50 years ago, West Germany embraced nuclear power

West German power companies have decided to go ahead with two nuclear power station projects…. Compared with the U.S. and Britain, Germany has been relatively backward in the application of nuclear energy…. The slow German start is only partly the result of restrictions placed upon German nuclear research after the war. — Science News, September 16, 1967

Update
Both East and West Germany embraced nuclear power until antinuclear protests in the 1970s gathered steam. In 1998, the unified German government began a nuclear phaseout, which Chancellor Angela Merkel halted in 2009. The 2011 Fukushima nuclear disaster in Japan caused a rapid reversal. Germany closed eight of its nuclear plants immediately, and announced that all nuclear power in the country would go dark by 2022 (SN Online: 6/1/11). A pivot to renewable energy — wind, solar, hydropower and biomass — produced 188 billion kilowatt-hours of electricity in 2016, nearly 32 percent of German electricity usage.

R.I.P. Cassini

After 20 years in space and 13 years orbiting Saturn, the veteran spacecraft spent its last 90 seconds or so firing its thrusters as hard as it could to keep sending Saturnian secrets back to Earth for as long as possible.

The spacecraft entered Saturn’s atmosphere at about 3:31 a.m. PDT on September 15 and immediately began running through all of its stabilizing procedures to try to keep itself upright. The signal that Cassini had reached its destination arrived at Earth at 4:54 a.m., and cut out about a minute later as the spacecraft lost its battle with Saturn’s atmosphere.
“The signal from the spacecraft is gone, and within the next 45 seconds, so will be the spacecraft,” Cassini project manager Earl Maize announced from the mission control center at NASA’s Jet Propulsion Lab. “I hope you’re all as deeply proud of this amazing accomplishment. Congratulations to you all. This has been an incredible mission, an incredible spacecraft, and you’re all an incredible team. I’m going to call this the end of mission. Project manager, off the net.”

With that, the mission control team erupted in applause, hugs and some tears.
It’s the end of an era. But the spacecraft’s last moments at Saturn will answer questions that couldn’t have been addressed any other way.
Going out in a blaze of glory seems fitting. Since its launch in 1997, the probe traveled a total of 7.9 billion kilometers. It gathered more than 635 gigabytes of science data and took more than 450,000 images. It completed 294 orbits of Saturn, discovered six named moons and made 162 close, deliberate flybys of the ringed planet’s largest and most interesting moons.
The last flyby sealed Cassini’s fate. On September 11, at 12:04 p.m., Cassini passed by Saturn’s largest moon Titan one last time ( SN Online: 9/11/17 ). The moon’s gravity nudged Cassini on an irretrievable trajectory into the giant planet’s atmosphere.
Also blame the moons — particularly lake-dappled Titan and watery Enceladus — for why Cassini went out in such dramatic fashion. The mission team decided to sacrifice the spacecraft when it ran out of fuel, rather than risk a collision with one of those potentially habitable moons and contaminating it with any still-lingering earthly microbes.

“Because of planetary protection and our desire to go back to Enceladus, go back to Titan, go back to the Saturn system, we must protect those bodies for future exploration,” Jim Green, director of NASA’s planetary science division, said at a news conference on September 13.

Even in its months-long death spiral, Cassini collected unprecedented observations. Starting in April, the spacecraft made 22 dives through the unexplored region between Saturn and its rings. Measurements of the gravity and composition in that zone will help solve outstanding mysteries. How long is Saturn’s day? How much material is in the rings? When and how did the rings form?

To answer that last question in particular, “you have to fly between the planet and the rings,” says planetary scientist Matthew Hedman of the University of Idaho in Moscow, who uses Cassini data to study the rings. “That’s risky. We had to wait until the end of the mission to take that risk.”
On September 13 and 14, Cassini took a last look around the Saturn system’s greatest hits, taking a color mosaic image of Saturn and the rings, a movie sequence of Enceladus setting behind Saturn, Titan and tiny moonlets in the rings that pull the icy ring particles around themselves to form features called propellers.

Inside the mission control center on the afternoon of September 14, a hushed operations team waited for Cassini to come online for the last time to start sending the last pictures back (SNOnline: 9/15/17). Then flight engineer Michael Staab at JPL suddenly broke the silence. “Yeah!” he yelled, pumping both arms in the air. Cassini’s last signal had just come in.

“That tells us that the spacecraft is nice and healthy, she’s doing just fine. She’s doing exactly what she’s supposed to do, like she’s done for 13 years,” Staab said. “We’re just gonna track her now, all the way in.”
In the wee hours of September 15, the spacecraft reconfigured itself to shift from a recording device to a transmitting probe. As of that moment, its last and only job was to stream everything it could sense directly back to Earth in real time. Turning so that its ion neutral mass spectrometer was facing directly towards Saturn, Cassini could taste the atmosphere for the first time and investigate a phenomenon called “ring rain,” in which water and ice from the rings splash into the atmosphere. This idea was introduced in the early 1980s, but Cassini has already shown that it’s more complicated than previously thought.

“We’re trying to find out exactly what is coming from the rings and what is due to the atmosphere,” Hunter Waite, Cassini team lead for the mass spectrometer instrument and an atmospheric scientist at the Southwest Research Institute in San Antonio, said at the Sept. 13 news conference. “That final plunge will allow us to do that.”
That plunge happened at about 3:31 a.m., when Cassini entered the atmosphere about 10 degrees north of the equator, falling at around 34 kilometers per second. It took data constantly, directly measuring the temperature, magnetic field, plasma density and composition of the upper layers of Saturn’s atmosphere for the first time ever.
When it hit the atmosphere, Cassini started firing its thrusters to keep its antenna pointed at Earth despite the forces of the atmosphere trying to knock it askew. But about a minute later, the atmosphere won, when Cassini was about 1,400 kilometers above the cloud tops.

What happened next, scientists can only imagine. Models suggest this fiery demise: The spacecraft attempted to stabilize itself, but to no avail. It started to tumble faster and faster. Atmospheric friction broke the spacecraft apart, bit by bit — first its thermal blankets burned off, then aluminum components started to melt. The spacecraft probably fell another 1,000 kilometers as it disintegrated like a meteor, Maize said.

Saturn’s atmosphere crushed and melted the bits and pieces, until they completely dissociated and became part of the very planet the spacecraft had been sent to observe.

When all was said and done, the spacecraft lasted about 30 seconds longer than expected. That may help ensure the team got enough data to figure out Saturn’s rotation period, science team member Michele Dougherty of Imperial College London said at a post-mission news conference September 15. “I’m hoping we can do it, I’m not going to promise. Ask me in three months’ time.”

There are no planned future missions to Saturn, although some Cassini alumni are already working on proposals.
Outer solar system astronomers are now setting their sights on Jupiter and its icy, possibly life-friendly moons. The European Space Agency’s Jupiter Icy Moons Explorer (JUICE) and NASA’s Europa Clipper both hope to launch around 2022. Those missions may pave the way for a lander on Europa (SN Online: 2/18/17), which could directly look for life in that moon’s subsurface seas.

Planetary scientist Kevin Hand at JPL, who is leading the science definition team for the proposed Europa lander, feels a debt to Cassini.

“When you’re at the earliest frontiers of exploration, it’s hard to feel sad,” he said. “The wake we’re experiencing right now for Cassini, it’s not so much an end but the early steps that pave the way for the next stage of exploration.”

Even Maize is more proud than mourning.

“This is exactly the way we always planned it. It’s sad that we’re losing this incredible discovery machine,” he said in the moments leading up to Cassini’s disintegration. “But the real sense here is just, all right, we got it!”

From day one, a frog’s developing brain is calling the shots

Frog brains get busy long before they’re fully formed. Just a day after fertilization, embryonic brains begin sending signals to far-off places in the body, helping oversee the layout of complex patterns of muscles and nerve fibers. And when the brain is missing, bodily chaos ensues, researchers report online September 25 in Nature Communications.

The results, from brainless embryos and tadpoles, broaden scientists’ understanding of the types of signals involved in making sure bodies develop correctly, says developmental biologist Catherine McCusker of the University of Massachusetts Boston. Scientists are familiar with short-range signals among nearby cells that help pattern bodies. But because these newly described missives travel all the way from the brain to the far reaches of the body, they are “the first example of really long-range signals,” she says.
Celia Herrera-Rincon of Tufts University in Medford, Mass., and colleagues came up with a simple approach to tease out the brain’s influence on the growing body. Just one day after fertilization, the scientists lopped off the still-forming brains of African clawed frog embryos. These embryos survive to become tadpoles even without brains, a quirk of biology that allowed the researchers to see whether the brain is required for the body’s development.
The answer was a definite — and surprising — yes, Herrera-Rincon says. Long before the brain is mature, it’s already organizing and guiding organ behavior, she says. Brainless tadpoles had bungled patterns of muscles. Normally, muscle fibers form a stacked chevron pattern. But in tadpoles lacking a brain, this pattern didn’t form correctly. “The borders between segments are all wonky,” says study coauthor Michael Levin, also of Tufts University. “They can’t keep a straight line.”
Nerve fibers that crisscross tadpoles’ bodies also grew in an abnormal pattern. Levin and colleagues noticed extra nerve fibers snaking across the brainless tadpoles in a chaotic pattern, “a nerve network that shouldn’t be there,” he says.

Muscle and nerve abnormalities are the most obvious differences. But brainless tadpoles probably have more subtle defects in other parts of their bodies, such as the heart. The search for those defects is the subject of ongoing experiments, Levin says.
In addition to keeping patterns on point, the young frog brain may protect its body from chemical assaults. A molecule that binds to certain proteins on cells in the body had no effect on normal embryos. But when given to brainless embryos, the same molecule caused their spinal cords and tails to grow crooked. These results suggest that early in development, brains keep embryos safe from agents that would otherwise cause harm.

“The brain is instructing cells that are really a long way away from it,” Levin says. While the precise identities of these long-range signals aren’t known, the researchers have some ideas. When brainless embryos were dosed with a drug that targets cells that typically respond to the chemical messenger acetylcholine, the muscle pattern improved. Similarly, the addition of a protein called HCN2 that can tweak the activity of cells also seemed to improve muscle development. More work is needed before scientists know whether these interventions are actually mimicking messaging from the early brain, and if so, how.

Frog development isn’t the same as mammalian development, but frog development “is pretty applicable to human biology,” McCusker says. In fundamental ways, humans and frogs are built from the same molecular toolbox, she says. So the results hint that a growing human brain might also interact similarly with a growing human body.

A baby ichthyosaur’s last meal revealed

As far as last meals go, squid isn’t a bad choice. Cephalopod remains appear to dominate the stomach contents of a newly analyzed ichthyosaur fossil from nearly 200 million years ago.

The ancient marine reptiles once roamed Jurassic seas and commonly pop up in England’s fossil-rich coast near Lyme Regis. But a lot of ichthyosaur museum specimens lack records of where they came from, making their age difficult to place.

Dean Lomax of the University of Manchester and his colleagues reexamined one such fossil. Based on its skull, they identified the creature as a newborn Ichthyosaurus communis. Microfossils of shrimp and amoeba species around the ichthyosaur put the specimen at 199 million to 196 million years old, the researchers estimate.

Tiny hook structures stand out in the newborn’s ribs — most likely the remnants of prehistoric black squid arms. Another baby ichthyosaur fossil that lived more recently had a stomach full of fish scales. So the new find suggests a shift in the menu for young ichthyosaurs at some point in their evolutionary history, the researchers write October 3 in Historical Biology.

Climate change may threaten these bamboo-eating lemurs

The only lemurs so dependent on bamboo that they gnaw on hardened, nutrient-poor stems during the dry season might dwindle away as those seasons grow longer.

Reconstructing the history of the greater bamboo lemur (Prolemur simus) in Madagascar suggests that drier areas over thousands of years already have lost their populations. As the region dries further due to climate change and the bad-bamboo months in the last holdouts lengthen, remaining populations of these critically endangered lemurs might go hungry and fade away too, an international research team warns online October 26 in Current Biology.

Other animals, even another lemur species, will eat lots of bamboo shoots and leaves. But the greater bamboo lemur is the only mammal besides the giant panda that sticks with bamboo during the dry season. That’s when the plants stop sprouting and offer only culm, the tough, old, yellowing stems poor in nutrients. Culm hasn’t reached the hard stage of bamboo that’s used as a building material. “Nobody wants to eat that,” says study coauthor Alistair Evans, an evolutionary morphologist at Monash University in Melbourne, Australia.

This lemur species with its extreme diet had already been feared extinct once, around the middle of the last century, but relic populations turned up. Current survivors remain more toward the eastern part of the island, where dry seasons are apparently survivable, at least for now.

EPA OKs first living pest-control mosquito for use in United States

In a big step toward catching up with the rest of the world, the United States cleared the way for using mosquitoes as a commercial pest control for the first time.

The U.S. Environmental Protection Agency has approved using a strain of male Asian tiger mosquitoes (Aedes albopictus) as a biopesticide in the District of Columbia and 20 states, including California and New York. Kentucky-based MosquitoMate was granted the right to sell these mosquitoes, called ZAP Males, for the next five years, the agency announced November 7.
These male mosquitoes are not genetically modified. Instead they carry a strain of Wolbachia bacteria that turns them into saboteur dads. When they mate with wild females not carrying the strain, the offspring will die and the population should dwindle. Males don’t bite, so releasing them should not add extra vexation.

Releases of Wolbachia-bearing mosquitoes for pest control already go on in other countries, such as Brazil, although with a different bacterial strain and a different strategy.

This same company has also been testing the effectiveness of a different mosquito species, Aedes aegypti, also carrying bad-dad Wolbachia, near Key West, Fla. (These mosquitoes are not commercially available.) The tests “ended a bit early due to [Hurricane] Irma,” says Stephen Dobson of MosquitoMate, “but we think that we have some good data despite this complication.”

See these first-of-a-kind views of living human nerve cells

The human brain is teeming with diversity. By plucking out delicate, live tissue during neurosurgery and then studying the resident cells, researchers have revealed a partial cast of neural characters that give rise to our thoughts, dreams and memories.

So far, researchers with the Allen Institute for Brain Science in Seattle have described the intricate shapes and electrical properties of about 100 nerve cells, or neurons, taken from the brains of 36 patients as they underwent surgery for conditions such as brain tumors or epilepsy. To reach the right spot, surgeons had to remove a small hunk of brain tissue, which is usually discarded as medical waste. In this case, the brain tissue was promptly packed up and sent — alive — to the researchers.
Once there, the human tissue was kept on life support for several days as researchers analyzed the cells’ shape and function. Some neurons underwent detailed microscopy, which revealed intricate branching structures and a wide array of shapes. The cells also underwent tiny zaps of electricity, which allowed researchers to see how the neurons might have communicated with other nerve cells in the brain. The Allen Institute released the first publicly available database of these neurons on October 25.

A neuron called a pyramidal cell, for instance, has a bushy branch of dendrites (orange in 3-D computer reconstruction, above) reaching up from its cell body (white circle). Those dendrites collect signals from other neural neighbors. Other dendrites (red) branch out below. The cell’s axon (blue) sends signals to other cells that spur them to action.
Like the chandelier cell, a Martinotti cell (below) quiets other cells with messages coming from its tangled, tall axon, which spans several layers of the brain’s cortex — the wrinkly, outer layer that’s involved in higher-level thought. And in a basket cell (above), axon branches, which allow the nerve cell to send messages to other neurons, cluster densely around the cell body.
Because the neurons play different roles in the brain, the new collection could help researchers figure out the details of those diverse jobs. Similar data exist for cells taken from the brains of other animals, such as mice, but until now, data on live cells from people have been scarce.

“These neurons are amazingly beautiful,” says Ed Lein, a neuroscientist at the Allen Institute who works on the project. “They look like trees. They’re much more complex than similar cells in a mouse.”

Hidden hoard hints at how ancient elites protected the family treasures

BOSTON — Long before anyone opened a bank account or rented a safe deposit box, wealth protection demanded a bit of guile and a broken beer jug. A 3,100-year-old jewelry stash was discovered in just such a vessel, unearthed from an ancient settlement in Israel called Megiddo in 2010. Now the find is providing clues to how affluent folk hoarded their valuables at a time when fortunes rested on fancy metalwork, not money.

At the fortress city of Megiddo, a high-ranking Canaanite family stashed jewelry in a beer jug and hid it in a courtyard’s corner under a bowl, possibly under a veil of cloth, Eran Arie of the Israel Museum in Jerusalem, said November 17 at the annual meeting of the American Schools of Oriental Research.
The hoard’s owners removed the jug’s neck and inserted a bundle of 35 silver items, including earrings and a bracelet, which were wrapped in two linen cloths. Other valuables were then added to the jug, including around 1,300 beads of silver and electrum — an alloy of gold and silver — that had probably been threaded into an elaborate necklace. There were 10 additional pieces of electrum jewelry, including a pair of basket-shaped earrings, each displaying a carved, long-legged bird.
A Canaanite city palace stood only about 30 meters from the Iron Age building that housed the courtyard, Arie said. Due to the lesser building’s strategic location, its inhabitants must have held key government positions, he proposed. “For the family that lived there, the hoard represented the lion’s share of their wealth.” Those family members presumably fled around the time the structure that held the jewelry hoard was destroyed in a catastrophic event, possibly a battle.
The Megiddo hoard was hidden but not buried, giving its owners quick access to their valuables. But no one ever retrieved the treasure. “We will never know why no one returned to claim this hoard,” Arie said.

Here’s what really happened to Hanny’s Voorwerp

The weird glowing blob of gas known as Hanny’s Voorwerp was a 10-year-old mystery. Now, Lia Sartori of ETH Zurich and colleagues have come to a two-pronged solution.

Hanny van Arkel, then a teacher in the Netherlands, discovered the strange bluish-green voorwerp, Dutch for “object,” in 2008 as she was categorizing pictures of galaxies as part of the Galaxy Zoo citizen science project.

Further observations showed that the voorwerp was a glowing cloud of gas that stretched some 100,000 light-years from the core of a massive nearby galaxy called IC 2497. The glow came from radiation emitted by an actively feeding black hole in the galaxy.
To excite the voorwerp’s glow, the black hole and its surrounding accretion disk, the active galactic nucleus, or AGN, should have had the brightness of about 2.5 trillion suns; its radio emission, however, suggested the AGN emitted the equivalent of a relatively paltry 25,000 suns. Either the AGN was obscured by dust, or the black hole slowed its eating around 100,000 years ago, causing its brightness to plunge.

Sartori and colleagues made the first direct measurement of the AGN’s intrinsic brightness using NASA’s NuSTAR telescope, which observed IC 2497 in high-energy X-rays that cut through the dust.

They found that the AGN is obscured by dust and it is dimmer than expected; the feeding has slowed way down. The team reported on arXiv.org on November 20 that IC 2497’s heart is as bright as 50 billion to 100 billion suns, meaning it dropped in brightness by a factor of 50 in the past 100,000 years — a less dramatic drop than previously thought.
“Both hypotheses that we thought before are true,” Sartori says.

Sartori plans to analyze NuSTAR observations of other voorwerpjes to see if their galaxies’ black holes are also in the process of shutting down — or even booting up.

“If you look at these clouds, you get information on how the black hole was in the past,” she says. “So we have a way to study how the activity of supermassive black holes varies on superhuman time scales.”

Editor’s note: This story was updated December 5, 2017, to clarify that the brightness measured by the researchers came from the accretion disk around an actively eating black hole, not the black hole itself.

Narwhals react to certain dangers in a really strange way

When escaping from humans, narwhals don’t just freeze or flee. They do both.

These deep-diving marine mammals have similar physiological responses to those of an animal frozen in fear: Their heart rate, breathing and metabolism slow, mimicking a “deer in the headlights” reaction. But narwhals (Monodon monoceros) take this freeze response to extremes. The animals decrease their heart rate to as slow as three beats per minute for more than 10 minutes, while pumping their tails as much as 25 strokes per minute during an escape dive, an international team of researchers reports in the Dec. 8 Science.
“That was astounding to us because there are other marine mammals that can have heart rates that low but not typically for that long a period of time, and especially not while they’re swimming as hard as they can,” says Terrie Williams, a biologist at the University of California, Santa Cruz. So far, this costly escape has been observed only after a prolonged interaction with humans.

Usually, narwhals will escape natural predators such as killer whales by stealthily slipping under ice sheets or huddling in spots too shallow for their pursuers, Williams says. But interactions with humans — something that will happen increasingly as melting sea ice opens up the Arctic — may be changing that calculus.
“When narwhals detect humans, they often dive quickly and disappear from sight,” says Kristin Laidre, an ecologist at the University of Washington in Seattle who studies marine mammals in the Arctic.
Williams and her colleagues partnered with indigenous hunters in East Greenland to capture narwhals in nets. Then, the researchers stuck monitoring equipment to the narwhals’ backs with suction cups and released the creatures. The team tracked the tail stroke rate and cardiovascular response of the narwhals after their release, and determined how much energy the animals used during their deep escape dives.

During normal dives, narwhals reduce their heart rate to about 10 to 20 beats per minute to conserve oxygen while spending prolonged time underwater. These regular deep dives to forage for food don’t require rigorous exercise. But during escape dives after being entangled in a net for an hour or longer, “the heart rates were going down to levels of three and four beats per minute, and being maintained at that level for 10 minutes at a time,” Williams says.

The narwhals were observed making multiple dives to depths of 45 to 473 meters in the hours following escape. When fleeing, the tusked animals expended about three to six times as much energy as they normally burn while resting. The authors calculated that the frantic getaway, combined with what they called “cardiac freeze,” severely and rapidly depletes the narwhals’ available oxygen in their lungs, blood and muscles — using 97 percent of the creatures’ oxygen stores compared with 52 percent on normal dives of similar depth and duration.

“There is a concern from our group that this is just pushing the biology of these animals beyond what they can do,” Williams says. As human activity increases in the Arctic, there may be more chance of inciting this potentially harmful escape response in narwhals.

The creatures may also become more vulnerable to other human-caused disturbances, such as seismic exploration, hunting and noise from large vessels and fishing boats. The researchers plan to investigate whether these activities cause the same flee-and-freeze reaction, and whether this extreme response affects narwhals’ long-term health.

This study “provides a new physiological angle on the vulnerability of narwhals to anthropogenic disturbance, which is likely to increase in the Arctic with sea ice loss,” Laidre says. Better understanding the human impacts on narwhals is essential for conservation of this species, she adds.