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  • richardmitnick 12:59 pm on September 25, 2021 Permalink | Reply
    Tags: "Misfit Meteorite Sheds Light on Solar System History", , Cosmochemistry, , , The Nedagolla meteorite   

    From Sky & Telescope : “Misfit Meteorite Sheds Light on Solar System History” 

    From Sky & Telescope

    September 21, 2021
    Jure Japelj

    Scientists have discovered the first meteorite that doesn’t fall into one of two fundamental groups. The meteorite provides a unique glimpse into the era of asteroid formation and migration.

    1
    Artist’s impression of the asteroid belt. Credit: NASA / JPL-Caltech (US).

    The meteorite would be just another one among thousands found on Earth if it weren’t for its unusual composition. Researchers have long tried to understand its origin, and now they might have solved the mystery. In a recent study to be published in Meteoritics & Planetary Science, scientists found that the Nedagolla meteorite is a product of a collision between two asteroids of distinct origin. Its unique history opens up a new window into the research of the early stages of solar system formation.

    Two Meteorite Families

    Meteorites are time capsules that illuminate the era of planet formation. The solar system formed from a cloud of interstellar gas and dust that collapsed under its own gravity. Particles within the resulting protoplanetary disk collided and stuck, forming ever larger planetesimals, which became the parent bodies of the meteorites found on Earth.

    Meteorites come in different flavors [Space Science Reviews]. Depending on whether iron or silicates dominate, meteorites are traditionally classified as iron, stony, or stony-iron. Composition also depends on whether the meteorites originate from bodies that underwent melting, or whether the parent body was unmelted and therefore more pristine. By these classifiers, Nedagolla is an ungrouped iron meteorite.

    But one can also look at isotopes. Isotopes are elements with the same number of protons but a different number of neutrons, and they can carry a lot of information, including the time of a rock’s formation.

    “About 10 years ago, the community realized that there is an isotopic dichotomy in meteoritic material,” says graduate student Fridolin Spitzer (University of Münster [Westfälische Wilhelms-Universität Münster] (DE)), who was first author of the new study. Cosmochemists thus use isotopes to classify meteorites of all sorts, regardless of their chemical composition, as either non-carbonaceous chondrite (NC) or the carbonaceous chondrite (CC). (These groups were initially differentiated by the amount of carbon, but now the terms are used more generally.)

    There is only one exception: “Nedagolla is the first one that does not consistently fall into one of the two categories but seems to fall in between,” says Spitzer.

    Scientists suspect that the two isotope classes formed in two different parts of the protoplanetary disk: The NCs in the disk’s inner part and the CCs in the outer solar system, beyond the Jupiter´s orbit. So where does that put the Nedagolla meteorite?

    Scientists have discovered the first meteorite that doesn’t fall into one of two fundamental groups. The meteorite provides a unique glimpse into the era of asteroid formation and migration.
    Artist’s impression of the asteroid belt
    NASA / JPL-Caltech

    A fireball embellished the night sky over India on January 23, 1870. Accompanied by a thunderous detonation, the fiery mass crashed in the village of Nedagolla with enough force to leave the bystanders stunned. The impact left behind a bit over 4 kilograms of cosmic rock — the Nedagolla meteorite.

    The meteorite would be just another one among thousands found on Earth if it weren’t for its unusual composition. Researchers have long tried to understand its origin, and now they might have solved the mystery. In a recent study to be published in Meteoritics & Planetary Science (preprint available here), scientists found that the Nedagolla meteorite is a product of a collision between two asteroids of distinct origin. Its unique history opens up a new window into the research of the early stages of solar system formation.
    Two Meteorite Families

    Meteorites are time capsules that illuminate the era of planet formation. The solar system formed from a cloud of interstellar gas and dust that collapsed under its own gravity. Particles within the resulting protoplanetary disk collided and stuck, forming ever larger planetesimals, which became the parent bodies of the meteorites found on Earth.

    Meteorites come in different flavors. Depending on whether iron or silicates dominate, meteorites are traditionally classified as iron, stony, or stony-iron. Composition also depends on whether the meteorites originate from bodies that underwent melting, or whether the parent body was unmelted and therefore more pristine. By these classifiers, Nedagolla is an ungrouped iron meteorite.

    But one can also look at isotopes. Isotopes are elements with the same number of protons but a different number of neutrons, and they can carry a lot of information, including the time of a rock’s formation.

    “About 10 years ago, the community realized that there is an isotopic dichotomy in meteoritic material,” says graduate student Fridolin Spitzer (University of Münster, Germany), who was first author of the new study. Cosmochemists thus use isotopes to classify meteorites of all sorts, regardless of their chemical composition, as either non-carbonaceous chondrite (NC) or the carbonaceous chondrite (CC). (These groups were initially differentiated by the amount of carbon, but now the terms are used more generally.)

    There is only one exception: “Nedagolla is the first one that does not consistently fall into one of the two categories but seems to fall in between,” says Spitzer.

    Scientists suspect that the two isotope classes formed in two different parts of the protoplanetary disk: The NCs in the disk’s inner part and the CCs in the outer solar system, beyond the Jupiter´s orbit. So where does that put the Nedagolla meteorite?

    Asteroid Migrations and Collisions

    After performing a new and independent analysis of the meteorite’s composition, the team proposes that its unique isotopic imprint comes from a collision of NC and CC planetesimals. “The two bodies collided, and this induced melting because of high impact velocities, and it induced mixing of materials from these two bodies,” explains Spitzer.

    Here things become interesting. Most meteorites originate from the asteroid belt, a region between the orbits of Mars and Jupiter. So, the CC-type meteorites had to migrate to the inner part of the solar system at some point, otherwise the Nedagolla meteorite wouldn´t exist.

    1
    A schematic view of the protoplanetary disk in the first few million years after its formation. The NC (red) and CC (blue) planetesimals formed in the inner and outer disk, respectively. The growing Jupiter might have separated the two classes. Credit: Bermingham et al. 2020.

    “The reason why we have any CC material to analyze on Earth, which is in itself an NC body, is because, during the disk evolution, planets like Jupiter migrated inwards and outwards, scattering material around the Solar System,” says Katherine Bermingham (Rutgers University).

    But the details are still murky. For example, did Jupiter’s movements create the isotopic divide? And why did one region of the disk have a consistently different mixture of material compared to the other?

    With the Nedagolla meteorite, scientists obtained the first isotopic evidence that the NC and CC bodies mingled. Its composition suggests that at least the CC body had a metallic core. Furthermore, the formative collision couldn’t have happened earlier than about 7 million years after the disk’s formation.

    Such information measured for a larger sample of similar meteorites would be invaluable. “I think it is important that the community does more of this kind of work to see if we can figure out better time constraints on NC-CC mixing,” says Bermingham. “There are a lot of ungrouped iron meteorites out there, and maybe this signature will be found in those that we haven’t studied yet.”

    See the full article here .

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    Please help promote STEM in your local schools.


    Stem Education Coalition

    Sky & Telescope, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

    Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

    Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

    “Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”

     
  • richardmitnick 2:03 pm on July 10, 2021 Permalink | Reply
    Tags: "New Type of Stellar Grain Discovered", Allende meteorite (which fell to Earth in 1969), CAIs: calcium- and aluminum-rich inclusions found in certain meteorites., , Cosmochemistry, , , Rubidium-87, Unusually high amounts of strontium-84-a relatively rare light isotope of the element strontium that is so-named for the 84 neutrons in its nucleus.   

    From California Institute of Technology (US) : “New Type of Stellar Grain Discovered” 

    Caltech Logo

    From California Institute of Technology (US)

    July 09, 2021
    Robert Perkins
    (626) 395‑1862
    rperkins@caltech.edu

    Unusual chemistry of grain could tell scientists more about the origin of Earth’s water.

    1
    Allende meteorite (which fell to Earth in 1969)

    Scientists have discovered a new type of star dust whose composition indicates that it formed during a rare form of nucleosynthesis (the process through which new atomic nuclei are created) and could shed new light on the history of water on Earth.

    A team led by cosmochemists from Caltech and Victoria University of Wellington (NZ) studied ancient minerals aggregates within the Allende meteorite (which fell to Earth in 1969) and found that many of them had unusually high amounts of strontium-84-a relatively rare light isotope of the element strontium that is so-named for the 84 neutrons in its nucleus.

    “Strontium-84 is part of a family of isotopes produced by a nucleosynthetic process, named the p-process, which remains mysterious,” says Caltech’s François L. H. Tissot, assistant professor of geochemistry. “Our results points to the survival of grains possibly containing pure strontium-84. This is exciting, as the physical identification of such grains would provide a unique chance to learn more about the p-process.”

    Tissot and collaborator Bruce L. A. Charlier of Victoria University of Wellington are co-lead authors on a study describing the findings that was published in Science Advances on July 9.

    “This is really interesting,” Charlier says. “We want to know what the nature of this material is and how it fits into the mix of ingredients that went to form the recipe for the planets.”

    Strontium (atomic symbol: Sr), a chemically reactive metal, has four stable isotopes: strontium-84 and its heavier cousins that have 86, 87, or 88 neutrons in their nuclei.

    3
    Strontium. https://www.britannica.com/science/strontium.

    Scientists have found that strontium is useful when attempting to date objects from the early solar system because one of its heavy isotopes, strontium-87, is produced by the decay of the radioactive isotope rubidium-87 (atomic symbol: Rb).

    4
    Rubidium. https://www.britannica.com/science/rubidium

    Rubidium-87 has a very long half-life, 49 billion years, which is more than three times the age of the universe. Half-life represents the amount of time required for the radioactivity of an isotope to drop to one-half its original value, allowing these isotopes to serve as chronometers for dating samples on varying time scales. The most famous radioactive isotope used for dating is carbon-14, the radioactive isotope of carbon; with its half-life of roughly 5,700 years, carbon-14 can be used to determine the ages of organic (carbon-containing) materials on human timescales, up to about 60,000 years. Rubidium-87, in contrast, can be used to date the oldest objects in the universe, and, closer to home, the objects in the solar system.

    What is particularly attractive about using the Rb–Sr pair for dating is that rubidium is a volatile element—that is, it tends to evaporate to form a gas phase at even relatively low temperatures—while strontium is not volatile. As such, rubidium is present at a higher proportion in solar system objects that are rich in other volatiles (such as water), because they formed at lower temperatures.

    5
    A CAI inclusion in the Allende meteorite. This inclusion contains strontium, which was isolated and studied by Tissot and colleagues.

    Counterintuitively, Earth has an Rb/Sr ratio that is 10 times lower than that of water-rich meteorites, implying that the planet either accreted from water-poor (and thus rubidium-poor) materials or it accreted from water-rich materials but lost most of its water over time as well as its rubidium. Understanding which of these scenarios took place is important for understanding the origin of water on Earth.

    In theory, the Rb–Sr chronometer should be able to tease apart these two scenarios, as the amount of Sr-87 produced by radioactive decay in a given amount of time will not be the same if Earth started with a lot of rubidium versus less of the material.

    In the latter scenario, i.e., with less rubidium, the newly formed Earth would have been poor in volatiles such as water, thus the amount of Sr-87 in the earth and in volatile-poor meteorites would be similar to that observed in the oldest-known solar system solids, the so-called CAIs. CAIs are calcium- and aluminum-rich inclusions found in certain meteorites. Dating back 4.567 billion years, CAIs represent the first objects that condensed in the early solar nebula, the flattened, rotating disk of gas and dust from which the solar system was born. As such, CAls offer a geologic window into how and from what type of stellar materials the solar system formed.

    “They are critical witnesses to the processes that were happening while the solar system was forming,” says Tissot.

    However, the composition of CAIs has long muddled scientists’ ability to determine if Earth formed mostly dry or not. That is because CAls, unlike other solar-system materials, have anomalous ratios of the four strontium isotopes, with a slightly elevated proportion of strontium-84. Thus, they pose a challenge to the validity of the rubidium–strontium dating system. And they also raise a key question: Why are they different?

    To learn more, Tissot and Charlier took nine specimens of so-called fine-grained CAls. Fine-grained CAIs have preserved their condensate (that is, snowflake-like) texture, which testifies to their pristine nature.

    The team painstakingly leached out these CAIs by bathing them in gradually harsher acids to strip away the more chemically reactive minerals (and the strontium they contain), leaving a concentrate of only the most resistant fraction. The final sample contained almost pure Sr-84, while a typical sample is composed of 0.56 percent Sr-84.

    “Step-leaching is a little bit of a blunt instrument because you are not entirely sure what exactly it is you are destroying at each step,” Charlier says. “But the nub of what we’ve found is, once you have stripped away 99 percent of the common components within the CAIs, what we are left with is something highly exotic that we weren’t expecting.”

    “The signature is unlike anything else found in the solar system,” Tissot says. The grains carrying this signature, Tissot and Charlier concluded, must have formed prior to the birth of the solar system and survived that cataclysmic process during which stellar grains were heated to extremely high temperatures, vaporized, and then condensed into solid materials.

    Given the relative abundance of strontium-84, the discovery points to the likely existence in meteorites of nanometer-sized grains containing almost pure strontium-84 that were formed during a rare nucleosynthetic process before the formation of the solar system itself. The nature of these grains is still a mystery, as only their isotopic composition in strontium reveals their existence. But the high levels of Sr-84 in the CAIs suggest that Earth and volatile-poor meteorites have more strontium-87 than CAIs, favoring the scenario in which Earth accreted with more water and volatile elements, which were subsequently lost within the first few million years after their formation.

    Co-authors include Caltech graduate student Ren T. Marquez, Hauke Vollstaedt of Thermo Fisher Scientific in Bremen, Germany, Nicolas Dauphas of the University of Chicago (US), and Colin J. N. Wilson of Victoria University of Wellington. Funding to support this research came from Victoria University of Wellington, Caltech, National Aeronautics Space Agency (US), the National Science Foundation (US), and Massachusetts Institute of Technology (US).

    See the full article here .


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    Please help promote STEM in your local schools.

    Stem Education Coalition

    Caltech campus

    The California Institute of Technology (US) is a private research university in Pasadena, California. The university is known for its strength in science and engineering, and is one among a small group of institutes of technology in the United States which is primarily devoted to the instruction of pure and applied sciences.

    Caltech was founded as a preparatory and vocational school by Amos G. Throop in 1891 and began attracting influential scientists such as George Ellery Hale, Arthur Amos Noyes, and Robert Andrews Millikan in the early 20th century. The vocational and preparatory schools were disbanded and spun off in 1910 and the college assumed its present name in 1920. In 1934, Caltech was elected to the Association of American Universities, and the antecedents of National Aeronautics and Space Administration (US)’s Jet Propulsion Laboratory, which Caltech continues to manage and operate, were established between 1936 and 1943 under Theodore von Kármán.

    Caltech has six academic divisions with strong emphasis on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. First-year students are required to live on campus, and 95% of undergraduates remain in the on-campus House System at Caltech. Although Caltech has a strong tradition of practical jokes and pranks, student life is governed by an honor code which allows faculty to assign take-home examinations. The Caltech Beavers compete in 13 intercollegiate sports in the NCAA Division III’s Southern California Intercollegiate Athletic Conference (SCIAC).

    As of October 2020, there are 76 Nobel laureates who have been affiliated with Caltech, including 40 alumni and faculty members (41 prizes, with chemist Linus Pauling being the only individual in history to win two unshared prizes). In addition, 4 Fields Medalists and 6 Turing Award winners have been affiliated with Caltech. There are 8 Crafoord Laureates and 56 non-emeritus faculty members (as well as many emeritus faculty members) who have been elected to one of the United States National Academies. Four Chief Scientists of the U.S. Air Force and 71 have won the United States National Medal of Science or Technology. Numerous faculty members are associated with the Howard Hughes Medical Institute(US) as well as National Aeronautics and Space Administration(US). According to a 2015 Pomona College(US) study, Caltech ranked number one in the U.S. for the percentage of its graduates who go on to earn a PhD.

    Research

    Caltech is classified among “R1: Doctoral Universities – Very High Research Activity”. Caltech was elected to the Association of American Universities in 1934 and remains a research university with “very high” research activity, primarily in STEM fields. The largest federal agencies contributing to research are National Aeronautics and Space Administration(US); National Science Foundation(US); Department of Health and Human Services(US); Department of Defense(US), and Department of Energy(US).

    In 2005, Caltech had 739,000 square feet (68,700 m^2) dedicated to research: 330,000 square feet (30,700 m^2) to physical sciences, 163,000 square feet (15,100 m^2) to engineering, and 160,000 square feet (14,900 m^2) to biological sciences.

    In addition to managing JPL, Caltech also operates the Caltech Palomar Observatory(US); the Owens Valley Radio Observatory(US);the Caltech Submillimeter Observatory(US); the W. M. Keck Observatory at the Mauna Kea Observatory(US); the Laser Interferometer Gravitational-Wave Observatory at Livingston, Louisiana and Richland, Washington; and Kerckhoff Marine Laboratory(US) in Corona del Mar, California. The Institute launched the Kavli Nanoscience Institute at Caltech in 2006; the Keck Institute for Space Studies in 2008; and is also the current home for the Einstein Papers Project. The Spitzer Science Center(US), part of the Infrared Processing and Analysis Center(US) located on the Caltech campus, is the data analysis and community support center for NASA’s Spitzer Infrared Space Telescope [no longer in service].

    Caltech partnered with University of California at Los Angeles(US) to establish a Joint Center for Translational Medicine (UCLA-Caltech JCTM), which conducts experimental research into clinical applications, including the diagnosis and treatment of diseases such as cancer.

    Caltech operates several Total Carbon Column Observing Network(US) stations as part of an international collaborative effort of measuring greenhouse gases globally. One station is on campus.

     
  • richardmitnick 11:27 am on May 15, 2021 Permalink | Reply
    Tags: "Solar Wind From the Centre of the Earth", Cosmochemistry, , High-precision noble gas analyses indicate that solar wind particles from our primordial Sun were encased in the Earth’s core over 4.5 billion years ago., Isotopic ratios of helium and neon are typical for the solar wind., Noble gas mass spectrometer, The research group has long been measuring solar noble gas isotopes of helium and neon in igneous rock of oceanic islands like Hawaii and Réunion., The scientists found solar noble gases in an iron meteorite they studied., The team postulates that solar wind particles in the primordial Solar System were trapped by the precursor materials of the Washington County parent asteroid.,   

    From U Heidelberg [Ruprecht-Karls-Universität Heidelberg] (DE): “Solar Wind From the Centre of the Earth” 

    U Heidelberg bloc

    From U Heidelberg [Ruprecht-Karls-Universität Heidelberg] (DE)

    14 May 2021

    Model for the Earth’s core: Heidelberg researchers verify presence of solar noble gases in metal of an iron meteorite.

    1
    Meteorite example. Washington University of St. Louis.
    [Washington County iron meteorite-no image available.]

    High-precision noble gas analyses indicate that solar wind particles from our primordial Sun were encased in the Earth’s core over 4.5 billion years ago. Researchers from the Institute of Earth Sciences at Heidelberg University have concluded that the particles made their way into the overlying rock mantle over millions of years. The scientists found solar noble gases in an iron meteorite they studied. Because of their chemical composition, such meteorites are often used as natural models for the Earth’s metallic core.

    The rare class of iron meteorites make up only five percent of all known meteorite finds on Earth. Most are fragments from inside larger asteroids that formed metallic cores in the first one to two million years of our Solar System. The Washington County iron meteorite now being studied at the Klaus Tschira Laboratory for Cosmochemistry at the Institute of Earth Sciences was found nearly 100 years ago. Its name comes from the location in Colorado (USA) where it was discovered. It resembles a metal discus, is six cm thick, and weighs approx. 5.7 kilograms, according to Prof. Dr Mario Trieloff, head of the Geo- and Cosmochemistry research group.

    The researchers were finally able to definitively prove the presence of a solar component in the iron meteorite. Using a noble gas mass spectrometer, they determined that the samples from the Washington County meteorite contain noble gases whose isotopic ratios of helium and neon are typical for the solar wind. According to Dr Manfred Vogt, a member of the Trieloff team, ”the measurements had to be extraordinarily accurate and precise to differentiate the solar signatures from the dominant cosmogenic noble gases and atmospheric contamination”. The team postulates that solar wind particles in the primordial Solar System were trapped by the precursor materials of the Washington County parent asteroid. The noble gases captured along with the particles were dissolved into the liquid metal from which the asteroid’s core formed.

    The results of their measurements allowed the Heidelberg researchers to draw a conclusion by analogy that the core of the planet Earth might also contain such noble gas components. Yet another scientific observation supports this assumption. Prof. Trieloff’s research group has long been measuring solar noble gas isotopes of helium and neon in igneous rock of oceanic islands like Hawaii and Réunion. These magmatites derive from a special form of volcanism sourced by mantle plumes rising from thousands of kilometres deep in the Earth’s mantle. Their particularly high solar gas content makes them fundamentally different from the shallow mantle as represented by volcanic activity of submarine mid-ocean mountain ridges. “We always wondered why such different gas signatures could exist at all in a slowly albeit constantly convecting mantle,” states the Heidelberg researcher.

    Their findings appear to confirm the assumption that the solar noble gases in mantle plumes originate in the planet’s core – and hence signify solar wind particles from the centre of the Earth. “Just one to two percent of a metal with a similar composition as the Washington Country meteorite in the Earth’s core would be enough to explain the different gas signatures in the mantle,” states Dr Vogt. The Earth’s core may therefore play a previously underappreciated active role in the geochemical development of the Earth’s mantle.

    The research was funded by the Klaus Tschira Foundation. The results of the intricate, high-resolution noble gas measurements were published in the journal Communications Earth and Environment. A researcher from the MPG Institute for Chemistry (Otto Hahn Institute) [MPG Institut für Chemie – Otto Hahn Institut] (DE) in Mainz also assisted with the project.

    See the full article here .

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    Please help promote STEM in your local schools.

    Stem Education Coalition

    U Heidelberg Campus

    Founded in 1386, From U Heidelberg [Ruprecht-Karls-Universität Heidelberg] (DE) , a state university of BadenWürttemberg, is Germany’s oldest university. In continuing its timehonoured tradition as a research university of international standing the Ruprecht-Karls-University’s mission is guided by the following principles:
    Firmly rooted in its history, the University is committed to expanding and disseminating our knowledge about all aspects of humanity and nature through research and education. The University upholds the principle of freedom of research and education, acknowledging its responsibility to humanity, society, and nature.

     
  • richardmitnick 4:40 pm on June 24, 2019 Permalink | Reply
    Tags: "The Interiors of Exoplanets May Well Hold the Key to Their Habitability", , , “The heart of habitability is in planetary interiors” concluded Carnegie geochemist George Cody, , Cosmochemistry, , Deep Carbon Observatory’s Biology Meets Subduction project, Findings from the Curiosity rover that high levels of the gas methane had recently been detected on Mars., , , PREM-Preliminary Reference Earth Model, This idea that subsurface life on distant planets could be identified by their byproducts in the atmosphere has just taken on a new immediacy, We’ve only understood the Earth’s structure for the past hundred years.   

    From Many Worlds: “The Interiors of Exoplanets May Well Hold the Key to Their Habitability” 

    NASA NExSS bloc

    NASA NExSS

    Many Words icon

    From Many Worlds

    June 23, 2019
    Marc Kaufman

    1
    Scientists have had a working — and evolving — understanding of the interior of the Earth for only a century or so. But determining whether a distant planet is truly habitable may require an understanding of its inner dynamics — which will for sure be a challenge to achieve. (Harvard-Smithsonian Center for Astrophysics)

    The quest to find habitable — and perhaps inhabited — planets and moons beyond Earth focuses largely on their location in a solar system and the nature of its host star, the eccentricity of its orbit, its size and rockiness, and the chemical composition of its atmosphere, assuming that it has one.

    Astronomy, astrophysics, cosmochemistry and many other disciplines have made significant progress in characterizing at least some of the billions of exoplanets out there, although measuring the chemical makeup of atmospheres remains a immature field.

    But what if these basic characteristics aren’t sufficient to answer necessary questions about whether a planet is habitable? What if more information — and even more difficult to collect information — is needed?

    That’s the position of many planetary scientists who argue that the dynamics of a planet’s interior are essential to understand its habitability.

    With our existing capabilities, observing an exoplanet’s atmospheric composition will clearly be the first way to search for signatures of life elsewhere. But four scientists at the Carnegie Institution of Science — Anat Shahar, Peter Driscoll, Alycia Weinberger, and George Cody — argued in a recent perspective article in Science that a true picture of planetary habitability must consider how a planet’s atmosphere is linked to and shaped by what’s happening in its interior.

    They argue that on Earth, for instance, plate tectonics are crucial for maintaining a surface climate where life can fill every niche. And without the cycling of material between the planet’s surface and interior, the convection that drives the Earth’s magnetic field would not be possible and without a magnetic field, we would be bombarded by cosmic radiation.

    1
    What makes a planet potentially habitable and what are signs that it is not. This graphic from the Carnegie paper illustrates the differences (Shahar et al.)

    “The perspective was our way to remind people that the only exoplanet observable right now is the atmosphere, but that the atmospheric composition is very much linked to planetary interiors and their evolution,” said lead author Shahar, who is trained in geological sciences. “If there is a hope to one day look for a biosignature, it is crucial we understand all the ways that interiors can influence the atmospheric composition so that the observations can then be better understood.”

    “We need a better understanding of how a planet’s composition and interior influence its habitability, starting with Earth,” she said. “This can be used to guide the search for exoplanets and star systems where life could thrive, signatures of which could be detected by telescopes.”

    It all starts with the formation process. Planets are born from the rotating ring of dust and gas that surrounds a young star.

    The elemental building blocks from which rocky planets form–silicon, magnesium, oxygen, carbon, iron, and hydrogen–are universal. But their abundances and the heating and cooling they experience in their youth will affect their interior chemistry and, in turn, defining factors such ocean volume and atmospheric composition.

    “One of the big questions we need to ask is whether the geologic and dynamic features that make our home planet habitable can be produced on planets with different compositions,” Carnegie planetary scientist Peter Driscoll explained in a release.

    In the next decade as a new generation of telescopes come online, scientists will begin to search in earnest for biosignatures in the atmospheres of rocky exoplanets. But the colleagues say that these observations must be put in the context of a larger understanding of how a planet’s total makeup and interior geochemistry determines the evolution of a stable and temperate surface where life could perhaps arise and thrive.

    “The heart of habitability is in planetary interiors,” concluded Carnegie geochemist George Cody.

    Our knowledge of the Earth’s interior starts with these basic contours: it has a thin outer crust, a thick mantle, and a core the size of Mars. A basic question that can be asked and to some extent answered now is whether this structure is universal for small rocky planets. Will these three layers be present in some form in many other rocky planets as well?

    Earlier preliminary research published in the The Astrophysical Journal suggests that the answer is yes – they will have interiors very similar to Earth.

    “We wanted to see how Earth-like these rocky planets are. It turns out they are very Earth-like,” said lead author Li Zeng of the Harvard-Smithsonian Center for Astrophysics (CfA)

    To reach this conclusion Zeng and his co-authors applied a computer model known as the Preliminary Reference Earth Model (PREM), which is the standard model for Earth’s interior. They adjusted it to accommodate different masses and compositions, and applied it to six known rocky exoplanets with well-measured masses and physical sizes.

    They found that the other planets, despite their differences from Earth, all should have a nickel/iron core containing about 30 percent of the planet’s mass. In comparison, about a third of the Earth’s mass is in its core. The remainder of each planet would be mantle and crust, just as with Earth.

    “We’ve only understood the Earth’s structure for the past hundred years. Now we can calculate the structures of planets orbiting other stars, even though we can’t visit them,” adds Zeng.

    The model assumes that distant exoplanets have chemical compositions similar to Earth. This is reasonable based on the relevant abundances of key chemical elements like iron, magnesium, silicon, and oxygen in nearby systems. However, planets forming in more or less metal-rich regions of the galaxy could show different interior structures.

    While thinking about exoplanetary interiors—and some day finding ways to investigate them — is intriguing and important, it’s also apparent that there’s a lot more to learn about role of the Earth’s interior in making the planet habitable.

    In 2017, for instance, an interdisciplinary group of early career scientists visited Costa Rica’s subduction zone, (where the ocean floor sinks beneath the continent) to find out if subterranean microbes can affect geological processes that move carbon from Earth’s surface into the deep interior.

    3
    Donato Giovannelli and Karen Lloyd collect samples from the crater lake in Poás Volcano in Costa Rica. (Katie Pratt)

    The study shows that microbes consume and trap a small but measurable amount of the carbon sinking into the trench off Costa Rica’s Pacific coast. The microbes may also be involved in chemical processes that pull out even more carbon, leaving cement-like veins of calcite in the crust.

    According to their new study in Nature, the answer is yes.

    In all, microbes and calcite precipitation combine to trap about 94 percent of the carbon squeezed out from the edge of the oceanic plate as it sinks into the mantle during subduction. This carbon remains naturally sequestered in the crust, where it cannot escape back to the surface through nearby volcanoes in the way that much carbon ultimately recycles.

    These unexpected findings have important implications for how much carbon moves from Earth’s surface into the interior, especially over geological timescales. The research is part of the Deep Carbon Observatory’s Biology Meets Subduction project.

    Overall, the study shows that biology has the power to affect carbon recycling and thereby deep Earth geology.

    “We already knew that microbes altered geological processes when they first began producing oxygen from photosynthesis,” said Donato Giovannelli of University of Naples, Italy (and who I knew from time spent at the Earth-Life Science Institute Tokyo.) He is a specialist in extreme environments and researches what they can tell us about early Earth and possibly other planets.

    “I think there are probably even more ways that biology has had an outsized impact on geology, we just haven’t discovered them yet.”

    The findings also shows, Giovanelli told me, that subsurface microbes might have a similarly outsized effect on the composition and balancing of atmospheres—“hinting to the possibility of detecting the indirect effect of subsurface life through atmosphere measurements of exoplanets,” he said.

    5
    The 2003 finding by Michael Mumma and Geronimo Villanueva of NASA Goddard Space Flight Center showing signs of major plumes of methane on Mars. While some limited and seasonably determined concentrations of methane have been detected since, there has been nothing to compare with the earlier high methane readings Mars — until just last week. (NASA/ M. Mumma et al)

    This idea that subsurface life on distant planets could be identified by their byproducts in the atmosphere has just taken on a new immediacy with findings from the Curiosity rover that high levels of the gas methane had recently been detected on Mars. Earlier research had suggested that Mars had some subsurface methane, but the amount appeared to be quite minimal — except as detected once back in 2003 by NASA scientists.

    None of the researchers now or in the past have claimed that they know the origin of the methane — whether it is produced biologically or through other planetary processes. But on Earth, some 90 percent of methane comes from biology — bacteria, plants, animals.

    Could, then, these methane plumes be a sign that life exists (or existed) below the surface of Mars? It’s possible, and highlights the great importance of what goes on below the surface of planets and moons.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    About Many Worlds
    There are many worlds out there waiting to fire your imagination.

    Marc Kaufman is an experienced journalist, having spent three decades at The Washington Post and The Philadelphia Inquirer, and is the author of two books on searching for life and planetary habitability. While the “Many Worlds” column is supported by the Lunar Planetary Institute/USRA and informed by NASA’s NExSS initiative, any opinions expressed are the author’s alone.

    This site is for everyone interested in the burgeoning field of exoplanet detection and research, from the general public to scientists in the field. It will present columns, news stories and in-depth features, as well as the work of guest writers.

    About NExSS

    The Nexus for Exoplanet System Science (NExSS) is a NASA research coordination network dedicated to the study of planetary habitability. The goals of NExSS are to investigate the diversity of exoplanets and to learn how their history, geology, and climate interact to create the conditions for life. NExSS investigators also strive to put planets into an architectural context — as solar systems built over the eons through dynamical processes and sculpted by stars. Based on our understanding of our own solar system and habitable planet Earth, researchers in the network aim to identify where habitable niches are most likely to occur, which planets are most likely to be habitable. Leveraging current NASA investments in research and missions, NExSS will accelerate the discovery and characterization of other potentially life-bearing worlds in the galaxy, using a systems science approach.
    The National Aeronautics and Space Administration (NASA) is the agency of the United States government that is responsible for the nation’s civilian space program and for aeronautics and aerospace research.

    President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA’s predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

    Since that time, most U.S. space exploration efforts have been led by NASA, including the Apollo moon-landing missions, the Skylab space station, and later the Space Shuttle. Currently, NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle and Commercial Crew vehicles. The agency is also responsible for the Launch Services Program (LSP) which provides oversight of launch operations and countdown management for unmanned NASA launches. Most recently, NASA announced a new Space Launch System that it said would take the agency’s astronauts farther into space than ever before and lay the cornerstone for future human space exploration efforts by the U.S.

    NASA science is focused on better understanding Earth through the Earth Observing System, advancing heliophysics through the efforts of the Science Mission Directorate’s Heliophysics Research Program, exploring bodies throughout the Solar System with advanced robotic missions such as New Horizons, and researching astrophysics topics, such as the Big Bang, through the Great Observatories [Hubble, Chandra, Spitzer, and associated programs. NASA shares data with various national and international organizations such as from the [JAXA]Greenhouse Gases Observing Satellite.

     
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