That is not some sort of weird crescent on the Saturn moon Iapetus, The dark area is a deposit of dark material and is on the leading side as the moon orbits Saturn. The dark material is said to be a reddish brown color and has a low albedo, reflecting only about four percent of the light that hits it which I think is about the same as charcoal.

NASA – Iapetus is a world of contrast, with light and dark regions fitting together like cosmic puzzle pieces.

Cassini Regio on Iapetus (914 miles or 1,471 kilometers across) is covered in a layer of dark, dusty material creating a stark contrast to the much brighter region that surrounds it. This leads to the moon’s distinctive, two-toned appearance. To learn more about the cause of the contrast between regions, see PIA06166.

This view looks toward Saturn-facing hemisphere of Iapetus. North on Iapetus is up and rotated 20 degrees to the right. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on March 11, 2017.

The view was obtained at a distance of approximately 1.6 million miles (2.6 million kilometers) from Iapetus. Image scale is 9 miles (15 kilometers) per pixel.

Image: NASA/JPL-Caltech/Space Science Institute

Curious Travels on Pahrump Hills

I must say I’m a bit surprised at the diversity of minerals in the samples between sites.

NASA scientists have found a wide diversity of minerals in the initial samples of rocks collected by the Curiosity rover in the lowermost layers of Mount Sharp on Mars, suggesting that conditions changed in the water environments on the planet over time.

Curiosity landed near Mount Sharp in Gale Crater in August 2012. It reached the base of the mountain in 2014. Layers of rocks at the base of Mount Sharp accumulated as sediment within ancient lakes around 3.5 billion years ago. Orbital infrared spectroscopy had shown that the mountain’s lowermost layers have variations in minerals that suggest changes in the area have occurred.

In a paper published recently in Earth and Planetary Science Letters, scientists in the Astromaterials Research and Exploration Science (ARES) Division at NASA’s Johnson Space Center in Houston report on the first four samples collected from the lower layers of Mount Sharp.

“We went to Gale Crater to investigate these lower layers of Mount Sharp that have these minerals that precipitated from water and suggest different environments,” said Elizabeth Rampe, the first author of the study and a NASA exploration mission scientist at Johnson. “These layers were deposited about 3.5 billion years ago, coinciding with a time on Earth when life was beginning to take hold. We think early Mars may have been similar to early Earth, and so these environments might have been habitable.”

The minerals found in the four samples drilled near the base of Mount Sharp suggest several different environments were present in ancient Gale Crater. There is evidence for waters with different pH and variably oxidizing conditions. The minerals also show that there were multiple source regions for the rocks in “Pahrump Hills” and “Marias Pass.”

The paper primarily reports on three samples from the Pahrump Hills region. This is an outcrop at the base of Mount Sharp that contains sedimentary rocks scientists believe formed in the presence of water. The other sample, called “Buckskin,” was reported last year, but those data are incorporated into the paper.

Studying such rock layers can yield information about Mars’ past habitability, and determining minerals found in the layers of sedimentary rock yields much data about the environment in which they formed. Data collected at Mount Sharp with the Chemistry and Mineralogy (CheMin) instrument on Curiosity showed a wide diversity of minerals.

At the base are minerals from a primitive magma source; they are rich in iron and magnesium, similar to basalts in Hawaii. Moving higher in the section, scientists saw more silica-rich minerals. In the “Telegraph Peak” sample, scientists found minerals similar to quartz. In the “Buckskin” sample, scientists found tridymite. Tridymite is found on Earth, for example, in rocks that formed from partial melting of Earth’s crust or in the continental crust — a strange finding because Mars never had plate tectonics.

In the “Confidence Hills” and “Mojave 2” samples, scientists found clay minerals, which generally form in the presence of liquid water with a near-neutral pH, and therefore could be good indicators of past environments that were conducive to life. The other mineral discovered here was jarosite, a salt that forms in acidic solutions. The jarosite finding indicates that there were acidic fluids at some point in time in this region.

There are different iron-oxide minerals in the samples as well. Hematite was found near the base; only magnetite was found at the top. Hematite contains oxidized iron, whereas magnetite contains both oxidized and reduced forms of iron. The type of iron-oxide mineral present may tell scientists about the oxidation potential of the ancient waters.

The authors discuss two hypotheses to explain this mineralogical diversity. The lake waters themselves at the base were oxidizing, so either there was more oxygen in the atmosphere or other factors encouraged oxidation. Another hypothesis — the one put forward in the paper — is that later-stage fluids arose. After the rock sediments were deposited, some acidic, oxidizing groundwater moved into the area, leading to precipitation of the jarosite and hematite. In this scenario, the environmental conditions present in the lake and in later groundwater were quite different, but both offered liquid water and a chemical diversity that could have been exploited by microbial life.

“We have all this evidence that Mars was once really wet but now is dry and cold,” Rampe said. “Today, much of the water is locked up in the poles and in the ground at high latitudes as ice. We think that the rocks Curiosity has studied reveal ancient environmental changes that occurred as Mars started to lose its atmosphere and water was lost to space.”

In the paper, the authors discuss whether this specific area on Mars is a mark of this event happening or just a natural drying of this area. Scientists will search for answers to these questions as the rover moves up the mountain.

Image: NASA/JPL-Caltech/MSSS

NASA also provided a link to the paper (downloadable PDF)

NASA’s Newest Astronauts

One presumably young lady said in the comments for this video: “I will be in one of these videos someday.” and to that I say, I hope so!!

Also it could go without saying (and almost did), Good luck and congratulations to the new astronauts!

Symbiotic Star

NASA – In biology, “symbiosis” refers to two organisms that live close to and interact with one another. Astronomers have long studied a class of stars – called symbiotic stars – that co-exist in a similar way. Using data from NASA’s Chandra X-ray Observatory and other telescopes, astronomers are gaining a better understanding of how volatile this close stellar relationship can be.

R Aquarii (R Aqr, for short) is one of the best known of the symbiotic stars. Located at a distance of about 710 light years from Earth, its changes in brightness were first noticed with the naked eye almost a thousand years ago. Since then, astronomers have studied this object and determined that R Aqr is not one star, but two: a small, dense white dwarf and a cool red, giant star.

The red giant star has its own interesting properties. In billions of years, our Sun will turn into a red giant once it exhausts the hydrogen nuclear fuel in its core and begins to expand and cool. Most red giants are placid and calm, but some pulsate with periods between 80 and 1,000 days like the star Mira and undergo large changes in brightness. This subset of red giants is called “Mira variables.”

The red giant in R Aqr is a Mira variable and undergoes steady changes in brightness by a factor of 250 as it pulsates, unlike its white dwarf companion that does not pulsate. There are other striking differences between the two stars. The white dwarf is about ten thousand times brighter than the red giant. The white dwarf has a surface temperature of some 20,000 K while the Mira variable has a temperature of about 3,000 K. In addition, the white dwarf is slightly less massive than its companion but because it is much more compact, its gravitational field is stronger. The gravitational force of the white dwarf pulls away the sloughing outer layers of the Mira variable toward the white dwarf and onto its surface.
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Pesquet Peeks

I hope he has a framed copy of this image on his wall.

ESA – ESA astronaut Thomas Pesquet looking out of the International Space Station’s Cupola window shortly before the end of his six-month Proxima mission.

Thomas commented: “The day of return is approaching: I can’t wait to be on Earth again and see my loved ones… but I will certainly miss the view”

Credit: ESA

Ultra-Bright Galaxies From Hubble

Light from 8 to 11.5 BILLION years ago. Be sure to click the image to get a larger view or if you want a really large image go to Hubblesite and you can download one for your desktop.

Hubblesite — These six images, taken by the Hubble Space Telescope, reveal a jumble of misshapen-looking galaxies punctuated by exotic patterns such as arcs, streaks, and smeared rings. These unusual features are the stretched shapes of the universe’s brightest infrared galaxies that are boosted by natural cosmic magnifying lenses. Some of the oddball shapes in the images also may have been produced by spectacular collisions between distant, massive galaxies in a sort of cosmic demolition derby.

This so-called gravitational lensing occurs when the intense gravity of a massive galaxy or cluster of galaxies magnifies the light of fainter, more distant background sources. The “lenses” are foreground massive galaxies whose gravity magnifies and distorts images of the distant bright infrared galaxies behind them.

The faraway galaxies are as much as 10,000 times more luminous than our Milky Way. The lensing phenomenon allows for features as small as about 100 light-years or less across to be seen in the background galaxies.

The galaxies existed between 8 billion and 11.5 billion years ago, when the universe was making stars more vigorously than it is today. The galaxies are ablaze with runaway star formation, pumping out more than 10,000 new stars a year. The star-birth frenzy creates lots of dust, which enshrouds the galaxies, making them too faint to detect in visible light. But they glow fiercely in infrared light, shining with the brilliance of 10 trillion to 100 trillion suns.

The infrared galaxies in these images are part of a Hubble survey of 22 distant ultra-luminous infrared galaxies that were found by ground- and space-based observatories. The images were taken in infrared light by Hubble’s Wide Field Camera 3. Color has been added to highlight details in the galaxies.

Tiny Mimas

Here’s a nice perspective on how huge Saturn really is compared to Mimas(upper right).

Image: NASA/JPL-Caltech/Space Science Institute

NASA — The low angle of sunlight along the slim crescent of Saturn’s moon Enceladus (313 miles or 504 kilometers across) highlights the many fractures and furrows on its icy surface.

This view looks toward the Saturn-facing hemisphere of Enceladus, which is dimly illuminated in the image above by sunlight reflected off Saturn. North on Enceladus is up and rotated 14 degrees to the left. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 26, 2016.

The view was obtained at a distance of approximately 104,000 miles (168,000 kilometers) from Enceladus. Image scale is 3,303 feet (1 kilometer) per pixel.

Did Enceladus Tip Over?

Here’s an annotated version.

mage credit: NASA/JPL-Caltech/Space Science Institute/Cornell University

NASA/JPL – Working with image data from NASA’s Cassini mission, researchers have found evidence that Saturn’s moon Enceladus may have tipped over, reorienting itself so that terrain closer to its original equator was relocated to the poles. This phenomenon is known as true polar wander.

Researchers discovered a chain of basins across the surface of Enceladus along with a pair of depressions that line up with an equator and poles, respectively, if the moon’s axis of rotation was reoriented by about 55 degrees of latitude.

These maps look toward the icy moon’s southern hemisphere, with colors representing highs and lows. Purple represents the lowest elevations, while red represents the highest.

The map at left shows the surface of Enceladus in its possible ancient orientation, millions of years ago. The chain of basins representing topographic lows can be seen in blue and purple, running along the equator, with an additional low region around the original south pole. The region that encloses the moon’s currently active south polar terrain, with its long, linear “tiger stripe” fractures, would have been at middle latitudes just south of the equator. The map at right shows the current orientation of Enceladus.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, California, manages the mission for NASA’s Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.