Water may have killed Mars’ magnetic field


Mars’ missing magnetic field may have drowned in the planet’s core.

An excess of hydrogen, split off from water molecules and stored in the Martian mantle, could have shut down convection, switching the magnetic field off forever, planetary scientist Joseph O’Rourke proposed March 21 at the Lunar and Planetary Science Conference.

Planetary scientists think magnetic fields are produced by the churning of a planet’s molten iron core. Convection relies on denser materials sinking into the core, and lighter stuff rising to the surface. The movement of iron, which can carry a charge, generates a strong magnetic field that can protect a planet’s atmosphere from being ravaged by solar wind (SN Online: 8/18/17).

But if lighter material, like hydrogen, settles close to the iron core, it could block dense material from sinking deep enough to keep convection going, said O’Rourke, of Arizona State University in Tempe.

“Too much hydrogen and you can shut down convection entirely,” he said. “Hydrogen is a heartless killer.”

O’Rourke and his ASU colleague S.-H. Dan Shim suggested the hydrogen could come from water locked up in Martian minerals. Near the hot core, water would split into hydrogen and oxygen. The oxygen would form compounds with other elements and stay high in the mantle, but the hydrogen could sit atop the core and effectively suffocate the dynamo.

The question is whether Mars’ minerals would have had what it took to deliver the hydrogen at the right time. Mars’ crust is rich in the mineral olivine, which does not bond well with water and so is relatively dry.

In the planet’s interior, pressure forces olivine to transform into the minerals wadsleyite and ringwoodite, which hold more water. Deeper still, the mineral turns into bridgmanite and becomes dry again. For a time, that bridgmanite layer could act as a buffer against water, allowing the core to keep convecting. But as the mantle cooled, the bridgmanite layer would shrink and eventually disappear, O’Rourke’s study suggests.

Whether Mars’ interior ever had that saving layer of bridgmanite depends on how big its core is — a property that may be tested by NASA’s InSight Mars lander, launching on May 5, O’Rourke said. Mars did have a magnetic field more than 4 billion years ago. Scientists have struggled to explain how it vanished, leaving the planet vulnerable to solar winds, which probably stripped away its atmosphere and surface water (SN: 12/12/15, p. 31).

If hydrogen shut down the planet’s generator, it would have had to act fast. Previous observations suggest the magnetic field disappeared relatively rapidly, over 100 million years.

Another theory by James Roberts of the Johns Hopkins Applied Physics Lab in Laurel, Md., suggests a large impact could have shut down the dynamo by heating the outermost core, which would have kept it from sinking.

“It’s actually a similar idea to O’Rourke’s,” Roberts says. It may take many more sophisticated Mars missions to figure out what really happened.

Source : Science News


Somewhere in the brain is a storage device for memories


People tend to think of memories as deeply personal, ephemeral possessions — snippets of emotions, words, colors and smells stitched into our unique neural tapestries as life goes on. But a strange series of experiments conducted decades ago offered a different, more tangible perspective. The mind-bending results have gained unexpected support from recent studies.

In 1959, James Vernon McConnell, a psychologist at the University of Michigan in Ann Arbor, painstakingly trained small flatworms called planarians to associate a shock with a light. The worms remembered this lesson, later contracting their bodies in response to the light. Continue reading “Somewhere in the brain is a storage device for memories”

Artificial insulin-releasing cells may make it easier to manage diabetes

Artificial insulin-secreting cells

Artificial cells made from scratch in the lab could one day offer a more effective, patient-friendly diabetes treatment.

Diabetes, which affects more than 400 million people around the world, is characterized by the loss or dysfunction of insulin-making beta cells in the pancreas. For the first time researchers have created synthetic cells that mimic how natural beta cells sense blood sugar concentration and secrete just the right amount of insulin. Experiments with mice show that these cells can regulate blood sugar for up to five days, researchers report online October 30 in Nature Chemical Biology. Continue reading “Artificial insulin-releasing cells may make it easier to manage diabetes”

How gut bacteria may affect anxiety

illustration of human gut

Tiny molecules in the brain may help gut bacteria hijack people’s emotions.

Bacteria living in the human gut have strange influence over mood, depression and more, but it has been unclear exactly how belly-dwelling bacteria exercise remote control of the brain (SN: 4/2/16, p. 23). Now research in rodents suggests that gut microbes may alter the inventory of microRNAs — molecules that help keep cells in working order by managing protein production — in brain regions involved in controlling anxiety.

The findings, reported online August 25 in Microbiome, could help scientists develop new treatments for some mental health problems.

Mounting evidence indicates “that the way we think and feel might be able to be controlled by our gut microbiota,” says study coauthor Gerard Clarke, a psychiatrist at University College Cork in Ireland. For instance, the presence or absence of gut bacteria can influence whether a mouse exhibits anxiety-like behaviors, such as avoiding bright lights or open spaces.

Clarke and colleagues compared normal mice, whose gastrointestinal tracts were teeming with bacteria, with mice bred in sterile environments, whose guts didn’t contain any microbes. The researchers discovered that in brain regions involved in regulating anxiety — the amygdala and prefrontal cortex — microbe-free mice had an overabundance of some types of microRNA and a shortage of others compared with normal mice. After scientists exposed some sterilized mice to microbes, the rodents’ microRNA levels more closely matched those of normal mice.

The team also examined microRNAs in the amygdala and prefrontal cortex of rats whose gut bacteria had been decimated by antibiotics. These rats overproduced or underproduced some of the same microRNAs that were off-kilter in bacteria-free mice. The researchers suspect that gut bacteria affect their host’s anxiety levels by tampering with microRNAs in specific parts of the brain.

“I was a little surprised by the findings — in a positive way — because I think not many people so far have thought about microRNAs in this context,” says Peter Holzer, a neurogastroenterologist at the Medical University of Graz in Austria who wasn’t involved in the study. “It’s heading into a new area in gut-brain research that hasn’t been pursued.”

Researchers still aren’t sure how these bacteria dial microRNA production up and down in the brain. Maybe the microbes send signals along the vagus nerve, a kind of information highway that runs from gut to brain. Or perhaps bacteria churn out molecular by-products that provoke the immune system to produce chemicals that cause the brain to produce more or less of particular microRNAs. Outlining microbes’ mental manipulation scheme from start to finish “is still a work in progress,” Clarke says.

Next the team wants to see if probiotic drugs can cultivate certain types of bacteria in the gut, and therefore fine-tune microRNA levels in specific parts of the brain. If scientists can adjust microRNA abundances in a way that assuages anxiety, it could help lead to the development of new medications for psychiatric and neurological disorders.

MicroRNA-based medications may be unrealistic in the short term, though, says gastroenterologist Kirsten Tillisch of UCLA. “People tend to like to extrapolate these types of results to humans and start moving quickly towards clinical applications. It is just so tempting,” says Tillisch, who was not involved in the study. “But we know historically the translation from lab animal to human is hit-and-miss.”

source: Science News