Month: February 2017

Saturn’s Rings Viewed In The Mid-Infrared Show Bright Cassini Division

A team of researchers has succeeded in measuring the brightnesses and temperatures of Saturn’s rings using the mid-infrared images taken by the Subaru Telescope in 2008. The images are the highest resolution ground-based views ever made. They reveal that, at that time, the Cassini Division and the C ring were brighter than the other rings in the mid-infrared light and that the brightness contrast appeared to be the inverse of that seen in the visible light. The data give important insights into the nature of Saturn’s rings.

The beautiful appearance of Saturn and its rings has always fascinated people. The rings consist of countless numbers of ice particles orbiting above Saturn’s equator. However, their detailed origin and nature remain unknown. Spacecraft- and ground-based telescopes have tackled that mystery with many observations at various wavelengths and methods. The international Cassini mission led by NASA has been observing Saturn and its rings for more than 10 years, and has released a huge number of beautiful images.

Subaru Views Saturn

The Subaru Telescope also has observed Saturn several times over the years. Dr. Hideaki Fujiwara, Subaru Public Information Officer/Scientist, analyzed data taken in January 2008 using the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the telescope to produce a beautiful image of Saturn for public information purposes. During the analysis, he noticed that the appearance of Saturn’s rings in the mid-infrared part of the spectrum was totally different from what is seen in the visible light

Saturn’s main rings consist of the C, B, and A rings, each with different populations of particles. The Cassini Division separates the B and A rings. The 2008 image shows that the Cassini Division and the C ring are brighter in the mid-infrared wavelengths than the B and A rings appear to be. This brightness contrast is the inverse of how they appear in the visible light, where the B and A rings are always brighter than the Cassini Division and the C ring.

“Thermal emission” from ring particles is observed in the mid-infrared, where warmer particles are brighter. The team measured the temperatures of the rings from the images, which revealed that the Cassini Division and the C ring are warmer than the B and A rings. The team concluded that this was because the particles in the Cassini Division and C ring are more easily heated by solar light due to their sparser populations and darker surfaces.

On the other hand, in the visible light, observers see sunlight being reflected by the ring particles. Therefore, the B and A rings, with their dense populations of particles, always seem bright in the visible wavelengths, while the Cassini Division and the C ring appear faint. The difference in the emission process explains the inverse brightnesses of Saturn’s rings between the mid-infrared and the visible-light views.

Changing Angles Change the Brightnesses

It turns out that the Cassini Division and the C ring are not always brighter than the B and A rings, even in the mid-infrared. The team investigated images of Saturn’s rings taken in April 2005 with COMICS, and found that the Cassini Division and the C ring were fainter than the B and A rings at that time, which is the same contrast to what was seen in the visible light.

The team concluded that the “inversion” of the brightness of Saturn’s rings between 2005 and 2008 was caused by the seasonal change in the ring opening angle to the Sun and Earth. Since the rotation axis of Saturn inclines compared to its orbital plane around the Sun, the ring opening angle to the Sun changes over a 15-year cycle. This makes a seasonal variation in the solar heating of the ring particles. The change in the opening angle viewed from the Earth affects the apparent filling factor of the particles in the rings. These two variations — the temperature and the observed filling factor of the particles — led to the change in the mid-infrared appearance of Saturn’s rings.

The data taken with the Subaru Telescope revealed that the Cassini Division and the C ring are sometimes bright in the mid-infrared though they are always faint in visible light. “I am so happy that the public information activities of the Subaru Telescope, of which I am in charge, led to this scientific finding,” said Dr. Fujiwara. “We are going to observe Saturn again in May 2017 and hope to investigate the nature of Saturn’s rings further by taking advantages of observations with space missions and ground-based telescopes.”

Mars More Earth-Like Than Moon-Like

Mars’ mantle may be more complicated than previously thought. In a new study published in the Nature-affiliated journal Scientific Reports, researchers at LSU document geochemical changes over time in the lava flows of Elysium, a major martian volcanic province.

LSU Geology and Geophysics graduate researcher David Susko led the study with colleagues at LSU including his advisor Suniti Karunatillake, the University of Rahuna in Sri Lanka, the SETI Institute, Georgia Institute of Technology, NASA Ames, and the Institut de Recherche en Astrophysique et Planétologie in France.

They found that the unusual chemistry of lava flows around Elysium is consistent with primary magmatic processes, such as a heterogeneous mantle beneath Mars’ surface or the weight of the overlying volcanic mountain causing different layers of the mantle to melt at different temperatures as they rise to the surface over time.

Elysium is a giant volcanic complex on Mars, the second largest behind Olympic Mons. For scale, it rises to twice the height of Earth’s Mount Everest, or approximately 16 kilometers. Geologically, however, Elysium is more like Earth’s Tibesti Mountains in Chad, the Emi Koussi in particular, than Everest. This comparison is based on images of the region from the Mars Orbiter Camera, or MOC, aboard the Mars Global Surveyor, or MGS, Mission.

Elysium is also unique among martian volcanoes. It’s isolated in the northern lowlands of the planet, whereas most other volcanic complexes on Mars cluster in the ancient southern highlands. Elysium also has patches of lava flows that are remarkably young for a planet often considered geologically silent.

“Most of the volcanic features we look at on Mars are in the range of 3-4 billion years old,” Susko said. “There are some patches of lava flows on Elysium that we estimate to be 3-4 million years old, so three orders of magnitude younger. In geologic timescales, 3 million years ago is like yesterday.”

In fact, Elysium’s volcanoes hypothetically could still erupt, Susko said, although further research is needed to confirm this. “At least, we can’t yet rule out active volcanoes on Mars,” Susko said. “Which is very exciting.”

Susko’s work in particular reveals that the composition of volcanoes on Mars may evolve over their eruptive history. In earlier research led by Karunatillake, assistant professor in LSU’s Department of Geology and Geophysics, researchers in LSU’s Planetary Science Lab, or PSL, found that particular regions of Elysium and the surrounding shallow subsurface of Mars are geochemically anomalous, strange even relative to other volcanic regions on Mars. They are depleted in the radioactive elements thorium and potassium. Elysium is one of only two igneous provinces on Mars where researchers have found such low levels of these elements so far.

“Because thorium and potassium are radioactive, they are some of the most reliable geochemical signatures that we have on Mars,” Susko said. “They act like beacons emitting their own gamma photons. These elements also often couple in volcanic settings on Earth.”

In their new paper, Susko and colleagues started to piece together the geologic history of Elysium, an expansive volcanic region on Mars characterized by strange chemistry. They sought to uncover why some of Elysium’s lava flows are so geochemically unusual, or why they have such low levels of thorium and potassium. Is it because, as other researchers have suspected, glaciers located in this region long ago altered the surface chemistry through aqueous processes? Or is it because these lava flows arose from different parts of Mars’ mantle than other volcanic eruptions on Mars?

Perhaps the mantle has changed over time, meaning that more recent volcanic eruption flows differ chemically from older ones. If so, Susko could use Elysium’s geochemical properties to study how Mars’ bulk mantle has evolved over geologic time, with important insights for future missions to Mars. Understanding the evolutionary history of Mars’ mantle could help researchers gain a better understanding of what kinds of valuable ores and other materials could be found in the crust, as well as whether volcanic hazards could unexpectedly threaten human missions to Mars in the near future. Mars’ mantle likely has a very different history than Earth’s mantle because the plate tectonics on Earth are absent on Mars as far as researchers know. The history of the bulk interior of the red planet also remains a mystery.

Susko and colleagues at LSU analyzed geochemical and surface morphology data from Elysium using instruments on board NASA’s Mars Odyssey Orbiter (2001) and Mars Reconnaissance Orbiter (2006). They had to account for the dust that blankets Mars’ surface in the aftermath of strong dust storms, to make sure that the shallow subsurface chemistry actually reflected Elysium’s igneous material and not the overlying dust.

Through crater counting, the researchers found differences in age between the northwest and the southeast regions of Elysium — about 850 million years of difference. They also found that the younger southeast regions are geochemically different from the older regions, and that these differences in fact relate to igneous processes, not secondary processes like the interaction of water or ice with the surface of Elysium in the past.

“We determined that while there might have been water in this area in the past, the geochemical properties in the top meter throughout this volcanic province are indicative of igneous processes,” Susko said. “We think levels of thorium and potassium here were depleted over time because of volcanic eruptions over billions of years. The radioactive elements were the first to go in the early eruptions. We are seeing changes in the mantle chemistry over time.”

“Long-lived volcanic systems with changing magma compositions are common on Earth, but an emerging story on Mars,” said James Wray, study co-author and associate professor in the School of Earth and Atmospheric Sciences at Georgia Tech.

Wray led a 2013 study that showed evidence for magma evolution at a different martian volcano, Syrtis Major, in the form of unusual minerals. But such minerals could be originating at the surface of Mars, and are visible only on rare dust-free volcanoes.

“At Elysium we are truly seeing the bulk chemistry change over time, using a technique that could potentially unlock the magmatic history of many more regions across Mars,” he said.

Susko speculates that the very weight of Elysium’s lava flows, which make up a volcanic province six times higher and almost four times wider than its morphological sister on Earth, Emi Koussi, has caused different depths of Mars’ mantle to melt at different temperatures. In different regions of Elysium, lava flows may have come from different parts of the mantle. Seeing chemical differences in different regions of Elysium, Susko and colleagues concluded that Mars’ mantle might be heterogeneous, with different compositions in different areas, or that it may be stratified beneath Elysium.

Overall, Susko’s findings indicate that Mars is a much more geologically complex body than originally thought, perhaps due to various loading effects on the mantle caused by the weight of giant volcanoes.

“It’s more Earth-like than moon-like,” Susko said. “The moon is cut and dry. It often lacks the secondary minerals that occur on Earth due to weathering and igneous-water interactions. For decades, that’s also how we envisioned Mars, as a lifeless rock, full of craters with a number of long inactive volcanoes. We had a very simple view of the red planet. But the more we look at Mars, the less moon-like it becomes. We’re discovering more variety in rock types and geochemical compositions, as seen across the Curiosity Rover’s traverse in Gale Crater, and more potential for viable resource utilization and capacity to sustain a human population on Mars. It’s much easier to survive on a complex planetary body bearing the mineral products of complex geology than on a simpler body like the moon or asteroids.”

Susko plans to continue clarifying the geologic processes that cause the strange chemistry found around Elysium. In the future, he will study these chemical anomalies through computational simulations, to determine if recreating the pressures in Mars’ mantle caused by the weight of giant volcanoes could affect mantle melting to yield the type of chemistry observed within Elysium.

Dating The Milky Way’s Disc

When a star like our sun gets to be very old, after another seven billion years or so, it will no longer be able to sustain burning its nuclear fuel. With only about half of its mass remaining, it will shrink to a fraction of its radius and become a white dwarf star. White dwarfs are common, the most famous one being the companion to the brightest star in the sky, Sirius. As remnants of some of the oldest stars in the galaxy, white dwarfs offer an independent means of dating the lifetimes of different galactic populations.

A globular cluster is a roughly spherical ensemble of stars (as many as several million) that are gravitationally bound together and typically located in the outer regions of galaxies. The white dwarf stars in the Milly Way’s globular clusters reveal an age spread of between eleven and thirteen billion years. By contrast, the thick disk of the galaxy is thought to be older than ten billion years but that figure is not very well constrained. White dwarfs in the disc can be used to refine those age estimates and, since they are closer and brighter to us than those in globular clusters, they can provide more detailed information. However, they are not located in well-defined regions like clusters and so they are also harder to spot.

CfA astronomer Warren Brown and his colleagues used the 6.5-m Multiple Mirror Telescope (MMT) to obtain spectra of fifty-seven white dwarf candidate stars in the disk first discovered in all-sky surveys. Modeling the spectra of these stars revealed a mixture of types (for example, some stars had atmospheres of pure helium and others of pure hydrogen) and also an age for the disc of eleven billion years. The result is consistent with the current age estimates for the thick disc but also suggests that the current minimum age estimate might be increased. Additional measurements are needed to refine the age range, and the scientists predict that large-scale sky surveys now underway will significantly increase the number of non-cluster white dwarfs and enable the determination of their parameters.

New Study Reaffirms Fluctuation of Earth’s Magnetic Field Prior to Full Reversal

A team of researchers from Tel Aviv University, The Hebrew University and the University of California has used ancient jar handles to chart the strength of the Earth’s magnetic field over a 600-year period. In their paper published in Proceedings of the National Academy of Sciences, the team describes how they were able to accurately date the jar handles, which allowed for measuring the geomagnetic field over time.

The geomagnetic field shields life on Earth from a constant stream of cosmic radiation. In this new effort, the researchers sought to learn more about the intensity of the field over time using ancient evidence and to apply this information to understanding how it might behave in the future.

As the team explains, iron oxide particles embedded in clay used to make jars can be used as a measuring device because they become fixed in alignment while the clay is still soft due to the geomagnetic field – once the jar undergoes firing, the particles remain frozen in place. In addition, ancient jar makers stamped and inscribed the handles for tax purposes, leaving clear clues about when they were made.

Thus, to create a single measurement, the researchers would date a given jar handle using historical texts, then examine the iron oxide particles to get a reading regarding magnetic strength. By repeating this process for jar handles created between the 6th and 2nd centuries BCE, the team was able to create a magnetic field strength timeline.

The researchers report that the jar handles revealed a gradual reduction in field strength over the course of the six centuries under study, and that there were also spikes and drops in field strength during some time periods. They found, for example, that field strength spiked at the end of the 8th century BEC, and then sagged again afterwards, losing approximately 27 percent of its strength.

These fluctuations, the team suggests, indicate that we do not need to be worried about the weakening field that has been observed over the past 180 years-they believe it represents normal fluctuations. The new data may also help planet scientists better understand the nature of the geomagnetic field and to answer some questions, such as why fluctuations and changes in direction occur.

BREAKING NEWS: New Study Suggests Electric Discharge Between Earth’s Core and Magnetic Field

This news release highlights the observation of charged particles in the form of what is sometimes described as “sprites”, which is an electrical discharge which surges from “below” to “above”. It is similar to the mechanics of a local lightening/thunderstorm we witness here on Earth. To the typical observer, it appears that lightening comes down from the heavens and strikes the Earth; however, it is the intense impulse of charge which comes from the ground which produces high voltage.

The existence of these upper atmosphere sprites has been reported by pilots for years sparking a healthy debate as to their cause and how they exist. ESA astronaut Andreas Mogensen during his mission on the International Space Station in 2015 was asked to take pictures over thunderstorms with the most sensitive camera on the orbiting outpost to look for these brief features.

Denmark’s National Space Institute has now published the results of photos taken by ESA astronaut Andreas Mogensen, of upper atmosphere discharges, sometimes referred to as blue lightening or ‘sprites’. The video taken by Mogensen were from the (ISS) International Space Station. (shown below)

The cause or effects of these charged particle events are not well understood. Researched data does suggest a connection between Earth’s magnetic field and Earth’s core. With this hypothesis as a foundation, my personal research suggest a continued conjunction goes beyond our Heliosphere and into our galaxy Milky Way.

The blue discharges and jets are examples of a little-understood part of our atmosphere called the heliosphere. The Heliosphere is the outer atmosphere of the Sun and marks the edge of the Sun’s magnetic influence in space. The solar wind that streams out in all directions from the rotating Sun is a magnetic plasma, and it fills the vast space between the planets in our solar system.

The magnetic plasma from the Sun does not conjoin with the magnetic plasma between the stars in our galaxy, allowing the solar wind carves out a bubble-like atmosphere that shields our solar system from the majority of galactic cosmic rays.

Andreas concludes, “It is not every day that you get to capture a new weather phenomenon on film, so I am very pleased with the result – but even more so that researchers will be able to investigate these intriguing thunderstorms in more detail soon.”

Earth’s Hottest, Most Buoyant Mantle Plumes Draw From A Primordial Reservoir Older Than The Moon

Earth’s mantle — the layer between the crust and the outer core — is home to a primordial soup even older than the moon. Among the main ingredients is helium-3 (He-3), a vestige of the Big Bang and nuclear fusion reactions in stars. And the mantle is its only terrestrial source.

Scientists studying volcanic hotspots have strong evidence of this, finding high helium-3 relative to helium-4 in some plumes, the upwellings from Earth’s deep mantle. Primordial reservoirs in the deep Earth, sampled by a small number of volcanic hotspots globally, have this ancient He-3/4 signature.

Inspired by a 2012 paper that proposed a correlation between such hotspots and the velocity of seismic waves moving through Earth’s interior, UC Santa Barbara geochemist Matthew Jackson teamed with the authors of the original paper — Thorsten Becker of the University of Texas at Austin and Jasper Konter of the University of Hawaii — to show that only the hottest hotspots with the slowest wave velocity draw from the primitive reservoir formed early in the planet’s history. Their findings appear in the journal Nature.

“We used the seismology of the shallow mantle — the rate at which seismic waves travel through Earth below its crust — to make inferences about the deeper mantle,” said Jackson, an assistant professor in UCSB’s Department of Earth Science. “At 200 km, the shallow mantle has the largest variability of seismic velocities — more than 6 percent, which is a lot. What’s more, that variability, which we hypothesize relates to temperature, correlates with He-3.”

For their study, the researchers used the latest seismic models of Earth’s velocity structure and 35 years of helium data. When they compared oceanic hotspots with high levels of He-3/4 to seismic wave velocities, they found that these represent the hottest hotspots, with seismic waves that move more slowly than they do in cooler areas. They also analyzed hotspot buoyancy flux, which can be used to measure how much melt a particular hotspot produces. In Hawaii, the Galapagos Islands, Samoa and Easter Island as well as in Iceland, hotspots had high buoyancy levels, confirming a basic rule of physics: the hotter, the more buoyant.

“We found that the higher the hotspot buoyancy flux, the more melt a hotspot was producing and the more likely it was to have high He-3/4,” Jackson said. “Hotter plumes not only have slower seismic velocity and a higher hotspot buoyancy flux, they also are the ones with the highest He-3/4. This all ties together nicely and is the first time that He-3/4 has been correlated with shallow mantle velocities and hotspot buoyancy globally.”

Becker noted that correlation does not imply causality, “but it is pretty nifty that we found two strong correlations, which both point to the same physically plausible mechanism: the primordial stuff gets picked up preferentially by the most buoyant thermochemical upwellings.”

The authors also wanted to know why only the hottest, most buoyant plumes sample high He-3/4.

“The explanation that we came up with — which people who do numerical simulations have been suggesting for a long time — is that whatever this reservoir is with primitive helium, it must be really dense so that only the hottest, most buoyant plumes can entrain some of it to the surface,” Jackson said. “That makes sense and it also explains how something so ancient could survive in the chaotically convecting mantle for 4.5 billion years. The density contrast makes it more likely that the ancient helium reservoir is preserved rather than mixed away.”

“Since this correlation of geochemistry and seismology now holds from helium isotopes in this work to the compositions we examined in 2012, it appears that overall hotspot geochemical variations will need to be re-examined from the perspective of buoyancy,” Konter concluded.

Scientists Estimate Solar Nebula’s Lifetime

About 4.6 billion years ago, an enormous cloud of hydrogen gas and dust collapsed under its own weight, eventually flattening into a disk called the solar nebula. Most of this interstellar material contracted at the disk’s center to form the sun, and part of the solar nebula’s remaining gas and dust condensed to form the planets and the rest of our solar system.

Now scientists from MIT and their colleagues have estimated the lifetime of the solar nebula — a key stage during which much of the solar system evolution took shape.

This new estimate suggests that the gas giants Jupiter and Saturn must have formed within the first 4 million years of the solar system’s formation. Furthermore, they must have completed gas-driven migration of their orbital positions by this time.

“So much happens right at the beginning of the solar system’s history,” says Benjamin Weiss, professor of earth, atmospheric, and planetary sciences at MIT. “Of course the planets evolve after that, but the large-scale structure of the solar system was essentially established in the first 4 million years.”

Weiss and MIT postdoc Huapei Wang, the first author of this study, report their results today in the journal Science. Their co-authors are Brynna Downey, Clement Suavet, and Roger Fu from MIT; Xue-Ning Bai of the Harvard-Smithsonian Center for Astrophysics; Jun Wang and Jiajun Wang of Brookhaven National Laboratory; and Maria Zucolotto of the National Museum in Rio de Janeiro.

Spectacular recorders

By studying the magnetic orientations in pristine samples of ancient meteorites that formed 4.563 billion years ago, the team determined that the solar nebula lasted around 3 to 4 million years. This is a more precise figure than previous estimates, which placed the solar nebula’s lifetime at somewhere between 1 and 10 million years.

The team came to its conclusion after carefully analyzing angrites, which are some of the oldest and most pristine of planetary rocks. Angrites are igneous rocks, many of which are thought to have erupted onto the surface of asteroids very early in the solar system’s history and then quickly cooled, freezing their original properties — including their composition and paleomagnetic signals — in place.

Scientists view angrites as exceptional recorders of the early solar system, particularly as the rocks also contain high amounts of uranium, which they can use to precisely determine their age.

“Angrites are really spectacular,” Weiss says. “Many of them look like what might be erupting on Hawaii, but they cooled on a very early planetesimal.”

Weiss and his colleagues analyzed four angrites that fell to Earth at different places and times.

“One fell in Argentina, and was discovered when a farm worker was tilling his field,” Weiss says. “It looked like an Indian artifact or bowl, and the landowner kept it by this house for about 20 years, until he finally decided to have it analyzed, and it turned out to be a really rare meteorite.”

The other three meteorites were discovered in Brazil, Antarctica, and the Sahara Desert. All four meteorites were remarkably well-preserved, having undergone no additional heating or major compositional changes since they originally formed.

Measuring tiny compasses

The team obtained samples from all four meteorites. By measuring the ratio of uranium to lead in each sample, previous studies had determined that the three oldest formed around 4.563 billion years ago. The researchers then measured the rocks’ remnant magnetization using a precision magnetometer in the MIT Paleomagnetism Laboratory.

“Electrons are little compass needles, and if you align a bunch of them in a rock, the rock becomes magnetized,” Weiss explains. “Once they’re aligned, which can happen when a rock cools in the presence of a magnetic field, then they stay that way. That’s what we use as records of ancient magnetic fields.”

When they placed the angrites in the magnetometer, the researchers observed very little remnant magnetization, indicating there was very little magnetic field present when the angrites formed.

The team went a step further and tried to reconstruct the magnetic field that would have produced the rocks’ alignments, or lack thereof. To do so, they heated the samples up, then cooled them down again in a laboratory-controlled magnetic field.

“We can keep lowering the lab field and can reproduce what’s in the sample,” Weiss says. “We find only very weak lab fields are allowed, given how little remnant magnetization is in these three angrites.”

Specifically, the team found that the angrites’ remnant magnetization could have been produced by an extremely weak magnetic field of no more than 0.6 microteslas, 4.563 billion years ago, or, about 4 million years after the start of the solar system.

In 2014, Weiss’ group analyzed other ancient meteorites that formed within the solar system’s first 2 to 3 million years, and found evidence of a magnetic field that was about 10-100 times stronger — about 5-50 microtesla.

“It’s predicted that once the magnetic field drops by a factor of 10-100 in the inner solar system, which we’ve now shown, the solar nebula goes away really quickly, within 100,000 years,” Weiss says. “So even if the solar nebula hadn’t disappeared by 4 million years, it was basically on its way out.”

The planets align

The researchers’ new estimate is much more precise than previous estimates, which were based on observations of faraway stars.

“What’s more, the angrites’ paleomagnetism constrains the lifetime of our own solar nebula, while astronomical observations obviously measure other faraway solar systems,” Wang adds. “Since the solar nebula lifetime critically affects the final positions of Jupiter and Saturn, it also affects the later formation of the Earth, our home, as well as the formation of other terrestrial planets.”

Now that the scientists have a better idea of how long the solar nebula persisted, they can also narrow in on how giant planets such as Jupiter and Saturn formed. Giant planets are mostly made of gas and ice, and there are two prevailing hypotheses for how all this material came together as a planet. One suggests that giant planets formed from the gravitational collapse of condensing gas, like the sun did. The other suggests they arose in a two-stage process called core accretion, in which bits of material smashed and fused together to form bigger rocky, icy bodies. Once these bodies were massive enough, they could have created a gravitational force that attracted huge amounts of gas to ultimately form a giant planet.

According to previous predictions, giant planets that form through gravitational collapse of gas should complete their general formation within 100,000 years. Core accretion, in contrast, is typically thought to take much longer, on the order of 1 to several million years. Weiss says that if the solar nebula was around in the first 4 million years of solar system formation, this would give support to the core accretion scenario, which is generally favored among scientists.

“The gas giants must have formed by 4 million years after the formation of the solar system,” Weiss says. “Planets were moving all over the place, in and out over large distances, and all this motion is thought to have been driven by gravitational forces from the gas. We’re saying all this happened in the first 4