Connect with us

(5 August 2020 – Rice University) Using data from NASA’s InSight Lander on Mars, Rice University seismologists have made the first direct measurements of three subsurface boundaries from the crust to the core of the red planet.

An artist’s impression of Mars’ inner structure. The topmost layer is the crust, and beneath it is the mantle, which rests on a solid inner core. (courtesy: NASA/JPL-Caltech)

“Ultimately it may help us understand planetary formation,” said Alan Levander, co-author of a study available online this week in Geophysical Research Letters. While the thickness of Mars’ crust and the depth of its core have been calculated with a number of models, Levander said the InSight data allowed for the first direct measurements, which can be used to check models and ultimately to improve them.

“In the absence of plate tectonics on Mars, its early history is mostly preserved compared with Earth,” said study co-author Sizhuang Deng, a Rice graduate student. “The depth estimates of Martian seismic boundaries can provide indications to better understand its past as well as the formation and evolution of terrestrial planets in general.”

Finding clues about Mars’ interior and the processes that formed it are key goals for InSight, a robotic lander that touched down in November 2018. The probe’s dome-shaped seismometer allows scientists to listen to faint rumblings inside the planet, in much the way that a doctor might listen to a patient’s heartbeat with a stethoscope.

Seismometers measure vibrations from seismic waves. Like circular ripples that mark the spot where a pebble disturbed the surface of a pond, seismic waves flow through planets, marking the location and size of disturbances like meteor strikes or earthquakes, which are aptly called marsquakes on the red planet. InSight’s seismometer recorded more than 170 of these from February to September 2019.

Seismic waves are also subtly altered as they pass through different kinds of rock. Seismologists have studied the patterns in seismographic recordings on Earth for more than a century and can use them to map the location of oil and gas deposits and much deeper strata.

“The traditional way to investigate structures beneath Earth is to analyze earthquake signals using dense networks of seismic stations,” said Deng. “Mars is much less tectonically active, which means it will have far fewer marsquake events compared with Earth. Moreover, with only one seismic station on Mars, we cannot employ methods that rely on seismic networks.”

Levander, Rice’s Carey Croneis Professor of Earth, Environmental and Planetary Sciences, and Deng analyzed InSight’s 2019 seismology data using a technique called ambient noise autocorrelation. “It uses continuous noise data recorded by the single seismic station on Mars to extract pronounced reflection signals from seismic boundaries,” Deng said.

The first boundary Deng and Levander measured is the divide between Mars’ crust and mantle almost 22 miles (35 kilometers) beneath the lander.

The second is a transition zone within the mantle where magnesium iron silicates undergo a geochemical change. Above the zone, the elements form a mineral called olivine, and beneath it, heat and pressure compress them into a new mineral called wadsleyite. Known as the olivine-wadsleyite transition, this zone was found 690-727 miles (1,110-1,170 kilometers) beneath InSight.

“The temperature at the olivine-wadsleyite transition is an important key to building thermal models of Mars,” Deng said. “From the depth of the transition, we can easily calculate the pressure, and with that, we can derive the temperature.”

The third boundary he and Levander measured is the border between Mars’ mantle and its iron-rich core, which they found about 945-994 miles (1,520-1,600 kilometers) beneath the lander. Better understanding this boundary “can provide information about the planet’s development from both a chemical and thermal point of view,” Deng said.

The research was supported by Rice’s Department of Earth, Environmental and Planetary Sciences.

Source link

0

Space

Astronomers solve mystery of how planetary nebulae are shaped

Astronomers solve mystery of how planetary nebulae are shaped

(17 September 2020 – Center for Astrophysics | Harvard & Smithsonian) Following extensive observations of stellar winds around cool evolved stars scientists have figured out how planetary nebulae get their mesmerizing shapes.

The findings, published in Science, contradict common consensus, and show that not only are stellar winds aspherical, but they also share similarities with planetary nebulae.

Gallery of stellar winds around cool aging stars, showing a variety of morphologies, including disks, cones, and spirals. The blue color represents material that is coming towards you, red is material that is moving away from you. Image 8, in particular, shows the stellar wind of R Aquilae, which resembles the structure of rose petals. (courtesy: L. Decin, ESO/ALMA)

An international team of astronomers focused their observations on stellar winds—particle flows—around cool red giant stars, also known as asymptotic giant branch (AGB) stars. “AGB stars are cool luminous evolved stars that are in the last stages of evolution just before turning into a planetary nebula,” said Carl Gottlieb, an astronomer at the Center for Astrophysics | Harvard & Smithsonian, and a co-author on the paper. “Through their winds, AGB stars contribute about 85% of the gas and 35% of the dust from stellar sources to the Galactic Interstellar Medium and are the dominant suppliers of pristine building blocks of interstellar material from which planets are ultimately formed.”

Despite being of major interest to astronomers, a large, detailed collection of observational data for the stellar winds surrounding AGB stars—each made using the exact same method—was lacking prior to the study, which resulted in a long-standing scientific misconception: that stellar winds have an overall spherical symmetry. “The lack of such detailed observational data caused us to initially assume that the stellar winds have an overall spherical geometry, much like the stars they surround,” said Gottlieb. “Our new observational data shapes a much different story of individual stars, how they live, and how they die. We now have an unprecedented view of how stars like our Sun will evolve during the last stages of their evolution.”

Observations with the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile revealed something strange: the shape of the stellar winds didn’t conform with scientific consensus. “We noticed these winds are anything but round,” said Professor Leen Decin of KU Leuven University in Belgium, and the lead author on the paper. “Some of them are actually quite similar to planetary nebulae.” The new findings may have a significant impact on calculations of galactic and stellar evolution, most pointedly for the evolution of Sun-like stars. “Our findings change a lot,” said Decin. “Since the complexity of stellar winds was not accounted for in the past, any previous estimate of the mass-loss rate of old stars could be wrong by up to a factor of 10.”

The observations revealed many different shapes, further connecting stellar wind formation to that of planetary nebulae. “The winds we observed exhibit various shapes that are similar to planetary nebulae,” said Gottlieb. “Some are disk-like, while others are shaped like eyes, spiral structures, and even arcs.”

Astronomers quickly realized that the shapes weren’t formed randomly, and that companions—low-mass stars and heavy planets—in the vicinity of the AGB stars were influencing the shapes and patterns. “Just like a spoon that you stir in a cup of coffee with some milk can create a spiral pattern, the companion sucks material towards it as it revolves around the star and shapes the stellar wind,” said Decin. “All of our observations can be explained by the fact that the stars have a companion.”

In addition, the study provides a strong foundation for understanding Sun-like stars and the future of the Sun itself. “In about five billion years, the Sun will become more luminous,” said Gottlieb. “Its radius will expand to a length that is comparable to the current distance between the Sun and Earth, and it will enter the AGB phase.” Decin added, “Jupiter or even Saturn—because they have such a big mass—are going to influence whether the Sun spends its last millennia at the heart of a spiral, a butterfly or any of the other entrancing shapes we see in planetary nebulae today. Our current simulations predict that Jupiter and Saturn will create a weak spiral structure in the wind of the Sun once it is an AGB star.”

About Center for Astrophysics | Harvard & Smithsonian

Headquartered in Cambridge, Mass., the Center for Astrophysics | Harvard & Smithsonian (CfA) is a collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Source link

0
Continue Reading

Space

Global helium abundance measurements in solar corona

Global helium abundance measurements in solar corona

(18 September 2020 – Naval Research Laboratory) Two U.S. Naval Research Laboratory Space Science Division (SSD) researchers joined an international cadre of scientists July 27 in presenting the results of the first simultaneous global solar corona images of the helium and hydrogen emission that is helping scientists to better understand the space environment.

The paper, “Global Helium Abundance Measurements in the Solar Corona,” was published online in Nature Astronomy and discusses the abundance of helium relative to hydrogen in the solar corona, the outer atmosphere of the sun, seen from earth only during eclipses.

NRL Astrophysicist Dennis Wang, Ph.D., software lead for the HElium Resonance Scattering in the Corona and HEliosphere (HERSCHEL) rocket flight, was responsible for flight and ground software. His NRL colleague, Research Physicist Martin Laming, Ph.D., managed the new model of element abundance fractionation, to include helium.

A composite image of the Sun showing the hydrogen (left) and helium (center and right) in the low corona. The helium at depletion near the equatorial regions is evident. (courtesy: NASA)

“Understanding space weather is important for space situational awareness, that is, forecasting and mitigating the effects of solar activity on Navy and Defense Department satellites,” said Laming. “This was one case where instead of explaining the observations after the fact, I was able to see a prediction I had made come true.”

The HERSCHEL sounding rocket, launched Sep. 14, 2009, provided a number of technological advances in space-based remote sensing. Using a concept developed at NRL for a coronagraph functioning in the extreme ultraviolet regime of the electromagnetic spectrum, the helium coronagraph obtained the first images of the solar atmosphere in the region of the solar wind source surface from light resonantly scattered from helium ions.

The leading model for solar wind variability used by the Department of Defense and National Oceanic and Atmospheric Administration space weather forecasters is an NRL SSD product, known as the Wang, Sheely, Arge Model which is based on simple assumptions about the relation of the solar magnetic field structure and the solar wind, and is reasonably successful in predicting the overall variability of the solar wind as it reaches Earth.

Geomagnetic storms impact radio frequency transmission at frequencies refracted, or reflected, by the ionosphere. The Navy uses magnetic sensors in various battlespace applications, which could be disrupted during large geomagnetic storms and Coronal Mass Ejections. These are major reasons why the Navy is interested in disruptions of the Earth’s magnetic field structure in these measurements.

“There is a long chain of work efforts that go from fundamental understanding of the solar atmosphere, to specifying the observables that need to be monitored before we eventually get to reliable Space Weather forecasts,” said Laming. “In the future, service members should anticipate more reliable satellite-based Command, Control, Communications, Computers, Intelligence, Surveillance, and Reconnaissance.”

Laming demonstrates a strong belief in his model’s prediction capability and his understanding of the sun’s corona adding, “I think we all have more confidence in my model and the conclusions one might draw from it.”

About the U.S. Naval Research Laboratory

NRL is a scientific and engineering command dedicated to research that drives innovative advances for the Navy and Marine Corps from the seafloor to space and in the information domain. NRL headquarters is located in Washington, D.C., with major field sites in Stennis Space Center, Mississippi; Key West, Florida; and Monterey, California, and employs approximately 2,500 civilian scientists, engineers and support personnel.

Source link

0
Continue Reading

Space

hints of fresh ice in northern hemisphere

hints of fresh ice in northern hemisphere

(18 September 2020 – JPL) New composite images made from NASA’s Cassini spacecraft are the most detailed global infrared views ever produced of Saturn’s moon Enceladus. And data used to build those images provides strong evidence that the northern hemisphere of the moon has been resurfaced with ice from its interior.

Cassini’s Visible and Infrared Mapping Spectrometer (VIMS) collected light reflected off Saturn, its rings and its ten major icy moons – light that is visible to humans as well as infrared light. VIMS then separated the light into its various wavelengths, information that tells scientists more about the makeup of the material reflecting it.

The VIMS data, combined with detailed images captured by Cassini’s Imaging Science Subsystem, were used to make the new global spectral map of Enceladus.

In these detailed infrared images of Saturn’s icy moon Enceladus, reddish areas indicate fresh ice that has been deposited on the surface. (courtesy: NASA/JPL-Caltech/University of Arizona/LPG/CNRS/University of Nantes/Space Science Institute)

Cassini scientists discovered in 2005 that Enceladus – which looks like a highly reflective, bright white snowball to the naked eye – shoots out enormous plumes of ice grains and vapor from an ocean that lies under the icy crust. The new spectral map shows that infrared signals clearly correlate with that geologic activity, which is easily seen at the south pole. That’s where the so-called “tiger stripe” gashes blast ice and vapor from the interior ocean.

But some of the same infrared features also appear in the northern hemisphere. That tells scientists not only that the northern area is covered with fresh ice but that the same kind of geologic activity – a resurfacing of the landscape – has occurred in both hemispheres. The resurfacing in the north may be due either to icy jets or to a more gradual movement of ice through fractures in the crust, from the subsurface ocean to the surface.

“The infrared shows us that the surface of the south pole is young, which is not a surprise because we knew about the jets that blast icy material there,” said Gabriel Tobie, VIMS scientist with the University of Nantes in France and co-author of the new research published in Icarus.

“Now, thanks to these infrared eyes, you can go back in time and say that one large region in the northern hemisphere appears also young and was probably active not that long ago, in geologic timelines.”

Managed by NASA’s Jet Propulsion Laboratory in Southern California, Cassini was an orbiter that observed Saturn for more than 13 years before exhausting its fuel supply. The mission plunged it into the planet’s atmosphere in September 2017, in part to protect Enceladus, which has the potential of holding conditions suitable for life, with its ocean likely heated and churned by hydrothermal vents like those on Earth’s ocean floors.

The Cassini-Huygens mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. JPL, a division of Caltech in Pasadena, manages the mission for NASA’s Science Mission Directorate in Washington. JPL designed, developed and assembled the Cassini orbiter.

Source link

0
Continue Reading

Trending