Scientists Improve Brown Dwarf Weather Forecasts

Scientists Improve Brown Dwarf Weather Forecasts:

Dim objects called brown dwarfs, less massive than the Sun but more massive than Jupiter, have powerful winds and clouds -- specifically, hot patchy clouds made of iron droplets and silicate dust. Scientists recently realized these giant clouds can move and thicken or thin surprisingly rapidly, in less than an Earth day, but did not understand why.

Now, researchers have a new model for explaining how clouds move and change shape in brown dwarfs, using insights from NASA's Spitzer Space Telescope. Giant waves cause large-scale movement of particles in brown dwarfs' atmospheres, changing the thickness of the silicate clouds, researchers report in the journal Science. The study also suggests these clouds are organized in bands confined to different latitudes, traveling with different speeds in different bands.

"This is the first time we have seen atmospheric bands and waves in brown dwarfs," said lead author Daniel Apai, associate professor of astronomy and planetary sciences at the University of Arizona in Tucson.

Just as in Earth's ocean, different types of waves can form in planetary atmospheres. For example, in Earth's atmosphere, very long waves mix cold air from the polar regions to mid-latitudes, which often lead clouds to form or dissipate.

The distribution and motions of the clouds on brown dwarfs in this study are more similar to those seen on Jupiter, Saturn, Uranus and Neptune. Neptune has cloud structures that follow banded paths too, but its clouds are made of ice. Observations of Neptune from NASA's Kepler spacecraft, operating in its K2 mission, were important in this comparison between the planet and brown dwarfs.

"The atmospheric winds of brown dwarfs seem to be more like Jupiter's familiar regular pattern of belts and zones than the chaotic atmospheric boiling seen on the Sun and many other stars," said study co-author Mark Marley at NASA's Ames Research Center in California's Silicon Valley.

Brown dwarfs can be thought of as failed stars because they are too small to fuse chemical elements in their cores. They can also be thought of as "super planets" because they are more massive than Jupiter, yet have roughly the same diameter. Like gas giant planets, brown dwarfs are mostly made of hydrogen and helium, but they are often found apart from any planetary systems. In a 2014 study using Spitzer, scientists found that brown dwarfs commonly have atmospheric storms.

Due to their similarity to giant exoplanets, brown dwarfs are windows into planetary systems beyond our own. It is easier to study brown dwarfs than planets because they often do not have a bright host star that obscures them.

"It is likely the banded structure and large atmospheric waves we found in brown dwarfs will also be common in giant exoplanets," Apai said.

Using Spitzer, scientists monitored brightness changes in six brown dwarfs over more than a year, observing each of them rotate 32 times. As a brown dwarf rotates, its clouds move in and out of the hemisphere seen by the telescope, causing changes in the brightness of the brown dwarf. Scientists then analyzed these brightness variations to explore how silicate clouds are distributed in the brown dwarfs.

Researchers had been expecting these brown dwarfs to have elliptical storms resembling Jupiter's Great Red Spot, caused by high-pressure zones. The Great Red Spot has been present in Jupiter for hundreds of years and changes very slowly: Such "spots" could not explain the rapid changes in brightness that scientists saw while observing these brown dwarfs. The brightness levels of the brown dwarfs varied markedly just over the course of an Earth day.

To make sense of the ups and downs of brightness, scientists had to rethink their assumptions about what was going on in the brown dwarf atmospheres. The best model to explain the variations involves large waves, propagating through the atmosphere with different periods. These waves would make the cloud structures rotate with different speeds in different bands.

University of Arizona researcher Theodora Karalidi used a supercomputer and a new computer algorithm to create maps of how clouds travel on these brown dwarfs.

"When the peaks of the two waves are offset, over the course of the day there are two points of maximum brightness," Karalidi said. "When the waves are in sync, you get one large peak, making the brown dwarf twice as bright as with a single wave."

The results explain the puzzling behavior and brightness changes that researchers previously saw. The next step is to try to better understand what causes the waves that drive cloud behavior.

JPL manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech in Pasadena, California. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at the Infrared Processing and Analysis Center at Caltech. Caltech manages JPL for NASA.

Credit: spitzer.caltech.edu

Astrophysicists Predict Earth-Like Planet in Star System Only 16 Light Years Away

Astrophysicists Predict Earth-Like Planet in Star System Only 16 Light Years Away:

Astrophysicists at the University of Texas at Arlington have predicted that an Earth-like planet may be lurking in a star system just 16 light years away. The team investigated the star system Gliese 832 for additional exoplanets residing between the two currently known alien worlds in this system. Their computations revealed that an additional Earth-like planet with a dynamically stable configuration may be residing at a distance ranging from 0.25 to 2.0 astronomical unit (AU) from the star.

“According to our calculations, this hypothetical alien world would probably have a mass between 1 to 15 Earth's masses,” said the lead author Suman Satyal, UTA physics researcher, lecturer and laboratory supervisor. The paper is co-authored by John Griffith, UTA undergraduate student and long-time UTA physics professor Zdzislaw Musielak.

The astrophysicists published their findings this week as “Dynamics of a probable Earth-Like Planet in the GJ 832 System” in The Astrophysical Journal.

UTA Physics Chair Alexander Weiss congratulated the researchers on their work, which underscores the University’s commitment to data-driven discovery within its Strategic Plan 2020: Bold Solutions | Global Impact.

“This is an important breakthrough demonstrating the possible existence of a potential new planet orbiting a star close to our own,” Weiss said. “The fact that Dr. Satyal was able to demonstrate that the planet could maintain a stable orbit in the habitable zone of a red dwarf for more than 1 billion years is extremely impressive and demonstrates the world class capabilities of our department’s astrophysics group.”

Gliese 832 is a red dwarf and has just under half the mass and radius of our sun. The star is orbited by a giant Jupiter-like exoplanet designated Gliese 832b and by a super-Earth planet Gliese 832c. The gas giant with 0.64 Jupiter masses is orbiting the star at a distance of 3.53 AU, while the other planet is potentially a rocky world, around five times more massive than the Earth, residing very close its host star—about 0.16 AU.

For this research, the team analyzed the simulated data with an injected Earth-mass planet on this nearby planetary system hoping to find a stable orbital configuration for the planet that may be located in a vast space between the two known planets.

Gliese 832b and Gliese 832c were discovered by the radial velocity technique, which detects variations in the velocity of the central star, due to the changing direction of the gravitational pull from an unseen exoplanet as it orbits the star. By regularly looking at the spectrum of a star – and so, measuring its velocity – one can see if it moves periodically due to the influence of a companion.

"We also used the integrated data from the time evolution of orbital parameters to generate the synthetic radial velocity curves of the known and the Earth-like planets in the system,” said Satyal, who earned his Ph.D. in Astrophysics from UTA in 2014. "We obtained several radial velocity curves for varying masses and distances indicating a possible new middle planet," the astrophysicist noted.

For instance, if the new planet is located around 1 AU from the star, it has an upper mass limit of 10 Earth masses and a generated radial velocity signal of 1.4 meters per second. A planet with about the mass of the Earth at the same location would have radial velocity signal of only 0.14 m/s, thus much smaller and hard to detect with the current technology.

“The existence of this possible planet is supported by long-term orbital stability of the system, orbital dynamics and the synthetic radial velocity signal analysis”, Satyal said. “At the same time, a significantly large number of radial velocity observations, transit method studies, as well as direct imaging are still needed to confirm the presence of possible new planets in the Gliese 832 system.”

In 2014, Noyola, Satyal and Musielak published findings related to radio emissions indicating that an exomoon could be orbiting an exoplanet in The Astrophysical Journal, where they suggested that interactions between Jupiter’s magnetic field and its moon Io may be used to detect exomoons at distant exoplanetary systems.

Zdzislaw Musielak joined the UTA physics faculty in 1998 following his doctoral program at the University of Gdansk in Poland and appointments at the University of Heidelberg in Germany; Massachusetts Institute of Technology, NASA Marshall Space Flight Center and the University of Alabama in Huntsville.

Suman Satyal is a research assistant, laboratory supervisor and physics lecturer at UTA and his research area includes the detection of exoplanets and exomoons, and orbital stability analysis of Exoplanets in single and binary star systems. He previously worked in the National Synchrotron Light Source located at the Brookhaven National Laboratory in New York, where he measured the background in auger-photoemission coincidence spectra associated with multi-electron valence band photoemission processes.

Credit: uta.edu

Astrophysicists Explain the Mysterious Behavior of Cosmic Rays

Astrophysicists Explain the Mysterious Behavior of Cosmic Rays:

A team of scientists from Russia and China has developed a model which explains the nature of high-energy cosmic rays (CRs) in our Galaxy. These CRs have energies exceeding those produced by supernova explosions by one or two orders of magnitude. The model focuses mainly on the recent discovery of giant structures called Fermi bubbles. The paper was published in EPJ Web of Conferences.

One of the key problems in the theory of the origin of cosmic rays (high-energy protons and atomic nuclei) is their acceleration mechanism. The issue was addressed by Vitaly Ginzburg and Sergei Syrovatsky in the 1960s when they suggested that CRs are generated during supernova (SN) explosions in the Galaxy. A specific mechanism of charged particle acceleration by SN shock waves was proposed by Germogen Krymsky and others in 1977. Due to the limited lifetime of the shocks, it is estimated that the maximum energy of the accelerated particles cannot exceed 0.1-1.0 PeV.

The question arises of how to explain the nature of particles with energies above 1 PeV. A major breakthrough in researching the acceleration processes of such particles came when the Fermi Gamma-ray Space Telescope detected two gigantic structures emitting radiation in gamma-ray band in the central area of the Galaxy in November 2010. The discovered structures are elongated and are symmetrically located in the Galactic plane perpendicular to its center, extending 50,000 light-years, or roughly half of the diameter of the Milky Way disk. These structures became known as Fermi bubbles. Later, the Planck telescope team discovered their emission in the microwave band.

The nature of Fermi bubbles is still unclear, however the location of these objects indicates their connection to past or present activity in the center of the galaxy, where a central black hole of 106 solar masses is believed to be located. Modern models relate the bubbles to star formation and/or an energy release in the Galactic center as a result of tidal disruption of stars during their accretion onto a central black hole. The bubbles are not considered to be unique phenomena observed only in the Milky Way and similar structures can be detected in other galactic systems with active nuclei.

Dmitry Chernyshov (MIPT graduate), Vladimir Dogiel (MIPT staff member) and their colleagues from Hong Kong and Taiwan have published a series of papers on the nature of Fermi bubbles. They have shown that X-ray and gamma-ray emission in these areas is due to various processes involving relativistic electrons accelerated by shock waves resulting from stellar matter falling into a black hole. In this case, the shock waves should accelerate both protons and nuclei. However, in contrast to electrons, relativistic protons with bigger masses hardly lose their energy in the Galactic halo and can fill up the entire volume of the galaxy. The authors of the paper suggest that giant Fermi bubbles shock fronts can re-accelerate protons emitted by SN to energies greatly exceeding 1 PeV.

Analysis of cosmic ray re-acceleration showed that Fermi bubbles may be responsible for the formation of the CR spectrum above the “knee” of the observed spectrum, i.e., at energies greater than 3 PeV. To put this into perspective, the energy of accelerated particles in the Large Hadron Collider is also about 1 PeV.

"The proposed model explains the spectral distribution of the observed CR flux. It can be said that the processes we described are capable of re-accelerating galactic cosmic rays generated in supernova explosions. Unlike electrons, protons have a significantly greater lifetime, so when accelerated in Fermi bubbles, they can fill up the volume of the Galaxy and be observed near the Earth. Our model suggests that the cosmic rays containing high-energy protons and nuclei with energy lower than 1 PeV (below the energy range of the observed spectrum’s "knee"), were generated in supernova explosions in the Galactic disk. Such CRs are re-accelerated in Fermi bubbles to energies over 1 PeV (above the "knee"). The final cosmic ray distribution is shown on the spectral diagram," says Vladimir Dogiel.

The researchers have proposed an explanation for the peculiarities in the CR spectrum in the energy range from 3 PeV to 1 EeV. The scientists have proven that particles produced during the SN explosions and which have energies lower than 3 PeV experience re-acceleration in Fermi bubbles when they move from the galactic disk to the halo. Reasonable parameters of the model describing the particles’ acceleration in Fermi bubbles can explain the nature of the spectrum of cosmic rays above 3 PeV. The spectrum below this range remains undisturbed. Thus, the model is able to produce spectral distribution of cosmic rays that is identical to the one observed.

Credit: mipt.ru

Astrophysicist Predicts Detached Eclipsing White Dwarfs to Merge Into an Exotic Star

Astrophysicist Predicts Detached Eclipsing White Dwarfs to Merge Into an Exotic Star:

A University of Oklahoma astrophysicist, Mukremin Kilic, and his team have discovered two detached, eclipsing double white dwarf binaries with orbital periods of 40 and 46 minutes, respectively. White dwarfs are the remnants of Sun-like stars, many of which are found in pairs, or binaries. However, only a handful of white dwarf binaries are known with orbital periods less than one hour in the Milky Way—a galaxy made up of two hundred billion stars—and most have been discovered by Kilic and his colleagues.

“Short-period white dwarf binaries are interesting because they generate gravitational waves. One of the new discoveries emits so much gravitational waves that it is a new verification source for the upcoming Laser Interferometer Space Antenna—a gravitational wave satellite,” Kilic said.

Kilic, an astrophysics professor in the Homer L. Dodge Department of Physics and Astronomy, with OU graduate students Alekzander Kosakowski and A. Gianninas, and collaborator Warren R. Brown, Smithsonian Astrophysical Observatory, discovered the two white dwarf binaries using the MMT 6.5-meter telescope, a joint facility of the Smithsonian Institution and the University of Arizona. Observations at the Apache Point Observatory 3.5-meter telescope revealed that one of the binaries is eclipsing, only the seventh known eclipsing white dwarf binary.

In the future, Kilic and his team will watch in real time as the stars eclipse to measure how they are getting closer and closer—a sign they will likely merge. What occurs when the white dwarfs make contact continues to be a mystery at this point. One possibility is an explosion—a phenomenon known as a supernova. Kilic predicts these two stars will come together and create an “exotic star,” known as R Coronae Borealis. These stars are often identified for their spectacular declines in brightness at irregular intervals. There are only about 65 R Coronae Borealis stars known in our galaxy.

“The existence of double white dwarfs that merge in 20 to 35 million years is remarkable,” Brown said. “It implies that many more such systems must have formed and merged over the age of the Milky Way.”

Kilic’s paper, “Discovery of a Detached, Eclipsing 40 Min Period Double White Dwarf Binary and a Friend: Implications for He+CO White Dwarf Mergers,” is available at https://arxiv.org/abs/1708.05287 in The Astrophysical Journal. Support for this project was provided by the Smithsonian Institution, the National Science Foundation and the National Atmospheric and Space Administration.

Credit: ou.edu

Two Newly Discovered Asteroids to Whiz by Earth on Tuesday

Two Newly Discovered Asteroids to Whiz by Earth on Tuesday:

Two space rocks detected this week are slated to pass by our planet on Tuesday, Aug. 22. The newly found asteroids, designated 2017 PV25 and 2017 QT1, are expected to miss the Earth at a distance of 5.5 lunar distances (LD) and 2.6 LD respectively (or 2.1 and 1 million kilometers).

2017 PV25 is an Apollo-type asteroid discovered Aug. 15 by the Asteroid Terrestrial-Impact Last Alert System (ATLAS) at the Mauna Loa Observatory (MLO), Hawaii. It is an astronomical survey system for detection of dangerous asteroids a few weeks to days before their close approaches to Earth.

According to astronomers, 2017 PV25 has an absolute magnitude of 24.7 and a diameter between 23 and 71 meters. This near-Earth object (NEO) has a semimajor axis of about 1.06 AU and it takes it approximately one year and one month to fully orbit the sun. The space rock will miss our planet at 16:16 UTC with a relative velocity of 6.46 km/s.

2017 QT1 is also an Apollo-type asteroid, first spotted on Aug. 17 using the Pan-STARRS 1 (PS1) telescope at the summit of Haleakala on the Hawaiian island of Maui. The Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) is an astronomical survey consisting of astronomical cameras, telescopes and a computing facility, surveying the sky for moving objects on a continual basis.

2017 QT1 is expected to pass by our planet at 18:24 UTC with a relative velocity of 20.6 km/s. The asteroid has an absolute magnitude of 26.7 and a diameter between 8 and 27 meters. This NEO has a semimajor axis of about 2.55 AU and an orbital period of approximately four years.

On Aug. 20, there were 1,803 Potentially Hazardous Asteroids (PHAs) detected and none of them is on a collision course with our planet. PHAs are asteroids larger than 100 meters that can come closer to Earth than 19.5 LD.

Scientists Create ‘Diamond Rain’ That Forms in the Interior of Icy Giant Planets

Scientists Create ‘Diamond Rain’ That Forms in the Interior of Icy Giant Planets:

In an experiment designed to mimic the conditions deep inside the icy giant planets of our solar system, scientists were able to observe “diamond rain” for the first time as it formed in high-pressure conditions. Extremely high pressure squeezes hydrogen and carbon found in the interior of these planets to form solid diamonds that sink slowly down further into the interior.

The glittering precipitation has long been hypothesized to arise more than 5,000 miles below the surface of Uranus and Neptune, created from commonly found mixtures of just hydrogen and carbon. The interiors of these planets are similar—both contain solid cores surrounded by a dense slush of different ices. With the icy planets in our solar system, “ice” refers to hydrogen molecules connected to lighter elements, such as carbon, oxygen and/or nitrogen.

Researchers simulated the environment found inside these planets by creating shock waves in plastic with an intense optical laser at the Matter in Extreme Conditions (MEC) instrument at SLAC National Accelerator Laboratory’s X-ray free-electron laser, the Linac Coherent Light Source (LCLS). SLAC is one of 10 Department of Energy (DOE) Office of Science laboratories.

In the experiment, the scientists were able to see that nearly every carbon atom of the original plastic was incorporated into small diamond structures up to a few nanometers wide. On Uranus and Neptune, the study authors predict that diamonds would become much larger, maybe millions of carats in weight. Researchers also think it’s possible that over thousands of years, the diamonds slowly sink through the planets’ ice layers and assemble into a thick layer around the core.

The research published in Nature Astronomy on August 21.

“Previously, researchers could only assume that the diamonds had formed,” said Dominik Kraus, scientist at Helmholtz Zentrum Dresden-Rossendorf and lead author on the publication. “When I saw the results of this latest experiment, it was one of the best moments of my scientific career.”

Earlier experiments that attempted to recreate diamond rain in similar conditions were not able to capture measurements in real time, because we currently can create these extreme conditions under which tiny diamonds form only for very brief time in the laboratory. The high-energy optical lasers at MEC combined with LCLS’s X-ray pulses—which last just femtoseconds, or quadrillionths of a second—allowed the scientists to directly measure the chemical reaction.

Other prior experiments also saw hints of carbon forming graphite or diamond at lower pressures than the ones created in this experiment, but with other materials introduced and altering the reactions.

The results presented in this experiment is the first unambiguous observation of high-pressure diamond formation from mixtures and agrees with theoretical predictions about the conditions under which such precipitation can form and will provide scientists with better information to describe and classify other worlds.

In the experiment, plastic simulates compounds formed from methane—a molecule with just one carbon bound to four hydrogen atoms that causes the distinct blue cast of Neptune.

The team studied a plastic material, polystyrene, that is made from a mixture of hydrogen and carbon, key components of these planets’ overall chemical makeup. 

In the intermediate layers of icy giant planets, methane forms hydrocarbon (hydrogen and carbon) chains that were long hypothesized to respond to high pressure and temperature in deeper layers and form diamond rain.

The researchers used high-powered optical laser to create pairs of shock waves in the plastic with the correct combination of temperature and pressure. The first shock is smaller and slower and overtaken by the stronger second shock. When the shock waves overlap, that’s the moment the pressure peaks and when most of the diamonds form, Kraus said. 

During those moments, the team probed the reaction with pulses of X-rays from LCLS that last just 50 femtoseconds. This allowed them to see the small diamonds that form in fractions of a second with a technique called femtosecond X-ray diffraction. The X-ray snapshots provide information about the size of the diamonds and the details of the chemical reaction as it occurs.

“For this experiment, we had LCLS, the brightest X-ray source in the world,” said Siegfried Glenzer, professor of photon science at SLAC and a co-author of the paper. “You need these intense, fast pulses of X-rays to unambiguously see the structure of these diamonds, because they are only formed in the laboratory for such a very short time.”

When astronomers observe exoplanets outside our solar system, they are able to measure two primary traits—the mass, which is measured by the wobble of stars, and radius, observed from the shadow when the planet passes in front of a star. The relationship between the two is used to classify a planet and help determine whether it may be composed of heavier or lighter elements.

“With planets, the relationship between mass and radius can tell scientists quite a bit about the chemistry,” Kraus said. “And the chemistry that happens in the interior can provide additional information about some of the defining features of the planet.”

Information from studies like this one about how elements mix and clump together under pressure in the interior of a given planet can change the way scientists calculate the relationship between mass and radius, allowing scientists to better model and classify individual planets. The falling diamond rain also could be an additional source of energy, generating heat while sinking towards the core.

“We can’t go inside the planets and look at them, so these laboratory experiments complement satellite and telescope observations,” Kraus said.

The researchers also plan to apply the same methods to look at other processes that occur in the interiors of planets.

In addition to the insights they give into planetary science, nanodiamonds made on Earth could potentially be harvested for commercial purposes—uses that span medicine, scientific equipment and electronics. Currently, nanodiamonds are commercially produced from explosives; laser production may offer a cleaner and more easily controlled method.

Research that compresses matter, like this study, also helps scientists understand and improve fusion experiments where forms of hydrogen combine to form helium to generate vast amounts of energy. This is the process that fuels the sun and other stars but has yet to be realized in a controlled way for power plants on Earth.

In some fusion experiments, a fuel of two different forms of hydrogen is surrounded by a plastic layer that reaches conditions similar to the interior of planets during a short-lived compression stage. The LCLS experiment on plastic now suggests that chemistry may play an important role in this stage. 

“Simulations don’t really capture what we’re observing in this field,” Glenzer said. “Our study and others provide evidence that matter clumping in these types of high-pressure conditions is a force to be reckoned with.”

The research collaboration includes scientists from Helmholtz Zentrum Dresden-Rossendorf in Germany, University of California-Berkeley, Lawrence Livermore National Laboratory, Lawrence Berkeley National Laboratory, GSI Helmholtz Center for Heavy Ion Research in Germany, Osaka University in Japan, Technical University of Darmstadt in Germany, European XFEL, University of Michigan, University of Warwick in the United Kingdom and SLAC.

The research was supported by DOE’s Office of Science and the National Nuclear Security Administration. LCLS is a DOE Office of Science User Facility. 

Credit: slac.stanford.edu

Great American Solar Eclipse of 2017 Wows Skywatchers

Great American Solar Eclipse of 2017 Wows Skywatchers:

The “Great American Eclipse” has officially ended. The first glimpses of the first total solar eclipse to cross the United States from coast to coast in 99 years began in Oregon, with totality just after 1 p.m. ET. What started as a tiny crescent of the moon's shadow turned into a perfectly beautiful eclipse in city after city. It ended in South Carolina about 3 p.m. ET. A partial solar eclipse was visible until just after 4 p.m. in the Southeast.

NASA’s G-III aircraft picked up the stunning celestial event in Salem, Oregon, showing the black orb of the moon covering the blazing sun to create a glowing halo.

The awe-inspiring moment cast total blackness over the area.

It then stretched across 13 other states: Idaho, a sliver of Montana, Wyoming, Nebraska, Kansas, a tiny portion of Iowa, Missouri, Illinois, Kentucky, Tennessee, Georgia, North Carolina and South Carolina.

In most places, the total eclipse lasted less than one minute, but the longest period of darkness lasted 2 minutes and 44 seconds over Shawnee National Forest in southern Illinois.

Millions of people moved to get into the path of darkness, putting on their protective glasses to gaze at the sky in wonder.

It was the first total solar eclipse visible from America's lower 48 states in 38 years, and the first since 1918 to track from coast to coast.

In Washington, D.C., where the sun was about 80 percent obscured by the moon, President Trump, Melania Trump and their son, Barron Trump, took in the scene from the Blue Room Balcony just after 2:30 p.m. ET.

The president waved to the onlookers at the White House, and gave a thumbs-up gesture when a reporter inquired about the view. He observed the eclipse at its apex wearing glasses with Mrs. Trump for about 90 seconds.

The Atlantic coastal city of Charleston was the final big urban area tasked with saying goodbye to the eclipse. It experienced the full shadow at 2:47 p.m. ET.

Then totality headed out past Fort Sumter in Charleston Harbor, across the coastal wetlands and out into the Atlantic.

Although, the US had exclusive rights on totality, a partial eclipse was visible across all of North America and the north of South America.

Parts of western Europe were also set to see the moon take a little chunk out of the sun at the end of the day just before the star dipped below the horizon.

The next total solar eclipse on Earth is on July 2, 2019, over the South Pacific, Chile, Argentina.

Credit: cnn.com, nypost.com, nytimes.com, bbc.com

The Moving Martian Bow Shock

The Moving Martian Bow Shock:

As the energetic particles of the solar wind speed across interplanetary space, their motion is modified by objects in their path. A study, based on data from ESA's Mars Express orbiter, has thrown new light on a surprising interaction between the planet Mars and supersonic particles in the solar wind.

Scientists have long been aware that a feature known as a bow shock forms upstream of a planet – rather like the bow of a ship, where the water is slowed and then diverted around the obstacle.

The bow shock marks a fairly sharp boundary where the solar wind slows suddenly as it begins to plough into a planet's magnetosphere or outer atmosphere.

In the case of Mars, which does not generate a global magnetic field and has a thin atmosphere, the main obstacle to the solar wind is the ionosphere – a region of electrically charged particles in its upper atmosphere.

Furthermore, the relatively small size, mass and gravity of Mars enable the formation of an extended exosphere – the outermost layer of the atmosphere, where gaseous atoms and molecules escape into space and interact directly with the solar wind.

Observations made by numerous spacecraft over many decades have shown that variations in the ionosphere and exosphere play a role in changes in the location of the bow shock boundary.

As expected, the distance of the Martian bow shock from the planet increases as the dynamic pressure of the solar wind decreases. This is rather like a weakening of the bow wave ahead of a ship as the water's flow slows down.

On the other hand, increases in the distance of the Martian bow shock coincide with increases in the amount of incoming solar radiation at extreme ultraviolet (EUV) wavelengths. Consequently, the rate at which ions and electrons are produced from atoms and molecules in the upper atmosphere increases. This results in increased thermal pressure within the ionosphere, enabling it to better counteract the incoming solar wind flow.

At the same time, newly created ions within the extended exosphere are picked up and accelerated by the electromagnetic fields carried by the solar wind. The result is a slowdown in the solar wind and a shift in the position of the bow shock.

Another possible factor in influencing the bow shock's location is the orbit of Mars. The planet's distance from the Sun is much more elliptical than that of Earth, ranging from 206 million km to 249 million km – a 20% difference.

A team of European scientists has investigated how and why the bow shock's location varies during the Martian year. In a paper published online in the 21 November 2016 issue of the Journal of Geophysical Research: Space Physics, the team has analysed more than five Martian years of measurements from the Mars Express Analyser of Space Plasma and EneRgetic Atoms (ASPERA-3) Electron Spectrometer (ELS) to identify 11 861 bow shock crossings. This is the first analysis of the bow shock to be based on data obtained over such a prolonged period and during all Martian seasons.

As Mars Express crosses the Martian bow shock the ELS instrument typically registers a sudden increase in flux of electrons across a wide range of energies (typically up to a few hundred eV).

The scientists discovered that, on average, the bow shock is closer to Mars near aphelion (the planet's furthest point from the Sun), and further away from Mars near perihelion (the planet's closest point to the Sun). The bow shock's average distance from Mars, when measured from above the terminator (the day-night boundary) reaches a minimum of 8102 km around aphelion, while its maximum distance of 8984 km occurs around perihelion. This is an overall variation of approximately 11% during each Martian orbit.

The team also verified previous findings that the bow shock in the southern hemisphere is, on average, located farther away from Mars than in the northern hemisphere. However, this hemispherical asymmetry is small (a total distance variation of 2.4%), and the same annual variations in the bow shock occur irrespective of the hemisphere.

Solar wind density (and, therefore, dynamic pressure), the strength of the interplanetary magnetic field, and solar irradiation, are all expected to reduce with distance from the Sun. Since these parameters impact the bow shock location in different ways, the team wanted to find out which is the dominant factor throughout the Martian year.

Their somewhat surprising discovery was that the bow shock's location is more sensitive to variations in the solar EUV output than to solar wind dynamic pressure variations.

This may be largely due to the well recognized impact of EUV on the density and thermal pressure of the ionosphere, and the expansion of the exosphere (see above). These processes create buffers against the solar wind.

However, the variations in bow shock distance also correlate with annual changes in the amount of dust in the Martian atmosphere. The Martian dust storm season occurs around perihelion, when the planet is warmer and receives more solar radiation.

"Dust storms have been previously shown to interact with the upper atmosphere and ionosphere of Mars, so there may be an indirect coupling between the dust storms and bow shock location," said Benjamin Hall, lead author of the paper, who was until recently at the University of Leicester, and is currently a researcher at Lancaster University, UK.

"However, we do not draw any further conclusions on how the dust storms could directly impact the location of the Martian bow shock and leave such an investigation to a future study.

"It seems likely that no single mechanism can explain our observations, but rather a combined effect of all of them. At this point none of them can be excluded.

"Future investigations of links between atmospheric dust loading and the Martian upper atmosphere are needed, involving joint investigations by ESA's Mars Express and Trace Gas Orbiter, and NASA's MAVEN mission. Early data from MAVEN seem to confirm the trends that we discovered."

"Similar investigations were made by the ASPERA instrument that was flown on board the Venus Express orbiter, enabling us to compare physical processes and conditions at two very different planets that both have weak magnetic fields," said Dmitri Titov, ESA's Mars Express Project Scientist.

"This demonstrates the value of using the same instrumentation to explore different worlds."

Credit: ESA

Dino-Killing Asteroid Could Have Thrust Earth into Two Years of Darkness

Dino-Killing Asteroid Could Have Thrust Earth into Two Years of Darkness:

Tremendous amounts of soot, lofted into the air from global wildfires following a massive asteroid strike 66 million years ago, would have plunged Earth into darkness for nearly two years, new research finds. This would have shut down photosynthesis, drastically cooled the planet, and contributed to the mass extinction that marked the end of the age of dinosaurs.

These new details about how the climate could have dramatically changed following the impact of a 10-kilometer-wide asteroid will be published Aug. 21 in the Proceedings of the National Academy of Sciences. The study, led by the National Center for Atmospheric Research (NCAR) with support from NASA and the University of Colorado Boulder, used a world-class computer model to paint a rich picture of how Earth’s conditions might have looked at the end of the Cretaceous Period, information that paleobiologists may be able to use to better understand why some species died, especially in the oceans, while others survived.

Scientists estimate that more than three-quarters of all species on Earth, including all non-avian dinosaurs, disappeared at the boundary of the Cretaceous-Paleogene periods, an event known as the K-Pg extinction. Evidence shows that the extinction occurred at the same time that a large asteroid hit Earth in what is now the Yucatán Peninsula. The collision would have triggered earthquakes, tsunamis, and even volcanic eruptions.

Scientists also calculate that the force of the impact would have launched vaporized rock high above Earth's surface, where it would have condensed into small particles known as spherules. As the spherules fell back to Earth, they would have been heated by friction to temperatures high enough to spark global fires and broil Earth's surface. A thin layer of spherules can be found worldwide in the geologic record.

"The extinction of many of the large animals on land could have been caused by the immediate aftermath of the impact, but animals that lived in the oceans or those that could burrow underground or slip underwater temporarily could have survived," said NCAR scientist Charles Bardeen, who led the study. "Our study picks up the story after the initial effects — after the earthquakes and the tsunamis and the broiling. We wanted to look at the long-term consequences of the amount of soot we think was created and what those consequences might have meant for the animals that were left."

Other study co-authors are Rolando Garcia and Andrew Conley, both NCAR scientists, and Owen “Brian” Toon, a researcher at the University of Colorado Boulder.

In past studies, researchers have estimated the amount of soot that might have been produced by global wildfires by measuring soot deposits still preserved in the geologic record. For the new study, Bardeen and his colleagues used the NCAR-based Community Earth System Model (CESM) to simulate the effect of the soot on global climate going forward. They used the most recent estimates of the amount of fine soot found in the layer of rock left after the impact (15,000 million tons), as well as larger and smaller amounts, to quantify the climate's sensitivity to more or less extensive fires.

In the simulations, soot heated by the Sun was lofted higher and higher into the atmosphere, eventually forming a global barrier that blocked the vast majority of sunlight from reaching Earth's surface. “At first it would have been about as dark as a moonlit night," Toon said.

While the skies would have gradually brightened, photosynthesis would have been impossible for more than a year and a half, according to the simulations. Because many of the plants on land would have already been incinerated in the fires, the darkness would likely have had its greatest impact on phytoplankton, which underpin the ocean food chain. The loss of these tiny organisms would have had a ripple effect through the ocean, eventually devastating many species of marine life.

The research team also found that photosynthesis would have been temporarily blocked even at much lower levels of soot. For example, in a simulation using only 5,000 million tons of soot — about a third of the best estimate from measurements — photosynthesis would still have been impossible for an entire year.

In the simulations, the loss of sunlight caused a steep decline in average temperatures at Earth's surface, with a drop of 50 degrees Fahrenheit (28 degrees Celsius) over land and 20 degrees Fahrenheit (11 degrees Celsius) over the oceans.

While Earth's surface cooled in the study scenarios, the atmosphere higher up in the stratosphere actually became much warmer as the soot absorbed light from the Sun. The warmer temperatures caused ozone destruction and allowed for large quantities of water vapor to be stored in the upper atmosphere. The water vapor then chemically reacted in the stratosphere to produce hydrogen compounds that led to further ozone destruction. The resulting ozone loss would have allowed damaging doses of ultraviolet light to reach Earth's surface after the soot cleared.

The large reservoir of water in the upper atmosphere formed in the simulations also caused the layer of sunlight-blocking soot to be removed abruptly after lingering for years, a finding that surprised the research team. As the soot began to settle out of the stratosphere, the air began to cool. This cooling, in turn, caused water vapor to condense into ice particles, which washed even more soot out of the atmosphere. As a result of this feedback loop — cooling causing precipitation that caused more cooling — the thinning soot layer disappeared in just a few months.

While the scientists think the new study gives a robust picture of how large injections of soot into the atmosphere can affect the climate, they also caution that the study has limitations.

For example, the simulations were run in a model of modern-day Earth, not a model representing what Earth looked like during the Cretaceous Period, when the continents were in slightly different locations. The atmosphere 66 million years ago also contained somewhat different concentrations of gases, including higher levels of carbon dioxide.

Additionally, the simulations did not try to account for volcanic eruptions or sulfur released from the Earth's crust at the site of the asteroid impact, which would have resulted in an increase in light-reflecting sulfate aerosols in the atmosphere.

The study also challenged the limits of the computer model's atmospheric component, known as the Whole Atmosphere Community Climate Model (WACCM).

"An asteroid collision is a very large perturbation — not something you would normally see when modeling future climate scenarios," Bardeen said. "So the model was not designed to handle this and, as we went along, we had to adjust the model so it could handle some of the event's impacts, such as warming of the stratosphere by over 200 degrees Celsius."

These improvements to WACCM could be useful for other types of studies, including modeling a "nuclear winter" scenario. Like global wildfires millions of years ago, the explosion of nuclear weapons could also inject large amounts of soot into the atmosphere, which could lead to a temporary global cooling.

"The amount of soot created by nuclear warfare would be much less than we saw during the K-Pg extinction," Bardeen said. "But the soot would still alter the climate in similar ways, cooling the surface and heating the upper atmosphere, with potentially devastating effects."

Credit: ucar.edu

Best Ever Image of a Star’s Surface and Atmosphere

Best Ever Image of a Star’s Surface and Atmosphere:

Using ESO’s Very Large Telescope Interferometer astronomers have constructed the most detailed image ever of a star — the red supergiant star Antares. They have also made the first map of the velocities of material in the atmosphere of a star other than the Sun, revealing unexpected turbulence in Antares’s huge extended atmosphere. The results were published in the journal Nature.

To the unaided eye the famous, bright star Antares shines with a strong red tint in the heart of the constellation of Scorpius (The Scorpion). It is a huge and comparatively cool red supergiant star in the late stages of its life, on the way to becoming a supernova.

A team of astronomers, led by Keiichi Ohnaka, of the Universidad Católica del Norte in Chile, has now used ESO’s Very Large Telescope Interferometer (VLTI) at the Paranal Observatory in Chile to map Antares’s surface and to measure the motions of the surface material. This is the best image of the surface and atmosphere of any star other than the Sun.

The VLTI is a unique facility that can combine the light from up to four telescopes, either the 8.2-meter Unit Telescopes, or the smaller Auxiliary Telescopes, to create a virtual telescope equivalent to a single mirror up to 200 metes across. This allows it to resolve fine details far beyond what can be seen with a single telescope alone.

“How stars like Antares lose mass so quickly in the final phase of their evolution has been a problem for over half a century,” said Keiichi Ohnaka, who is also the lead author of the paper. “The VLTI is the only facility that can directly measure the gas motions in the extended atmosphere of Antares — a crucial step towards clarifying this problem. The next challenge is to identify what’s driving the turbulent motions.”

Using the new results the team has created the first two-dimensional velocity map of the atmosphere of a star other than the Sun. They did this using the VLTI with three of the Auxiliary Telescopes and an instrument called AMBER to make separate images of the surface of Antares over a small range of infrared wavelengths. The team then used these data to calculate the difference between the speed of the atmospheric gas at different positions on the star and the average speed over the entire star. This resulted in a map of the relative speed of the atmospheric gas across the entire disc of Antares — the first ever created for a star other than the Sun.

The astronomers found turbulent, low-density gas much further from the star than predicted, and concluded that the movement could not result from convection, that is, from large-scale movement of matter which transfers energy from the core to the outer atmosphere of many stars. They reason that a new, currently unknown, process may be needed to explain these movements in the extended atmospheres of red supergiants like Antares.

“In the future, this observing technique can be applied to different types of stars to study their surfaces and atmospheres in unprecedented detail. This has been limited to just the Sun up to now,” concludes Ohnaka. “Our work brings stellar astrophysics to a new dimension and opens an entirely new window to observe stars.”

Credit: ESO

Black Holes: Scientists 'Excited' by Observations Suggesting Formation Scenarios

Black Holes: Scientists 'Excited' by Observations Suggesting Formation Scenarios:

Physicists have described how observations of gravitational waves limit the possible explanations for the formation of black holes outside of our galaxy; either they are spinning more slowly than black holes in our own galaxy or they spin rapidly but are ‘tumbled around’ with spins randomly oriented to their orbit. The paper, published in Nature, is based on data that came about following landmark observations of gravitational waves by the LIGO gravitational wave detector in 2015 and again in 2017.

In our own galaxy we have been able to electromagnetically observe black holes orbited by stars and map their behavior – notably their rapid spinning.

Gravitational waves carry information about the dramatic origins of black that cannot otherwise be obtained. Physicists concluded that the first detected gravitational waves, in September 2015, were produced during the final fraction of a second of the merger of two black holes to produce a single, more massive spinning black hole. Collisions of two black holes had been predicted, but never observed.

As such, gravitational waves present the best and only way to get a deep look at the population of stellar-mass binary black holes beyond our galaxy. This paper states that the black holes seen via gravitational waves are different to those previously seen in our galaxy in one of two possible ways.

The first possibility is that the black holes are spinning slowly. If that is the case it suggests that something different is happening to the stars that form these black holes than those observed in our galaxy.

The second possibility is that the black holes are spinning rapidly, much like those in our galaxy, but have been ‘tumbled’ during formation and are therefore no longer aligned with orbit. If this is the case, it would mean that the black holes are living in a dense environment – most likely within star clusters. That would make for a considerably more dynamic formation.

There is, however, also the chance that both possibilities are true – that there are instances of black holes spinning slowly in the field and instances of black holes spinning rapidly in a dense environment.

Dr Will Farr, from the School of Physics and Astronomy at the University of Birmingham, explained, “By presenting these two explanations for the observed behavior, and ruling out other scenarios, we are providing those who study and try to explain the formation of black holes a target to hit. In our field, knowing the question to ask is almost as important as getting the answer itself.”

Professor Ilya Mandel, also from the University of Birmingham, added “We will know which explanation is right within the next few years. This is something that has only been made possible by the recent LIGO detections of gravitational waves. This field is in its infancy; I’m confident that in the near future we will look back on these first few detections and rudimentary models with nostalgia and a much better understanding of how these exotic binary systems form.”

The team was led by researchers from the University of Birmingham in the UK alongside the University of Maryland, University of Chicago and Kavli Institute for Theoretical Physics in the US.

Credit: birmingham.ac.uk

Scientists Detect First X-rays from Mystery Supernovas

Scientists Detect First X-rays from Mystery Supernovas:

Exploding stars lit the way for our understanding of the universe, but researchers are still in the dark about many of their features. A team of scientists, including scholars from the University of Chicago, appear to have found the first X-rays coming from type Ia supernovas. Their findings are published online Aug. 23 in the Monthly Notices of the Royal Astronomical Society.

Astronomers are fond of type Ia supernovas, created when a white dwarf star in a two-star system undergoes a thermonuclear explosion, because they burn at a specific brightness. This allows scientists to calculate how far away they are from Earth, and thus to map distances in the universe. But a few years ago, scientists began to find type Ia supernovas with a strange optical signature that suggested they carried a very dense cloak of circumstellar material surrounding them.

Such dense material is normally only seen from a different type of supernova called type II, and is created when massive stars start to lose mass. The ejected mass collects around the star; then, when the star collapses, the explosion sends a shockwave hurtling at supersonic speeds into this dense material, producing a shower of X-rays. Thus we regularly see X-rays from type II supernovas, but they have never been seen from type Ia supernovas.

When the UChicago-led team studied the supernova 2012ca, recorded by the Chandra X-ray Observatory, however, they detected X-ray photons coming from the scene.

“Although other type Ia’s with circumstellar material were thought to have similarly high densities based on their optical spectra, we have never before detected them with X-rays,” said study co-author Vikram Dwarkadas, research associate professor in the Department of Astronomy and Astrophysics.

The amounts of X-rays they found were small—they counted 33 photons in the first observation a year and a half after the supernova exploded, and ten in another about 200 days later—but present.

“This certainly appears to be a Ia supernova with substantial circumstellar material, and it looks as though it’s very dense,” he said. “What we saw suggests a density about a million times higher what we thought was the maximum around Ia’s.”

It’s thought that white dwarfs don’t lose mass before they explode. The usual explanation for the circumstellar material is that it would have come from a companion star in the system, but the amount of mass suggested by this measurement was very large, Dwarkadas said—far larger than one could expect from most companion stars. “Even the most massive stars do not have such high mass-loss rates on a regular basis,” he said. “This once again raises the question of how exactly these strange supernovas form.”

“If it’s truly a Ia, that’s a very interesting development because we have no idea why it would have so much circumstellar material around it,” he said.

“It is surprising what you can learn from so few photons,” said lead author and Caltech graduate student Chris Bochenek; his work on the study formed his undergraduate thesis at UChicago. “With only tens of them, we were able to infer that the dense gas around the supernova is likely clumpy or in a disk.”

More studies to look for X-rays, and even radio waves coming off these anomalies, could open a new window to understanding such supernovas and how they form, the authors said.

Credit: uchicago.edu

Study Captures Science Data from Great American Eclipse

Study Captures Science Data from Great American Eclipse:

Two NASA WB-57F research aircraft successfully tracked the August 21 solar eclipse as part of a NASA project led by Southwest Research Institute (SwRI) to study the solar corona and Mercury’s surface. “The visible and infrared data look spectacular,” said SwRI senior research scientist Dr. Amir Caspi, principal investigator of the project. “We’re already seeing some surprising features, and we are very excited to learn what the detailed analysis will reveal.”

The team began initial analysis of the data gathered during the flights, showing clear images of the Sun’s outer atmosphere and thermal images of Mercury’s surface. Initial results are expected to be released in a few months and presented at the fall meeting of the American Geophysical Union in December 2017.

Total solar eclipses are unique opportunities for scientists to study the hot atmosphere above the Sun’s visible surface. The faint light from the corona is usually overpowered by intense emissions from the Sun itself. During a total eclipse, however, the Moon blocks the glare from the bright solar disk and darkens the sky, allowing weaker coronal emissions to be observed.

“This is the best observed eclipse ever,” said Dr. Dan Seaton, co-investigator of the project from the University of Colorado. “With the results from the WB-57s and complementary observations from space and other experiments on the ground, we have an opportunity to answer some of the most fundamental questions about the nature of the corona.”

The eclipse also provided an opportunity for scientists to study Mercury, which is notoriously difficult to image because of its proximity to the Sun. “The infrared images of Mercury were much brighter than we originally expected,” said Caspi. Using infrared observations in near darkness through very little atmosphere, the team received data enabling it, for the first time, to attempt to estimate the surface temperature distribution over the planet’s night side. “It will be incredibly interesting to dig into these data,” said Dr. Constantine Tsang, SwRI senior research scientist and a co-investigator on the project.

The team used stabilized telescopes with sensitive, high-speed, visible-light and infrared cameras aboard the research aircraft from an altitude of 50,000 feet, providing a significant advantage over ground-based observations. These are the first astronomical observations for the Houston-based WB-57Fs. Southern Research, of Birmingham, Ala., built the Airborne Imaging and Recording Systems (AIRS) and worked with the scientific team to upgrade its DyNAMITE telescopes onboard the planes with solar filters and improved data recorders and operating software.

“The pilots, instrument operators, and engineers did a phenomenal job getting us exactly the data we asked for,” said Caspi. “Achieving this quality of measurement required an enormous effort and precise timing, and everyone hit their mark exactly. I am honored to be part of such an exceptionally talented and professional team, and grateful for everyone’s dedication and hard work.”

The SwRI-led team includes scientists from the University of Colorado, the National Center for Atmospheric Research High Altitude Observatory, and the Smithsonian Astrophysical Observatory, as well as international colleagues at Trinity College Dublin in Ireland and the Royal Observatory of Belgium.

Credit: swri.org