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  • richardmitnick 12:47 pm on March 1, 2017 Permalink | Reply
    Tags: , Cassini, Peeking Through the Haze: A Look at Titan’s Bright Surface Features, Principal Component Analysis (PCA),   

    From astrobites: “Peeking Through the Haze: A Look at Titan’s Bright Surface Features” 

    Astrobites bloc

    Astrobites

    Mar 1, 2017
    Kerrin Hensley

    Title: Compositional Similarities and Distinctions Between Titan’s Evaporitic Terrains
    Authors: S.M. MacKenzie and Jason W. Barnes
    First Author’s Institution: University of Idaho
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    Status: Published in the Astrophysical Journal, open access

    Titan, Saturn’s largest moon, is the only solar system object other than the Earth to have a thick atmosphere and standing surface liquid. When the Cassini spacecraft began observing Titan, it even discovered lakes and seas dotting the northern hemisphere.

    NASA/ESA/ASI Cassini Spacecraft
    NASA/ESA/ASI Cassini Spacecraft

    Don’t fire up your rocket just yet, though—because Titan is so cold, the lakes and seas are filled with liquid methane and ethane rather than water.

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    Wikipedia

    Titan’s thick, methane-rich atmosphere makes it difficult to observe the surface at visible wavelengths. Luckily, there are several windows in the near-infrared through which light can pass and reveal the surface. Seven of these windows overlap with the wavelength range covered by Cassini’s Visual and Infrared Mapping Spectrometer (VIMS). By looking at how the brightness of the surface changes with wavelength, we can learn about the composition of the surface material. Figure 1 depicts a three-color map of Titan’s surface made with VIMS. The pinkish regions show where the surface reflects strongly at 5 microns.

    3
    Figure 1. Map of Titan’s surface from Cassini. Red is 5 microns, green is 2 microns, and blue is 1.3 microns. Many of the major geographic regions are labeled. Some of the regions selected for this study are indicated with the white arrows.

    The 5-micron-bright regions are found circling lakes in the northern hemisphere, in dry lake beds in both hemispheres, and in the desert-like equatorial regions. The bright rings around the lakes are believed to be evaporites—solid material left behind after the liquid it was dissolved in evaporates. This explains the presence of the bright material surrounding the lakes and the dry lake beds, but what about the desert? Linking 5-micron-bright regions in what is today a desert to the bright rings around the lakes could provide evidence that the equatorial regions of Titan were once covered with liquid.

    In this paper, the authors searched for a compositional link between the bright regions in the desert and the evaporites around the lakes and seas. They used an absorption feature at 4.92 microns in order to investigate whether or not the 5-micron-bright material in each of these regions is the same. The 4.92-micron absorption feature has been observed previously in the desert region, but no one has been able to definitively say what compound causes it. Because of this, finding the same feature in the desert and around the lakes can indicate that the regions are geologically similar, but can’t yet tell us about the chemical makeup of the material.

    The authors used Principal Component Analysis (PCA) to isolate the weak 4.92-micron absorption feature. PCA is a mathematical method that separates the individual components that make up an observed signal. In this case, the main contributors to the signal (i.e. the “principal components”) could be changes in the surface reflectivity, instrumental noise, or compositional variations. Once the components have been separated, the unwanted contributors can be removed. As a result, PCA can be used to isolate a signal that is much smaller than the background noise. (PCA is also used in the direct detection of exoplanets and is described in more detail here.) After applying PCA, the authors observed the 4.92-micron absorption feature in both the desert and around the lakes, strengthening the hypothesis that the desert once had liquid. However, they also found that not all of the lake regions had the absorption feature, and some of the regions that did have it didn’t have it in every observation. They suggested that material with a crystalline structure that reflects light more strongly at some angles or transient effects like methane rain could cause the absorption feature to appear intermittently.

    What causes some lake regions to have the absorption feature while others don’t? The authors suggested that the material that causes the 4.92-micron absorption feature could be just one of several solids that are left behind as the lakes evaporate away. Whether or not a lake rim has the absorption feature could be a function of how far the evaporation has progressed. As evaporation proceeds, materials that are more soluble precipitate out in sequence. We could see a 5-micron-bright evaporite ring without the absorption feature if the lake hasn’t evaporated enough for the material causing the absorption to precipitate out. The authors even have a suggestion for why this might happen to some lakes in the northern hemisphere but not others—lakes closest to the north pole might experience more methane rainfall than more southern lagoons, periodically halting the evaporation before the absorbing material can crystallize.

    Although the authors posit many explanations for the mysterious behavior of the 4.92-micron absorption feature, they can’t yet settle on one cause. It’s not surprising that Titan, an inhospitable but strangely familiar world with complex geology and weather systems, presents a challenge to astronomers. In the future, by modeling how Titan’s climate changes over time, we can hope to learn more about what causes the distribution of evaporites on Titan’s surface.

    See the full article here .

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    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 12:35 pm on July 6, 2016 Permalink | Reply
    Tags: , , Cassini, Magnetic Rope' observed for the first time between Saturn and the Sun,   

    From UCL: ” ‘Magnetic Rope’ observed for the first time between Saturn and the Sun” 

    UCL bloc

    University College London

    6 July 2016
    No writer credit

    This post is dedicated to J.T., who just accessed social media.

    A twisted magnetic field structure, previously never seen before at Saturn, has now been detected for the first time, using instrumentation built at UCL and Imperial College.

    When the Sun’s magnetic field interacts with the Earth’s magnetic field (the magnetosphere), a complex process occurs called magnetic reconnection which can twist the field into a helical shape.

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    No image caption. No image credit

    These twisted helically structured magnetic fields are called flux ropes or “flux transfer events” (FTEs) and are observed at Earth and even more commonly at Mercury. The conditions that allow FTEs to be generated at a planet worsen with distance from the Sun, however they have been observed at all the planets out to Jupiter.

    The observation of this phenomenon at Saturn has been elusive. Searches have been undertaken to find an FTE with NASA’s Cassini spacecraft, with reports published of none being found. Up until now….

    NASA/ESA/ASI Cassini Spacecraft
    NASA/ESA/ASI Cassini Spacecraft

    The Cassini spacecraft has been in orbit around Saturn since 2004, and after many years analyzing the data collected, Cassini has observed the first FTE at Saturn. The observed magnetic signature was successfully compared to that of a model to show that Cassini indeed observed a flux rope at this giant magnetosphere, and that the spacecraft passed close to the structure’s center. It is also estimated that the flux rope could be up to 8300 kilometers wide.

    “Contrary to previous ideas about Saturn’s magnetosphere being unlike its terrestrial counterpart, these findings reveal that Saturn at times behaves and interacts with the Sun in much the same way as Earth.” Jamie Jasinski, UCL Space and Climate Physics PhD graduate now based at the University of Michigan, and lead author of the new paper published today in Geophysical Research Letters. Click here for link to paper.

    This not only shows that magnetic reconnection occurs at Saturn but also that Saturn’s magnetic field can at times interact with the Sun in much the same way as at Earth.

    The analysis was completed using a particle spectrometer built at UCL and a magnetometer built at Imperial College, both of which are onboard NASA’s Cassini spacecraft.

    The Cassini mission will end in November 2017, when the spacecraft will be steered into the planet to study it, before disintegrating in Saturn’s thick atmosphere.

    See the full article here .

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    UCL campus

    UCL was founded in 1826 to open up higher education in England to those who had been excluded from it – becoming the first university in England to admit women students on equal terms with men in 1878.

    Academic excellence and research that addresses real-world problems inform our ethos to this day and are central to our 20-year strategy.

     
  • richardmitnick 2:49 pm on July 6, 2011 Permalink | Reply
    Tags: , Cassini, ,   

    From NASA JPL and CalTech: “Cassini Captures Images and Sounds of Saturn Storm” 

    July 06, 2011

    “Scientists analyzing data from NASA’s Cassini spacecraft now have the first-ever, up-close details of a Saturn storm that is eight times the surface area of Earth.

    On Dec. 5, 2010, Cassini first detected the storm that has been raging ever since. It appears approximately 35 degrees north latitude of Saturn. Pictures from Cassini’s imaging cameras show the storm wrapping around the entire planet covering approximately 2 billion square miles (4 billion square kilometers).

    i1
    The huge storm churning through the atmosphere in Saturn’s northern hemisphere overtakes itself as it encircles the planet in this true-color view from NASA’s Cassini spacecraft. Image credit: NASA/JPL-Caltech/SSI

    The storm is about 500 times larger than the biggest storm previously seen by Cassini during several months from 2009 to 2010. Scientists studied the sounds of the new storm’s lightning strikes and analyzed images taken between December 2010 and February 2011. Data from Cassini’s radio and plasma wave science instrument showed the lightning flash rate as much as 10 times more frequent than during other storms monitored since Cassini’s arrival to Saturn in 2004. The data appear in a paper published this week in the journal Nature.”

    See the full article here.

     
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