Month: November 2018

Mars Moon Got Its Grooves From Rolling Stones

A new study bolsters the idea that strange grooves crisscrossing the surface of the Martian moon Phobos were made by rolling boulders blasted free from an ancient asteroid impact.

The research, published in Planetary and Space Science, uses computer models to simulate the movement of debris from Stickney crater, a huge gash on one end of Phobos’ oblong body. The models show that boulders rolling across the surface in the aftermath of the Stickney impact could have created the puzzling patterns of grooves seen on Phobos today.

“These grooves are a distinctive feature of Phobos, and how they formed has been debated by planetary scientists for 40 years,” said Ken Ramsley, a planetary science researcher at Brown University who led the work. “We think this study is another step toward zeroing in on an explanation.”

Phobos’ grooves, which are visible across most of the moon’s surface, were first glimpsed in the 1970s by NASA’s Mariner and Viking missions. Over the years, there has been no shortage of explanations put forward for how they formed. Some scientists have posited that large impacts on Mars have showered the nearby moon with groove-carving debris. Others think that Mars’ gravity is slowly tearing Phobos apart, and the grooves are signs of structural failure.

Still other researchers have made the case that there’s a connection between the grooves and the Stickney impact. In the late 1970s, planetary scientists Lionel Wilson and Jim Head proposed the idea that ejecta — bouncing, sliding and rolling boulders — from Stickney may have carved the grooves. Head, a professor in Brown’s department of Earth, Environmental and Planetary Sciences, was also a coauthor of this new paper.

For a moon the size of the diminutive Phobos (27 kilometers across at its widest point), Stickney is a huge crater at 9 kilometers across. The impact that formed it would have blown free tons of giant rocks, making the rolling boulder idea entirely plausible, Ramsley says. But there are also some problems with the idea.

For example, not all of the grooves are aligned radially from Stickney as one might intuitively expect if Stickney ejecta did the carving. And some grooves are superposed on top of each other, which suggests some must have already been there when superposed ones were created. How could there be grooves created at two different times from one single event? What’s more, a few grooves run through Stickney itself, suggesting that the crater must already have been there when the grooves formed. There’s also a conspicuous dead spot on Phobos where there are no grooves at all. Why would all those rolling boulders just skip one particular area?

To explore those questions, Ramsley designed computer models to see if there was any chance that the “rolling boulder model” could recreate these confounding patterns. The models simulate the paths of the boulders ejected from Stickney, taking into account Phobos’ shape and topography, as well as its gravitational environment, rotation and orbit around Mars.

Ramsley said he had no expectations for what the models might show. He wound up being surprised at how well the model recreated the groove patterns seen on Phobos.

“The model is really just an experiment we run on a laptop,” Ramsley said. “We put all the basic ingredients in, then we press the button and we see what happens.”

The models showed that the boulders tended to align themselves in sets of parallel paths, which jibes with the sets of parallel grooves seen on Phobos. The models also provide a potential explanation for some of the other more puzzling groove patterns.

The simulations show that because of Phobos’ small size and relatively weak gravity, Stickney stones just keep on rolling, rather than stopping after a kilometer or so like they might on a larger body. In fact, some boulders would have rolled and bounded their way all the way around the tiny moon. That circumnavigation could explain why some grooves aren’t radially aligned to the crater. Boulders that start out rolling across the eastern hemisphere of Phobos produce grooves that appear to be misaligned from the crater when they reach the western hemisphere.

That round-the-globe rolling also explains how some grooves are superposed on top of others. The models show that grooves laid down right after the impact were crossed minutes to hours later by boulders completing their global journeys. In some cases, those globetrotting boulders rolled all the back to where they started — Stickney crater. That explains why Stickney itself has grooves.

Then there’s the dead spot where there are no grooves at all. That area turns out to be a fairly low-elevation area on Phobos surrounded by a higher-elevation lip, Ramsley says. The simulations showed that boulders hit that lip and take a flying leap over the dead spot, before coming down again on the other side.

“It’s like a ski jump,” Ramsley said. “The boulders keep going but suddenly there’s no ground under them. They end up doing this suborbital flight over this zone.”

All told, Ramsley says, the models answer some key questions about how ejecta from Stickney could have been responsible for Phobos’ complicated groove patterns.

“We think this makes a pretty strong case that it was this rolling boulder model accounts for most if not all the grooves on Phobos,” Ramsley said.

Vietnam Faces New Tropical Storm Threat After Landslides Kill At Least 13

On the heels of deadly Tropical Storm Toraji, a budding tropical storm will bring a renewed risk of flooding and mudslides to Vietnam this weekend.

At least 13 people are dead after landslides destroyed several homes and buried victims in some villages in the resort city of Nha Trang on Sunday, according to the Associated Press. Four others remain missing.

Torrential rain from Toraji is being blamed for triggering the landslides.

According to preliminary weather data, nearly 380 mm (15 inches) of rain inundated Nha Trang over the course of 18 hours ending early Sunday afternoon, local time.

As cleanup and recovery efforts continue, residents are facing a new tropical threat.

The tropical depression unloading heavy rain on the Philippines is expected to slam into southern Vietnam this weekend.

“The warm waters of the South China Sea will cause the depression to strengthen into a strong tropical storm or minimal typhoon before it reaches Vietnam,” according to AccuWeather Senior Meteorologist Dave Houk.

Thousands Flee As Guatemalan Volcano Erupts Again

Thousands of Guatemalans are evacuating their homes as the Volcán de Fuego, or Volcano of Fire, erupts again near the city of Antigua.

The volcano has erupted repeatedly this year. In June, more than 100 people were killed in a violent eruption that spewed lava, ash and rocks over nearby villages.

Now, as the volcano resumes erupting once again, evacuations are underway.

Nearly 4,000 people have been cleared out of the disaster zone, including more than 2,000 housed in shelters, the government agency responsible for natural disasters says.

Whether or not local communities evacuate is up to local leaders and residents, reports Prensa Libre, a Guatemalan newspaper. The paper writes that according to authorities, all the affected communities were warned about the volcanic activity on Sunday.

The evacuations come after new lava flows were detected and following hours of mounting concern from groups monitoring the volcano’s activity.

On Sunday, the volcano was registering more than a dozen weak or moderate explosions per hour, raising concerns of hazardous lava flows.

Now those concerns have become a real risk. Glowing eruptions are rising 1,000 meters (more than 3,000 feet) above the crater. The volcano has created a column of ash stretching nearly 3 miles above sea level and multiple lava flows, with the longest more than a mile and a half long.

Ash is drifting toward Guatemala City, The Associated Press reports.

Guatemalan officials say this is the fifth eruption of the Volcano of Fire so far this year.

40-Foot Waves Batter The Canary Islands After Storm Causes Dozens To Evacuate

Waves as high as 6 metres pummelled apartment buildings in the Canary Islands as wild weather forced dozens to evacuate.

Local media reported 65 apartments were evacuated as waves crashed ashore in Tenerife’s Mesa del Mar, ripping the railings from apartment balconies. Local mayor Alvaro Davila reportedly said no-one had been injured.

Thirty-nine people were also evacuated from the town of Garachico on Saturday night amid the stormy weather, local media said.

Meanwhile, wild weather continued to batter Spain, as the national weather agency declared Valencia and Alicante on red alert, the maximum risk level, due to heavy rain on Monday.

Mallorca was placed on orange alert, designating serious risk, and the rest of the Balearic islands and Murcia in southern Spain received the third-tier yellow alert designated as risky.

Ultra-Hot Gas Around Remnants Of Sun-Like Stars

Solving a decades-old mystery, an international team of astronomers have discovered an extremely hot magnetosphere around a white dwarf, a remnant of a star like our Sun. The work was led by Dr Nicole Reindl, Research Fellow of the Royal Commission 1851, based at the University of Leicester, and is published today (7 November) in the journal Monthly Notices of the Royal Astronomical Society.

White dwarfs are the final stage in the lives of stars like our Sun. At the end of their lives, these stars eject their outer atmospheres, leaving behind a hot, compact and dense core that cools over billions of years. The temperature on their surfaces is typically around 100,000 degrees Celsius (in comparison the surface of the Sun is 5500 degrees).

Some white dwarfs though challenge scientists, as they show evidence for highly ionised metals. In astronomy ‘metals’ describe every element heavier than helium, and high ionisation here means that all but one of the outer electrons usually in their atoms have been stripped away. That process needs a temperature of 1 million degrees Celsius, so far higher than the surface of even the hottest white dwarf stars.

Reindl’s team used the 3.5-metre Calar Alto telescope in Spain to discover and observe a white dwarf in the direction of the constellation of Triangulum, catalogued as GALEXJ014636.8+323615, located 1200 light years from the Sun. Analysing the light from the white dwarf with a technique known as spectroscopy, where the light is dispersed into its constituent colours, revealed the signatures of highly ionised metals. Intriguingly these varied over a period of six hours — the same time it takes for the white dwarf to rotate.

Reindl and her team conclude that the magnetic field around the star — the magnetosphere — traps material flowing from its surface. Shocks within the magnetosphere heat the material dramatically, stripping almost all the electrons from the metal atoms.

“It’s like a doughnut made up of ultra-hot material that surrounds the already very hot star” explains Reindl.

“The axis of the magnetic field of the white dwarf is tilted from its rotational axis. This means that the amount of shock-heated material we see varies as the star rotates.

‘After decades of finding more and more of these obscure stars without having a clue where these highly ionised metals come from,” she continues, “our shock-heated magnetosphere model finally explains their origin.”

Magnetospheres are found around other types of stars, but this is the first report of one around a white dwarf. The discovery might have far-reaching consequences. “We simply didn’t take this into account,” admits Reindl. “Ignoring their magnetospheres could mean measurements of other basic properties of white dwarfs are wrong, like their temperatures and masses.”

It may be that a quarter of white dwarfs go through a stage of trapping and super-heating material. Reindl and her team now plan to model them in detail and to extend their research by studying more of these fascinating objects.

Scientists Theorize New Origin Story For Earth’s Water

Earth’s water may have originated from both asteroidal material and gas left over from the formation of the Sun, according to new research. The new finding could give scientists important insights about the development of other planets and their potential to support life.

In a new study in the Journal of Geophysical Research: Planets, a journal of the American Geophysical Union, researchers propose a new theory to address the long-standing mystery of where Earth’s water came from and how it got here.

The new study challenges widely-accepted ideas about hydrogen in Earth’s water by suggesting the element partially came from clouds of dust and gas remaining after the Sun’s formation, called the solar nebula.

To identify sources of water on Earth, scientists have searched for sources of hydrogen rather than oxygen, because the latter component of water is much more abundant in the solar system.

Many scientists have historically supported a theory that all of Earth’s water came from asteroids because of similarities between ocean water and water found on asteroids. The ratio of deuterium, a heavier hydrogen isotope, to normal hydrogen serves as a unique chemical signature of water sources. In the case of Earth’s oceans, the deuterium-to-hydrogen ratio is close to what is found in asteroids.

But the ocean may not be telling the entire story of Earth’s hydrogen, according to the study’s authors.

“It’s a bit of a blind spot in the community,” said Steven Desch, a professor of astrophysics in the School of Earth and Space Exploration at Arizona State University in Tempe, Arizona and co-author of the new study, led by Peter Buseck, Regents’ Professor in the School of Earth and Space Exploration and School of Molecular Sciences at Arizona State University. “When people measure the [deuterium-to-hydrogen] ratio in ocean water and they see that it is pretty close to what we see in asteroids, it was always easy to believe it all came from asteroids.”

More recent research suggests hydrogen in Earth’s oceans does not represent hydrogen throughout the entire planet, the study’s authors said. Samples of hydrogen from deep inside the Earth, close to the boundary between the core and mantle, have notably less deuterium, indicating this hydrogen may not have come from asteroids. Noble gases helium and neon, with isotopic signatures inherited from the solar nebula, have also been found in the Earth’s mantle.

In the new study, researchers developed a new theoretical model of Earth’s formation to explain these differences between hydrogen in Earth’s oceans and at the core-mantle boundary as well as the presence of noble gases deep inside the planet.

Modeling Earth’s beginning

According to their new model, several billion years ago, large waterlogged asteroids began developing into planets while the solar nebula still swirled around the Sun. These asteroids, known as planetary embryos, collided and grew rapidly. Eventually, a collision introduced enough energy to melt the surface of the largest embryo into an ocean of magma. This largest embryo would eventually become Earth.

Gases from the solar nebula, including hydrogen and noble gases, were drawn in by the large, magma-covered embryo to form an early atmosphere. Nebular hydrogen, which contains less deuterium and is lighter than asteroidal hydrogen, dissolved into the molten iron of the magma ocean.

Through a process called isotopic fractionation, hydrogen was pulled towards the young Earth’s center. Hydrogen, which is attracted to iron, was delivered to the core by the metal, while much of the heavier isotope, deuterium, remained in the magma which eventually cooled and became the mantle, according to the study’s authors. Impacts from smaller embryos and other objects then continued to add water and overall mass until Earth reached its final size.

This new model would leave Earth with noble gases deep inside its mantle and a lower deuterium-to-hydrogen ratio in its core than in its mantle and oceans.

The authors used the model to estimate how much hydrogen came from each source. They concluded most was asteroidal in origin, but some of Earth’s water did come from the solar nebula.

“For every 100 molecules of Earth’s water, there are one or two coming from solar nebula,” said Jun Wu, assistant research professor in the School of Molecular Sciences and School of Earth and Space Exploration at Arizona State University and lead author of the study.

An insightful model

The study also offers scientists new perspectives about the development of other planets and their potential to support life, the authors said. Earth-like planets in other solar systems may not all have access to asteroids loaded with water. The new study suggests these exoplanets could have obtained water through their system’s own solar nebula.

“This model suggests that the inevitable formation of water would likely occur on any sufficiently large rocky exoplanets in extrasolar systems,” Wu said. “I think this is very exciting.”

Anat Shahar, a geochemist at the Carnegie Institution for Science, who was not involved with the study, noted the hydrogen fractionation factor, which describes how the deuterium-to-hydrogen ratio changes when the element dissolves in iron, is currently unknown and difficult to measure. For the new study, this property of hydrogen had to be estimated.

The new model, which fits in well with current research, could be tested once experiments reveal the hydrogen fractionation factor, Shahar said.

“This paper is a very creative alternative to what is an old problem,” Shahar said. “The authors have done a good job of estimating what these different fractionation factors would be without having the experiments.”

Astronomers Find Pairs Of Black Holes At The Centers Of Merging Galaxies

For the first time, a team of astronomers has observed several pairs of galaxies in the final stages of merging together into single, larger galaxies. Peering through thick walls of gas and dust surrounding the merging galaxies’ messy cores, the research team captured pairs of supermassive black holes — each of which once occupied the center of one of the two original smaller galaxies — drawing closer together before they coalescence into one giant black hole.

Led by University of Maryland alumnus Michael Koss (M.S. ’07, Ph.D. ’11, astronomy), a research scientist at Eureka Scientific, Inc., with contributions from UMD astronomers, the team surveyed hundreds of nearby galaxies using imagery from the W.M. Keck Observatory in Hawaii and NASA’s Hubble Space Telescope. The Hubble observations represent more than 20 years’ worth of images from the telescope’s lengthy archive. The team described their findings in a research paper published on November 8, 2018, in the journal Nature.

“Seeing the pairs of merging galaxy nuclei associated with these huge black holes so close together was pretty amazing,” Koss said. “In our study, we see two galaxy nuclei right when the images were taken. You can’t argue with it; it’s a very ‘clean’ result, which doesn’t rely on interpretation.”

The high-resolution images also provide a close-up preview of a phenomenon that astronomers suspect was more common in the early universe, when galaxy mergers were more frequent. When the black holes finally do collide, they will unleash powerful energy in the form of gravitational waves — ripples in space-time recently detected for the first time by the twin Laser Interferometer Gravitational-wave Observatory (LIGO) detectors.

The images also presage what will likely happen in a few billion years, when our Milky Way galaxy merges with the neighboring Andromeda galaxy. Both galaxies host supermassive black holes at their center, which will eventually smash together and merge into one larger black hole.

The team was inspired by a Hubble image of two interacting galaxies collectively called NGC 6240, which later served as a prototype for the study. The team first searched for visually obscured, active black holes by sifting through 10 years’ worth of X-ray data from the Burst Alert Telescope (BAT) aboard NASA’s Neil Gehrels Swift Observatory.

“The advantage to using Swift’s BAT is that it observes high-energy, ‘hard’ X-rays,” said study co-author Richard Mushotzky, a professor of astronomy at UMD and a fellow of the Joint Space-Science Institute (JSI). “These X-rays penetrate through the thick clouds of dust and gas that surround active galaxies, allowing the BAT to see things that are literally invisible in other wavelengths.”

The researchers then combed through the Hubble archive, zeroing in on the merging galaxies they spotted in the X-ray data. They then used the Keck telescope’s super-sharp, near-infrared vision to observe a larger sample of the X-ray-producing black holes not found in the Hubble archive.

The team targeted galaxies located an average of 330 million light-years from Earth — relatively close by in cosmic terms. Many of the galaxies are similar in size to the Milky Way and Andromeda galaxies. In total, the team analyzed 96 galaxies observed with the Keck telescope and 385 galaxies from the Hubble archive.

Their results suggest that more than 17 percent of these galaxies host a pair of black holes at their center, which are locked in the late stages of spiraling ever closer together before merging into a single, ultra-massive black hole. The researchers were surprised to find such a high fraction of late-stage mergers, because most simulations suggest that black hole pairs spend very little time in this phase.

To check their results, the researchers compared the survey galaxies with a control group of 176 other galaxies from the Hubble archive that lack actively growing black holes. In this group, only about one percent of the surveyed galaxies were suspected to host pairs of black holes in the later stages of merging together.

This last step helped the researchers confirm that the luminous galactic cores found in their census of dusty interacting galaxies are indeed a signature of rapidly-growing black hole pairs headed for a collision. According to the researchers, this finding is consistent with theoretical predictions, but until now, had not been verified by direct observations.

“People had conducted studies to look for these close interacting black holes before, but what really enabled this particular study were the X-rays that can break through the cocoon of dust,” explained Koss. “We also looked a bit farther in the universe so that we could survey a larger volume of space, giving us a greater chance of finding more luminous, rapidly-growing black holes.”

It is not easy to find galactic nuclei so close together. Most prior observations of merging galaxies have caught the coalescing black holes at earlier stages, when they were about 10 times farther away. The late stage of the merger process is so elusive because the interacting galaxies are encased in dense dust and gas, requiring very high-resolution observations that can see through the clouds and pinpoint the two merging nuclei.

“Computer simulations of galaxy smashups show us that black holes grow fastest during the final stages of mergers, near the time when the black holes interact, and that’s what we have found in our survey,” said Laura Blecha, an assistant professor of physics at the University of Florida and a co-author of the study. Blecha was a JSI Prize Postdoctoral Fellow in the UMD Department of Astronomy prior to joining UF’s faculty in 2017. “The fact that black holes grow faster and faster as mergers progress tells us galaxy encounters are really important for our understanding of how these objects got to be so monstrously big.”

Future infrared telescopes such as NASA’s highly anticipated James Webb Space Telescope (JWST), slated for launch in 2021, will provide an even better view of mergers in dusty, heavily obscured galaxies. For nearby black hole pairs, JWST should also be capable of measuring the masses, growth rates and other physical parameters for each black hole.

“There might be other objects that we missed. Even with Hubble, many nearby galaxies at low redshift cannot be resolved — the two nuclei just merge into one,” said study co-author Sylvain Veilleux, a professor of astronomy at UMD and a JSI Fellow. “With JWST’s higher angular resolution and sensitivity to the infrared, which can pass through the dusty cores of these galaxies, searches for these nearby objects should be easy to do. Also with JWST, we will be able to push toward larger distances, to see objects at higher redshift. With these observations, we can begin to explore the fraction of objects that are merging in the youngest, most distant regions of the universe — which should be fairly frequent.”