led a team that laser scanned the inside surfaces of several partial H. naledi skulls to create virtual casts, or endocasts, of brain surfaces. An endocast reproduces the shape and, with varying success, details of the surface of the brain that were imprinted on the walls of the braincase while an individual was alive. Such brain impressions are not always clear, which has sparked debate over how to interpret them.

Two grooves identified on an endocast from a partial H. naledi skull frame the language-related section of Broca’s area in humans today, Hurst said. H. naledi’s brain also possessed folds of tissue that largely covered a surface section where the grooves converged. Similar folds of tissue typically cover the surface of Broca’s area in modern human brains.
The general shape of that part of the frontal brain in humans differs greatly from that of living apes and fossil hominids dating to at least 700,000 to 1 million years years ago, Hurst added.

H. naledi also displays a humanlike pattern of surface features at the back of the brain, although to a lesser extent than at the brain’s front, Holloway said. Endocasts for this analysis came from two other partial H. naledi skulls.

Specific protrusions and other features at the back of H. naledi’s brain are more pronounced on the left side, Holloway said. In people today, the same left-sided bias in brain organization is associated with right-handedness.

In the past, Holloway and anthropologist Dean Falk of Florida State University in Tallahassee have sharply disagreed over how to identify neural features on fossil endocasts, including a key groove in tissue at the back of the brain. After hearing Hurst and Holloway’s presentations, Falk expressed doubt that H. naledi’s brain was as humanlike as they concluded.

Shortly after the presentations, Hurst and Falk hashed out their differences head-to-head as they jointly studied a solid cast of the partial H. naledi brain surface displaying proposed signs of Broca’s area. They agreed on much about the fossil species’ neural setup, with one major exception. “I’m skeptical that two frontal [grooves] frame an area that corresponds to Broca’s area,” Falk said. If she’s right, then H. naledi communicated much less like present-day people than proposed by Hurst. Falk plans to study the new endocasts more closely and compare them with endocasts of other fossil hominids.

The benefits of statins for people older than 75 remain unclear, a new analysis finds. Statins did not reduce heart attacks or coronary heart disease deaths, nor did they reduce deaths from any cause, compared with people not taking statins, researchers report online May 22 in JAMA Internal Medicine.

Recently published guidelines cited insufficient data to recommend statins for people older than age 75 who don’t have a history of cardiovascular disease. The new analysis considered a subset of older adults enrolled in a study of heart attack prevention and mortality conducted from 1994 to 2002. The sample included 2,867 adults ages 65 and older who had hypertension, 1,467 of whom took a statin.

There was no meaningful difference in the frequency of heart attacks or coronary heart disease deaths between those who took statins and those who did not. There was also no significant difference in deaths from any cause, both overall and among participants ages 65 to 74 or those 75 and older.

Statin use may be associated with muscle damage and fatigue, which could especially impact older adults and put them at higher risk for physical decline, the authors say.

For a third time, scientists have detected the infinitesimal reverberations of spacetime: gravitational waves.

Two black holes stirred up the spacetime wiggles, orbiting one another and spiraling inward until they fused into one jumbo black hole with a mass about 49 times that of the sun. Ripples from that union, which took place about 3 billion light-years from Earth, zoomed across the cosmos at the speed of light, eventually reaching the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, which detected them on January 4.
“These are the most powerful astronomical events witnessed by human beings,” Michael Landry, head of LIGO’s Hanford, Wash., observatory, said during a news conference May 31 announcing the discovery. As the black holes merged, they converted about two suns’ worth of mass into energy, radiated as gravitational waves.
LIGO’s two detectors, located in Hanford and Livingston, La., each consist of a pair of 4-kilometer-long arms. They act as outrageously oversized rulers to measure the stretching of spacetime caused by gravitational waves. According to Einstein’s theory of gravity, the general theory of relativity, massive objects bend the fabric of space and create ripples when they accelerate — for example, when two objects orbit one another. Gravitational ripples are tiny: LIGO is tuned to detect waves that stretch and squeeze the arms by a thousandth of the diameter of a proton. Black hole collisions are one of the few events in the universe that are catastrophic enough to produce spacetime gyrations big enough to detect.
The two black holes that spawned the latest waves were particularly hefty, with masses about 31 and 19 times that of the sun, scientists report June 1 in Physical Review Letters. LIGO’s first detection, announced in February 2016, came from an even bigger duo: 36 and 29 times the mass of the sun (SN: 3/5/16, p. 6). Astrophysicists don’t fully understand how such big black holes could have formed. But now, “it seems that these are not so uncommon, so clearly there’s a way to produce these massive black holes,” says physicist Clifford Will of the University of Florida in Gainesville. LIGO’s second detection featured two smaller black holes, 14 and eight times the mass of the sun (SN: 7/9/16, p. 8).
Weighty black holes are difficult to explain, because the stars that collapsed to form them must have been even more massive. Typically, stellar winds steadily blow away mass as a star ages, leading to a smaller black hole. But under certain conditions, those winds might be weak — for example, if the stars contain few elements heavier than helium or have intense magnetic fields (SN Online: 12/12/16). The large masses of LIGO’s black holes suggest that they formed in such environments.

Scientists also disagree about how black holes partner up. One theory is that two neighboring stars each explode and produce two black holes, which then spiral inward. Another is that black holes find one another within a dense cluster of stars, as massive black holes sink to the center of the clump (SN Online: 6/19/16).

The new detection provides some support for the star cluster theory: The pattern of gravitational waves LIGO observed hints that one of the black holes might be spinning in the opposite direction from its orbit. Like a cosmic do-si-do, each black hole in a pair twirls on its own axis as it spirals inward. Black holes that pair up as stars are likely to have their spins aligned with their orbits. But if the black holes instead find one another in the chaos of a star cluster, they could spin any which way. The potentially misaligned black hole LIGO observed somewhat favors the star cluster scenario. The measurement is “suggestive, but it’s not definite,” says astrophysicist Avi Loeb of Harvard University.

Scientists will need more data to sort out how the black hole duos form, says physicist Emanuele Berti of the University of Mississippi in Oxford. “Probably the truth is somewhere in between.” Various processes could contribute to the formation of black hole pairs, Berti says.

As with previous detections of gravitational waves, the scientists used their measurements to test general relativity. For example, while general relativity predicts that gravitational waves travel at the speed of light, some alternative theories of gravity predict that gravitational waves of different energies travel at different speeds. LIGO scientists found no evidence of such an effect, vindicating Einstein once again.

Now, with three black hole mergers under their belts, scientists are looking forward to a future in which gravitational wave detections become routine. The more gravitational waves scientists detect, the better they can test their theories. “There are already surprises that make people stop and revisit some old ideas,” Will says. “To me that’s very exciting.”

Paper wasps have a knack for recognizing faces, and a new study adds to our understanding of what that means in a wasp’s brain.

Most wasps of a given species look the same, but some species of paper wasp (Polistes sp.) display varied colors and markings. Recognizing these patterns is at the core of the wasps’ social interactions.

One species, Polistes fuscatus, is especially good at detecting differences in faces — even better than they are at detecting other patterns. To zero on the roots of this ability, biologist Ali Berens of Georgia Tech and her colleagues set up recognition exercises of faces and basic patterns for P. fuscatus wasps and P. metricus wasps — a species that doesn’t naturally recognize faces but can be trained to do so in the lab. After the training, scientists extracted DNA from the wasps’ brains and looked at which bits of DNA or genes were active.

The researchers found 237 genes that were at play only in P. fuscatus during facial recognition tests. A few of the genes have been linked to honeybee visual learning, and some correspond to brain signaling with the neurotransmitters serotonin and tachykinin. In the brain, picking up on faces goes beyond basic pattern learning, the researchers conclude June 14 in the Journal of Experimental Biology.

It’s possible that some of the same genes also play a broader role in how organisms such as humans and sheep tell one face from another.

Ancient rock artists were drawn to echo chambers. Members of early farming communities in Europe painted images in rock-shelters where sounds bounced off walls and into the surrounding countryside, researchers say.

Rock-shelters lacking such sound effects were passed up, at least in the central Mediterranean, report archaeologist Margarita Díaz-Andreu of the University of Barcelona and colleagues in the July Journal of Archaeological Science. In landscapes with many potential rock art sites, “the few shelters chosen to be painted were those that have special acoustic properties,” Díaz-Andreu says.
Some hunter-gatherer and farming groups studied over the past couple centuries believed in spirits that dwell in rock and reveal their presence via echoes. But acoustic evidence of special echoing properties at rock art sites is rare.

Díaz-Andreu’s team studied two rock art sites in 2015 and 2016. Baume Brune is a kilometer-long cliff in southeastern France. Of 43 naturally formed cavities in the cliff, only eight contain paintings, which include treelike figures and horned animals. Rock art in the Valle d’Ividoro, on Italy’s east coast, appears in an 800-meter-long section of a gorge. Only three of its 11 natural shelters contain painted images. Researchers generally date these French and Italian paintings to between roughly 6,500 and 5,000 years ago, several thousand years after the Stone Age had ended, Díaz-Andreu says.

To investigate the acoustics of the decorated and unadorned shelters, the researchers developed a new technique for determining the direction, intensity and timing of sound waves arriving at a particular point from every direction. A special microphone connected to a digital recorder measured the acoustic properties of any echoes set off by balloons popped just outside each rock-shelter. This setup was moved to various spots outside the caves to record the acoustic reach of reflected popping sounds. Echo measurements in France were taken at distances ranging from 22 to 36 meters from cliff shelters. Due to rougher terrain in Italy, measurements there were taken at distances ranging from 77 to 300 meters.
Then, the acoustic data were transformed into 3-D, slow-motion depictions of echoes, represented by moving circles, indicating where sound reflections originated. At both sites, shelters with rock paintings displayed better echoing properties than undecorated shelters, Díaz-Andreu says. And in each location, the shelter that best reflected echoes had the highest number of paintings.
“This novel technique shows a clear correlation between audible echoes and decorated shelters,” says music archaeologist Riitta Rainio of the University of Helsinki in Finland, who did not participate in the new study.

Echoes that bounce off steep rock cliffs bordering three lakes in northern Finland also attracted ancient artists, Rainio says. She and her colleagues took acoustic measurements at Finland’s painted cliffs from 2013 to 2016. Microphones placed on boats positioned at different spots on nearby lakes measured sound waves generated, in most trials, by a starter’s pistol. These Finnish paintings date to between around 7,200 and 3,000 years ago, Rainio says.

In some cases, echoes reflect directly from cliff paintings. “That, and possible drumming figures painted on the cliffs, suggest that sound played some role in rituals at these sites,” Rainio says. Her team will report its findings in an upcoming Journal of Archaeological Method and Theory.

Creators of older Stone Age cave art also appear to have focused on sites where echoes abounded, says archaeologist Paul Pettitt of Durham University in England. For instance, many roughly 14,000- to 12,000-year-old animal drawings and engravings at France’s Niaux Cave cluster in a cathedral-like chamber where sounds echo loudly.

“The new study provides convincing evidence that echoes, which were scientifically inexplicable to prehistoric people, played a determining role in how art was created,” Pettitt says.

Babies are little heartbreakers — literally. Genetic variants linked to fertility are also linked to coronary artery disease, a new study finds.

It’s not uncommon to find genes that affect more than one trait, but this is the first time scientists have seen a genetic connection between reproduction and heart disease, the researchers report online June 22 in PLOS Genetics. “Evolution is on a buy now, pay later plan,” says coauthor Stephen Stearns, an evolutionary biologist at Yale University. The connection “leads to a view of us as a bundle of trade-offs,” he says. And in this case, genes’ reproductive benefits apparently outweigh even lethal side effects later in life.
Coronary artery disease — one of the most deadly diseases worldwide — results from plaque accumulation in the arteries that supply blood to the heart. That type of buildup, which can start in young adulthood, has afflicted humans for millennia, and scientists have wondered why the genetic variants complicit in the disease haven’t yet been weeded out of the gene pool.

“There must be some advantage to these genes that makes them worth keeping,” says Shari Grossman, a geneticist at the Broad Institute in Cambridge, Mass., who was not involved in the study.

Researchers examined genetic variants associated with coronary artery disease and found evidence that they spread rapidly through the human population within the last 10,000 years or so. This implies that sometime in relatively recent human history these tweaked genes provided an evolutionary advantage.

Then the researchers reviewed 143 previous studies and discovered many of these same genes were linked to — and probably enhanced — important reproductive functions, such as male and female fertility as well as fetal development and survival. This suggests that the genetic quirks associated with coronary artery disease persisted because the people who had them bore more children.

Having birthrate-boosting genes was probably particularly advantageous in the last several thousand years because of the transition to agriculture, Stearns says. Agriculture led to people settling down and eventually moving to cities, where rampant infectious diseases hiked mortality rates, especially among children. People with these genetic variants would have been more likely to continue their lineage, even if they were predisposed to suffer heart problems later on.
This study may be a warning for gene therapy, since it suggests there are many genetic connections between different bodily functions that scientists don’t yet understand, Stearns says. If doctors want to treat coronary artery disease by editing a person’s DNA, it’s important to know what other traits might be affected.

The new findings also raise questions about the various functions of other disease-related genes, says Hamdi Mbarek, a molecular geneticist at Vrije University Amsterdam who was not involved in the work. For instance, a future study could examine whether genes associated with cancer have any hidden evolutionary benefits.

A bad bacterium may make colon cancer worse.

Streptococcus gallolyticus spurred growth of some colon cancer cells in lab dishes and in mice, researchers report July 13 in PLOS Pathogens. S. gallolyticus stimulates a biochemical chain reaction that scientists already knew is involved in the development of colon cancer, the researchers discovered.

Bacteria had to be in direct contact with tumor cells to speed growth, but exactly how the bacteria do that isn’t yet known. Further investigation could help researchers find ways to block the microbe’s action, leading to better treatments for colorectal cancer, says microbiologist Yi Xu of Texas A&M University Health Science Center in Houston.
People who have heart valve or blood infections of S. gallolyticus (previously known as S. bovis) often also have colorectal tumors. The bacterium has also been found growing on tumors in some colorectal cancer patients. But doctors couldn’t tell from association studies whether the bacteria were egging on tumors or were innocent bystanders.

Xu and colleagues grew S. gallolyticus in lab dishes with several different types of human cells. Three types of colon cancer cells grew faster, producing about 50 to 60 percent more cells within 24 hours, with the bacteria than they did when cultured with no bacteria or with a harmless, milk-fermenting bacterium called Lactococcus lactis. Normal human colon cells, kidney cells, lung cancer cells and two strains of colon cancer cells didn’t respond to the bacteria. Those results could mean that the bacterium doesn’t spur on all colon cancers, says Cynthia Sears, an infectious disease specialist at Johns Hopkins University School of Medicine who was not involved in the work. Finding out what makes some cells more vulnerable to the bacteria will be important for future studies, she says.

“It deserves a deeper look,” Sears says.

Colon cancer‒prone mice infected with S. gallolyticus had more and bigger tumors than those found in mice inoculated with L. lactis or with a saline solution.

Xu and colleagues don’t know all the details of how S. gallolyticus promotes colon cancer growth. But the researchers discovered that when the bacteria glom onto responsive colon cancer cells, the microbes boost a signal sent through a relay chain known as the beta-catenin pathway. That pathway was already known to be involved in generating colorectal tumors. The researchers have some evidence that S. gallolyticus may also work through other chemical signaling pathways to enhance colon cancer growth.
Whether the bacterium can initiate colon cancer isn’t clear, Xu says.

Researchers will also need to investigate how S. gallolyticus works with or against other microbes that live in the colon, says Ran Blekhman, a geneticist at the University of Minnesota in Minneapolis. The study is part of a growing trend away from merely associational studies toward discovering how microbes function in the body, he says. “This is basically the next step in microbiome research.”

Big, rogue planets — ones without parent stars — are rare.

A new census of free-floating Jupiter-mass planets determined that these worlds are a tenth as common as previous estimates suggested. The results appear online July 24 in Nature.

Planets can go rogue in two ways: They can get kicked out of their parent planetary systems or form when a ball of gas and dust collapses (SN: 4/4/15, p. 22).

In the new study, Przemek Mróz of the Astronomical Observatory of the University of Warsaw and colleagues estimated the number of large, rogue planets in our galaxy using a technique called microlensing. When an object with a mass of a planet passes in front of a distant, background star, the gravity of the planet acts as a gravitational magnifying glass. It distorts and focuses the light, giving up the planet’s existence.
Mróz and colleagues looked at 2,617 microlensing events recorded between 2010 and 2015 and determined which were caused by a rogue planet. For every typical star, called main sequence stars, there are 0.25 free-floating Jupiter-mass planets, the analysis suggests.

The new result sharply contrasts an estimate published in 2011, which suggested that rogue Jupiters are almost twice as common as main sequence stars. About 90 percent of stars in the universe are main sequence stars, so if that estimate were accurate, there should be a lot of free-floating Jupiters.

“That result changed our conceptual framework of the universe just a little bit,” says astronomer Michael Liu of the University of Hawaii in Honolulu. It challenged long-held ideas about how planets go rogue because the known methods wouldn’t generate enough planets to account for all the wanderers.

The 2011 result was based on a relatively small sample of microlensing events, only 474. Since then, infrared telescope images haven’t detected as many free-floating planets as expected. “Over the years, serious doubts were cast over the claims of a large population of Jupiter-mass free-floaters,” Mróz says.

David Bennett, coauthor of the 2011 study, agrees that the new census failed to find evidence for a large population of Jupiter-mass rogue planets. He notes, however, that the new data do reveal four times as many Jupiter-mass failed stars called brown dwarfs than predicted in the original census. So some of the rogues that were originally classified as planets may, in fact, be failed stars. Bennett, of NASA’s Goddard Space Flight Center in Greenbelt, Md., and colleagues are working on a new analysis of potential rogues with nearly 3,000 microlensing events and plan to compare their results with those from the new census.
Liu says the latest census is much more in line with theories of how planets form. Most rogues should be Earth-mass or a little heavier. Those lighter planets get tossed out of their planetary systems much easier than behemoths like Jupiter. Still, the smaller planets are harder to detect.

The new microlensing analysis did identify several events in which stars brightened and dimmed in less than half a day. Such short events hint at the existence of Earth-mass free-floaters because smaller planets with less gravity should brighten a distant star more briefly than more massive stars. Determining whether those small planets are really rogue and counting how many there are will take better telescopes, the team notes.

A species gets only one chance to explore its solar system for the first time.

For humans, that chance began 40 years ago this month, when the twin Voyager spacecraft embarked on their “grand tour” of the solar system. A new PBS documentary airing on August 23, The Farthest: Voyager in Space, chronicles their journey to send home the first close-ups of the giant planets and to bring a message about life on Earth to the stars.
Voyagers’ launch dates took advantage of a rare planetary alignment. In 1977, the giant planets — Jupiter, Saturn, Uranus and Neptune — lined up in such a way that a spacecraft could swing past all four in less than 15 years, stealing some gravitational oomph from each world as it went.

That lucky alignment happens only once every 176 years. When NASA’s administrator went to President Richard Nixon to ask for funding for Voyager, he allegedly said: “The last time the planets were lined up like that, President Jefferson was sitting at your desk. And he blew it.”

The Voyagers almost blew it, too. The first craft (Voyager 2, confusingly) launched on August 20, 1977. It experienced so much shaking that its onboard computer — which had as much computing power as a modern car key fob — thought it was failing and put itself in safe mode.
Engineers got it back on track and fixed the problem for Voyager 1’s launch. Then that spacecraft’s rocket had a fuel leak during launch. The craft was within 3½ seconds of running out of gas before it accelerated enough to reach Jupiter.

These nail-biters are mostly told through personal, entertaining anecdotes from Voyager team members. Historical footage from press conferences and newscasts grounds the story in its era. Everyone has big ’70s computers and big ’70s hair. Cuts from shots of the scientists today to their younger selves emphasize how much time has passed. It’s strange that such a high-tech and ambitious mission seems so vintage.

Even the Voyager footage of Jupiter and Saturn coming into view for the first time has a home video quality, especially compared with the sharp, colorful images that spacecraft send back from these planets today. Watching the footage felt like watching video of my parents’ wedding: I recognize everyone, but they look so different.

But the sense of awe that the Voyager images sparked is palpable. At the time, every picture was the best planetary picture ever taken. Much of what is known about the outer solar system now — Jupiter’s moon Io has volcanoes, Europa has an ocean, Neptune has a great churning hurricane that never stops — was glimpsed for the first time with Voyager.

The Voyager spacecraft are still out there, and one may have already left the solar system (SN: 8/23/14, p. 6). Good thing because both craft carry a message in a bottle: the Golden Record.

The Golden Record was a literal record to be played on a phonograph by any aliens that might encounter the spacecraft. The package included a needle, a speaker and graphical instructions on how to play the record. A listener would hear a two-hour sampling of sounds from Earth, including babies crying, whales singing, chimps screeching, trains, thunderstorms, Beethoven, Chuck Berry, greetings in 55 languages and astronomer Carl Sagan’s son saying, “Hello from the children of planet Earth.”

The Farthest weaves the story of exploration with the story of the making of the record. The record’s producers and champions recount how they pulled the whole thing together in just six weeks. What to leave in — a map to Earth, in case the aliens want to visit — and what to leave out — full frontal nudity — was fiercely debated.

At times, refrains of “Wow!” and “It was a first” feel repetitive. Some of the stock footage and spacecraft animations are a little cheesy. But The Farthest is a tender tribute, tinged with nostalgia and existential awe. For those like me, who weren’t alive or aware when the first pictures of Jupiter came back, The Farthest offers a sense of what we missed.