Gale Crater on Mars, falsely coloured to show differences in minerals on the surface. Credit: NASA/JPL-Caltech/Arizona State Univ.

Planetary science

Life could have survived in Mars crater

Gale Crater was warm and wet early in its history.

NASA’s Curiosity rover has been exploring Gale Crater on Mars since 2012, and has collected data showing many chemical variations in the crater’s sedimentary rocks. A team led by Joel Hurowitz of Stony Brook University in New York analysed the data and conclude that older rocks seem to have formed in relatively cold climates. By contrast, younger sediments suggest that environmental conditions were warmer and wetter. The crater could have been hospitable to life between 3.8 billion and 3.1 billion years ago, not long after it was first formed. 

In a separate study, a team led by Jens Frydenvang of the University of Copenhagen looked at data from elsewhere in the crater and found large amounts of silica that appear as light-coloured halos on the red rocks. As in hot springs on Earth, the silica was probably deposited by warm water percolating through the ground. It’s unclear when this water movement occurred, but it is likely to be some of the most-recent water flow in the crater, the authors say.

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Climate sciences

Deadly heat is on the rise

More than two billion people face at least 20 days of potentially lethal temperatures each year.

Heatwaves have killed thousands of people in 164 cities around the world since 1980 — and the risk of such events looks set to increase.

To identify climatic conditions associated with unusually high human mortality rates, Camilo Mora at the University of Hawaii at Manoa, Honolulu, and his colleagues analysed more than 900 papers published between 1980 and 2014. From this, they determined a threshold beyond which air temperatures, humidity and other factors can be lethal, and found that about 30% of the global population is currently exposed to potentially deadly heat for at least 20 days per year.

Climate projections suggest that by 2100, that percentage will be at least 48%, even if greenhouse-gas emissions are aggressively reduced. Heat-related health risks and mortality are likely to rise disproportionately in cities and humid regions in the tropics, the authors say.


Tumour DNA highlights targets for therapy

Blood test offers a way to identify those most likely to benefit from treatment for prostate cancer.

DNA floating in the blood provides a window into how people with prostate cancer will fare on drugs known as PARP inhibitors.

PARP inhibitors are used to treat tumours with mutations that disrupt particular DNA-repair pathways. Johann de Bono of the Institute of Cancer Research in London and his colleagues analysed blood samples from 46 people with prostate cancer in a clinical trial of the PARP inhibitor olaparib.

The team found that the amount of tumour DNA in the blood tended to fall more markedly in participants whose tumours shrank following therapy. In some patients who initially responded to treatment but then relapsed, the researchers detected additional mutations that corrected the original DNA-repair defect, allowing tumours to escape the effects of olaparib.

Scans of a mouse cornea get sharper by using improved optical coherence tomography


Innovative approach promises speckle-free scans

Image stacking can slash noise and boost resolution of medical technology.

An imaging technique used in cancer research and for diagnosing eye and heart disease has received a boost in resolution.

Optical coherence tomography allows scientists to map fine structure in living tissue, but it is limited by an image artefact called speckle. This is caused by interference that occurs when the laser beam strikes rough tissue surfaces.

Current speckle-reduction methods degrade image resolution. A team led by Adam de la Zerda at Stanford University in California improved on these by modulating the phase of the beam to vary the speckle pattern, and capturing up to 100 different images that were stacked and averaged to almost eliminate speckle noise.

The improved technique can resolve structures as small as sweat ducts on a human fingertip and the inner structure of a live mouse’s cornea.

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Snake disease turns up in Europe

A deadly fungus that causes skin lesions in snakes has been detected in wild European species for the first time.

Snake fungal disease, caused by Ophidiomyces ophiodiicola, infects at least 30 wild species in North America and can be fatal, but until now had not been reported in wild snakes in other continents.

Becki Lawson at the Institute of Zoology in London and her colleagues screened more than 300 moulted snake skins and around 30 carcasses, from 3 species in the United Kingdom and 1 in the Czech Republic. They found skin lesions on nearly one-quarter of carcasses and moulted skins. DNA analysis confirmed O. ophiodiicola infection in 31% of these samples, including grass snakes (Natrix natrix) and a dice snake (Natrix tessellata).

The European strains of the fungal pathogen were distinct from the North American ones. They were slower growing and may have existed at low levels in Europe for years, the authors say.

Wildfires as those currently raging in Portugal emit more harmful soot than thought

Atmospheric science

Wildfire pollution grossly underestimated

US survey records unprecedented levels of soot.

Wildfires pollute the air more than previously thought — especially when it comes to tiny particles that can lodge in the lungs and cause health problems.

Greg Huey at the Georgia Institute of Technology in Atlanta and his colleagues analysed data gathered by research aeroplanes from the smoke plumes of three major wildfires in the western United States in 2013. The burns emitted more than three times the amount of fine particulate matter, or soot, accounted for in the US National Emissions Inventory.

Earlier estimates of the amount of particulate matter produced by such fires came from controlled burns, but it seems wildfires release much more pollution into the air. The team also measured a range of chemicals coming from the wildfires, including some nitrate compounds spotted for the first time in plumes from burning biomass. Setting controlled burns that improve forest health and reduce the risk of devastating wildfires may be one way to prevent future air-quality problems, the authors say.


Ground-to-air quantum link achieved?

Researchers have transmitted photons to a speeding aircraft, demonstrating technology for space-based quantum communication.

Quantum encryption is secure because the laws of quantum physics guarantee that any eavesdropping would be detectable. But photons, which are used encode a shared quantum key, can travel only relatively short distances through fibres or air before being absorbed, making transmission through space more appealing for long-distance communication.

Thomas Jennewein at the University of Waterloo, Canada, and his collaborators sent photons to a receiver mounted on an aircraft passing overhead at the same apparent rate as a satellite and over distances of up to 10 kilometres. The team successfully transmitted photons in 7 of 14 attempts, generating quantum keys more than 800,000 bits long.

The authors say that this ‘uplink’ scheme, in which photons are generated at ground stations, could be simpler than a set-up used by rivals, which requires complex devices to be put into orbit.


How cats came to dominate the world

Domestic felines followed trade routes to spread into Europe.

Feline remains at ancient burial sites suggest that domestic cats existed in early societies in the Near East and Egypt. But scientists know little about how the animals advanced across the world.

Eva-Maria Geigl at the Institute Jacques Monod in Paris and her colleagues analysed mitochondrial DNA from 209 cats that lived between about 8000 BC and the twentieth century.

They found two distinct populations that contribute to modern domestic cats, one of which appeared in the Middle East and spread to Europe as early as 4400 BC. A separate lineage, initially common only to ancient Egyptian cats, spread to Europe and the Middle East from the fifth century AD onwards.

This move mirrors ancient trade routes, suggesting that a role as ship’s rat catcher might have helped cats to spread to Europe and beyond.


Hunting spiders lose web skills

Adaptations to create sticky traps leaves ground spiders without a safety harness.

Ground spiders (Gnaphosidae) specialize in catching prey that fights back fiercely, including ants and other spiders. They snare their prey with an unusually glue-like silk, which evolved from a thread normally used to anchor a web’s structural silks to surfaces.

Jonas Wolff at Macquarie University in Sydney, Australia, and his colleagues studied 11 species in slow-motion video and examined the biomechanics of their silk and silk-producing structures.

The researchers found that as the gluey silk evolved into a hunting tool, the glands that produce it became bigger, while those that make the main thread shrank. As a result, these ground spiders can no longer spin abseiling ‘draglines’ and are barely able to attach webs to the environment.

Drug discovery

New class of antibiotic found

Natural compound kills bacteria that are resistant to multiple antibiotics.

Richard Ebright at Rutgers University in Piscataway, New Jersey, Stefano Donadio at the biotechnology firm Naicons in Milan, Italy, and their team extracted the antibiotic — called pseudouridimycin — from microbes in soil. They found that it cured bacterial infections in mice and killed several strains of antibiotic-resistant bacteria in culture.

The drug works by stopping bacteria from making RNA — it inhibits the binding of a nucleoside triphosphate, a building block of nucleic acids. Other antibiotics also stop RNA synthesis, but not by the same mechanism. This means that few bacteria will be prepared for pseudouridimycin’s mode of attack, say the authors.The team showed that resistance to pseudouridimycin develops ten times more slowly than it does to rifampin, an existing drug that also inhibits RNA synthesis.

Antiviral drugs that block nucleoside triphosphates have transformed the treatment of hepatitis C and HIV, add the authors, who hope that the new drug will be similarly successful against bacteria.

Computer science

Robot can single out humans

A robot can learn to detect human motion by the tell-tale smoothness with which people move.

To work with humans, robots must discriminate between movements of living and non-living things — a challenging task. Alessia Vignolo at the Italian Institute of Technology in Genoa and her team developed a machine-learning algorithm that exploits the characteristic smoothness with which humans change speed and trajectory on a split-second timescale.

By observing how sharply motion changed, the algorithm learned to differentiate between human actions, such as rolling dough, and the movements of inanimate objects, such as toy trains. The program does not interpret objects on the basis of their appearance, so it was successful even when viewing unfamiliar actions and when a scene was partly obscured.

Installed in a humanoid robot, the algorithm was able to automatically direct the machine’s gaze at humans, a useful skill for social interaction, say the authors.

Astronomy and astrophysics

How galaxies grew

Milky-Way-like galaxies formed through gentle mergers according to mega-simulations.

Large disk-shaped galaxies such as the Milky Way grow bigger when external gas and dark matter merge into them with just the right speed and trajectory.

A team led by Robert Grand at the Heidelberg Institute for Theoretical Studies in Germany created one of the largest cosmological simulations ever run, and used it to show how features such as the Milky Way’s spiral arms came to be. The results suggest that when material flows gently into a growing galaxy, it bulks up the central disk and allows structures such as bars and spiral arms to form. By contrast, violent collisions tend to shred the galaxy and limit its growth, say the authors.

The model ran on two supercomputers over several months and included, for the first time, the effects of magnetic fields that pervade interstellar space. Astronomers can compare the results of the simulations with their observations to better understand galaxy formation, says the team.


How termite mounds begin

Collective digging, rather than depositing of soil, triggers mound building by termites.

No one knows for sure how termites collaborate to build complex structures, although researchers have long thought that a chemical, secreted by the creatures when they deposit soil, prompts others to start dropping soil in the same place.

Ben Green at Harvard University in Cambridge, Massachusetts, and his colleagues observed the behaviour of workers from two species of termite (Macrotermes) in soil-lined Petri dishes. Tracking the insects’ motion and behaviour, the researchers first observed random digging, after which termites clustered at the busiest excavation sites. Soil deposited at these sites became the basis for new mounds.

The observations fit with a simulation by the team in which mound building is initially driven by termites joining in at the most popular excavation sites; they fit less well, the authors say, with a model in which the insects deposit soil in response to a chemical signal.

Cell biology

A UV-free tan that protects skin

Drug that stimulates melanin production could shield skin from damage caused by the Sun.

A drug that can be applied to the skin can boost production of the pigment melanin and potentially protect against cancer.

A type of melanin known as eumelanin darkens skin and helps to shield cells from damage caused by ultraviolet (UV) light, but drugs known to promote its production in mice struggle to penetrate the tougher barrier of human skin.

David Fisher of Massachusetts General Hospital in Boston and his colleagues therefore looked for alternatives. They focused on compounds that inhibit SIK, a protein involved in the suppression of pigment synthesis. One such compound was found to stimulate eumelanin production in mice that produce low levels of the pigment owing to a genetic mutation.

To increase the chances of penetrating human skin, the researchers developed SIK inhibitors that were smaller and more soluble in lipids than the original compound. Two of these increased eumelanin production in human skin cells. The researchers hope that the compounds might be useful in combination with sunscreens.


Sea-ice ‘treadmill’ speeds up for polar bears

Faster-drifting sea ice forces bears to travel farther for food.

Shrinking Arctic sea ice has already reduced the roaming range of polar bears (Ursus maritimus), but the impact of changes in ice drift has not been explored. George Durner at the US Geological Survey in Anchorage, Alaska, and his team analysed data on sea-ice drift across the Beaufort and Chukchi seas between 1987 and 2013, along with the movements of a total of 273 radio-tagged polar bears during that period. They found an increased rate of westward ice drift since 1987, which coincided with bears walking eastward faster or for longer to reach their seal-hunting grounds.

Bears would need to catch up to three more seals each year to fuel this extra activity, say the authors, who add that faster-drifting ice could exacerbate the physiological stress that bears already face in the warming Arctic.


Genetic roots of sleepless nights

A large genomic study reveals a handful of genes associated with insomnia.

Previous research has suggested that genetic factors are involved in insomnia, but little was known about the specific risk genes for the sleep disorder. In a study of more than 113,000 people, Danielle Posthuma at the Vrije University Medical Center in Amsterdam and her colleagues compared the genomes of people who reported that they struggle to fall asleep or stay asleep at night with those of people who never or only sometimes experience such problems. The team found five genes and one section of the genome that were associated with insomnia. The gene with the strongest association, MEIS1, has previously been linked to restless legs syndrome. The analysis also revealed strong genetic correlations between insomnia and anxiety, neuroticism and depression. 

The findings could help researchers to uncover the molecular mechanisms behind insomnia.

Asteroids, comets and Kuiper belt

Xenon came from comets

Comets may have delivered more than one-fifth of Earth’s atmospheric xenon.

The planet’s mixture of xenon isotopes is unique within the Solar System, and the origins of a proportion of the heavy noble gas have long been a mystery. Bernard Marty at the University of Lorraine in Vandœuvre-lès-Nancy, France, and his colleagues analysed the xenon emanating from comet 67P/Churyumov–Gerasimenko, which was measured by the ROSINA spectrometer aboard the European Space Agency’s Rosetta spacecraft. 

Data from close flybys of the comet in May 2016 revealed a xenon isotopic signature that, when combined with xenon signatures from other known sources within the early Solar System, can account for Earth’s xenon mix. Comets that struck the planet early in its history probably brought enough of the element to account for 22% of its total today, say the authors. 


Early whales listened like their land-based ancestors

The first whales probably could not communicate underwater over long distances.

Modern whales use specialized hearing underwater, communicating through either high-frequency or low-frequency sounds. These adaptations seem to have emerged only after whales evolved to live entirely in water. 

Maeva Orliac and Mickaël Mourlam at the University of Montpellier in France studied two fossils of protocetes — extinct semi-aquatic relatives of modern whales — collected from marine deposits in Togo, Africa, that are 43 million to 46 million years old. They used high-resolution 3D X-ray imaging to reconstruct the internal structure of the early whales’ bony labyrinth, which houses the delicate organs of the inner ear. Its structure is different from that of modern whales and dolphins, and closer to that of the protocetes’ land-based relatives, such as pigs and camels.

This suggests that the first whales were unable to navigate by echolocation or use sound for long-distance communication underwater, the authors say.


Immunotherapy takes on tumours that can’t fix DNA 

Tests of an approved treatment reveal it could target various cancer types.

Drugs that boost immune responses to cancer can shrink tumours that lack certain DNA-repair mechanisms.

These tumours accumulate mutated proteins, some of which can alert the immune system that something is amiss. Luis Diaz, now at the Memorial Sloan-Kettering Cancer Center in New York City, and his colleagues tested therapeutic antibodies that block a protein called PD-1 in people whose tumours do not have the mismatch repair pathway, which fixes damaged DNA. Such immunotherapies are already approved to treat some cancers.

The researchers studied 12 different cancer types in 86 people. Tumours shrank in 53% of the participants and disappeared entirely in 21%. The authors suggest that this therapy could target a range of cancers that have certain DNA-repair mutations, regardless of where in the body the tumour grows.


A gel for lasting glucose control

Combining a diabetes drug with a gel-forming polymer could mean less frequent injections for people with the disease.

Diabetes drugs that mimic a signalling molecule called glucagon-like peptide-1 (GLP1) can control blood glucose levels, but they are short-lived in the body and have to be injected weekly. To make a GLP1 drug that lasts longer, Ashutosh Chilkoti at Duke University in Durham, North Carolina, and his colleagues fused GLP1 to a protein called ELP, which can be made to form a gel at specific temperatures. 

The researchers created a GLP1–ELP compound that solidifies as a gel when warmed by the body after injection. The drug is then gradually released as the gel dissolves. The compound stayed in the circulation for up to 10 days in mouse models of diabetes. In macaque monkeys (Macaca fascicularis), it stayed active for up to 17 days. 

If the compound is effective in humans, people with diabetes could require only one or two injections a month, the authors suggest. 


Coral predators get a boost from climate change

Coral-eating starfish grow more voracious in acidified waters.

The young of a coral-destroying starfish seem to eat more in water that has a lower pH. The finding highlights another way climate change, which causes ocean acidification, threatens coral reefs.

Adult crown-of-thorns starfish (Acanthaster planci) feast on coral, and population outbreaks can devastate reefs. Symon Dworjanyn at Southern Cross University in Coffs Harbour, Australia, and his colleagues grew juvenile crown-of-thorns and their food — coralline algae — in seawater of three different pH levels, the lowest being pH 7.6, which is a predicted pH for oceans in the next few decades if emissions remain high. The starfish ate more algae when either the pH of the water they were in was lower or their food had been grown at the lower pH. The researchers think the algae may be more nutritious in acidified waters because their chemical composition is altered, and could also have reduced defences.

Future acidification could increase the success of juvenile starfish, which would boost the number of adult coral-eaters, the authors warn.