Uranus's Moon Miranda: Bizarre Shape Explained

Uranus' icy moon Miranda is seen in this image from NASA's Voyager 2 probe on Jan. 24, 1986.

Credit: NASA/JPL-Caltech

The strange appearance of Uranus' moon Miranda may finally have an explanation.

Miranda resembles Frankenstein's monster, a bizarre jumble of parts that didn't quite merge properly.

Now, researchers suggest they may know why Miranda looks so odd: Constant squeezing and stretching from Uranus caused the moon's insides to heat up and churn.

Miranda is the innermost of Uranus' five major moons.

Though Miranda is only 293 miles (471 kilometers) wide, about one-seventh as large as Earth's moon, this ball of ice and rock possesses one of the oddest and most varied landscapes known among extraterrestrial bodies, including giant canyons up to 12 times deeper than the Grand Canyon.

"Miranda has a really bizarre, deformed surface," said study lead author Noah Hammond, a planetary scientist at Brown University in Rhode Island. "It's a really beautiful and exotic moon."

Miranda has three giant features known as coronae that are unique among known objects in the solar system.

They are shaped crudely, either like ovals or trapezoids, and each is least 120 miles (200 km) wide.

The coronae are separated from their more heavily cratered surroundings by belts of concentric ridges and troughs, making the coronae look like mismatched patches on a moth-eaten coat.

The three coronae, Arden, Elsinore and Inverness, are named after Scottish locations also mentioned in Shakespeare's plays.

This photo of Uranus' moon Miranda, taken by NASA's Voyager 2 probe in January 1986, shows an unusual "chevron" figure and regions of distinctly differing terrain on the mysterious satellite.

Credit: NASA/JPLView full size image

Researchers have long wondered how the coronae formed.

One possibility is that Miranda may have been disrupted by some catastrophic impact, after which its pieces chaotically reassembled.

The coronae formed as rocky material sank downward, triggering concentric wrinkles on Miranda's surface as it contracted, this idea goes.

Another possibility, one suggested by most scientists in the field, is that the coronae formed as buoyant domes of ice rose, causing Miranda's surface to crumple as matter was added to it.

However, it was not known where the heat to drive this ice upward might have come from. Since Miranda is relatively small, it would have cooled quickly after its creation, and it does not have the radioactive material that Earth possesses to help keep its innards hot.

Now, researchers show the gravitational pull of Uranus may have distorted Miranda enough to heat it up, leading its innards to churn much as Earth's does, thus explaining the coronae.

The gravity of Uranus pulls on Miranda, generating tidal forces, much as Earth's moondoes to Earth.

Tidal forces elsewhere in the solar system can be far greater than tidal effects on Earth, for instance, Jupiter's gravitational pull causes the solid rock surface of its third-largest moon Io to bulge up and down by as much as 300 feet (90 meters), generating enough heat to drive volcanic eruptions.

Miranda's orbit around Uranus was once eccentric, or oval-shaped, moving it closer to and farther from Uranus over time.

Three-dimensional computer simulations of Miranda's interior performed for the new study revealed the resulting tidal forces would repeatedly stretch and squeeze Miranda enough to generate substantial amounts of heat, about 5 gigawatts, or 2.5 times the peak power output of the huge Hoover Dam on the southwestern United States' Colorado River.

This heat would cause Miranda's icy mantle to churn with convection much like Earth's mantle of hot rock does. During convection, warm buoyant ice would have risen to Miranda's surface to contort it and create the coronae.

The research team's computer models accurately explained the locations of the coronae and the deformation patterns within the coronae, Hammond said.

"The features on Miranda may look really strange, but they formed in a way that is really similar to what happens on Earth, where convection in the interior drives surface deformation," Hammond told Space.com.

However, the scientists noted that for convection to drive Miranda's surface deformation, the moon's surface must be much weaker than predicted by laboratory experiments.

"The Earth has the same problem: For convection to deform Earth's surface, rocks have to behave weaker than expected," Hammond said.

"It'd be interesting to see what might explain the weakness seen in the surfaces of Miranda, Earth and elsewhere."

So far, scientists only know what Miranda's southern hemisphere looks like. NASA's Voyager 2 spacecraft photographed this part of the moon during its 1986 Uranus flyby but did not image Miranda's northern hemisphere.

"It'd be really interesting to think about what could be on the other side of Miranda," Hammond said. "Our study predicts there'd be one additional corona on Miranda's other side, and I would love to live long enough for a mission to go back to Uranus and test that hypothesis."

Hammond and his colleague Amy Barr detailed their findings online Sept. 15 in the journal Geology.

Mysterious rare five-hour space explosion explained

The X-ray image from the Swift X-ray Telescope of the gamma-ray burst GRB 130925. 

The white object in the center is the gamma-ray burst. 

The large diffuse region to the right is a cluster of galaxies. 

The other objects are X-ray-emitting celestial objects, most likely supermassive black holes at the centers of distant galaxies. 

The full image is approximately the size of the full moon. 

Credit: Phil Evans/ University of Leicester

Next week in St. Petersburg, Russia, scientists on an international team that includes Penn State University astronomers will present a paper that provides a simple explanation for mysterious ultra-long gamma-ray bursts, a very rare form of the most powerful explosions in the universe.

"The recent discovery of ultra-long gamma-ray bursts raised questions about whether some new physics is required to explain them, but our work suggests a much simpler explanation," said David Burrows, a Penn State professor of astronomy and astrophysics.

"Our analysis reveals that these rare gamma-ray bursts, which can last for hours, can be explained as standard explosions occurring in a region with a low density of matter that is located behind a cloud of dust when viewed from Earth."

Dick Willingale, an astronomer at the University of Leicester and a co-author of the study, said, "Not only is this result significant scientifically, but it shows the importance of international collaborations to build observatories, and of sharing information between those observatories."

Burrows is the lead scientist for the X-Ray Telescope on board the Swift satellite, one of two space observatories that the scientists used to collect data from the gamma-ray burst named GRB 130925A, which they observed last year while the energy from its explosion streamed toward Earth for more than five hours.

Swift is a NASA-led collaboration with Penn State in the United States, the University of Leicester and University College-London in the United Kingdom, and the Italian space agency and Brera Observatory in Italy.

The scientists also observed the ultra-long gamma-ray burst with the US/Russian satellite Konus-Wind.

"We could not have reached our conclusions without the Swift and Konus teams working together," Willingale said.

Burrows said it is not surprising that some gamma-ray bursts occur in a low-density region, nor is it surprising when one occurs behind a dust cloud.

"Our analysis of the observations from the two observatories shows that these two conditions existing simultaneously can explain our observations of the ultra-long gamma-ray burst GRB 130925A," Burrows said.

"One reason that these results are satisfying is that scientists generally prefer to find the simplest explanations for mysterious phenomena," he said.

Elliptical galaxies: Chandra helps explain 'red and dead galaxies'

Credit: X-ray: NASA /Chandra CXC /Stanford Univ /N.Werner et al.

NASA's Chandra X-ray Observatory has shed new light on the mystery of why giant elliptical galaxies have few, if any, young stars.

This new evidence highlights the important role that supermassive black holes play in the evolution of their host galaxies.

Because star-forming activity in many giant elliptical galaxies has shut down to very low levels, these galaxies mostly house long-lived stars with low masses and red optical colours.

Astronomers have therefore called these galaxies "red and dead."

Previously it was thought that these red and dead galaxies do not contain large amounts of cold gas—the fuel for star formation, helping to explain the lack of young stars.

ESA's Herschel Space Observatory

However, astronomers have used ESA's Herschel Space Observatory to find surprisingly large amounts of cold gas in some giant elliptical galaxies.

In a sample of eight galaxies, six contain large reservoirs of cold gas.

This is the first time that astronomers have seen large quantities of cold gas in giant elliptical galaxies that are not located at the center of a massive galaxy cluster.

With lots of cold gas, astronomers would expect many stars to be forming in these galaxies, contrary to what is observed.

To try to understand this inconsistency, astronomers studied the galaxies at other wavelengths, including X-rays and radio waves.

The Chandra observations map the temperature and density of hot gas in these galaxies.

For the six galaxies containing abundant cold gas, including NGC 4636 and NGC 5044 shown here, the X-ray data provide evidence that the hot gas is cooling, providing a source for the cold gas observed with Herschel.

However, the cooling process stops before the cold gas condenses to form stars. What prevents the stars from forming?

A strong clue comes from the Chandra images. The hot gas in the center of the six galaxies containing cold gas appears to be much more disturbed than in the cold gas-free systems.

This is a sign that material has been ejected from regions close to the central black hole. These outbursts are possibly driven, in part, by clumpy, cold gas that has been pulled onto the black hole.

The outbursts dump most of their energy into the center of the galaxy, where the cold gas is located, preventing the cold gas from cooling sufficiently to form stars.

The other galaxies in the sample, NGC 1399 and NGC 4472, are also forming few if any stars, but they have a very different appearance. No cold gas was detected in these galaxies, and the hot gas in their central regions is much smoother.

Additionally, they have powerful jets of highly energetic particles, as shown in radio images from the National Science Foundation's Karl G. Jansky Very Large Array.

These jets are likely driven by hot gas falling towards the central supermassive black holes.

By pushing against the hot gas, the jets create enormous cavities that are observed in the Chandra images, and they may heat the hot, X-ray emitting gas, preventing it from cooling and forming cold gas and stars.

The centers of NGC 1399 and NGC 4472 look smoother in X-rays than the other galaxies, likely because their more powerful jets produce cavities further away from the center, where the X-ray emission is fainter, leaving their bright cores undisturbed.

More information: A paper describing these results was published on 24 February 2014 in Monthly Notices of the Royal Astronomical Society: mnras.oxfordjournals.org/content/439/3/2291 , Preprint: arxiv.org/abs/1310.5450

Supernova Legacy Survey: Powerful ancient explosions explain new class of supernovae

A small portion of one of the fields from the Supernova Legacy Survey showing SNLS-06D4eu and its host galaxy (arrow). 

The supernova and its host galaxy are so far away that both are a tiny point of light that cannot be clearly differentiated in this image. 

The large, bright objects with spikes are stars in our own galaxy. 

Every other point of light is a distant galaxy. 

Credit: UCSB

Astronomers affiliated with the Supernova Legacy Survey (SNLS) have discovered two of the brightest and most distant supernovae ever recorded, 10 billion light-years away and a hundred times more luminous than a normal supernova. Their findings appear in the Dec. 20 issue of the Astrophysical Journal.

These newly discovered supernovae are especially puzzling because the mechanism that powers most of them—the collapse of a giant star to a black hole or normal neutron star—cannot explain their extreme luminosity.

Discovered in 2006 and 2007, the supernovae were so unusual that astronomers initially could not figure out what they were or even determine their distances from Earth.

"At first, we had no idea what these things were, even whether they were supernovae or whether they were in our galaxy or a distant one," said lead author D. Andrew Howell, a staff scientist at Las Cumbres Observatory Global Telescope Network (LCOGT) and adjunct faculty at UC Santa Barbara.

"I showed the observations at a conference, and everyone was baffled. Nobody guessed they were distant supernovae because it would have made the energies mind-bogglingly large. We thought it was impossible."

One of the newly discovered supernovae, named SNLS-06D4eu, is the most distant and possibly the most luminous member of an emerging class of explosions called superluminous supernovae.

These new discoveries belong to a special subclass of superluminous supernovae that have no hydrogen.

The new study finds that the supernovae are likely powered by the creation of a magnetar, an extraordinarily magnetized neutron star spinning hundreds of times per second.

Magnetars have the mass of the sun packed into a star the size of a city and have magnetic fields a hundred trillion times that of the Earth.

While a handful of these superluminous supernovae have been seen since they were first announced in 2009, and the creation of a magnetar had been postulated as a possible energy source, the work of Howell and his colleagues is the first to match detailed observations to models of what such an explosion might look like.

Co-author Daniel Kasen from UC Berkeley and Lawrence Berkeley National Lab created models of the supernova that explained the data as the explosion of a star only a few times the size of the sun and rich in carbon and oxygen.

The star likely was initially much bigger but apparently shed its outer layers long before exploding, leaving only a smallish, naked core.

More information: dx.doi.org/10.1088/0004-637X/779/2/98

Space mission to Venus might help explain origin of the Moon

The Moon's gravity field as mapped by NASA's Gravity Recovery and Interior Laboratory. 

Credit: NASA/JPL-CALTECH/MIT/GSFC

Robin Canup, a space scientist with the Southwest Research Institute in Colorado has published a Comment piece in the journal Nature proposing that a mission to Venus be considered to help better understand the development of our moon.

She suggests that current theories that describe how the moon came about rely too heavily on Mars data, which could be obscuring the real story.

Tim Elliot and Sarah Stewart offer their own opinions on the matter in a companion News & Views piece in the same journal.

Robin Canup

The general consensus among modern space scientists is that our moon came to exist as the result of a Mars size planet impacting the Earth—that impact, the thinking goes, would have caused a lot of debris (made up mainly of material from the impactor) being pushed into space which over would have coalesced over time into a disk and then eventually, into the moon as we know it today.

The problem with this theory, as Canup notes, is that evidence is mounting that indicates the moon, at least on its surface, is far more like the Earth than the theory suggests.

Silicate samples brought back from manned missions, for example have the same isotope composition as those found here on Earth.

It's possible the impacting body had a nearly identical composition to the Earth, but that seems unlikely considering the differences in composition between Earth, and say Mars.

That's part of the reason Canup argues, that we need to go to Venus. We don't have isotopic samples from that planet.

If we did go there and retrieve samples and then found them similar to those here on Earth, it would go a long way towards explaining why the Earth and Moon seem to be so similar.

Meanwhile, space scientists are left to consider other theories to explain not just how the moon was created and developed but how it and the Earth evolved together resulting in the relationship we have today.

Some have suggested that perhaps the impact was actually between two Earth-like bodies, or maybe, the Earth was spinning a lot faster way back when which would have resulted in a small impact causing a lot of Earth debris to be flung into space, leading to the formation of the moon.

The main point Canup seems to be making is that if we want to understand our own planet better, we need to understand the moon as well and to do that, we need more data—starting with surface samples from Venus, she notes, would be a great way to begin.

More information: Planetary science: Lunar conspiracies, by Robin Canup, Nature 504, 27–29 (05 December 2013) DOI: 10.1038/504027a

ESA SWARM: Explaining the earth's Magnetic Field - Animation video

An introduction to Earth's magnetic field: what it is, where it comes from and what are the benefits and advantages to life on Earth.

Astronomers explain why disk galaxies eventually look alike

Iowa State's Curtis Struck and IBM's Bruce Elmegreen are studying how galaxies evolve from the clumpy example on the left to the smooth example on the right. 

Credit: Sloan Digital Sky Survey.

It happens to all kinds of flat, disk galaxies – whether they're big, little, isolated or crowded in a cluster.

They all grow out of their irregular, clumped appearance and their older stars take on the same smooth look, predictably fading from a bright center to a dim edge.

Curtis Struck

Or, as Curtis Struck, an Iowa State University astronomer, wrote in a research summary: "In galaxy disks, the scars of a rough childhood, and adolescent blemishes, all smooth away with time."

How does that happen?
Struck, a professor of physics and astronomy who studies galaxy evolution and wrote the 2011 book "Galaxy Collisions," said a few explanations have been proposed, but most of those only covered certain types of galaxies.

There hasn't been an explanation for the nearly universal and exponential fade in the brightness of the lookalike disk galaxies.

To try to find an explanation, Struck and Bruce Elmegreen, a research scientist at IBM's Thomas J. Watson Research Center in Yorktown Heights, N.Y., built computer models simulating galaxy evolution and they think they've found a fundamental answer in the gravitational pull of the irregular, clumped structure of younger galaxies.

They report their findings in a paper, "Exponential Galaxy Disks from Stellar Scattering," just published online by the Astrophysical Journal Letters.

Struck and Elmegreen based their paper on the simplest possible galaxy model that still includes all the essential ingredients: a razor-thin disk and orbiting stars subject to the gravity of the massive clumps.

"We focused on the clumps," Struck said. "We thought the clumpy structure of young galaxy disks may be responsible for both its own erasure and the smooth universal brightness profile."

Struck said the models showed that's the case. The gravity of those clumps of interstellar gases and new stars alter the orbits of nearby stars.

In some cases, the changes are significant, scattering stars well away from their original and nearly circular orbits.

Over time, that scattering from circular to slightly elliptical orbits produces the smooth fade in brightness from the center of a galaxy to its edge.

We're talking a lot of time: "This process takes a few hundred million years to a few billion years," Struck said.

Do those findings match the data coming from the Hubble Space Telescope and large ground-based telescopes, tools that allow astronomers to see distant galaxies in their young and clumpy structure?

"Yes, they do fit the observed data coming back," Struck said.

Struck also said there's more work to be done to explain the mystery of the smooth, steady fade of older disk galaxies.

Struck and Elmegreen will gradually add more physical processes to their models to see how additional complexities affect what they've discovered about the fundamental process of star scattering.

Even so, Struck said the current models have provided a good explanation for the universal appearance of older disk galaxies.

"If there is some disturbance, some clumpiness in the galaxy," he said, "you eventually get this smooth profile."

More information: Paper: iopscience.iop.org/2041-8205/775/2/L35

Dark Matter: Can Simple Anapole theory explain it?

This is a comparison of an anapole field with common electric and magnetic dipoles. The anapole field, top, is generated by a toroidal electrical current. 

As a result, the field is confined within the torus, instead of spreading out like the fields generated by conventional electric and magnetic dipoles. 

Credit: Michael Smeltzer, Vanderbilt University

Most of the matter in the universe may be made out of particles that possess an unusual, donut-shaped electromagnetic field called an anapole.

This proposal, which endows dark matter particles with a rare form of electromagnetism, has been strengthened by a detailed analysis performed by a pair of theoretical physicists at Vanderbilt University: Professor Robert Scherrer and post-doctoral fellow Chiu Man Ho.

An article about the research was published online last month by the journal Physics Letters B.

"There are a great many different theories about the nature of dark matter. What I like about this theory is its simplicity, uniqueness and the fact that it can be tested," said Scherrer.

Robert Scherrer

In the article, titled "Anapole Dark Matter," the physicists propose that dark matter, an invisible form of matter that makes up 85 percent of the all the matter in the universe, may be made out of a type of basic particle called the Majorana fermion.

The particle's existence was predicted in the 1930's but has stubbornly resisted detection.

A number of physicists have suggested that dark matter is made from Majorana particles, but Scherrer and Ho have performed detailed calculations that demonstrate that these particles are uniquely suited to possess a rare, doughnut-shaped type of electromagnetic field called an anapole.

This field gives them properties that differ from those of particles that possess the more common fields possessing two poles (north and south, positive and negative) and explains why they are so difficult to detect.

"Most models for dark matter assume that it interacts through exotic forces that we do not encounter in everyday life. Anapole dark matter makes use of ordinary electromagnetism that you learned about in school – the same force that makes magnets stick to your refrigerator or makes a balloon rubbed on your hair stick to the ceiling," said Scherrer.

"Further, the model makes very specific predictions about the rate at which it should show up in the vast dark matter detectors that are buried underground all over the world. These predictions show that soon the existence of anapole dark matter should either be discovered or ruled out by these experiments."

More information: Anapole dark matter. Physics Letters B, 2013; 722 (4-5): 341 DOI: 10.1016/j.physletb.2013.04.039 ( adsabs.harvard.edu/abs/2013PhLB..722..341)

Orbital Sciences: Antares Rocket & Cygnus Spacecraft Explained - Infographic

Credit: Space.com 

All about our solar system, outer space and exploration

Virginia-based Orbital Sciences holds a $1.9 billion NASA contract to make eight unmanned supply runs to the International Space Station with its Antares rocket and Cygnus cargo ferry.

Antares Launcher
The two-stage Antares launch vehicle burns liquid oxygen (LOX) and kerosene (RP-1). The rocket's height overall is 131 feet (40 meters). Its liftoff weight is 530,000 pounds (240,000 kilograms). The Antares rocket was originally called Taurus 2.

Cygnus Cargo Tanker
The Cygnus pressurized cargo module can carry up to 5,952 pounds (2,700 kg) of payload to the International Space Station.

At the rear of Cygnus is a service module containing avionics, power, communications and command and control hardware. On the outside of the service module are twin fixed-wing gallium arsenide solar arrays capable of putting out 3.5 kilowatts of electricity.

Future Cygnus spacecraft will be enhanced with a larger pressurized cargo module and lightweight solar panels.

Ice Melt may explain Antarctica's sea ice expansion

Climate change is expanding Antarctica's sea ice, according to a scientific study in the journal Nature Geoscience.

The paradoxical phenomenon is thought to be caused by relatively cold plumes of fresh water derived from melting beneath the Antarctic ice shelves.

This melt water has a relatively low density, so it accumulates in the top layer of the ocean.

The cool surface waters then re-freeze more easily during Autumn and Winter.

This explains the observed peak in sea ice during these seasons, a team from the Royal Netherlands Meteorological Institute (KNMI) says in its peer-reviewed paper.

Climate scientists have been intrigued by observations that Antarctic sea ice shows a small but statistically significant expansion of about 1.9% per decade since 1985, while sea ice in the Arctic has been shrinking over past decades.

The researchers from the KNMI suggest the "negative feedback" effect outlined in their study is expected to continue into the future.

They tried to reproduce the observed changes in a computer-based climate model.

The sea ice expanded during Southern Hemisphere autumn and winter in response to the development of this fresh, cool surface layer, which floated on the denser, warmer salty sea water below.

Richard Bintanja

This fresh water is ultimately derived from enhanced melting at the base of the Antarctic ice shelves.

"Sea ice around Antarctica is increasing despite the warming global climate," said the study's lead author Richard Bintanja (Bintanja.NL), from the KNMI.

"This is caused by melting of the ice sheets from below," he told the Reuters news agency.

But there are other plausible explanations for Antarctic sea-ice expansion.

Paul Holland of the British Antarctic Survey (BAS) stuck to his findings last year that a shift in winds linked to climate change was blowing ice away from the coast, allowing exposed water in some areas to freeze and make yet more ice.

Paul Holland

"The possibility remains that the real increase is the sum of wind-driven and melt water-driven effects, of course. That would be my best guess, with the melt water effect being the smaller of the two," he told the London Science Media Centre.

The study in Nature Geoscience also asserts that the cool melt water layer may limit the amount of water sucked from the oceans that falls as snow on Antarctica. Cold air can hold less moisture than warm air.