Fractured ice sheets on Mars

By: Thomas Schmitt Attorney on November 20, 2019 / comment : 0 Astronomy, Space Exploration, Universe

Where the two hemispheres of Mars meet, the planet is covered in broken-up terrain: a sign that slow-but-steady flows of icy material once forged their way through the landscape, carving out a fractured web of valleys, cliffs and isolated mounds of rock.

This image shows a region of Mars named Deuteronilus Mensae. It comprises data gathered on 25 February 2018 during orbit 17913. The ground resolution is approximately 13 m/pixel and the images are centred at about 25.5°E/44°N. This image was created using data from the nadir and colour channels of the High Resolution Stereo Camera (HRSC). The nadir channel is aligned perpendicular to the surface of Mars, as if looking straight down at the surface. North is to the right [Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO]

Mars is a planet of two halves. Its hemispheres are drastically different; the smooth northern lowlands sit up to three kilometres below the rugged southern highlands, and the surface in Mars' northern regions appears to be far younger than the ancient swaths of the south.

Where these regions meet, they sometimes form a transition area filled with a wide range of intriguing geological features, patterns and processes: a type of landscape unique to Mars known as fretted terrain. Fretted terrain is found in a couple of key areas on Mars, and an especially good example, named Deuteronilus Mensae, can be seen in these images from Mars Express' High Resolution Stereo Camera (HRSC).

This landscape shows clear and widespread signs of significant, lasting erosion. As is common with fretted terrain, it contains a mix of cliffs, canyons, scarps, steep-sided and flat-topped mounds (mesa), furrows, fractured ridges and more, a selection of which can be seen dotted across the frame.

This colour-coded topographic view shows a region of Mars named Deuteronilus Mensae. Lower parts of the surface are shown in blues and purples, while higher altitude regions show up in whites, yellows and reds, as indicated on the scale to the top right. This view is based on a digital terrain model of the region, from which the topography of the landscape  can be derived. It comprises data gathered on 25 February 2018 during orbit 17913. The ground resolution is approximately 13 m/pixel and the images are centred at about 25.5°E/44°N. North is to the right [Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO]

These features were created as flowing material dissected the area, cutting through the existing landscape and carving out a web of winding channels. In the case of Deuteronilus Mensae, flowing ice is the most likely culprit. Scientists believe that this terrain has experienced extensive past glacial activity across numerous martian epochs.

It is thought that glaciers slowly but surely ate away at the plains and plateaus that once covered this region, leaving only a scattering of steep, flat, isolated mounds of rock in their wake.

Smooth deposits cover the floor itself, some marked with flow patterns from material slowly moving downhill—a mix of ice and accumulated debris that came together to form and feed viscous, moving flows of mass somewhat akin to a landslide or mudflow here on Earth.

This image from ESA’s Mars Express shows a region of Mars named Deuteronilus Mensae. This oblique perspective view was generated using a digital terrain model and Mars Express data gathered on 25 February 2018 during orbit 17913. The ground resolution is approximately 13 m/pixel and the images are centred at about 25.5°E/44°N. This image was created using data from the nadir and colour channels of the High Resolution Stereo Camera (HRSC). The nadir channel is aligned perpendicular to the surface of Mars, as if looking straight down at the surface [Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO]

Studies of this region by NASA's Mars Reconnaissance Orbiter have shown that most of the features seen here do indeed contain high levels of water ice. Estimates place the ice content of some glacial features in the region at up to 90%.

This suggests that, rather than hosting individual or occasional icy pockets and glaciers, Deuteronilus Mensae may actually represent the remnants of an old regional ice sheet. This ice sheet may once have covered the entire area, lying atop the plateaus and plains. As the martian climate changed this ice began to shift around and disappear, slowly revealing the rock beneath.

Overall, the features seen in these Mars Express images are reminiscent of the rock- and debris-covered glaciers found in cold regions of Earth. Glaciers may actually be relatively common on both past and present-day Mars; recent studies suggest that the planet may have belts of glacial activity above and below its equator, containing huge amounts of ice covered in thick protective layers of dust, and many other areas show signs of having hosted glaciers in the past—just like Deuteronilus Mensae.

This image from ESA’s Mars Express shows a region of Mars named Deuteronilus Mensae. This oblique perspective view was generated using a digital terrain model and Mars Express data gathered on 25 February 2018 during orbit 17913. The ground resolution is approximately 13 m/pixel and the images are centred at about 25.5°E/44°N. This image was created using data from the nadir and colour channels of the High Resolution Stereo Camera (HRSC). The nadir  channel is aligned perpendicular to the surface of Mars, as if looking straight down at the surface [Credit: ESA/DLR/FU Berlin, CC BY-SA 3.0 IGO]

Mars Express has been orbiting the Red Planet since 2003. Using the HRSC, which obtained these new images, the mission has continually mapped the martian surface and characterised various key properties of and phenomena on the planet—from the presence of a planet-wide groundwater system to intricate old river systems, various intriguing surface deposits, giant regional dust storms, spikes of tell-tale gases in the planet's atmosphere, and much more.

The mission will continue to explore the Red Planet in collaboration with the ESA-Roscosmos ExoMars Trace Gas Orbiter, which arrived at Mars in 2016, and the ExoMars Rosalind Franklin rover and its accompanying surface science platform, which will arrive in 2021.

Source: European Space Agency [November 21, 2019]

NASA scientists confirm water vapour on Europa

By: Thomas Schmitt Attorney on November 19, 2019 / comment : 0 Astrobiology, Astronomy, Space Exploration, Universe

Forty years ago, a Voyager spacecraft snapped the first closeup images of Europa, one of Jupiter's 79 moons. These revealed brownish cracks slicing the moon's icy surface, which give Europa the look of a veiny eyeball. Missions to the outer solar system in the decades since have amassed enough additional information about Europa to make it a high-priority target of investigation in NASA's search for life.

On the left is a view of Europa taken from 2.9 million kilometers (1.8 million miles) away on March 2, 1979 by the Voyager 1 spacecraft. Next is a color image of Europa taken by the Voyager 2 spacecraft during its close encounter on July 9, 1979. On the right is a view of Europa made from images taken by the Galileo spacecraft in the late 1990s [Credit: NASA/JPL]

What makes this moon so alluring is the possibility that it may possess all of the ingredients necessary for life. Scientists have evidence that one of these ingredients, liquid water, is present under the icy surface and may sometimes erupt into space in huge geysers. But no one has been able to confirm the presence of water in these plumes by directly measuring the water molecule itself. Now, an international research team led out of NASA's Goddard Space Flight Center in Greenbelt, Maryland, has detected the water vapor for the first time above Europa's surface. The team measured the vapor by peering at Europa through W. M. Keck Observatory in Hawaii, one of the world's biggest telescopes.

Confirming that water vapor is present above Europa helps scientists better understand the inner workings of the moon. For example, it helps support an idea, of which scientists are confident, that there's a liquid water ocean, possibly twice as big as Earth's, sloshing beneath this moon's miles-thick ice shell. Another source of water for the plumes, some scientists suspect, could be shallow reservoirs of melted water ice not far below Europa's surface. It's also possible that Jupiter's strong radiation field is stripping water particles from Europa's ice shell, though the recent investigation argued against this mechanism as the source of the observed water.

"Essential chemical elements (carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur) and sources of energy, two of three requirements for life, are found all over the solar system. But the third—liquid water—is somewhat hard to find beyond Earth," said Lucas Paganini, a NASA planetary scientist who led the water detection investigation. "While scientists have not yet detected liquid water directly, we've found the next best thing: water in vapor form."

In a study published in the journal Nature Astronomy, Paganini and his team reported that they detected enough water releasing from Europa (5,202 pounds, or 2,360 kilograms, per second) to fill an Olympic-size swimming pool within minutes. Yet, the scientists also found that the water appears infrequently, at least in amounts large enough to detect from Earth, said Paganini: "For me, the interesting thing about this work is not only the first direct detection of water above Europa, but also the lack thereof within the limits of our detection method."


Indeed, Paganini's team detected the faint yet distinct signal of water vapor just once throughout 17 nights of observations between 2016 and 2017. Looking at the moon from Keck Observatory, the scientists saw water molecules at Europa's leading hemisphere, or the side of the moon that's always facing in the direction of the moon's orbit around Jupiter. (Europa, like Earth's moon, is gravitationally locked to its host planet, so the leading hemisphere always faces the direction of the orbit, while the trailing hemisphere always faces in the opposite direction.)

They used Keck Observatory's Near-Infrared Spectrograph (NIRSPEC), which measures the chemical composition of planetary atmospheres through the infrared light they emit or absorb. Molecules such as water emit specific frequencies of infrared light as they interact with solar radiation.

Mounting evidence for water

Before the recent water vapor detection, there have been many tantalizing findings on Europa. The first came from NASA's Galileo spacecraft, which measured perturbations in Jupiter's magnetic field near Europa while orbiting the gas giant planet between 1995 and 2003. The measurements suggested to scientists that electrically conductive fluid, likely a salty ocean beneath Europa's ice layer, was causing the magnetic disturbances. When researchers analyzed the magnetic disturbances more closely in 2018, they found evidence of possible plumes.

In the meantime, scientists announced in 2013 that they had used NASA's Hubble Space Telescope to detect the chemical elements hydrogen (H) and oxygen (O)—components of water (H2O)—in plume-like configurations in Europa's atmosphere. And a few years later, other scientists used Hubble to gather more evidence of possible plume eruptions when they snapped photos of finger-like projections that appeared in silhouette as the moon passed in front of Jupiter.

"This first direct identification of water vapor on Europa is a critical confirmation of our original detections of atomic species, and it highlights the apparent sparsity of large plumes on this icy world" said Lorenz Roth, an astronomer and physicist from KTH Royal Institute of Technology in Stockholm who led the 2013 Hubble study and was a co-author of this recent investigation.

Roth's research, along with other previous Europa findings, have only measured components of water above the surface. The trouble is that detecting water vapor at other worlds is challenging. Existing spacecraft have limited capabilities to detect it, and scientists using ground-based telescopes to look for water in deep space have to account for the distorting effect of water in Earth's atmosphere. To minimize this effect, Paganini's team used complex mathematical and computer modeling to simulate the conditions of Earth's atmosphere so they could differentiate Earth's atmospheric water from Europa's in data returned by the NIRSPEC.

"We performed diligent safety checks to remove possible contaminants in ground-based observations," said Avi Mandell, a Goddard planetary scientist on Paganini's team. "But, eventually, we'll have to get closer to Europa to see what's really going on."

Scientists will soon be able get close enough to Europa to settle their lingering questions about the inner and outer workings of this possibly habitable world. The forthcoming Europa Clipper mission, expected to launch in the mid-2020s, will round out half a century of scientific discovery that started with a modest photo of a mysterious, veiny eyeball.

When it arrives at Europa, the Clipper orbiter will conduct a detailed survey of Europa's surface, deep interior, thin atmosphere, subsurface ocean, and potentially even smaller active vents. Clipper will try to take images of any plumes and sample the molecules it finds in the atmosphere with its mass spectrometers. It will also seek out a fruitful site from which a future Europa lander could collect a sample. These efforts should further unlock the secrets of Europa and its potential for life.

Author: Lonnie Shekhtman | Source: W. M. Keck Observatory [November 20, 2019]

First global geologic map of Saturn's largest moon, Titan, completed

By: Thomas Schmitt Attorney on November 18, 2019 / comment : 0 Astronomy, Geology, Space Exploration, Universe

The first map showing the global geology of Saturn's largest moon, Titan, has been completed and fully reveals a dynamic world of dunes, lakes, plains, craters and other terrains.

The first global geologic map of Titan is based on radar and visible-light images from NASA's Cassini mission, which orbited Saturn from 2004 to 2017. Labels point to several of the named surface features [Credit: NASA/JPL-Caltech/ASU]

Planetary geologist David Williams of Arizona State University's School of Earth and Space Exploration worked with a team of researchers, led by planetary geologist Rosaly Lopes of NASA's Jet Propulsion Laboratory in Pasadena, California, to develop this global geologic map of Titan. The map, and their findings, which include the relative age of Titan's geological terrains, were recently published in the journal Nature Astronomy.

Titan is the only planetary body in our solar system other than Earth known to have stable liquid on its surface. But instead of water raining down from clouds and filling lakes and seas as on Earth, on Titan what rains down is methane and ethane—hydrocarbons that we think of as gases but that behave as liquids in Titan's frigid climate.

"Titan has an active methane-based hydrologic cycle that has shaped a complex geologic landscape, making its surface one of most geologically diverse in the solar system," said lead author Lopes.

"Despite the different materials, temperatures and gravity fields between Earth and Titan, many surface features are similar between the two worlds and can be interpreted as products of the same geologic processes. The map shows that the different geological terrains have a clear distribution with latitude, globally, and that some terrains cover far more area than others," Lopes said.

Lopes' team used data from NASA's Cassini mission, which operated between 2004 and 2017 and did more than 120 flybys of the Mercury-size moon Titan. Specifically, they used data from Cassini's radar imager to penetrate Titan's opaque atmosphere of nitrogen and methane. In addition, the team used data from Cassini's visible and infrared instruments, which were able to capture some of Titan's larger geologic features through the methane haze.

Artist rendition of the Cassini spacecraft with Saturn and Titan [Credit: NASA/JPL-CalTech]

"This study is an example of using combined data sets and instruments," Lopes said. "Although we did not have global coverage with synthetic aperture radar (SAR), we used data from other instruments and other modes from radar to correlate characteristics of the different terrain units, so we could infer what the terrains are even in areas where we don't have SAR coverage."

Williams' role in mapping Titan was to work with the JPL team to identify what geologic units could be determined using first the radar images and then to extrapolate those units to the non-radar-covered regions. To do so, Williams built on his experience working with radar images on NASA's Magellan Venus orbiter and from a previous regional geologic map of Titan that he developed.

"The Cassini mission revealed that Titan is a geologically active world, where hydrocarbons like methane and ethane take the role that water has on Earth," Williams said. "These hydrocarbons rain down on the surface, flow in streams and rivers, accumulate in lakes and seas, and evaporate into the atmosphere. It's quite an astounding world!"

Williams, who is also the director of the Ronald Greeley Center for Planetary Studies at ASU, has considerable experience working on the geologic mapping of small and unusual planetary objects, including Jupiter's volcanic moon Io, the asteroid Vesta, the dwarf planet Ceres and now Titan.

"We held meetings at ASU earlier this decade to figure out how to map Titan using the higher-resolution radar and lower-resolution visible images," explained Williams. "Titan mappers from NASA's Jet Propulsion Laboratory and Cornell University came to ASU to figure out how to do geologic mapping of this strange new world."

The experience of mapping small and unusual planetary objects will help Williams on an important task he will undertake in the next decade, to make the first global geologic map of metal asteroid (16) Psyche, the target of the ASU-led NASA Psyche mission scheduled to launch in 2022.

Author: Karin Valentine | Source: Arizona State University [November 18, 2019]

At future Mars landing spot, scientists spy mineral that could preserve signs of past life

By: Thomas Schmitt Attorney on November 12, 2019 / comment : 0 Astrobiology, Astronomy, Fossils, Space Exploration, Universe

Next year, NASA plans to launch a new Mars rover to search for signs of ancient life on the Red Planet. A new study shows that the rover's Jezero crater landing site is home to deposits of hydrated silica, a mineral that just happens to be particularly good at preserving biosignatures.

Jezero crater, where NASA plans to land a new Mars rover next year, is home to the remains of an ancient river delta. Researchers have now found deposits of hydrated silica, a mineral that's especially good at preserving microfossils and other signs of past life, near the delta [Credit: NASA/JPL/JHUAPL/MSSS/Brown University]

"Using a technique we developed that helps us find rare, hard-to-detect mineral phases in data taken from orbiting spacecraft, we found two outcrops of hydrated silica within Jezero crater," said Jesse Tarnas, a Ph.D. student at Brown University and the study's lead author. "We know from Earth that this mineral phase is exceptional at preserving microfossils and other biosignatures, so that makes these outcrops exciting targets for the rover to explore."

NASA announced late last year that its Mars 2020 rover would be headed to Jezero, which appears to have been home to an ancient lake. The star attraction at Jezero is a large delta deposit formed by ancient rivers that fed the lake. The delta would have concentrated a wealth of material from a vast watershed. Deltas on Earth are known to be good at preserving signs of life.

Adding hydrated silica to the mix at Jezero increases that preservation potential, the researchers say. One of the silica deposits was found on the edge of the delta at low elevation. It's possible that the minerals formed in place and represent the bottom layer of the delta deposit, which is a great scenario for preserving signs of life.

"The material that forms the bottom layer of a delta is sometimes the most productive in terms of preserving biosignatures," said Jack Mustard, a professor at Brown and study co-author. "So if you can find that bottomset layer, and that layer has a lot of silica in it, that's a double bonus."

For the study, researchers used data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument that flies aboard NASA's Mars Reconnaissance Orbiter. The technique applied to the CRISM data used big data analysis methods to tease out the weak spectral signature of the silica deposits.

A false-colour image of Jezero crater shows the edge of an ancient river delta, where researchers have spied hydrated silica, a mineral that's especially good at preserving microfossils and other signs of past life [Credit: NASA]

While the geologic context of the deposits suggests they could have formed at the base of the delta, it's not the only possibility, the researchers say. The minerals could have formed upstream in the watershed that fed Jezero and been washed subsequently into the crater, by volcanic activity or later episodes of water saturation in the Jezero crater lake. The rover should be able to isolate the real source, the researchers say.

"We can get amazing high-resolution images and compositional data from orbit, but there's a limit on what we can discern in terms of how these minerals formed," Tarnas said. "Given instruments on the rover, however, we should be able to constrain the origin of these deposits."

The rover will be able to perform fine-scale chemical analysis of the deposits and provide a close-up view of how the deposits are situated in relation to surrounding rock units. It will also have a sensor similar to CRISM to link orbital and lander data. That will go a long way to determining how the deposits formed. What's more, one instrument aboard the rover is able to look for complex organic material. If the silica deposits have high concentrations of organics, it would be an especially intriguing find, the researchers say.

And in addition to the work the rover does on site, it will also cache samples to be returned to Earth by future missions.

"If these deposits present themselves in the form of rocks that are big and competent enough to drill into, they could be put into the cache," Mustard said. "This work suggests that they'd be a great sample to have."

The research is published in Geophysical Research Letters.

Source: Brown University [November 12, 2019]

With Mars methane mystery unsolved, Curiosity serves scientists a new one: Oxygen

By: Thomas Schmitt Attorney on November 11, 2019 / comment : 0 Astrobiology, Astronomy, Space Exploration, Universe

For the first time in the history of space exploration, scientists have measured the seasonal changes in the gases that fill the air directly above the surface of Gale Crater on Mars. As a result, they noticed something baffling: oxygen, the gas many Earth creatures use to breathe, behaves in a way that so far scientists cannot explain through any known chemical processes.

A sunset at the Viking Lander 1 site, 1976  [Credit: NASA/JPL]

Over the course of three Mars years (or nearly six Earth years) an instrument in the Sample Analysis at Mars (SAM) portable chemistry lab inside the belly of NASA's Curiosity rover inhaled the air of Gale Crater and analyzed its composition. The results SAM spit out confirmed the makeup of the Martian atmosphere at the surface: 95% by volume of carbon dioxide (CO2), 2.6% molecular nitrogen (N2), 1.9% argon (Ar), 0.16% molecular oxygen (O2), and 0.06% carbon monoxide (CO).

They also revealed how the molecules in the Martian air mix and circulate with the changes in air pressure throughout the year. These changes are caused when CO2 gas freezes over the poles in the winter, thereby lowering the air pressure across the planet following redistribution of air to maintain pressure equilibrium. When CO2 evaporates in the spring and summer and mixes across Mars, it raises the air pressure.

Within this environment, scientists found that nitrogen and argon follow a predictable seasonal pattern, waxing and waning in concentration in Gale Crater throughout the year relative to how much CO2 is in the air. They expected oxygen to do the same. But it didn't. Instead, the amount of the gas in the air rose throughout spring and summer by as much as 30%, and then dropped back to levels predicted by known chemistry in fall. This pattern repeated each spring, though the amount of oxygen added to the atmosphere varied, implying that something was producing it and then taking it away.

"The first time we saw that, it was just mind boggling," said Sushil Atreya, professor of climate and space sciences at the University of Michigan in Ann Arbor. Atreya is a co-author of a paper on this topic published in the Journal of Geophysical Research: Planets.

As soon as scientists discovered the oxygen enigma, Mars experts set to work trying to explain it. They first double- and triple-checked the accuracy of the SAM instrument they used to measure the gases: the Quadrupole Mass Spectrometer. The instrument was fine. They considered the possibility that CO2 or water (H2O) molecules could have released oxygen when they broke apart in the atmosphere, leading to the short-lived rise. But it would take five times more water above Mars to produce the extra oxygen, and CO2 breaks up too slowly to generate it over such a short time. What about the oxygen decrease? Could solar radiation have broken up oxygen molecules into two atoms that blew away into space? No, scientists concluded, since it would take at least 10 years for the oxygen to disappear through this process.

Credit: Melissa Trainer/Dan Gallagher/NASA Goddard

"We're struggling to explain this," said Melissa Trainer, a planetary scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland who led this research. "The fact that the oxygen behavior isn't perfectly repeatable every season makes us think that it's not an issue that has to do with atmospheric dynamics. It has to be some chemical source and sink that we can't yet account for."

To scientists who study Mars, the oxygen story is curiously similar to that of methane. Methane is constantly in the air inside Gale Crater in such small quantities (0.00000004% on average) that it's barely discernable even by the most sensitive instruments on Mars. Still, it's been measured by SAM's Tunable Laser Spectrometer. The instrument revealed that while methane rises and falls seasonally, it increases in abundance by about 60% in summer months for inexplicable reasons. (In fact, methane also spikes randomly and dramatically. Scientists are trying to figure out why.)

With the new oxygen findings in hand, Trainer's team is wondering if chemistry similar to what's driving methane's natural seasonal variations may also drive oxygen's. At least occasionally, the two gases appear to fluctuate in tandem.

"We're beginning to see this tantalizing correlation between methane and oxygen for a good part of the Mars year," Atreya said. "I think there's something to it. I just don't have the answers yet. Nobody does."

Oxygen and methane can be produced both biologically (from microbes, for instance) and abiotically (from chemistry related to water and rocks). Scientists are considering all options, although they don't have any convincing evidence of biological activity on Mars. Curiosity doesn't have instruments that can definitively say whether the source of the methane or oxygen on Mars is biological or geological. Scientists expect that non-biological explanations are more likely and are working diligently to fully understand them.

Credit: Melissa Trainer/Dan Gallagher/NASA Goddard

Trainer's team considered Martian soil as a source of the extra springtime oxygen. After all, it's known to be rich in the element, in the form of compounds such as hydrogen peroxide and perchlorates. One experiment on the Viking landers showed decades ago that heat and humidity could release oxygen from Martian soil. But that experiment took place in conditions quite different from the Martian spring environment, and it doesn't explain the oxygen drop, among other problems.

Other possible explanations also don't quite add up for now. For example, high-energy radiation of the soil could produce extra O2 in the air, but it would take a million years to accumulate enough oxygen in the soil to account for the boost measured in only one spring, the researchers report in their paper.

"We have not been able to come up with one process yet that produces the amount of oxygen we need, but we think it has to be something in the surface soil that changes seasonally because there aren't enough available oxygen atoms in the atmosphere to create the behavior we see," said Timothy McConnochie, assistant research scientist at the University of Maryland in College Park and another co-author of the paper.

The only previous spacecraft with instruments capable of measuring the composition of the Martian air near the ground were NASA's twin Viking landers, which arrived on the planet in 1976. The Viking experiments covered only a few Martian days, though, so they couldn't reveal seasonal patterns of the different gases. The new SAM measurements are the first to do so. The SAM team will continue to measure atmospheric gases so scientists can gather more detailed data throughout each season. In the meantime, Trainer and her team hope that other Mars experts will work to solve the oxygen mystery.

"This is the first time where we're seeing this interesting behavior over multiple years. We don't totally understand it," Trainer said. "For me, this is an open call to all the smart people out there who are interested in this: See what you can come up with."

Author: Lonnie Shekhtman | Source: NASA's Goddard Space Flight Center [November 12, 2019]

Voyager 2 reaches interstellar space

By: Thomas Schmitt Attorney on November 03, 2019 / comment : 0 Astronomy, Space Exploration, Universe

Researchers at the University of Iowa report that the spacecraft Voyager 2 has entered the interstellar medium (ISM), the region of space outside the bubble-shaped boundary produced by wind streaming outward from the sun. Voyager 2, thus, becomes the second human-made object to journey out of our sun's influence, following Voyager 1's solar exit in 2012.

Iowa physicists have confirmed the spacecraft Voyager 2 has entered interstellar space, in effect leaving the solar system. Data from Voyager 2 has helped further characterize the structure of the heliosphere, structure of the heliosphere - the wind sock-shaped region created by the sun's wind as it extends to the boundary of the solar system [Credit: NASA JPL]

In a new study, the researchers confirm Voyager 2's passage on Nov. 5, 2018, into the ISM by noting a definitive jump in plasma density detected by an Iowa-led plasma wave instrument on the spacecraft. The marked increase in plasma density is evidence of Voyager 2 journeying from the hot, lower-density plasma characteristic of the solar wind to the cool, higher-density plasma of interstellar space. It's also similar to the plasma density jump experienced by Voyager 1 when it crossed into interstellar space.

"In a historical sense, the old idea that the solar wind will just be gradually whittled away as you go further into interstellar space is simply not true," says Iowa's Don Gurnett, corresponding author on the study, published in the journal Nature Astronomy. "We show with Voyager 2--and previously with Voyager 1--that there's a distinct boundary out there. It's just astonishing how fluids, including plasmas, form boundaries."

Gurnett, professor emeritus in the UI Department of Physics and Astronomy, is the principal investigator on the plasma wave instrument aboard Voyager 2. He is also the principal investigator on the plasma wave instrument aboard Voyager 1 and authored the 2013 study published in Science that confirmed Voyager 1 had entered the ISM.

Voyager 2's entry into the ISM occurred at 119.7 astronomical units (AU), or more than 11 billion miles from the sun. Voyager 1 passed into the ISM at 122.6 AU. The spacecraft were launched within weeks of each other in 1977, with different mission goals and trajectories through space. Yet they crossed into the ISM at basically the same distances from the sun.

That gives valuable clues to the structure of the heliosphere--the bubble, shaped much like a wind sock, created by the sun's wind as it extends to the boundary of the solar system.

"It implies that the heliosphere is symmetric, at least at the two points where the Voyager spacecraft crossed," says Bill Kurth, University of Iowa research scientist and a co-author on the study. "That says that these two points on the surface are almost at the same distance."

"There's almost a spherical front to this," adds Gurnett. "It's like a blunt bullet."

Data from the Iowa instrument on Voyager 2 also gives additional clues to the thickness of the heliosheath, the outer region of the heliosphere and the point where the solar wind piles up against the approaching wind in interstellar space, which Gurnett likens to the effect of a snowplow on a city street.

The Iowa researchers say the heliosheath has varied thickness, based on data showing Voyager 1 sailed 10 AU farther than its twin to reach the heliopause, a boundary where the solar wind and the interstellar wind are in balance and considered the crossing point to interstellar space. Some had thought Voyager 2 would make that crossing first, based on models of the heliosphere.

"It's kind of like looking at an elephant with a microscope," Kurth says. "Two people go up to an elephant with a microscope, and they come up with two different measurements. You have no idea what's going on in between. What the models do is try to take information that we have from those two points and what we've learned through the flight and put together a global model of the heliosphere that matches those observations."

The last measurement obtained from Voyager 1 was when the spacecraft was at 146 AU, or more than 13.5 billion miles from the sun. The plasma wave instrument is recording that the plasma density is rising, in data feeds from a spacecraft now so far away that it takes more than 19 hours for information to travel from the spacecraft to Earth.

"The two Voyagers will outlast Earth," Kurth says. "They're in their own orbits around the galaxy for five billion years or longer. And the probability of them running into anything is almost zero."

"They might look a little worn by then," Gurnett adds with a smile.

The Iowa study is one of five papers on Voyager 2 published in Nature Astronomy. These papers confirm the passage of Voyager 2 to interstellar space and provide details on the characteristics of the heliopause.

Author: Richard C. Lewis | Source: University of Iowa [November 04, 2019]

NASA's Curiosity Rover finds an ancient oasis on Mars

By: Thomas Schmitt Attorney on October 06, 2019 / comment : 0 Astrobiology, Astronomy, Space Exploration, Universe

If you could travel back in time 3.5 billion years, what would Mars look like? The picture is evolving among scientists working with NASA's Curiosity rover.

The network of cracks in this Martian rock slab called "Old Soaker" may have formed from the drying of a mud layer more than 3 billion years ago. The view spans about 3 feet (90 centimeters) left-to-right and combines  three images taken by the MAHLI camera on the arm of NASA's Curiosity Mars rover [Credit: NASA/JPL-Caltech/MSSS]

Imagine ponds dotting the floor of Gale Crater, the 100-mile-wide (150-kilometer-wide) ancient basin that Curiosity is exploring. Streams might have laced the crater's walls, running toward its base. Watch history in fast forward, and you'd see these waterways overflow then dry up, a cycle that probably repeated itself numerous times over millions of years.

That is the landscape described by Curiosity scientists in a Nature Geoscience paper published this week. The authors interpret rocks enriched in mineral salts discovered by the rover as evidence of shallow briny ponds that went through episodes of overflow and drying. The deposits serve as a watermark created by climate fluctuations as the Martian environment transitioned from a wetter one to the freezing desert it is today.

Scientists would like to understand how long this transition took and when exactly it occurred. This latest clue may be a sign of findings to come as Curiosity heads toward a region called the "sulfate-bearing unit," which is expected to have formed in an even drier environment. It represents a stark difference from lower down the mountain, where Curiosity discovered evidence of persistent freshwater lakes.

Gale Crater is the ancient remnant of a massive impact. Sediment carried by water and wind eventually filled in the crater floor, layer by layer. After the sediment hardened, wind carved the layered rock into the towering Mount Sharp, which Curiosity is climbing today. Now exposed on the mountain's slopes, each layer reveals a different era of Martian history and holds clues about the prevailing environment at the time.

Filled with briny lakes, the Quisquiro salt flat in South America's Altiplano represents the kind of landscape that scientists think may have existed in Gale Crater, which NASA's Curiosity rover is exploring [Credit: Maksym Bocharov]

"We went to Gale Crater because it preserves this unique record of a changing Mars," said lead author William Rapin of Caltech. "Understanding when and how the planet's climate started evolving is a piece of another puzzle: When and how long was Mars capable of supporting microbial life at the surface?"

He and his co-authors describe salts found across a 500-foot-tall (150-meter-tall) section of sedimentary rocks called "Sutton Island," which Curiosity visited in 2017. Based on a series of mud cracks at a location named "Old Soaker," the team already knew the area had intermittent drier periods. But the Sutton Island salts suggest the water also concentrated into brine.

Typically, when a lake dries up entirely, it leaves piles of pure salt crystals behind. But the Sutton Island salts are different: For one thing, they're mineral salts, not table salt. They're also mixed with sediment, suggesting they crystallized in a wet environment -- possibly just beneath evaporating shallow ponds filled with briny water.


Given that Earth and Mars were similar in their early days, Rapin speculated that Sutton Island might have resembled saline lakes on South America's Altiplano. Streams and rivers flowing from mountain ranges into this arid, high-altitude plateau lead to closed basins similar to Mars' ancient Gale Crater. Lakes on the Altiplano are heavily influenced by climate in the same way as Gale.

"During drier periods, the Altiplano lakes become shallower, and some can dry out completely," Rapin said. "The fact that they're vegetation-free even makes them look a little like Mars."

Signs of a Drying Mars

Sutton Island's salt-enriched rocks are just one clue among several the rover team is using to piece together how the Martian climate changed. Looking across the entirety of Curiosity's journey, which began in 2012, the science team sees a cycle of wet to dry across long timescales on Mars.

"As we climb Mount Sharp, we see an overall trend from a wet landscape to a drier one," said Curiosity Project Scientist Ashwin Vasavada of NASA's Jet Propulsion Laboratory in Pasadena, California. JPL leads the Mars Science Laboratory mission that Curiosity is a part of. "But that trend didn't necessarily occur in a linear fashion. More likely, it was messy, including drier periods, like what we're seeing at Sutton Island, followed by wetter periods, like what we're seeing in the 'clay-bearing unit' that Curiosity is exploring today."

This animation demonstrates the salty ponds and streams that scientists think may have been left behind as Gale Crater dried out over time. The bottom of the image is the floor of Gale Crater, with the peak being the side of Mount Sharp [Credit: ASU Knowledge Enterprise Development (KED), Michael Northrop]

Up until now, the rover has encountered lots of flat sediment layers that had been gently deposited at the bottom of a lake. Team member Chris Fedo, who specializes in the study of sedimentary layers at the University of Tennessee, noted that Curiosity is currently running across large rock structures that could have formed only in a higher-energy environment such as a windswept area or flowing streams.

Wind or flowing water piles sediment into layers that gradually incline. When they harden into rock, they become large structures similar to "Teal Ridge," which Curiosity investigated this past summer.

"Finding inclined layers represents a major change, where the landscape isn't completely underwater anymore," said Fedo. "We may have left the era of deep lakes behind."

Curiosity has already spied more inclined layers in the distant sulfate-bearing unit. The science team plans to drive there in the next couple years and investigate its many rock structures. If they formed in drier conditions that persisted for a long period, that might mean that the clay-bearing unit represents an in-between stage -- a gateway to a different era in Gale Crater's watery history.

"We can't say whether we're seeing wind or river deposits yet in the clay-bearing unit, but we're comfortable saying is it's definitely not the same thing as what came before or what lies ahead," Fedo said.

Source: NASA/Jet Propulsion Laboratory [October 07, 2019]

Weather on ancient Mars: Warm with occasional rain, turning cold

By: Thomas Schmitt Attorney on August 18, 2019 / comment : 0 Astrobiology, Astronomy, Space Exploration, Universe

A new study of conditions on Mars indicates that the climate 3 to 4 billion years ago was warm enough to provoke substantial rainstorms and flowing water, followed by a longer cold period where the water froze. This may have implications on the conditions for the development of life on Mars

Mars 2020 rover concept [Credit: NASA/JPL-Caltech]

Scientists have long known that water was abundant on ancient Mars, but there has been no consensus on whether liquid water was common, or whether it was largely frozen in ice. Was the temperature high enough to allow the water to flow? Did this happen over an extended period, or just occasionally? Was the surface a desert or frozen? Warm conditions make it much more likely that life would have developed independently on the surface of ancient Mars. Now a new comparison of patterns of mineral deposition on the red planet with similar depositions on Earth lends weight to the idea that early Mars had one or more long periods dominated by rainstorms and flowing water, with the water later freezing.

Presenting the findings today at the Goldschmidt Geochemistry Conference in Barcelona, Professor Briony Horgan (Purdue University) said: "We know there were periods when the surface of Mars was frozen; we know there were periods when water flowed freely. But we don't know exactly when these periods were, and how long they lasted. We have never sent unmanned missions to areas of Mars which can show us these earliest rocks, so we need to use Earth-bound science to understand the geochemistry of what may have happened there. Our study of weathering in radically different climate conditions such as the Oregon Cascades, Hawaii, Iceland, and other places on Earth, can show us how climate affects pattern of mineral deposition, like we see on Mars.

Here on Earth, we find silica deposition in glaciers which are characteristic of melting water. On Mars, we can identify similar silica deposits in younger areas, but we can also see older areas which are similar to deep soils from warm climates on Earth. This leads us to believe that on Mars 3 to 4 billion years ago, we had a general slow trend from warm to cold, with periods of thawing and freezing. If this is so, it is important in the search for possible life on Mars.

The site of the Mars2020 landing. Chemical Alteration by Water, Jezero Crater Delta: On ancient Mars, water carved channels and transported sediments to form fans and deltas within lake basins  (colour enhanced to show mineral types) [Credit: NASA/JPL-Caltech/MSSS/JHU-APL]

We know that the building blocks of life on Earth developed very soon after the Earth's formation, and that flowing water is essential for life's development. So evidence that we had early, flowing water on Mars, will increase the chances that simple life may have developed at around the same time as it did on Earth. We hope that the Mars 2020 mission will be able to look more closely at these minerals, and begin to answer exactly what conditions existed when Mars was still young".

Analysis of the surface geology of Mars supports a trend from a warm to a cold climate, but the climate models themselves don't support this, due to the limited heat arriving from the young Sun.

"If our findings are correct, then we need to keep working on the Mars climate models, possibly to include some chemical or geological, or other process which might have warmed the young planet", said Horgan

The research team compared Earth data to Martian minerals detected using the NASA CRISM spectrometer, currently orbiting Mars, which can remotely identify surface chemicals where water once existed. They also took data from the Mars Curiosity Rover. Professor Horgan is a co-investigator on the Mars 2020 mission, due to be launched in July 2020 and to begin to explore the Jezero Crater in February 2021.

Commenting, Professor Scott McLennan (Stony Brook University) said, "What is especially exciting about this work is that it used well understood Earth based geological processes from regions that are good analogs for Mars. The results not only make sense from the perspective of developing climate evolution models for Mars but also demonstrated a possible mechanism for forming the most interesting and perplexing and non-crystalline components that have been found in all of the samples analysed so far by the Curiosity rover".

Source: Goldschmidt Conference [August 19, 2019]