Like an interplanetary parfait, the dwarf planet Ceres appears to have layers.

A pliable outer shell of minerals, ices and salts encapsulates a core of solid rock, a new study suggests. This first peek inside Ceres — courtesy of NASA’s Dawn spacecraft — can help researchers explain some mysteries on the surface and provide insight into the many ways planets and asteroids might be assembled. Ryan Park, a planetary scientist at the Jet Propulsion Laboratory in Pasadena, Calif., and colleagues report the findings online August 3 in Nature.
“Before we got to Ceres, we didn’t know what the interior looked like,” Park says. “Its evolution is more complex than what we envisioned.”

Ceres is the largest body in the asteroid belt, the field of rocks that lies between the orbits of Mars and Jupiter. The Dawn spacecraft has been orbiting Ceres since March 6, 2015, its second stop after spending 14 months at the asteroid Vesta (SN: 4/4/15, p. 9). As Dawn loops around Ceres, slight changes in the speed of the spacecraft — deviations of less than 0.1 millimeters per second — reveal the dwarf planet’s gravity field. By combining these measurements with images that show the overall shape of Ceres, the researchers deduced how mass is spread out inside. The core has a density similar to some meteorites; the shell (roughly 70 to 190 kilometers thick) is about two-thirds as dense.
Mountains on Ceres appear to float on a deformable layer of minerals and volatile elements that easily evaporate, Park and collaborators report. If Ceres were completely solid, then gravity over a mountain would be stronger than the surrounding terrain because of the increased mass. But gravity on Ceres doesn’t vary with topography, the researchers find. This suggests that mountains and hills displace mass beneath the surface, “like how a boat floats on water,” says Park. To keep the underlying layer slightly flexible, the temperature inside Ceres must be warm relative to the surface. That heat could come from radioactive decay or be left over from when Ceres assembled itself over 4 billion years ago.
This segregation of material — a solid core topped with a malleable crust — can help researchers learn about the environment in which Ceres formed, says Simone Marchi, a planetary scientist at the Southwest Research Institute in Boulder, Colo. Densities within these layers can lead to estimates of how much ice and radioactive material lies buried beneath the surface, he says — abundances which depend on how far from the sun Ceres was born.

Understanding the internal structure could also be key to solving a mystery: No craters on Ceres are wider than about 280 kilometers, which is odd given what researchers know about the population of rocks that should have slammed into it (SN: 9/5/15, p. 8). Something probably eroded those craters, though it’s not yet clear what. Marchi speculates that the erosion has something to do with Ceres’ internal evolution and composition.

Aside from getting an idea of how Ceres is put together, the findings can be applied to other worlds both in our solar system and around other stars, says Peter Thomas, a planetary scientist at Cornell University. Insight from Ceres adds “a whole new dimension of things that may not have been imagined before,” he says. “How many different kinds of objects — planets, dwarf planets, asteroids — can you get?”

New investigations of England’s infamously fraudulent Piltdown Man fossils reveal a mix of clever and clumsy methods used by one man to fool early 20th century scientists for 40 years.

Lawyer and amateur archaeologist Charles Dawson modified orangutan and human bones to resemble what scientists of the time anticipated a “missing link” between apes and humans would look like, say paleoanthropologist Isabelle De Groote of Liverpool John Moores University in England and colleagues. Dawson and British paleontologist Arthur Smith Woodward announced the discovery of what they called Eoanthropus dawsoni, or Dawson’s dawn man, in December 1912.
Consistent forgery techniques employed on an orangutan jaw, four orangutan teeth and six braincase pieces from two or perhaps three humans point to Dawson as the lone culprit who planted faux fossils in a gravel deposit near Piltdown village, De Groote’s team reports August 10 in Royal Society Open Science. The results provide the strongest evidence to date that Dawson had no help in perpetrating the hoax.

“Hopefully this is the final, or close to the final, nail in the coffin of the Piltdown story, confirming Dawson’s guilt and sole responsibility,” says archaeologist Miles Russell of the Bournemouth University in Poole, England.

As an artifact collector for a local museum, with access to collections of animal bones, Dawson could easily have obtained an orangutan jaw, Russell says. Russell previously argued that Dawson not only created Piltdown Man on his own but also fabricated many finds in his personal collection, including an alleged reptile/mammal hybrid fossil.
High-resolution 3-D imaging by De Groote’s team shows that the orangutan jaw was cracked lengthwise, probably while being stretched by hand from its two ends. Dawson had to widen the jaw’s tooth sockets to remove two molar teeth, which in great apes have telltale curved roots, the researchers say. Dawson then filed the teeth to appear more humanlike and repositioned them in their sockets. A thin layer of putty kept the teeth in place.
“I was surprised by how major some of the modifications were, changes which had not been noticed before,” says study coauthor Chris Stringer, a paleoanthropologist at the Natural History Museum in London.

Since publication of a scientific paper in 1953 and a 1955 book exposing the Piltdown Man hoax — long after Dawson’s death in 1916 — a lengthy list of proposed coconspirators in the embarrassing affair has accumulated. Names include Smith Woodward and French priest Teilhard de Chardin, who attended some Piltdown excavations.

Dawson didn’t need their help, De Groote says. Imaging studies of the internal structure of Piltdown orangutan teeth indicate they came from the same individual. So do matching sequences of mitochondrial DNA extracted from two teeth, one of which came from a second Piltdown site. Before he died, Dawson had informed Smith Woodward of further Eoanthropus finds about three kilometers from the first site.

Dawson did a better job of forging humanlike wear on a tooth from the second site. He may have learned from comments of some early scientific critics of Piltdown Man, the investigators suspect.

Gravel was placed in cavities of two Piltdown teeth, through holes where the roots had been damaged. These cavities were plugged with pebbles held in place by the same putty used on the orangutan jaw.

Dawson created his forgery from at least two human skulls, since remains from the same rear section of the braincase were planted at both Piltdown sites, De Groote’s group says.

Dawson had access to medieval burials during his archaeological work. He could have selected the thickest skull fragments he could find from medieval individuals to pass off as Piltdown Man, Russell suggests. Dawson knew that such bones would appear particularly apelike. Radiocarbon dating of Piltdown skull fragments remains inconclusive.

To match the color of Piltdown gravel, Dawson stained his phony fossils reddish brown. He did the same to nonhuman animal bones, stone tools and a carved bone that were planted as part of the sham.

Dawson’s ambition to be elected a Fellow of the Royal Society, a major scientific honor that he was nominated for but didn’t receive, may have motivated him to fake finds that culminated in Piltdown Man, the researchers say.

The new study demonstrates that Dawson “satiated his attention-seeking by perpetrating skillful, and not so skillful, fraud,” says paleoanthropologist Bernard Wood of George Washington University in Washington, D.C. When Dawson faked a skull that his peers wanted to be real at least as badly as he wanted official recognition, “they gave him pass after pass.”

Editor’s note: This story was updated on August 3, 2016, to correct the scale bar on the image of the tooth.

Primates may have some high-flying relatives. Colugos, small mammals that glide from treetop to treetop in forests throughout Southeast Asia, have an evolutionary history that’s long been debated. Their teeth look similar to tree shrews’ teeth, while other skull and genetic features resemble those of primates. (Past studies have even linked colugos to bats and other insect-eating mammals.)

In an effort to settle the debate, William Murphy, a geneticist at Texas A&M University in College Station, and colleagues have deciphered the genome of a male Sunda colugo (Galeopterus variegatus) from West Java, Indonesia. Comparing colugo DNA with 21 other mammal genomes, the team found that colugos are most closely related to primates, while tree shrews took different evolutionary paths to arrive at similar traits. There are also changes in genes related to vision and gliding that are unique to colugos, the researchers report August 10 in Science Advances.
Genetic data from colugos preserved in museums also show that the animals are more diverse than suspected. While only two species have been described in the wild, the team found at least seven separate genetic lineages, which may represent individual species.

A large study of human genetic variation finds more than 7 million spots where one person’s DNA can differ from another’s. Analyses of such variants, compiled from cataloging the genes from more than 60,000 people, are already offering doctors helpful insights into diseases such as schizophrenia and some heart conditions.

Researchers from the Exome Aggregation Consortium first presented their analysis of the ExAC database online at bioRxiv.org last year (SN: 12/12/15, p. 8). Now, the project is getting its official debut in the Aug. 18 Nature.
An exome is just the protein-producing genes in a person’s genetic instruction book, or genome. Researchers from nearly two dozen studies around the world pooled exome data they had collected from 60,706 people, nearly 10 times more data than any previous study of human genetic variation. The people in the study were far more racially and ethnically diverse than any previous study as well, and included both people with various diseases and healthy people.

Any one person carries tens of thousands of DNA variants, said Daniel MacArthur, a geneticist at Massachusetts General Hospital in Boston, in a telephone press briefing. The ExAC team found that, on average, one in every eight DNA bases (the information-encoding chemical building blocks of DNA) differs among people. In total, the researchers recorded more than 7.4 million DNA variants, most of them changes in single DNA bases.

ExAC researchers released the data in 2014 for other scientists to use. Already these data have contributed to the day-to-day interpretation of genetic information in the clinic, says Eliezer Van Allen, a medical oncologist at Harvard Medical School. “It gives a new look into the drivers of human genetic diversity.”

A companion paper published August 17 in Nature Genetics, for instance, found that people are missing some genes or have extra copies of other genes. On average, people have 0.81 deleted genes and 1.75 duplicated genes. The analysis echoed previous studies in showing that people with schizophrenia are more likely to have such missing or duplicated genes, particularly genes important in the brain.
It’s a relief to researchers that the paper confirms the results of previous schizophrenia studies, says Jennifer Mulle, a psychiatric geneticist at Emory University in Atlanta who was not involved in the work. “We all breathe a collective sigh of relief that this thing we thought to be true continues to be true,” she says.
Now, the challenge is to figure out what all of the variations mean.

Two independent studies suggest that the ExAC data could give doctors and researchers a clearer picture of the gene changes that contribute to heart conditions known as cardiomyopathies.

As DNA sequencing studies, which decipher people’s genetic makeup, became more common in the last 10 years, researchers amassed a growing number of rare DNA variants implicated in causing the heart diseases. “There was always a lot of doubt cast about whether these [variants] were real or not,” says Roddy Walsh, a geneticist at Imperial College London.

Walsh and colleagues used the ExAC data and DNA data from 7,855 cardiomyopathy patients to reevaluate the likelihood that a particular variant would cause a heart problem. Finding a variant in heart patients that is rarely seen in people without the disease suggests the variant could be causing the disease. But if the variant appears just as often in the general population that don’t have cardiomyopathies as in patients, it is unlikely to cause disease.

Of the people in ExAC, 11.7 percent carry variants associated with hypertrophic cardiomyopathy, Walsh and colleagues report August 17 in Genetics in Medicine. That’s far more people than expected for a rare inherited heart condition, which strikes about one in 500 people. Those data and other evidence suggest that many of the variants implicated in the disease are actually benign, the researchers say.

ExAC data alone aren’t enough to rule out a potentially disease-causing variant, says Benjamin Meder, a cardiologist at Heidelberg University Hospital in Germany. Researchers don’t know the full medical history of the ExAC volunteers. Some may have undetected cases of cardiomyopathy, or others may have been misdiagnosed as having the disease, which could throw off the results, he says. It’s important to clearly define who has a disease and who doesn’t before conducting genetic studies, Meder says. “This paper does it the wrong way around.” Still, he says the study does offer some valuable insights into the genetics of heart problems.

Misdiagnosing a genetic disease can negatively affect entire families, says Isaac Kohane, a biomedical informaticist at Harvard Medical School. For instance, people related to a young person who collapses on the basketball court and is found to carry a rare variant associated with the heart condition may also be screened for the genetic variant. Family members carrying the disease-associated variant may be treated for a condition they don’t have.

Such misdiagnosis is much more likely for African-Americans, Kohane and colleagues report August 17 in the New England Journal of Medicine. Five variants previously associated with hypertrophic cardiomyopathy kept popping up again and again in the general population most of whom do not have the heart condition, Kohane’s team found. Those variants are far too common to cause a rare genetic disorder; 2.9 to 27.1 percent of black Americans were found to carry at least one copy of the variants, while 0.02 to 2.9 percent of white Americans had one of the variants.

Kohane and colleagues now say the variants are benign. The mistake could have been avoided if researchers had included even a few black Americans in their studies, most of which involved people of European descent who carry only a fraction of the genetic diversity found people with recent African ancestry. The researchers calculate that the ExAC data, with its great genetic diversity, could rule out many benign variants including ones carried by 0.1 percent of the population.

COLUMBIA, Mo. — If you find a daddy longlegs in your house, don’t be scared. “Daddy longlegs are actually pretty docile animals when it comes to interacting with humans,” says evolutionary biologist Kasey Fowler-Finn, who studies the arachnids at St. Louis University. Specifically, she studies daddy longlegs sex. She is using this common group of arachnids (they’re not spiders) to explore how mating behaviors can be shaped by evolutionary forces.

Daddy longlegs — which can be found in forests, in leaf litter, on tree trunks and, of course, in your garage in eastern North America — are a group of harvestmen with elongated legs. And like all harvestmen, their second pair of legs, which is used in sensory exploration instead of walking, is particularly long.

But what makes daddy longlegs especially interesting is what happens when they mate. “Most of us just think ‘ew’ when we see them, but they have this really fascinating suite of [mating] behaviors,” Fowler-Finn said July 31 at the 53rd Annual Conference of the Animal Behavior Society. “The same basic stuff happens with all species in the clade, but the details vary quite a bit.”

The mating ritual starts with individuals bumping into each other (scientists don’t yet know how males and females find one another). “Then shortly thereafter, males will attempt to engage the females in what’s called a ‘mating embrace,’” Fowler-Finn said. “They hook their pedipalps [a type of appendage on the front of the arachnid] behind the female’s sensory legs … and then there’s a bunch of back and forth between males and females that varies in duration across species.” Mating can last for 15 seconds in some species, and three to four hours in others. The male then delivers a nuptial gift and his ejaculate, and the pair separates.

There can be a lot of aggression during all of this, with males and females biting each other and even losing legs during mating. And this, too, can vary from species to species. Leiobunum vittatum encounters, for instance, are almost always violent, while L. aldrichi matings are aggressive only about half of the time.

L. aldrichiis one of Fowler-Finn’s favorites. “The male actually grabs the female’s second leg … and then they shake them by one leg,” she said. “And, in fact, this is so particular to the second leg that males who initially grab other legs on the female will continue to search until they find that second leg. So there’s something really cool going on here.” What that might be, though, is a mystery.

Fowler-Finn is still working out whether characteristics of the various daddy longlegs species can predict their mating styles. But she noted that she and her colleagues are finding a lot of variation in behavior not just across species but also by geographic area. She suspects that as she and her team describe these differences, they are going to find evidence for plenty of new species to scare the arachnophobes out there.

Over the last several years, spacecraft have beamed back images from all across the solar system, revealing a complex tapestry of landscapes. Dust shapes the scenery on comet 67P, whereas ice rules on Pluto and the moons of Saturn.

At first glance, many of these terrains seem the same — mountains, craters and canyons show up everywhere. But each world adds its own geologic signature that marks the land as utterly alien.

While several of the spacecraft’s missions will end in the coming year, a fleet of new explorers ensures that our interplanetary adventures are far from over.

Bonobos — chimpanzees’ sister species — don’t get the credit they deserve as tool users.

Bonobos in a sanctuary’s protected forests in the Democratic Republic of Congo crack nuts with stones nearly as well as wild chimps in other parts of Africa do, researchers report online August 26 in the American Journal of Primatology. Wild bonobos have rarely been observed using tools and have never been reported to pound open nuts with stones (SN: 9/19/15, p. 22).

All 18 adult and adolescent bonobos tracked during April and May 2015 cracked oil palm nuts with stones of various sizes that researchers had placed near oil palm trees, says a team led by Johanna Neufuss of the University of Kent in England. Bonobos chose pounding stones well-suited to busting palm oil nutshells. These animals employed 15 grips to hold nut-cracking stones, including 10 grips not previously observed in nonhuman primates.

Genetic surgery is far away for humans — Optimism concerning application of genetic experiments to improve mankind is unwarranted now, a Canadian pediatrician told the Third International Congress of Human Genetics meeting in Chicago…. Although striking and sometimes controversial experiments in genetic surgery have in fact been performed in multicellular systems, he explained, public demand seems likely to outstrip scientific resources for the treatment of many forms of genetic disease. — Science News, September 24, 1966

UPDATE
Things are looking up for “genetic surgery.” Gene therapy has been around since the 1980s, but researchers have recently developed more precise gene-editing tools, including one that sent a child’s leukemia into remission in 2015. Scientists are most excited about a molecular scalpel known as CRISPR/Cas9 that cuts and manipulates DNA (SN: 9/3/16, p. 22). Researchers are optimistic about the tool’s potential to treat several diseases, but it may be a while before CRISPR is widely used.

Inside a large cave in northwestern Australia’s remote Kimberley region, someone painted an elongated, yamlike shape on a ceiling at least 16,000 years ago, new research suggests. That long-ago creation in the unnamed cavern adds fuel to the argument that rock art in Australia goes back even earlier to the continent’s first inhabitants, researchers contend.

This discovery joins a small number of drawings and paintings from Down Under that have been dated to around the same time or earlier, say archaeologist June Ross of the University of New England in Armidale, Australia, and colleagues. Some scientists have questioned the accuracy of these dates. But the new work, Ross’ team asserts, gives a critical boost to a previous, contested report that a piece of Kimberley rock art depicting a humanlike figure painted over a hand stencil dates to a minimum of about 16,400 years ago.
Ross’ group also obtained minimum age estimates, ranging from around 5,100 to 530 years, for nine other pieces of Kimberley rock art, the researchers report August 31 in PLOS ONE.
People first reached Australia around 50,000 years ago ( SN: 3/15/03, p. 173 ). Researchers generally assume the continent’s colonizers brought rock art traditions with them from Asia. In southeastern Australia’s Yaranda Cave, for instance, claw marks of a type of marsupial that died out around 50,000 years ago appear on top of pigmented human finger marks, says Robert Bednarik, an independent scholar and self-taught rock art authority based in Caulfield South, Australia. But it is difficult to accurately date such art.
Ross’ team — like the researchers who dated the humanlike figure — focused on dating sand grains found inside mud wasps’ nests that the insects built on cave walls and ceilings, covering parts of artistic depictions. Eventually, surviving nests fossilized. Light-induced release of radiation from sand grains in the lab enabled calculations of the time since each grain was last exposed to sunlight, providing a minimum age for the painting beneath the nest.
Four pieces of Kimberley rock art — but not the proposed 16,000-year-old painting — also yielded radiocarbon dates from bits of surviving nests and beeswax stuck to drawings.

Without a confirming radiocarbon date, the new minimum age estimate of 16,000 years for the yamlike Kimberley painting is provisional, Bednarik says. But the timeframe isn’t out-of-bounds. Mineral deposits partly covering hand stencils in an Indonesian cave date to nearly 40,000 years old (SN: 11/15/14, p. 6), although, similarly, no radiocarbon dates exist to confirm that. And researchers have known for decades that meandering impressions on the walls of Koonalda Cave in southern Australian, made by pigment-coated human fingers, must be older than 15,000 years, Bednarik says. The marked walls in Koonalda Cave became inaccessible after that time.

Cosmic mismatch
Researchers used supernovas, cosmic microwave background radiation and patterns of galaxy clusters to measure the Hubble constant — the rate at which the universe expands — but their results were mismatched, Emily Conover reported in “Debate persists on cosmic expansion” (SN: 8/6/16, p. 10).

Reader J.R. Kennedy thought that light-dimming space dust and debris might explain the discrepancy.

Gas and dust in space can have an impact on the brightness of standard candles — objects with known brightness such as type 1a supernovas and some variable stars, Conover says. But astronomers correct for those discrepancies in their measurements.
In the absence of gas and dust, a candle’s apparent brightness should decrease in relation to its distance from Earth. “But if there’s dust in the way, it can make the candle dim more than that,” Conover says. “However, this intervening material doesn’t dim the candle quite in the same way as distance does. It will dim the shorter, bluer wavelengths of light more than the redder ones. Astronomers can look for this effect to identify the impact of dust and correct for it.” So the mismatch stands.
Great escape
High-speed video captured how the o­ffspring of red-eyed tree frogs prematurely break free from their eggs when in danger, Helen Thompson reported in “Under threat, tadpoles make early escape” (SN: 8/6/16, p. 32).
Online reader myndflyte wondered if early hatching had any long-term de-velopmental effects on the tadpoles.

There’s definitely a trade-off involved in hatching early to escape a predator or some other threat, Thompson says. Past work by tree frog researcher Karen Warkentin, now at Boston University, shows that red-eyed tree frog embryos grow tails and mouthparts in the last few days of their roughly weeklong incubation. Those that hatch earlier, up to four days if threatened, tend to be underdeveloped with smaller bodies and shorter tails. “In the short term, this developmental deficit puts early hatchlings at greater risk of getting eaten by pond shrimp and fish than their older brethren,” Thompson says. “But there’s also evidence to suggest that early hatchers compensate down the line and grow at higher rates as tadpoles.”

More to the story
Although the death rate from motor vehicle crashes in the United States has declined since 2000, the country still tops 19 other high-income nations in m­otor vehicle deaths, Alex Maddon wrote in “U.S. still leads in fatal motor vehicle crashes” (SN: 8/6/16, p. 5).

Some readers took issue with the conclusions presented and thought the researchers should have measured fatalities per miles driven instead of per population. “Using a per capita metric makes the U.S. look unsafe when the opposite is true,” John Underwood wrote. “Since A-mericans drive more miles per year than the other countries in the chart, we will have the highest fatality rate per 100,000 population.”

It’s true that fatalities per miles driven changes the ranking. Using the measure “per 100 million vehicle miles traveled,” the United States drops to fifth place, says Deputy M-anaging Editor, Features Cori Vanchieri. When the researchers looked at deaths per 10,000 registered vehicles, however, the United States still topped the list. The researchers’ overall message is that the United States could further reduce crash deaths if seat belt use goes up and alcohol-impaired driving and speeding go down.

Clarification
“Under threat, tadpoles make early escape” (SN: 8/6/16, p. 32) states that the tree frog embryos gape their mouths to stretch out their egg membranes. Not all embryos gape their mouths, and ultimately, an enzyme secreted from the embryo’s snout breaks open the membrane.