Category Archives: Science

The ancient hunt in which the tracker’s skill united reason and imagination

“The San people of the Kalahari desert are the last tribe on Earth to use what some believe to be the most ancient hunting technique of all: the persistence hunt; they run down their prey,” says David Attenborough:

 

“The hunter pays tribute to his quarry’s courage and strength. With ceremonial gestures that ensure that its spirit returns to the desert sands from which it came. While it was alive, he lived and breathed with it and felt its every movement in his own body, and at the moment of its death, he shared its pain. He rubs its saliva into his own legs to relieve the agony of his own burning muscles, and he gives thanks for the life he has taken so that he may sustain the lives of his family waiting for him back in their settlement.”

Louis Liebenberg, author of The Art of Tracking: The Origin of Science, argues that the rational skills required by the ancient tracker provided the basis of scientific reasoning.

The first creative science, practiced by possibly some of the earliest members of Homo sapiens who had modern brains and intellects, may have been the tracking of game animals…

[Continue reading at my new site: Attention to the Unseen]

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A quantum communications satellite proved its potential in 2017

Science News reports: During the world’s first telephone call in 1876, Alexander Graham Bell summoned his assistant from the other room, stating simply, “Mr. Watson, come here. I want to see you.” In 2017, scientists testing another newfangled type of communication were a bit more eloquent. “It is such a privilege and thrill to witness this historical moment with you all,” said Chunli Bai, president of the Chinese Academy of Sciences in Beijing, during the first intercontinental quantum-secured video call.

The more recent call, between researchers in Austria and China, capped a series of milestones reported in 2017 and made possible by the first quantum communications satellite, Micius, named after an ancient Chinese philosopher (SN: 10/28/17, p. 14).

Created by Chinese researchers and launched in 2016, the satellite is fueling scientists’ dreams of a future safe from hacking of sensitive communiqués. One day, impenetrable quantum cryptography could protect correspondences. A secret string of numbers known as a quantum key could encrypt a credit card number sent over the internet, or encode the data transmitted in a video call, for example. That quantum key would be derived by measuring the properties of quantum particles beamed down from such a satellite. Quantum math proves that any snoops trying to intercept the key would give themselves away.

“Quantum cryptography is a fundamentally new way to give us unconditional security ensured by the laws of quantum physics,” says Chao-Yang Lu, a physicist at the University of Science and Technology of China in Hefei, and a member of the team that developed the satellite. [Continue reading…]

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Macron awards U.S. scientists grants to move to France and escape from Trump’s anti-science regime

The Associated Press reports: Eighteen climate scientists from the US and elsewhere have hit the jackpot as France’s president, Emmanuel Macron, awarded them millions of euros in grants to relocate to France for the rest of Donald Trump’s presidential term.

The “Make Our Planet Great Again” grants – a nod to Trump’s “Make America Great Again” campaign slogan – are part of Macron’s efforts to counter Trump on the climate change front. Macron announced a contest for the projects in June, hours after Trump declared he would withdraw the US from the Paris climate accord.

More than 5,000 people from about 100 countries expressed interest in the grants. Most of the applicants – and 13 of the 18 winners – were US-based researchers.

Macron’s appeal “gave me such a psychological boost, to have that kind of support, to have the head of state saying I value what you do”, said winner Camille Parmesan, of the University of Texas at Austin. She will be working at an experimental ecology station in the Pyrenees on how human-made climate change is affecting wildlife.

In an interview with The Associated Press, Parmesan described funding challenges for climate science in the US and a feeling that “you are having to hide what you do”. [Continue reading…]

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Matter inside a neutron star is so dense that a teaspoonful would weigh a billion tons

Science News reports: On astrophysicists’ charts of star stuff, there’s a substance that still merits the label “here be dragons.” That poorly understood material is found inside neutron stars — the collapsed remnants of once-mighty stars — and is now being mapped out, as scientists better characterize the weird matter.

The detection of two colliding neutron stars, announced in October (SN: 11/11/17, p. 6), has accelerated the pace of discovery. Since the event, which scientists spied with gravitational waves and various wavelengths of light, several studies have placed new limits on the sizes and masses possible for such stellar husks and on how squishy or stiff they are.

“The properties of neutron star matter are not very well known,” says physicist Andreas Bauswein of the Heidelberg Institute for Theoretical Studies in Germany. Part of the problem is that the matter inside a neutron star is so dense that a teaspoonful would weigh a billion tons, so the substance can’t be reproduced in any laboratory on Earth.

In the collision, the two neutron stars merged into a single behemoth. This remnant may have immediately collapsed into a black hole. Or it may have formed a bigger, spinning neutron star that, propped up by its own rapid rotation, existed for a few milliseconds — or potentially much longer — before collapsing. The speed of the object’s demise is helping scientists figure out whether neutron stars are made of material that is relatively soft, compressing when squeezed like a pillow, or whether the neutron star stuff is stiff, standing up to pressure. This property, known as the equation of state, determines the radius of a neutron star of a particular mass. [Continue reading…]

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What the Pliocene epoch can teach us about future warming on Earth

Science News reports: Imagine a world where the polar ice sheets are melting, sea level is rising and the atmosphere is stuffed with about 400 parts per million of carbon dioxide. Sound familiar? It should. We’re living it. But the description also matches Earth a little over 3 million years ago, in the middle of the geologic epoch known as the Pliocene.

To understand how our planet might respond as global temperatures rise, scientists are looking to warm periods of the past. These include the steamy worlds of the Cretaceous Period, such as around 90 million years ago, and the boundary of the Paleocene and Eocene epochs, about 56 million years ago.

But to many researchers, the best reference for today’s warming is the more recent Pliocene, which lasted from 5.3 million to 2.6 million years ago. The mid-Pliocene was the last time atmospheric CO2 levels were similar to today’s, trapping heat and raising global temperatures to above the levels Earth is experiencing now.

New research is illuminating how the planet responded to Pliocene warmth. One set of scientists has fanned out across the Arctic, gathering geologic clues to how temperatures there may have been as much as 19 degrees Celsius higher than today. The warmth allowed trees to spread far to the north, creating Arctic forests where three-toed horses, giant camels and other animals roamed. When lightning struck, wildfires roared across the landscape, spewing soot into the air and altering the region’s climate.

Other researchers are pushing the frontiers of climate modeling, simulating how the oceans, atmosphere and land responded as Pliocene temperatures soared. One new study shows how the warmth may have triggered huge changes in ocean circulation, setting up an enormous overturning current in the Pacific Ocean, similar to the “conveyor belt” in today’s Atlantic that drives weather and climate. A second new paper suggests that the Greenland and Antarctic ice sheets might have responded differently to Pliocene heat, melting at different times.

All this research into the last great warm period is helping scientists think more deeply about how the future might play out. It may not be a road map to the next 100 years, but the Pliocene is a rough guide to the high sea levels, vanishing ice and altered weather patterns that might arrive hundreds to thousands of years from now.

“It’s a case study for understanding how warm climates function,” says Heather Ford, a paleoceanographer at the University of Cambridge. “It’s our closest analog for future climate change.” [Continue reading…]

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In mathematics, ‘you cannot be lied to’

Siobhan Roberts writes: A few years back, a prospective doctoral student sought out Sylvia Serfaty with some existential questions about the apparent uselessness of pure math. Serfaty, then newly decorated with the prestigious Henri Poincaré Prize, won him over simply by being honest and nice. “She was very warm and understanding and human,” said Thomas Leblé, now an instructor at the Courant Institute of Mathematical Sciences at New York University. “She made me feel that even if at times it might seem futile, at least it would be friendly. The intellectual and human adventure would be worth it.” For Serfaty, mathematics is about building scientific and human connections. But as Leblé recalled, Serfaty also emphasized that a mathematician has to find satisfaction in “weaving one’s own rug,” alluding to the patient, solitary work that comes first.

Born and raised in Paris, Serfaty first became intrigued by mathematics in high school. Ultimately she gravitated toward physics problems, constructing mathematical tools to forecast what should happen in physical systems. For her doctoral research in the late-1990s, she focused on the Ginzburg-Landau equations, which describe superconductors and their vortices that turn like little whirlwinds. The problem she tackled was to determine when, where and how the vortices appear in the static (time-independent) ground state. She solved this problem with increasing detail over the course of more than a decade, together with Étienne Sandier of the University of Paris-East, with whom she co-authored the book Vortices in the Magnetic Ginzburg-Landau Model.

In 1998, Serfaty discovered an irresistibly puzzling problem about how these vortices evolve in time. She decided that this was the problem she really wanted to solve. Thinking about it initially, she got stuck and abandoned it, but now and then she circled back. For years, with collaborators, she built tools that she hoped might eventually provide pathways to the desired destination. In 2015, after almost 18 years, she finally hit upon the right point of view and arrived at the solution.

“First you start from a vision that something should be true,” Serfaty said. “I think we have software, so to speak, in our brain that allows us to judge that moral quality, that truthful quality to a statement.”

And, she noted, “you cannot be cheated, you cannot be lied to. A thing is true or not true, and there is this notion of clarity on which you can base yourself.” [Continue reading…]

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Mysterious object seen speeding past sun could be ‘visitor from another star system’

The Guardian reports: A mysterious object detected hurtling past our sun could be the first space rock traced back to a different solar system, according to astronomers tracking the body.

While other objects have previously been mooted as having interstellar origins, experts say the latest find, an object estimated to be less than 400m in diameter, is the best contender yet.

“The exciting thing about this is that this may be essentially a visitor from another star system,” said Dr Edward Bloomer, astronomer at the Royal Observatory Greenwich.

If its origins are confirmed as lying beyond our solar system, it will be the first space rock known to come from elsewhere in the galaxy.

Published in the minor planet electronic circulars by the Minor Planet Center at the Harvard-Smithsonian Center for Astrophysics, the observations reveal that the object is in a strong hyperbolic orbit – in other words, it is going fast enough to escape the gravitational pull of the sun.

Objects originating from, and on long-period orbits within, our solar system can end up on a hyperbolic trajectory, and be ejected into interstellar space – for example if they swing close by a giant planet, since the planet’s gravity can cause objects to accelerate. But Dr Gareth Williams, associate director of the Minor Planet Center, said that wasn’t the case for the newly discovered body.

“When we run the orbit for this [object] back in time, it stays hyperbolic all the way out – there are no close approaches to any of the giant planets that could have given this thing a kick,” he said. “If we follow the orbit out into the future, it stays hyperbolic,” Williams added. “So it is coming from interstellar space and it is going to interstellar space.” [Continue reading…]

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Neutron star collision showers the universe with a wealth of discoveries

 

Science News reports: Two ultradense cores of dead stars have produced a long-awaited cosmic collision, showering scientists with riches.

The event was the first direct sighting of a smashup of neutron stars, which are formed when aging stars explode and leave behind a neutron-rich remnant. In the wake of the collision, the churning residue forged gold, silver, platinum and a smattering of other heavy elements such as uranium, researchers reported October 16 at a news conference in Washington, D.C. Such elements’ birthplaces were previously unknown, but their origins were revealed by the cataclysm’s afterglow.

“It really is the last missing piece” of the periodic table, says Anna Frebel, an astronomer at MIT who was not involved in the research. “This is heaven for anyone working in the field.” After the collision, about 10 times the Earth’s mass in gold was spewed out into space, some scientists calculated.

Using data gathered by about 70 different observatories, astronomers characterized the event in exquisite detail, releasing a slew of papers describing the results. A tremor of gravitational waves, spotted by the Advanced Laser Interferometer Gravitational-Wave Observatory, LIGO, on August 17, provided the first sign of the cataclysm. [Continue reading…]

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U.S. withdraws from UNESCO, saying it’s biased against Israel

Bloomberg reports: The Trump administration withdrew the U.S. from the United Nations cultural organization, saying it’s biased against Israel and citing its decision to admit the Palestinian territories as a member state.

The decision to quit the U.N. Educational, Scientific and Cultural Organization, which the U.S. co-founded in 1945, “was not taken lightly,” State Department spokeswoman Heather Nauert said in a statement Thursday. She cited the need for “fundamental reform in the organization, and continuing anti-Israel bias at UNESCO.”

The U.S. hasn’t been paying dues to UNESCO since 2011, when President Barack Obama’s administration stopped providing about $72 million a year after the Paris-based organization accepted Palestine as a full member. The arrears total almost $543 million, according to UNESCO. U.S. laws bar funding for any UN agency that gives Palestinians the status of a nation, and the U.S. lost its voting privilege in the organization in 2013.

That decision threw the organization into financial crisis because the U.S. had accounted for more than 20 percent of UNESCO’s annual budget. The U.S. also withdrew from the organization in 1984 but rejoined in 2003. [Continue reading…]

 

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Astronomers find half of the missing matter in the universe

The Guardian reports: It is one of cosmology’s more perplexing problems: that up to 90% of the ordinary matter in the universe appears to have gone missing.

Now astronomers have detected about half of this missing content for the first time, in a discovery that could resolve a long-standing paradox.

The conundrum first arose from measurements of radiation left over from the Big Bang, which allowed scientists to calculate how much matter there is in the universe and what form it takes. This showed that about 5% of the mass in the universe comes in the form of ordinary matter, with the rest being accounted for by dark matter and dark energy.

Dark matter has never been directly observed and the nature of dark energy is almost completely mysterious, but even tracking down the 5% of ordinary stuff has proved more complicated than expected. When scientists have counted up all the observable objects in the sky – stars, planets, galaxies and so on – this only seems to account for between a 10th and a fifth of what ought to be out there.

The deficit is known as the “missing baryon problem”, baryons being ordinary subatomic particles like protons and neutrons.

Richard Ellis, a professor of astrophysics at the University College London, said: “People agree that there’s a lot missing, raising the question where is it?” [Continue reading…]

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How toxic PCBs came to permeate life on Earth

Rebecca Altman writes: Deep in the Mariana Trench, at depths lower than the Rockies are high, rests a tin of reduced-sodium Spam.

NOAA scientists caught sight of it last year near the mouth of the Mariana’s Sirena Deep. It isn’t an isolated incursion, but it was nevertheless startling, the sight of those timeless golden letters bright against the deep ocean bottom.

Shortly after came news from another team of scientists who had found in the Mariana an innovation less familiar than shelf-stable meat, but far more significant. In the bodies of deep-dwelling creatures were found traces of industrial chemicals responsible for the rise of modern America—polychlorinated biphenyls.

PCBs had been detected in Hirondellea gigas, tiny shrimp-like amphipods scooped up by deepwater trawlers. Results from the expedition, led by Newcastle University’s hadal-zone expert Alan Jamieson, were preliminary released last year and then published in February.

PCBs have been found the world over—from the bed of the Hudson River to the fat of polar bears roaming the high Arctic—but never before in the creatures of the extreme deep, a bioregion about which science knows relatively little.

How PCBs reached the Mariana is still under investigation. Jamieson and colleagues speculated on multiple, regional sources. A nearby military base. The industrial corridors along the Asian coastline. And the Great Pacific Garbage Patch, where PCBs glom onto plastic particles caught in the current. Over time, the plastic degrades and descends into the depths, ferrying PCBs with them.

But the true origin of PCBs lies in another time and place, in Depression-era Alabama, and before that, 19th-century Germany at the pinnacle of German chemistry. [Continue reading…]

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In his journal, Thoreau discovered how to balance poetic wonder and scientific rigor

Andrea Wulf writes: In late 1849, two years after Henry David Thoreau left Walden Pond—where he had lived for two years, two months, and two days in a cabin that he had built himself—he began the process of completely reorienting his life again. His hermit-style interlude at the pond had attracted quite a bit of attention in his hometown of Concord, Massachusetts. “Living alone on the pond in ostentatious simplicity, right in sight of a main road,” his latest biographer, Laura Dassow Walls, writes, “he became a spectacle,” admired by some and belittled by others. Thoreau’s subsequent life change was less conspicuous. Yet it engaged him in a quest more enlightening and relevant today than the proud asceticism he flaunted throughout Walden, a book that has never ceased to inspire reverence or provoke contempt.

What the 32-year-old Thoreau quietly did in the fall of 1849 was to set up a new and systematic daily regimen. In the afternoons, he went on long walks, equipped with an array of instruments: his hat for specimen-collecting, a heavy book to press plants, a spyglass to watch birds, his walking stick to take measurements, and small scraps of paper for jotting down notes. Mornings and evenings were now dedicated to serious study, including reading scientific books such as those by the German explorer and visionary thinker Alexander von Humboldt, whose Cosmos (the first volume was published in 1845) had become an international best seller.

As important, Thoreau began to use his own observations in a new way, intensifying and expanding the journal writing that he’d undertaken shortly after graduating from Harvard in 1837, apparently at Ralph Waldo Emerson’s suggestion. In the evening, he often transferred the notes from his walks into his journal, and for the rest of his life, he created long entries on the natural world in and around Concord. Thoreau was staking out a new purpose: to create a continuous, meticulous documentary record of his forays. Especially pertinent two centuries after his birth, in an era haunted by inaction on climate change, he worried over a problem that felt personal but was also spiritual and political: how to be a rigorous scientist and a poet, imaginatively connected to the vast web of natural life. [Continue reading…]

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Why the Cassini mission to Saturn must end in a fiery dive

Space.com reports: After examining Saturn from up close for 13 years, the Cassini spacecraft is ending its long career with a boom — and there’s an important reason why.

Friday morning (Sept. 15), Cassini will complete the orbital pirouettes of its seven-year Solstice Mission and complete a self-destructing descent into Saturn’s atmosphere. This fierce ending is dramatic for a purpose: It will prevent Earth microbes from contaminating Saturn’s nearby moons.

When NASA’s Cassini spacecraft completed its first tour of Saturn in 2008, the mission team had to decide what would come next. [Cassini’s Saturn Crash 2017: How to Watch Its ‘Grand Finale’]

Cassini could have parted ways with the ringed planet. In 2009, studies showed that Cassini had enough fuel to reach Uranus or Neptune. Cassini could have traveled in the other direction, toward Jupiter, or it could have been sent to visit an assembly of asteroids known as the Centaurs in the outer limits of the solar system.

Instead, scientists chose to continue making discoveries about Saturn and its moons — first through a two-year extended mission known as the Cassini Equinox Mission, and then with a second extension in 2010 that would bring the spacecraft to the very limit of the fuel it carried. That made it clear that Cassini’s third mission, the Solstice Mission, would be how the spacecraft would end its career. It was during these missions that scientists discovered that two of Saturn’s moons, Titan and Enceladus, showed signs that they were well suited to life. But why the fiery plummet?

“The spacecraft will burn up and disintegrate like a meteor in the upper atmosphere of Saturn,” Preston Dyches, of NASA’s Jet Propulsion Laboratory (JPL), told Space.com via email. “This was determined to be the best way to ensure the safe disposal of the spacecraft, so that there would be no chance of future contamination of Enceladus by any hardy microbes that might have stowed away on board all these years.” [Continue reading…]

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Pope blasts climate change doubters: cites moral duty to act

The Associated Press reports: Pope Francis has sharply criticized climate change doubters, saying history will judge those who failed to take the necessary decisions to curb heat-trapping emissions blamed for the warming of the Earth.

Francis was asked about climate change and the spate of hurricanes that have pummeled the U.S., Mexico and the Caribbean recently as his charter plane left Colombia on Sunday and flew over some of the devastated areas.

“Those who deny this must go to the scientists and ask them. They speak very clearly,” he said, referring to experts who blame global warming on man-made activities.

Francis said scientists have also clearly charted what needed to be done to reverse course on global warming and said individuals and politicians had a “moral responsibility” to do their part.

“These aren’t opinions pulled out of thin air. They are very clear,” he said. “Then they (leaders) decide and history will judge those decisions.”

Francis has made caring for the environment a hallmark of his papacy, writing an entire encyclical about how the poor in particular are most harmed when multinationals move into exploit natural resources. During his visit to Colombia, Francis spoke out frequently about the need to preserve the country’s rich biodiversity from overdevelopment and exploitation.

For those who have denied climate change, or delayed actions to counter it, he responded with an Old Testament saying: “Man is stupid.”

“When you don’t want to see, you don’t see,” he said.

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Trump’s war on science

In an editorial, the New York Times says: The news was hard to digest until one realized it was part of a much larger and increasingly disturbing pattern in the Trump administration. On Aug. 18, the National Academies of Sciences, Engineering and Medicine received an order from the Interior Department that it stop work on what seemed a useful and overdue study of the health risks of mountaintop-removal coal mining.

The $1 million study had been requested by two West Virginia health agencies following multiple studies suggesting increased rates of birth defects, cancer and other health problems among people living near big surface coal-mining operations in Appalachia. The order to shut it down came just hours before the scientists were scheduled to meet with affected residents of Kentucky.

The Interior Department said the project was put on hold as a result of an agencywide budgetary review of grants and projects costing more than $100,000.

This was not persuasive to anyone who had been paying attention. From Day 1, the White House and its lackeys in certain federal agencies have been waging what amounts to a war on science, appointing people with few scientific credentials to key positions, defunding programs that could lead to a cleaner and safer environment and a healthier population, and, most ominously, censoring scientific inquiry that could inform the public and government policy. [Continue reading…]

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Massive black hole discovered near heart of the Milky Way

The Guardian reports: An enormous black hole one hundred thousand times more massive than the sun has been found hiding in a toxic gas cloud wafting around near the heart of the Milky Way.

If the discovery is confirmed, the invisible behemoth will rank as the second largest black hole ever seen in the Milky Way after the supermassive black hole known as Sagittarius A* that is anchored at the very centre of the galaxy.

Astronomers in Japan found evidence for the new object when they turned a powerful telescope in the Atacama desert in Chile towards the gas cloud in the hope of understanding the strange movement of its gases. Unlike those that make up other interstellar clouds, the gases in this cloud – including hydrogen cyanide and carbon monoxide – move at wildly different speeds.

Observations from the Alma telescope in Chile showed that molecules in the elliptical cloud, which is 200 light years from the centre of the Milky Way and 150 trillion kilometres wide, were being pulled around by immense gravitational forces. The most likely cause, according to computer models, was a black hole no more than 1.4 trillion km across. [Continue reading…]

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Millennia ago, eclipses provided rare opportunities to measure the universe

Tyler Nordgren writes: As a kid visiting the Oregon coast I often wondered, “How wide is the ocean, and what is there beyond the horizon?” As I grew older and turned my sights to the night sky, I wondered something very similar: “How far away are the stars, and are there other planets there?” Even though very few of us have ever circumnavigated the globe, and no human being has ever ventured into space beyond the moon, we do know some of the answers to these questions. Immensity isn’t immeasurable. While these vast numbers may make little sense in our daily lives, we at least know they are known.

Consider what it must have been like to live in a world where this was not true: where the sense of immeasurability, the certainty of the unfathomable, was commonplace, and the thought that the world could be known was a novel idea. The philosopher Anaxagoras was born in about 500 B.C. in the eastern Mediterranean on what is now the coast of Turkey. It was a time when philosophy had only recently turned its attention to the natural world. Less than a hundred years before, Thales of Miletus supposedly predicted the solar eclipse that ended a war, thus implying that our world was predictable and events were not just the random whims of the gods.

In such a world of physical phenomena, Anaxagoras was the first, as far as we know, to understand that eclipses occur when one heavenly body blocks the light from another. This rejection of gods and dragons as the causes of eclipses was a revolutionary thought by itself, but Anaxagoras took it further: If solar eclipses happened only because the Earth had moved into the shadow of the moon, he reasoned, then the size of the shadow must tell us something about the size of the moon. Additionally, since the moon covered the sun, the sun must be farther away. Yet to appear nearly the same size, the sun must be larger than the moon. Herein lies the power of scientific thought: Measure the extent of the shadow sweeping across the Earth, and you know the moon must be at least as big as the shadow, and the sun larger still. Mysticism provided no such opportunity: If eclipses occur when a demon devours the sun, there is no reason to believe that any measurement we make here on Earth should reveal the demon’s size.[Continue reading…]

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Moon had a magnetic field for at least a billion years longer than thought

Science News reports: The moon had a magnetic field for at least 2 billion years, or maybe longer.

Analysis of a relatively young rock collected by Apollo astronauts reveals the moon had a weak magnetic field until 1 billion to 2.5 billion years ago, at least a billion years later than previous data showed. Extending this lifetime offers insights into how small bodies generate magnetic fields, researchers report August 9 in Science Advances. The result may also suggest how life could survive on tiny planets or moons.

“A magnetic field protects the atmosphere of a planet or moon, and the atmosphere protects the surface,” says study coauthor Sonia Tikoo, a planetary scientist at Rutgers University in New Brunswick, N.J. Together, the two protect the potential habitability of the planet or moon, possibly those far beyond our solar system.

The moon does not currently have a global magnetic field. Whether one ever existed was a question debated for decades (SN: 12/17/11, p. 17). On Earth, molten rock sloshes around the outer core of the planet over time, causing electrically conductive fluid moving inside to form a magnetic field. This setup is called a dynamo. At 1 percent of Earth’s mass, the moon would have cooled too quickly to generate a long-lived roiling interior.

Magnetized rocks brought back by Apollo astronauts, however, revealed that the moon must have had some magnetizing force. The rocks suggested that the magnetic field was strong at least 4.25 billion years ago, early on in the moon’s history, but then dwindled and maybe even got cut off about 3.1 billion years ago. [Continue reading…]

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