PASADENA, Calif. — It’s hard being a comet sometimes. Comet 67P/Churyumov-Gerasimenko is developing stress fractures and might break apart in the next several hundred years.

Comet 67P is famous for its oddball shape. With two lobes joined together at a neck, it vaguely resembles an interplanetary peanut. The Rosetta spacecraft, which ended its 26-month visit to the comet in September (SN Online: 9/29/16), noticed a large crack in the neck in 2014. After the comet made its closest approach to the sun in August 2015, the fissure grew by several hundred meters and new cracks appeared.

The fractures appear to be developing as forces subtly bend the comet to and fro, Stubbe Hviid, a planetary scientist at the German Aerospace Center Institute of Planetary Research in Berlin, reported October 17 in a press conference at a meeting of the American Astronomical Society’s Division for Planetary Sciences. Hviid and colleagues combined maps from Rosetta with computer simulations of all the forces at work within the comet to determine how the cracks develop. They found that the two bulbous ends rock in opposite directions as the comet spins, flexing the neck and creating severe stress. Because the comet isn’t held together strongly — it’s a conglomeration of dust and ice not much stickier than snow, Hviid said — the neck is starting to break. After a few hundred more years, he said, the comet could fold itself in half as the two lobes snap apart and smoosh together.

VANCOUVER — Traces of long-lost human cousins may be hiding in modern people’s DNA, a new computer analysis suggests.

People from Melanesia, a region in the South Pacific encompassing Papua New Guinea and surrounding islands, may carry genetic evidence of a previously unknown extinct hominid species, Ryan Bohlender reported October 20 at the annual meeting of the American Society of Human Genetics. That species is probably not Neandertal or Denisovan, but a different, related hominid group, said Bohlender, a statistical geneticist at the University of Texas MD Anderson Cancer Center in Houston. “We’re missing a population or we’re misunderstanding something about the relationships,” he said.
This mysterious relative was probably from a third branch of the hominid family tree that produced Neandertals and Denisovans, an extinct distant cousin of Neandertals. While many Neandertal fossils have been found in Europe and Asia, Denisovans are known only from DNA from a finger bone and a couple of teeth found in a Siberian cave (SN: 12/12/15, p. 14).

Bohlender isn’t the first to suggest that remnants of archaic human relatives may have been preserved in human DNA even though no fossil remains have been found. In 2012, another group of researchers suggested that some people in Africa carry DNA heirlooms from an extinct hominid species (SN: 9/8/12, p. 9).

Less than a decade ago, scientists discovered that human ancestors mixed with Neandertals. People outside of Africa still carry a small amount of Neandertal DNA, some of which may cause health problems (SN: 3/5/16, p. 18). Bohlender and colleagues calculate that Europeans and Chinese people carry a similar amount of Neandertal ancestry: about 2.8 percent. Europeans have no hint of Denisovan ancestry, and people in China have a tiny amount — 0.1 percent, according to Bohlender’s calculations. But 2.74 percent of the DNA in people in Papua New Guinea comes from Neandertals. And Bohlender estimates the amount of Denisovan DNA in Melanesians is about 1.11 percent, not the 3 to 6 percent estimated by other researchers.

While investigating the Denisovan discrepancy, Bohlender and colleagues came to the conclusion that a third group of hominids may have bred with the ancestors of Melanesians. “Human history is a lot more complicated than we thought it was,” Bohlender said.

Another group of researchers, led by Eske Willerslev, an evolutionary geneticist at the Natural History Museum of Denmark in Copenhagen, recently came to a similar conclusion. Willerslev’s group examined DNA from 83 aboriginal Australians and 25 people from native populations in the Papua New Guinea highlands (SN: 10/15/16, p. 6). The researchers found Denisovan-like DNA in the study volunteers, the group reported October 13 in Nature. But the DNA is genetically distinct from Denisovans and may be from another extinct hominid. “Who this group is we don’t know,” Willerslev says. They could be Homo erectus or the extinct hominids found in Indonesia known as Hobbits (SN: 4/30/16, p. 7), he speculates.
But researchers don’t know how genetically diverse Denisovans were, says Mattias Jakobsson, an evolutionary geneticist at Uppsala University in Sweden. A different branch of Denisovans could be the group that mated with ancestors of Australians and Papuans.

Researchers know so little about the genetic makeup of extinct groups that it’s hard to say whether the extinct hominid DNA actually came from an undiscovered species, said statistical geneticist Elizabeth Blue of the University of Washington in Seattle. DNA has been examined from few Neandertal fossils, and Denisovan remains have been found only in that single cave in Siberia. Denisovans may have been widespread and genetically diverse. If that were the case, said Blue, the Papuan’s DNA could have come from a Denisovan population that had been separated from the Siberian Denisovans for long enough that they looked like distinct groups, much as Europeans and Asians today are genetically different from each other. But if Denisovans were not genetically diverse, the mysterious extinct ancestor could well be another species, she said.

Jakobsson says he wouldn’t be surprised if there were other groups of extinct hominids that mingled with humans. “Modern humans and archaic humans have met many times and had many children together,” he said.

Buzzkill
Astronomers confirmed the existence of an exoplanet, Proxima b, only 4.2 light-years from Earth, Christopher Crockett reported in “Planet orbits sun’s nearest neighbor” (SN: 9/17/16, p. 6).

Some readers thought there was too much excitement over the new potentially habitable planet.

Christina Gullion believes keeping Earth habitable in the face of a changing climate is more important than searching for other planets. “Off-planet exploration seems to me to be a counterproductive diversion of funds and scientific knowledge,” she wrote. “I think it is self-indulgently romantic to invest scarce resources in curiosity about life out there in the universe when we could be protecting and enhancing life here on Earth.” Although Proxima b is relatively close to Earth, Gullion correctly noted that it is still too far away to reach anytime soon.
Even if humans could travel to Proxima b, reader Steve Moore pointed out, scientists don’t know much about the planet. It could be tidally locked with its star and vulnerable to solar flares, he said, which would make it hard, if not impossible, for humans to live on.

Crockett agrees that enthusiasm for Proxima b should be tempered by the little we know about the planet — so far, only its minimum mass, orbit and a few details about its star. Tidal locking is possible, Crockett says, “though there’s an active debate about whether that would be OK for habitability or not.” And though solar flares also pose a threat to habitability, “a denser atmosphere might be able to withstand Proxima’s flares,” he says. “We just won’t know until we get better data on the planet.”
Despite all of the unknowns, Crockett still thinks it’s an exciting discovery. “The proximity of the planet means it’s probably going to come under a lot of scrutiny in the years and decades to come,” he says. “And knowing that there’s a planet right next door is pretty neat. I can’t wait to see what we learn about it.”
Pavlov’s fish
Researchers worry that escapes of farmed salmon, cobia and other fish into the ocean could weaken or harm native wildlife, Roberta Kwok reported in “Runaway fish” (SN: 9/17/16, p. 22).

“I wondered if anyone had considered training farm-raised fish to associate a sound or some other stimulus with food,” Rick Gelbmann asked. “Then when fish escape, the sound could be used to attract the fish, making it easier to recapture them.”

Scientists have successfully trained species such as Atlantic salmon to swim to a food source in response to a tone. But for runaways, this strategy “is basically impractical,” says Tim Dempster, a sustainable aqua­culture researcher. Fish often escape d­uring storms when it’s tough to deploy equipment. Escapees tend to flee quickly, so the sounds might not reach them. And farmers would have to train a huge number of fish just to potentially recapture a small fraction.

Bioacoustician Frédéric Bertucci notes that adding another source of human-made noise to the ocean could also affect nearby wild animals.

Star struck
Despite a new analysis of data from the Kepler Space Telescope, the slow-dimming and sporadic flickering of Tabby’s star remains a mystery, Christopher C­rockett reported in “Fading star still baffles a­stronomers” (SN: 9/17/16, p. 12).

Walt Davis wondered if the dimming could be caused by the star orbiting a black hole. “As the star moves closer to alignment behind [the black hole] … the star’s light rays are being more and more bent away from us,” he wrote.

“As weird as this star is, a black hole is probably not the culprit,” Crockett says. Astronomers would be able to detect the star’s orbital motion if it were orbiting a black hole, but the star appears to stay put. “And if gravity of a companion black hole was occasionally bending the starlight directed toward Earth, it would make the star appear brighter, not darker,” he says.

Tickle a rat and it will jump for joy, gleefully squeak and beg for more. In addition to describing these delightful reactions to a tickling hand, a new study identifies nerve cells in the brain that help turn rats into squirmy puddles of giggles.

The results, published November 11 in Science, offer insight into how the brain creates glee, an understudied emotion. “People really underrate the positive things — fun, happiness, joy,” says study coauthor Shimpei Ishiyama of Humboldt University of Berlin.
Scientists knew that rats seemed to enjoy a good tickle from a human, but how the brain creates that emotion was a mystery. Although no protocol existed, the tickling part of the experiment turned out to be “surprisingly easy,” Ishiyama says. He simply stuck his hand in the cages and scribbled his fingers in the rats’ fur, to their apparent delight. Tickled rats laughed by emitting an ultrasonic 50-kilohertz giggle that humans can’t hear. They also jumped for joy, an acrobatic feat called “Freudensprünge,” and chased Ishiyama’s hand around the cage. Using laughter as a measurement, Ishiyama and colleagues found that the belly, not back or tail, is a rat’s most ticklish spot.

This joyful response may be created in part by nerve cells in the somatosensory cortex. In people, this brain region responds to tickles and is usually associated with touch perception. In tickled rats, many nerve cells in the part of the somatosensory cortex that corresponds to the rodents’ trunks grew active, electrodes revealed. A light stroke activated some of these nerve cells, but not as many.

Because these nerve cells respond to touch, it’s not surprising that they grew active during a tickle, Ishiyama says. But additional experiments found active nerve cells when the rats were chasing a tickling hand without being touched — suggesting the cells are responding to something specific about a tickle, not just touch in general. What’s more, when the researchers used electrodes to stimulate the somatosensory cortex in untouched rats, the rats giggled.
It turns out that ticklishness is a flighty state, and not just because some rats like to be tickled more than others. Anxious rats on a platform and in bright lights emitted fewer laughlike vocalizations than calm rats, the researchers found. Nerve cells in the somatosensory cortex were less likely to fire off signals, too, results that highlight just how mood-dependent tickling is.

The new study shows for the first time that laughter can result from stimulation of the somatosensory cortex, says neuroscientist Elise Wattendorf of the University of Fribourg in Switzerland. The brain area’s involvement in both the sensory aspects of tickling and its social context is “unexpected, and constitutes an outstanding result,” she wrote in an e-mail. Using brain scans, Wattendorf and colleagues had previously found that the somatosensory cortex was active when people laughed as they were tickled.

Many brain studies focus on troubles such as depression, Ishiyama says. But by taking the opposite approach, he hopes to reveal new insights into how the brain creates and maintains happiness. Besides, he says, “it’s also fun to study fun.”

Chinese scientists have injected a person with CRISPR/Cas9-edited cells, marking the first time cells altered with the technique have been used in humans. Researchers used the powerful gene editor to alter immune cells to fight lung cancer, Nature reports November 15.

Immune cells called CAR-T cells have already been engineered using other gene-editing technologies. A baby’s leukemia was successfully treated in 2015 with CAR-T cells engineered with gene editors known as TALENs.

Chinese researchers led by oncologist Lu You of Sichuan University in Chengdu got approval to conduct the new trial this summer. U.S. researchers have gotten clearance to begin similar clinical trials.

You’s team removed immune cells from a patient with lung cancer. They then used CRISPR/Cas9 as molecular scissors to cut and inactivate the PD-1 gene in T cells. That gene’s protein usually holds immune cells back from attacking tumors. The hope is that the edited cells will now go on the offensive and help the patient fight cancer. Researchers plan to give the patient a second dose of engineered cells, Nature reports.

The researchers’ progress with the technique could spark a space race–style biomedical competition between the United States and China, Carl June, an immunotherapist at University of Pennsylvania in Philadelphia, told Nature. “I think this is going to trigger ‘Sputnik 2.0,’” he said, hopefully improving the end product.

In the early 1880s, Harvard Observatory director Edward Pickering put out a call for volunteers to help observe flickering stars. He welcomed women, in particular — and not just because he couldn’t afford to pay anything.

At the time, women’s colleges were producing graduates with “abundant training to make excellent observers,” Pickering wrote. His belief in women’s abilities carried over when he hired staff, even though critics of women’s higher education argued that women “originate almost nothing, so that human knowledge is not advanced by their work.”
Pickering and his “harem” sure proved the critics wrong.

In The Glass Universe, science writer Dava Sobel shines a light on the often-unheralded scientific contributions of the observatory’s beskirted “computers” who helped chart the heavens. By 1893, women made up nearly half of the observatory’s assistants, and dozens followed in their footsteps.

These women toiled tirelessly, marking times, coordinates and other notations for photographic images of the sky taken nightly and preserved on glass plates — the glass universe. These women’s routine mapping of the stars gave birth to novel ideas that advanced astronomy in ways still instrumental today — from how stars are classified to how galactic distances are measured.

Using diaries, letters, memoirs and scientific papers, Sobel recounts the accomplishments of these extraordinary women, going into enough scientific detail (glossary included) to satisfy curious readers and enough personal detail to bring these women’s stories to life.

Sobel traces the origin of the glass universe back to heiress Anna Palmer Draper. The book opens in 1882 with her exulting in hosting a party for the scientific glitterati under the glowing and novel Edison incandescent lights. Her husband, Henry Draper, a doctor and amateur astronomer, had pioneered a way to “fix” the stars on glass photographic plates. The resulting durable black-and-white images revealed spectral lines that could provide hints to a star’s elements — and eventually so much more. Henry’s premature death five days after the party launched Anna’s philanthropic support of the Harvard Observatory and the creation of the glass universe.
Other women featured in the book had a more hands-on impact on astronomy. For instance, Williamina Fleming came to the United States as a maid. But Pickering soon recognized her knack for mathematics. At the observatory, she read “the rune-like lines of the spectra,” Sobel writes, noticing patterns that led to the first iteration in 1890 of the Draper stellar classification system. That system, still used today, was later refined by the observations of other women.

Henrietta Leavitt, a promising Radcliffe College astronomy student slowly going deaf, joined the staff in 1895. While meticulously tracking the changing brightness of variable stars, she noticed a pattern: The brighter a star’s magnitude, the longer it took to cycle through all its variations. This period-luminosity law, published in 1912, became crucial in measuring the distance to stars. It underpinned Edwin Hubble’s law on cosmic expansion and led to discoveries about the shape of the Milky Way, our solar system’s place far from the galactic center and the existence of other galaxies.

The story belongs, too, to Pickering and his successor, Harlow Shapley. Perhaps partly motivated by economics at a time of shoestring budgets — in 1888, women computers earned just 25cents per hour — these men not only recognized, but also encouraged and heralded the women’s talent.

Sobel takes readers through World War II and a myriad of other moments starring women: first woman observatory head; first woman professor at Harvard (of astronomy, of course); discoveries of binary stars, the prevalence of hydrogen and helium in stars, and the existence of interstellar dust. In some cases, it took male astronomers to make those findings stick — the glass universe had a glass ceiling.

After World War II, radio astronomy emerged, and “the days of the human computer were numbered — by zeros and ones,” Sobel writes. Using film to photograph the stars ended in the 1970s. But the glass universe is far from obsolete. The roughly half-million plates hold the ghosts of pulsars, quasars and other stellar phenomena not even imagined when the plates were made. They also offer the promise of more discoveries to come, perhaps by the next generation of women astronomers.

The mountain goat (Oreamnos americanus) might be the world’s best climber, able to scale near-vertical cliffs with an ease rivaled only by the world’s best human rock climbers — who have the advantage of safety equipment and opposable thumbs. Just how the goats manage such climbs has been somewhat of a mystery. Researchers suspected that the big muscles in the animals’ neck and shoulders and their low center of mass play a role, but no one had studied this, in part because of the difficulty of doing research in the goats’ home territory — remote mountainous regions of the United States and Canada.

Enter YouTube.

The internet is peppered with videos of these animals’ amazing feats, and biomechanics researchers Ryan Lewinson and Darren Stefanyshyn of the University of Calgary saw an opportunity: There was no need to go to the mountain goats when they could simply go to YouTube.

The researchers found a video (below) that they thought would work for analysis. In it, a young male mountain goat climbs a hill in the Canadian Rockies. They focused on a section in which the animal makes a series of galloping leaps, picking out nine frames to analyze. In the first six frames, the mountain goat pushes off the rock face, with its hindlimbs in contact with the hill surface. In the last three frames, the animal pulls itself up the hill with its forelimbs.
During the push-off phase, the researchers found, the front legs stay close to the animal’s body while the back legs extend, creating a strong propulsive force upward. Then, the mountain goat uses those strong muscles in its neck and shoulders to propel its torso up the hill while keeping its elbows tucked in to keep the motion going straight up, the team reports in the December Zoology.

Now the question is, do all mountain goats climb this way? The researchers note that this was a study of just one animal, and a young one at that. Perhaps other mountain goats, either younger or older, climb in a different way. Plus, this was an opportunistic study, in which the researchers had no control over the setting.
“As a result,” they write, “it is not known if all mountain goats show the same movement pattern, or how this movement pattern changes in regards to the mountain slope the animal is climbing.”

In other words, they’ll need more than your YouTube videos to figure it out.

Corals in crisis
Algae that provide nutrients to corals turn toxic and lead the corals to “bleach” and sometimes die when ocean temperatures spike. Researchers are seeding damaged reefs with baby corals and breeding heat-tolerant corals to help these imperiled marine animals, Amy McDermott reported in “Rebuilding reefs” (SN: 10/29/16, p. 18).

Ronald Swager wondered if researchers could use genetic engineering to make heat-stressed algae nontoxic.

Gene-editing tools may help corals survive, but the research is still quite preliminary, says Janelle Thompson, an environmental microbiologist at MIT. Among the difficulties: Scientists do not know how exactly the algae become toxic on a molecular level and they can only guess at the role of most algal genes. “One of the main challenges is the size of the [algae] genome, which … is on par with human genomes,” Thompson says. And there are many genetic variations of algae, some of which are only compatible with specific corals. Researchers would have to engineer more than one type of algae.
Heat-tolerant algae exist, but so far they don’t seem to perform well at normal temperatures, says Peter Harrison of Southern Cross University in Lismore, Australia. Assuming biologists work through the technical hurdles of genetic engineering, many people will be concerned about releasing genetically modified algae into the oceans, Harrison says.

Codex contention
Once regarded as fake by some scientists, a 10-page, bark-paper book called the Grolier Codex is authentic, according to a recent study by Yale archaeologist Michael Coe and colleagues. It may be the oldest known manuscript of ancient America, Bruce Bower wrote in “Maya codex real, analysis claims” (SN: 10/29/16, p. 16).
Physicist and astronomer John Carlson of the University of Maryland in College Park took issue with the study and Science News’ reporting. Carlson’s letter has been edited for brevity.

“I was dismayed to see my own published work establishing the authenticity of the Maya ‘Grolier Codex’ as likely the ‘oldest surviving book on paper from the ancient Americas,’ presented as ‘new analysis’ by Michael Coe and collaborators.

“There was no mention of the source of the most crucial evidence — the only radiocarbon dating of the codex’s bark paper — nor was I contacted for comments. My work, beginning in the late 1970s (and first published in 1983), determined that what had been known as ‘page 11’ was actually the lower portion of ‘page 10.’ That finding, with other primary sources, established a sequence of skeletal Evening Star manifestations of the planet Venus, something that could not have been known to any alleged faker in the mid-1960s when the codex was discovered. This work helped convince the majority of Mesoamericanist experts in Maya epigraphy and codex studies that the codex was genuine.

“I was able to study the codex itself carefully on three occasions and obtained the first carbon-14 dates from the actual codex, placing it in the 13th century. All of this was published in my article ‘The Twenty Masks of Venus’ in Archaeoastronomy in 2014 and presented at the Pre-Columbian Society of Washington, D.C., in November 2014. The scholarly details are available along with many other primary sources on my website: umd.academia.edu/JohnBCarlson.”

In an e-mail response to Science News, Michael Coe emphasizes that his team’s paper credits Carlson for his work on the Grolier Codex. Coe says that even by 1973, well before Carlson’s publications appeared, specialists in Maya writing were convinced that the codex was genuine. The new paper for the first time examines the full range of drawings and writings in the codex, Coe asserts, fitting them in with what’s now known about ancient Maya religion and gods.

SAN FRANCISCO — Earth may have been a water world for much of its history, a new proposal contends. Just like in the Kevin Costner movie, the continents would have been mostly submerged below sea level. Previous proposals have suggested that Earth’s land area has remained comparatively unchanged throughout much of geologic time.

But geoscientist Cin-Ty Lee of Rice University in Houston proposes that Earth’s continents didn’t rise above the waves until around 700 million years ago, when the underlying mantle sufficiently cooled. Though many scientists are unconvinced, that continental rise may have contributed to the rapid diversification of life known as the Cambrian explosion. “The Earth is cooling and that actually has manifestations that dictate how life goes,” Lee said December 15 at the American Geophysical Union’s fall meeting.
Earth’s first continental crust formed billions of years ago. Slabs of this crust “float” above the underlying mantle like icebergs, with relatively cold roots than can extend tens of kilometers into the mantle. A continent’s elevation depends, in part, on the size of its root and the density of the mantle.

Earlier in Earth’s history when the mantle was hotter and less dense, the continents sat largely below sea level with only mountains peeking above the water’s surface, Lee proposed. The cooling of the mantle over time increased the relative buoyancy of the continents and lifted the landmasses above sea level. Considering mantle cooling rates and Earth’s topography, Lee proposes that this expansion of Earth’s dry land took place around 1 billion to 500 million years ago and lasted about 100 million years.

The new land would have altered carbon and nutrient cycles, Lee suggested. These effects could help explain large shifts in Earth’s climate around this time and might have nourished the Cambrian explosion. During that time, around 540 million to 500 million years ago, forerunners of the major groups of animals — from insects to mammals — first emerged.

This tale of rising continents may be overly simplistic, said Laurent Montési, a geodynamicist at the University of Maryland in College Park. Other factors such as the mass of the continents, the amount of water in the oceans and the rate of new crust formation on the seafloor could affect sea levels relative to the continents. The idea is worth considering, he said, “but the evidence is not completely there yet.”

Warning: Furry Logic is not, as the title might suggest, a detailed exploration of mammals’ reasoning skills. Instead, it’s a fun, informative chronicle of how myriad animals take advantage of the laws of physics.

Science writers Matin Durrani and Liz Kalaugher cite a trove of recent (and often surprising) research findings. They draw on their backgrounds — Durrani is a physicist, Kalaugher a materials scientist — to explain how animals exploit sound, light, electricity and magnetism, among other things, in pursuit of food, sex and survival. These creatures don’t consciously use physics the way that humans design and use tools, of course, but they are evolutionary marvels nonetheless.
Peacocks, for example, produce low-frequency sounds while shimmying their tail feathers (SN Online: 04/27/16). The birds use these sounds — and not just the sight of those colorful plumes — to impress females and fend off competing males. At the other end of the sonic spectrum, some bats use stealth echolocation to track down their preferred prey. Moths targeted by these bats have sensors that can pick up these ultrasonic calls, but the bats squeak so softly that a moth can’t hear its stalker until it is less than a half-second’s flight away.

Durrani and Kalaugher let readers know when the science isn’t settled. Researchers aren’t quite sure how peahens pick up males’ infrasonic signals, for example. Scientists also haven’t figured out how the archerfish spits so precisely (SN: 10/4/14, p. 8), knocking prey off low-hanging branches above the water as often as 94 percent of the time. The submerged fish must somehow gauge the angle at which light bends as it enters the water and then accurately compensate for refraction while spewing a stream of water. Amazingly, this feat may be innate rather than learned via trial and error.

Readers need not understand the intricacies of polarized light, Earth’s magnetic field or surface tension to enjoy Furry Logic. Nor is this book an exhaustive account of the characteristics and behavior of every animal that uses such phenomena in interesting ways. There should be plenty of material for a sequel to this fascinating book.