Tag: geology

The interior of Ceres

11:06 am

Using data from Dawn, scientists have created their first rough map of the internal structure of Ceres.

The data indicate that Ceres is “differentiated,” which means that it has compositionally distinct layers at different depths, with the densest layer at the core. Scientists also have found that, as they suspected, Ceres is much less dense than Earth, the moon, giant asteroid Vesta (Dawn’s previous target) and other rocky bodies in our solar system. Additionally, Ceres has long been suspected to contain low-density materials such as water ice, which the study shows separated from the rocky material and rose to the outer layer along with other light materials. “We have found that the divisions between different layers are less pronounced inside Ceres than the moon and other planets in our solar system,” Park said. “Earth, with its metallic crust, semi-fluid mantle and outer crust, has a more clearly defined structure than Ceres,” Park said.

Scientists also found that high-elevation areas on Ceres displace mass in the interior. This is analogous to how a boat floats on water: the amount of displaced water depends on the mass of the boat. Similarly, scientists conclude that Ceres’ weak mantle can be pushed aside by the mass of mountains and other high topography in the outermost layer as though the high-elevation areas “float” on the material below. This phenomenon has been observed on other planets, including Earth, but this study is the first to confirm it at Ceres.

In other words, Ceres behaves more like a semi-hardened blob of jello than a rock.

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Martian gullies not formed by water flow

9:38 am

The uncertainty of science: Spectroscopy of many of the gullies on Mars strongly suggests that water had nothing to do with their formation, even though these gullies resemble closely similar gullies on Earth that were carved by flowing water..

Color coding in light blue corresponds to surface composition of unaltered mafic material, of volcanic origin. Mafic material from the crater rim is carved and transported downslope along the gully channels. No hydrated minerals are observed within the gullies, in the data from CRISM, indicating limited interaction or no interaction of the mafic material with liquid water. These findings and related observations at about 100 other gully sites on Mars suggest that a mechanism not requiring liquid water may be responsible for carving these gullies on Mars. (Gullies on Mars are a different type of feature than seasonal dark streaks called recurring slope lineae or RSL; water in the form of hydrated salt has been identified at RSL sites.) [emphasis mine]

In other words, these gullies were formed by flowing lava, not water. Considering Mars’s lower gravity, one third that of Earth’s, we should not be surprised if lava is capable of doing things there that it is not generally capable of doing on Earth. In fact, we should remind ourselves constantly that Mars is an alien planet, and that conditions there are different enough to make any predictions based on our knowledge of Earth very unreliable.

More details here.

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Heading directly for Balanced Rock

9:32 am

Curiosity's course to Balanced Rock

As I predicted Sunday, the Curiosity science team is aiming the rover directly towards the gap in the mesas, dubbed the Murray Buttes, that also has the balanced rock seen in earlier images.

The image on the right shows the rover’s most recent two traverses, superimposed on a Mars Reconnaissance Orbiter image. I have cropped it to focus in on the area of most interest.

Based on the rover’s general rate of travel, I would expect them to enter the gap after about two or three more traverses. This means they will be there in about a week, since after each traverse they usually stop and do science and reconnaissance before resuming travel.

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Dormant volcano near Rome reawakens

9:47 am

A volcano near Rome that last erupted 36,000 years ago is now showing signs of re-awakening.

Scientists previously assumed Colli Albani, a 15-kilometer (9-mile) semicircle of hills outside Rome, was an extinct volcano since there was no record of it having erupted in human history. But in recent years, scientists have observed new steam vents, earthquakes and a rise in ground level in the hills and surrounding area. These observations, along with new evidence of past eruptions and satellite data, indicate Colli Albani is starting a new eruptive cycle and could potentially erupt in 1,000 years from now, according to a new study published in Geophysical Research Letters, a journal of the American Geophysical Union.

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Weird dunes on Mars

11:11 am

Weird dunes on Mars

Cool image time! The image on the right, cropped and reduced in resolution to fit here, shows an area of inexplicable dark dunes located in Mars’ high northern latitudes. Located in a circular depression (whose outline can be seen across the top and left side of the image), geologists only partly understand the processes producing these dunes. As the noted on the release webpage:

However, a circular depression (probably an old and infilled impact crater) has limited the amount of sand available for dune formation and influenced local winds. As a result, the dunes here form distinct dots and dashes. The “dashes” are linear dunes formed by bi-directional winds, which are not traveling parallel to the dune. Instead, the combined effect of winds from two directions at right angles to the dunes, funnels material into a linear shape. The smaller “dots” (called “barchanoid dunes”) occur where there is some interruption to the process forming those linear dunes. This process is not well understood at present and is one motivation for HiRISE to image this area.

Be sure to look at the full image, as it covers a wider area and shows dunes that travel in all directions, forming mazelike patterns that no theory presently explains.

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Geologists discover giant field of underground helium in Tanzania

2:53 pm

Geologists have discovered a gigantic new field of underground helium gas, located in Tanzania’s Rift Valley.

Researchers figure there’s about 54 billion cubic feet of helium in just one section of the valley. To put that in context, the Federal Helium Reserve in Texas, which supplies more than 40% of domestic helium needs and contains about 30% of the world’s total helium supply, right now holds about 24.2 billion cubic feet, per Live Science.

The discovery is also important in that it wasn’t an accident. The geologists located the helium based on their theories of where they should find it.

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More weird Pluto geology

9:13 am

fretted terrain

Cool image time! The New Horizons science team has released an image taken during the spacecraft’s fly-by of Pluto in July 2015 showing what they are calling “fretted terrain”.

The image above is a cropped reduced section of that image. It shows the strange transition zone between the higher elevation bright areas and the lower dark plains. As they note,

New Horizons scientists haven’t seen this type of terrain anywhere else on Pluto; in fact, it’s rare terrain across the solar system – the only other well-known example of such being Noctis Labyrinthus on Mars. The distinct interconnected valley network was likely formed by extensional fracturing of Pluto’s surface. The valleys separating the blocks may then have been widened by movement of nitrogen ice glaciers, or flowing liquids, or possibly by ice sublimation at the block margins.

In other words, they really don’t know what is going on.

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Mars’s giant tsunamis

10:19 am

New research using data from a variety of Mars orbiters suggests that large tsunamis previously smashed against the shores of the red planet, shaping the geography.

The group zeroed in on a region on Mars where the highlands known as Arabia Terra bump up against the lowlands of Chryse Planitia — a place where the waters of an ancient ocean might have lapped at the shoreline. Using imagery from several Mars-orbiting spacecraft, Rodriguez’s group identified two particular geological formations that they say formed during two different tsunamis. The first, older formation looks as if an enormous wave had rushed up onto the edge of the highlands, dropping boulders as big as 10 metres across. The water then drained back down into the ocean, leaving channels cut through the freshly deposited debris.

Then, millions of years passed. Temperatures dropped and glaciers crept across the landscape, scouring deep valleys. Finally, a second impact-generated tsunami came rushing again towards the shore. “But this time it is different,” Rodriguez says. Because the climate was so much colder, the tsunami moved over the landscape like an icy slurry. It froze before it had a chance to wash back into the ocean, leaving dense lobes of frozen debris on the ground.

They propose the waves were caused by large meteorite impacts. They also admit that there are large uncertainties in their theory and conclusions.

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Increased earthquake activity at Mount St. Helens

12:37 pm

Though the increase is not large enough to indicate the likelihood of another eruption, scientists have noted that for the past eight weeks the earthquake rates under Mount St. Helens has been increasing.

Over the last 8 weeks, there have been over 130 earthquakes formally located by the Pacific Northwest Seismic Network and many more earthquakes too small to be located. The earthquakes have low magnitudes of 0.5 or less; the largest a magnitude 1.3. Earthquake rates have been steadily increasing since March, reaching nearly 40 located earthquakes per week. These earthquakes are too small to be felt at the surface.

Once again, these quakes do yet not signal another eruption. They are more likely signs of the mountain’s continuing but long and slow adjustment back to silence after the 1980 eruption. Nonetheless, they bear watching, as a volcano will do what a volcano wants to do.

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Ice and volcanoes on ancient Mars?

1:03 pm

New data of past volcanic activity on Mars suggest that the red planet was once covered by at least one extensive ice sheet.

There is a great deal of uncertainty in this conclusion, however. They have found one example with the right geology to suggest past ice sheets under which volcanoes erupted. Translating this into an extensive ice sheet requires many assumptions that might not prove true with further research.

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Halo craters on Pluto

4:48 pm

More images from New Horizons reveal even more strange terrain on Pluto.

Data suggest that the bright rims are made of methane ice, while the dark crater floors are made of water ice, though why this has happened is a complete mystery. As they note at the link above, “Exactly why the bright methane ice settles on these crater rims and walls is a mystery; also puzzling is why this same effect doesn’t occur broadly across Pluto.”

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Evidence of water on Ceres?

9:21 am

water on Ceres?

New data from Dawn suggests that there is significant water locked in surface of Ceres’s north polar regions.

These data reflect the concentration of hydrogen in the upper yard (or meter) of regolith, the loose surface material on Ceres. The color information is based on the number of neutrons detected per second by GRaND. Counts decrease with increasing hydrogen concentration. The color scale of the map is from blue (lowest neutron count) to red (highest neutron count). Lower neutron counts near the pole suggest the presence of water ice within about a yard (meter) of the surface at high latitudes.

Note that the data has not detected water. The blue areas on the image to the right suggest an increased amount of hydrogen, which could only be held to the surface if it was locked in some molecule, with water being the most likely candidate. Like the Moon, until we actual capture some samples, it will be difficult to confirm with certainty the presence of water.

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Vast Martian dune fields

11:01 am

Olympia Undae dune field

Cool image time! In the past few days the Themis camera on Mars Odyssey has taken two pictures of the vast Olympia Undae dune field near Mars’s north pole. The image to the right is only a cropped, lower resolution section of one of those images.

The image was taken during the summer, so most of the winter CO2 frost has sublimated away. Unfortunately, the website does not provide a scale, though they say the full images each cover about 12 by 43 miles of territory. Yet, both images capture only very tiny portions of the dune field, which apparently goes on and on for many hundreds of miles in all directions, looking exactly the same wherever you look.

Just imagine trying to travel though this area. It is the epitome of a trackless waste. And without some form of GPS system getting lost forever would be incredibly easy.

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New close-up of Occator Crater’s spots

1:57 pm

Occator Crater central spot

The Dawn science team have released new images taken from the spacecraft’s low orbit observations, including a close-up of the central white spot at Occator Crater, the brightest spot on Ceres.

The image on the right is a cropped though full resolution version of the full image. I have reduced it only slightly. As they note,

Occator Crater, measuring 57 miles (92 kilometers) across and 2.5 miles (4 kilometers) deep, contains the brightest area on Ceres, the dwarf planet that Dawn has explored since early 2015. The latest images, taken from 240 miles (385 kilometers) above the surface of Ceres, reveal a dome in a smooth-walled pit in the bright center of the crater. Numerous linear features and fractures crisscross the top and flanks of this dome. Prominent fractures also surround the dome and run through smaller, bright regions found within the crater.

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A new gravity map of Mars

9:06 am

Using data from three orbiting NASA spacecraft scientists have created a new gravity map of Mars, showing the subtle variations in its gravitational field due to density differences within the planet.

The improved resolution of the new gravity map suggests a new explanation for how some features formed across the boundary that divides the relatively smooth northern lowlands from heavily cratered southern highlands. Also, the team confirmed that Mars has a liquid outer core of molten rock by analyzing tides in the Martian crust and mantle caused by the gravitational pull of the sun and the two moons of Mars. Finally, by observing how Mars’ gravity changed over 11 years – the period of an entire cycle of solar activity — the team inferred the massive amount of carbon dioxide that freezes out of the atmosphere onto a Martian polar ice cap when it experiences winter. They also observed how that mass moves between the south pole and the north pole with the change of season in each hemisphere.

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The first geology map of Pluto

10:19 am

Geology map of Pluto

The New Horizons science team has now released the first geology map of a portion of Pluto, seen by the spacecraft during its fly-by last year.

It is definitely worth your while to take a look at the full image, along with the legend explaining the different surface features. Most of the geological terms are merely descriptive, but the careful breakdown still provides a much deeper understanding of what is there.

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A river on Mars

11:02 am

A river on Mars

Cool image time! The science team for the high resolution camera on Mars Reconnaissance Orbiter this week released it monthly set of cool images. One of those images, which I have cropped and reduced to show it here, is of an ancient river on Mars, the formation process of which geologists still debate. As the scientists note,

The channel pattern, called “dendritic” because of its tree–like branching, begins at the top of the image and runs down over the rim of an ancient impact basin across the basin floor. The soil surface overlying these channels, and indeed the entire landscape, has been changed and reworked over the intervening millions of years, by the combined actions of wind and ice. Over time, the original channels become muted or even erased.

One thing I learned in writing an article for Astronomy about the rivers seen on Saturn’s moon Titan is that without plant life there is no known natural process to hold river banks in place. Instead, if the grade is shallow and not confined by bedrock cliffs, rivers will meander about randomly forming braided channels as there will be nothing on shore to hold the water within the same course. For example, on a lifeless Earth the water draining the central basin of the midwest United States would have flowed south across a wide scattered area covering the entire plains, rather than flowing within the courses of the Missouri and Mississippi rivers.

Thus, it is not surprising that this river on Mars appears muted or partly erased. It probably was never very clearly delineated in the first place.

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Water unneeded to produce wet gullies on Mars

9:51 pm

The uncertainty of science: New modeling suggests that the wet gullies seen on Mars can be produced by dry ice, not water.

The theory is not completely new, but Cedric Pilorget and François Forget, with the University of Paris-Sud, and Paris’ Pierre and Marie Curie University, respectively, flesh out the idea with some hard numbers. Their new computer model calculates seasonal changes and impacts of an underlying layer of regolith, a carbon dioxide ice layer and the carbon dioxide-dominated gas atmosphere above. The simulation can take into account a variety of latitudes, slopes and other parameters.

The scientists found that most of the gullies could be created in a process that does not require any liquid water.

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A movie of Ceres

9:09 am

Cool movie time! The Dawn science team has released a movie compiled from images taken by the spacecraft, showing in false color the entire dwarf planet’s rotation as well as doing a fly-over of Occator Crater with its double bright spot.

I have posted the movie below the fold. The false colors illustrate the different materials so far detected on the surface, and help explain the nature and origin of the surface features.
» Read more

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Bright spots on Ceres likely salt deposits

1:56 pm

Based on an analysis of Dawn images scientists now believe that the bright spots on Ceres are salt deposits, not water ice.

Le Corre and colleagues, using images from Dawn’s framing camera, suggest that these salt-rich areas were left behind when water-ice sublimated in the past. Impacts from asteroids would have unearthed the mixture of ice and salt. “The location of some bright spots also coincide with places where water vapor was detected by other spacecraft,” said Reddy, a PSI Research Scientist. “This gives us confidence that the bright spots are likely salt deposits left over by sublimating salty water.”

While the bright spots themselves are not ice, they are what is left over after salty water evaporates.

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Scientists begin another attempt to drill through the Earth’s crust

9:26 am

An expedition to the Indian Ocean is about to begin an effort to drill a core down through the Earth’s crust and into its mantle.

Geologists have been trying to drill through the contact between the crust and the mantle, called the Moho, since the 1960s, with no success. Either the projects have gone way over budget and been shut down, have failed due to engineering problems, or were stopped by the geology itself. This last issue is maybe the most interesting.

Expeditions have come close before. Between 2002 and 2011, four holes at a site in the eastern Pacific managed to reach fine-grained, brittle rock that geologists believe to be cooled magma sitting just above the Moho. But the drill could not punch through those tenacious layers. And in 2013, drillers at the nearby Hess Deep found themselves similarly limited by tough deep-crustal rocks

This new project hopes to learn from these past problems to obtain the first rock samples from below the Earth’s crust.

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Earth’s magnetic field might not be flipping

10:12 pm

The uncertainty of science: A new analysis of the past strength of the Earth’s magnetic field suggests that today’s field is abnormally strong and that, even with the 10% decline in the field’s strength in the past two centuries, it remains stronger than the average over the past 5 million years.

The new data also suggests that the field might not be about to shut down and then reverse polarity, as some scientists have theorized based on the 10% decline. Instead, the data says that the field’s unusual strength today only means that the decline is bringing it back to its average strength, and is not necessarily an indication of a pending reversal.

To put it mildly, there are a lot of uncertainties here, including questions about the database that has been used previously by geologists to estimate the past strength of the Earth’s magnetic field. The database might have been right, but the new study raises significant new questions.

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Study questions scientific dating method

8:32 am

The uncertainty of science: A new study has raised questions about the methods scientists have used to date the late heavy bombardment in the early solar system.

A study of zircons from a gigantic meteorite impact in South Africa, now online in the journal Geology, casts doubt on the methods used to date lunar impacts. The critical problem, says lead author Aaron Cavosie, a visiting professor of geoscience and member of the NASA Astrobiology Institute at the University of Wisconsin-Madison, is the fact that lunar zircons are “ex situ,” meaning removed from the rock in which they formed, which deprives geoscientists of corroborating evidence of impact. “While zircon is one of the best isotopic clocks for dating many geological processes,” Cavosie says, “our results show that it is very challenging to use ex situ zircon to date a large impact of known age.”

The problem is that the removal of the zircon from lunar rocks changes the data enough to make the dating unreliable. The method might work on Earth, but the dating done on Apollo samples can be questioned. This means that much of the supposed history of the solar system, centered on what planetary scientists call the late heavy bombardment, a period 4 billion years ago when the planets were being hit by innumerable impacts as they cleared the solar system of its dusty debris disk, might not have happened as dated from lunar samples. If so, our understanding of when that bombardment ended and life began to form on Earth might be considerably incorrect.

The solution? Get to the planets in person, where you can obtain many samples in situ and thus gather a much deeper understanding of the geology.

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Back from a weekend underground

9:22 pm

Bob Zimmerman underground

The picture on the right will explain why I have been silent posting since Friday. I have just returned with five friends from three days of caving in New Mexico, doing some wild caving plus my first visit to Carlsbad Caverns since 1992, guided by a local caver who has been helping me with my cave survey project in Arizona.

New Mexico probably has the largest concentration of truly large and spectacularly decorated caves in the entire world. I’ve caved there previously, but this was my first trip driving from Arizona. We went to two wild caves, one of which I had never visited before and a second that I had seen during my 1992 trip. The picture shows me in the latter, standing above a large clear pool near the back of the cave with some giant flowstone speleothems all around me.

The new cave contained a room dubbed Speleogasm, because every formation there, of which there are too many to count, is completely festooned with helectites and sodastraws in a mad protrusion that no geologist can as yet explain. Nor is there any way to describe it adequately or photograph it successfully. To witness it you need to go, requiring the specialized caving skills that include the techniques and equipment required to rappel and climb a 40 foot rope.

As always, the advantages of learning how to do this successfully is the reward of seeing things that few ever see. It is why engineers and scientists strive so hard to get planetary probes to distant planets. And why humans want to travel to the planets. For me, getting inside a remote and beautifully decorated cave will just have to do.

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An avalanche on Mars, as it happens

4:49 pm

Avalanche on Mars

Cool image time! In their routine monitoring for avalanches at the layered deposits at the Martian north pole, the Mars Reconnaissance Orbiter science team captured the avalanche on the right, as it happened.

This picture managed to capture a small avalanche in progress, right in the color strip. … The small white cloud in front of the brick red cliff is likely carbon dioxide frost dislodged from the layers above, caught in the act of cascading down the cliff. It is larger than it looks, more than 20 meters across, and (based on previous examples) it will likely kick up clouds of dust when it hits the ground.

They note that avalanches in this area of Mars are common in the spring when things are warming, and have been documented previously, but possibly not so dramatically.

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