Cohesive Forces that hold gravity-defying near-earth asteroid together revealed

An asteroid 1950 DA. Credit: NASA

Researchers at the University of Tennessee, Knoxville, have made a novel discovery that may potentially protect the world from future collisions with asteroids.

The team studied near-Earth asteroid 1950 DA and discovered that the body, which rotates so quickly it defies gravity, is held together by cohesive forces called van der Waals, never detected before on an asteroid.

The findings, published in this week's edition of the science journal Nature, have potential implications for defending our planet from a massive asteroid impact.

Previous research has shown that asteroids are loose piles of rubble held together by gravity and friction. However, the UT team found that 1950 DA is spinning so quickly that it defies these forces.

Ben Rozitis, a postdoctoral researcher; Eric MacLennan, a doctoral candidate; and Joshua Emery, an assistant professor in the Department of Earth and Planetary Sciences, wanted to know what keeps the body from breaking apart.

Looking at thermal images and orbital drift to calculate thermal inertia and bulk density, the team detected the action of cohesive forces in an environment with little gravity.

"We found that 1950 DA is rotating faster than the breakup limit for its density," said Rozitis. "So if just gravity were holding this rubble pile together, as is generally assumed, it would fly apart. Therefore, interparticle cohesive forces must be holding it together."

In fact, the rotation is so fast that at its equator, 1950 DA effectively experiences negative gravity. If an astronaut were to attempt to stand on this surface, he or she would fly off into space unless he or she were somehow anchored.

The presence of cohesive forces has been predicted in small asteroids, but definitive evidence has never been seen before.

The finding provides important information for efforts aimed at stopping an asteroid from crashing into Earth.

"Following the February 2013 asteroid impact in Chelyabinsk, Russia, there is renewed interest in figuring out how to deal with the potential hazard of an asteroid impact," said Rozitis.

"Understanding what holds these asteroids together can inform strategies to guard against future impacts."

This research reveals some potential techniques, such as a kinetic impactor which would deploy a massive object on a collision course with the asteroid, could exacerbate the impact's effects.

For example, this technique could destabilize the cohesive forces keeping the asteroid together, causing it to break apart into several threatening asteroids headed for Earth.

This may be what occurred with the asteroid P/2013 R3, which was caught by the Hubble Space Telescope in 2013 and 2014 coming undone, possibly due to a collision with a meteor.

"With such tenuous cohesive forces holding one of these asteroids together, a very small impulse may result in a complete disruption," said Rozitis.

The researchers' findings also have implications for space exploration. For example, the European Space Agency's Rosetta spacecraft landed on Comet 67P/Churyumov-Gerasimenko's surface last week and it may find a dusty surface dominated by such cohesive forces.

More information: Cohesive forces prevent the rotational breakup of rubble-pile asteroid (29075) 1950 DA, Nature, dx.doi.org/10.1038/nature13632

FERMI LAT: Data Holds New Clues To Dark Matter

At left is a map of gamma rays with energies between 1 and 3.16 GeV detected in the galactic center by Fermi's LAT; red indicates the greatest number. 

Prominent pulsars are labeled. 

Removing all known gamma-ray sources (right) reveals excess emission that may arise from dark matter annihilations.

Image courtesy T. Linden, Univ. of Chicago.

A new study of gamma-ray light from the center of our galaxy makes the strongest case to date that some of this emission may arise from dark matter, an unknown substance making up most of the material universe.

Using publicly available data from NASA's Fermi Gamma-ray Space Telescope, independent scientists at the Fermi National Accelerator Laboratory (Fermilab), the Harvard-Smithsonian Center for Astrophysics (CfA), the Massachusetts Institute of Technology (MIT) and the University of Chicago have developed new maps showing that the galactic center produces more high-energy gamma rays than can be explained by known sources and that this excess emission is consistent with some forms of dark matter.

Dan Hooper

"The new maps allow us to analyze the excess and test whether more conventional explanations, such as the presence of undiscovered pulsars or cosmic-ray collisions on gas clouds, can account for it," said Dan Hooper, an astrophysicist at Fermilab in Batavia, Ill., and a lead author of the study.

"The signal we find cannot be explained by currently proposed alternatives and is in close agreement with the predictions of very simple dark matter models."

The galactic center teems with gamma-ray sources, from interacting binary systems and isolated pulsars to supernova remnants and particles colliding with interstellar gas.

It's also where astronomers expect to find the galaxy's highest density of dark matter, which only affects normal matter and radiation through its gravity.

Large amounts of dark matter attract normal matter, forming a foundation upon which visible structures, like galaxies, are built.

No one knows the true nature of dark matter, but Weakly Interacting Massive Particles (WIMPs), represent a leading class of candidates.

Theorists have envisioned a wide range of WIMP types, some of which may either mutually annihilate or produce an intermediate, quickly decaying particle when they collide.

Both of these pathways end with the production of gamma rays -- the most energetic form of light -- at energies within the detection range of Fermi's Large Area Telescope (LAT).

When astronomers carefully subtract all known gamma-ray sources from LAT observations of the galactic center, a patch of leftover emission remains.

This excess appears most prominent at energies between 1 and 3 billion electron volts (GeV) -- roughly a billion times greater than that of visible light -- and extends outward at least 5,000 light-years from the galactic center.

Hooper and his colleagues conclude that annihilations of dark matter particles with a mass between 31 and 40 GeV provide a remarkable fit for the excess based on its gamma-ray spectrum, its symmetry around the galactic center, and its overall brightness.

Writing in a paper submitted to the journal Physical Review D, the researchers say that these features are difficult to reconcile with other explanations proposed so far, although they note that plausible alternatives not requiring dark matter may yet materialize.

"Dark matter in this mass range can be probed by direct detection and by the Large Hadron Collider (LHC), so if this is dark matter, we're already learning about its interactions from the lack of detection so far," said co-author Tracy Slatyer, a theoretical physicist at MIT in Cambridge, Mass.

"This is a very exciting signal, and while the case is not yet closed, in the future we might well look back and say this was where we saw dark matter annihilation for the first time."

More Information: "The Characterization of the Gamma-Ray Signal from the Central Milky Way: A Compelling Case for Annihilating Dark Matter" Authors: Tansu Daylan, Douglas P. Finkbeiner, Dan Hooper, Tim Linden, Stephen K. N. Portillo, Nicholas L. Rodd, Tracy R. Slatyer

Moon's Aitken Basin: Ancient crater could hold clues about moon's mantle

Red areas on the topographic image indicate high elevations, and blue or purple areas indicate low elevation. 

The South Pole Aitken basin could hold clues about the composition of the Moon's mantle. 

Credit: NASA/GSFC

Researchers from Brown University and the University of Hawaii have found some mineralogical surprises in the Moon's largest impact crater.

Data from the Moon Mineralogy Mapper that flew aboard India's Chandrayaan-1 lunar orbiter shows a diverse mineralogy in the subsurface of the giant South Pole Aitken basin.

The differing mineral signatures could be reflective of the minerals dredged up at the time of the giant impact 4 billion years ago, the researchers say.

If that's true, then the South Pole Aitken (SPA) basin could hold important information about the Moon's interior and the evolution of its crust and mantle.

The study, led by Brown graduate student Dan Moriarty, is published in online early view in the Journal of Geophysical Research: Planets.

At 2,500 kilometers across, the SPA is the largest impact basin on the Moon and perhaps the largest in the solar system.

Impacts of this size turn tons of solid rock into molten slush. It has been assumed generally that the melting process would obliterate any distinct signatures of pre-existing mineralogical diversity through extensive mixing, but this latest research suggests that might not be the case.

The study looked at smaller craters within the larger SPA basin made by impacts that happened millions of years after the giant impact that formed the basin.

Those impacts uncovered material from deep within the basin, offering important clues about what lies beneath the surface.

Specifically, the researchers looked at the central peaks of four craters within the basin. Central peaks form when material under the impact zone rebounds, forming an upraised rock formation in the middle of the crater. The tops of those peaks represent pristine material from below the impact zone.

Moon Mineralogy Mapper

Using Moon Mineralogy Mapper data, the researchers looked at the light reflected from each of the four central peaks. The spectra of reflected light give scientists clues about the makeup of the rocks.

The spectra showed substantial differences in composition from peak to peak. Some crater peaks were richer in magnesium than others.

One of the four craters, located toward the outer edge of the basin, contained several distinct mineral deposits within its own peak, possibly due to sampling a mixture of both upper and lower crust or mantle materials.

The varying mineralogy in these central peaks suggests that the SPA subsurface is much more diverse than previously thought.

"Previous studies have suggested that all the central peaks look very similar, and that was taken as evidence that everything's the same across the basin," Moriarty said.

"We looked in a little more detail and found significant compositional differences between these central peaks."

"The Moon Mineralogy Mapper has very high spatial and spectral resolution. We haven't really been able to look at the Moon in this kind of detail before."

The next step is figuring out where that diversity comes from.

Canada: Billion-year-old water could hold clues to life on Mars

A UK-Canadian team of scientists has discovered ancient pockets of water, which have been isolated deep underground for billions of years and contain abundant chemicals known to support life.

This water could be some of the oldest on the planet and may even contain life.

Not just that, but the similarity between the rocks that trapped it and those on Mars raises the hope that comparable life-sustaining water could lie buried beneath the red planet's surface.

The findings, published in Nature today, may force us to rethink which parts of our planet are fit for life, and could reveal clues about how microbes evolve in isolation.

Researchers from the universities of Manchester, Lancaster, Toronto and McMaster analysed water pouring out of boreholes from a mine 2.4 kilometres beneath Ontario, Canada.

They found that the water is rich in dissolved gases like hydrogen, methane and different forms – called isotopes – of noble gases such as helium, neon, argon and xenon. Indeed, there is as much hydrogen in the water as around hydrothermal vents in the deep ocean, many of which teem with microscopic life.

The hydrogen and methane come from the interaction between the rock and water, as well as natural radioactive elements in the rock reacting with the water.

These gases could provide energy for microbes that may not have been exposed to the sun for billions of years.

The crystalline rocks surrounding the water are thought to be around 2.7 billion years old but no-one thought the water could be the same age, until now.

Using ground-breaking techniques developed at the University of Manchester, the researchers show that the fluid is at least 1.5 billion years old, but could be significantly older.

Chris Ballentine

NERC-funded Professor Chris Ballentine of the University of Manchester, co-author of the study, and project director, says: 'We've found an interconnected fluid system in the deep Canadian crystalline basement that is billions of years old, and capable of supporting life. Our finding is of huge interest to researchers who want to understand how microbes evolve in isolation, and is central to the whole question of the origin of life, the sustainability of life, and life in extreme environments and on other planets.'

Before this finding, the only water of this age was found trapped in tiny bubbles in rock and is incapable of supporting life but the water found in the Canadian mine pours from the rock at a rate of nearly two litres per minute.

It has similar characteristics to far younger water flowing from a mine 2.8 kilometres below ground in South Africa that was previously found to support microbes.

Greg Holland

Ballentine and his colleagues don't yet know if the underground system in Canada sustains life, but Dr Greg Holland of Lancaster University, lead author of the study says: 'Our Canadian colleagues are trying to find out if the water contains life right now. What we can be sure of is that we have identified a way in which planets can create and preserve an environment friendly to microbial life for billions of years. This is regardless of how inhospitable the surface might be, opening up the possibility of similar environments in the subsurface of Mars.'

Professor Ballentine, based in Manchester's School of Earth, Atmospheric and Environmental Sciences, adds: 'While the questions about life on Mars raised by our work are incredibly exciting, the ground-breaking techniques we have developed at Manchester to date ancient waters also provide a way to calculate how fast methane gas is produced in ancient rock systems globally. The same new techniques can be applied to characterise old, deep groundwater that may be a safe place to inject carbon dioxide.'

David Willetts, Minister for Universities and Science, says: 'This is excellent pioneering research. It gives new insight into our planet. It has also developed new technology for carbon capture and storage projects. These have the potential for growth, job creation and our environment.'

More information: 
Deep fracture fluids isolated in the crust since the Precambrian era, by G. Holland, B. Sherwood Lollar, L. Li, G. Lacrampe-Couloume, G. F. Slater & C. J. Ballentine, in Nature, 16 May 2013. dx.doi.org/10.1038/nature12127