THE COSMIC DIARY NETWORK

Dunes in a colorful hole
Published 2/27/2017 in Lori Fenton's Blog Author lfenton
A Piece of Mars: Gray dunes have migrated over reddish rock, moving toward a narrowing cleft surrounded by tall tan cliffs. Bright lines on the dunes are exposed internal layers (bones of the dunes, really) that show you where the lee-side slopes once were (so you can tell they've moved to the left). The cliffs are made of layered rocks (extra points if you can find the fault), suggesting these are sedimentary layers, laid down long ago in Mars' geologic past. The whole HiRISE image is worth a long look, it's really amazing. (HiRISE ESP_049009_1520, NASA/JPL/Univ. of Arizona) read more ❯

Wonderful Potentially Habitable Worlds Around TRAPPIST-1
Published 2/22/2017 in Franck Marchis Blog Author Franck Marchis
In May 2016, Michael Gillon and his team announced the discovery of three Earth-sized exoplanets around TRAPPIST-1, an ultra cool M-dwarf star, using the small TRAPPIST telescope at ESO-La Silla, Chile. It was an exciting discovery—yet on that day no one could possibly have imagined that less than a year later they would make another significant discovery involving the same system. But here we are: today, they announced in Nature the discovery of seven potentially habitable Earth-like worlds. The star, named TRAPPIST-1, is a fairly inconspicuous star in our Milky Way. Small (8% the mass of the sun) and cold (half the temperature of the sun), it is a member of an ultra-cool dwarf population that represents 15% of the star population of our galaxy. In 2016, Gillon and his team detected the transit (i.e., the shadow of a planet passing... read more ❯

Who wins in the fight of wind vs. ice?
Published 2/21/2017 in Lori Fenton's Blog Author lfenton
A Piece of Mars: This is the crest of one of the largest dunes on Mars (0.5x0.5 km or 0.31x0.31 mi). The wind mostly blows from the right, slowly pushing sand up the windward slope. But frost accumulates on (and probably in) the sand during winter, and sometimes it gets too heavy and slides down the steepest slope (toward the left), carving out big gullies in the sand. And then the wind blows some more, trying to erase the gullies by 1) making ripples, 2) burying the gullies (the featureless blue patches are grainfall, which is a fancy term for sand that fell as airfall), and 3) forming dust devils that leave faint but wide tracks. Who wins this fight, wind or ice? Neither: gravity wins (it usually does). (HiRISE ESP_020876_1330, NASA/JPL/Univ. of Arizona) read more ❯

Mars' yin-yangs
Published 2/13/2017 in Lori Fenton's Blog Author lfenton
A Piece of Mars: Is this 480x270 m (0.3x0.17 mi) scene showing a 150 m (492 ft) wide yin-yang symbol on Mars? Sort of, maybe, if you blur your eyes and lend me artistic license, but it's not doing so intentionally. One side of the crater is dark and the other is light. Both have their tone because of windblown material blown from the same direction, but the different materials collected where they did for different reasons. The dark material is probably mafic sand (iron and magnesium-rich, like what's found near many volcanoes), which was bounced along the ground from the lower right, and collected in the lee of the crater rim. The bright material is much finer-grained, dust carried aloft, and it probably settled down on the far side of the crater, and outside as well, as the crater rim poked into the wind and provided enough shelter to... read more ❯

The two-faced dunes of Mars
Published 2/6/2017 in Lori Fenton's Blog Author lfenton
A Piece of Mars: The focus of this 0.96x0.96 km (0.6x0.6 mi) scene is one of many two-faced dunes on Mars. The bright sunlit slope is one face, formed recently by wind blowing from the upper right. The dark shaded slope is the other face - it's a little older, formed by wind blowing from the left. Together these two winds alternate, probably in different seasons, forcing the sand into a needle-shaped point that carries sand in a direction that is, give or take, the sum of those two winds. Two-faced dunes like this are rare on Earth, as winds here typically quickly erase older crestlines. (HiRISE ESP_021716_1685, NASA/JPL/Univ. of Arizona) read more ❯

Dunes + Craters = Mars
Published 1/30/2017 in Lori Fenton's Blog Author lfenton
A Piece of Mars: How do you tell when a planetary landscape shows Mars, instead of Mercury or the Moon or Europa? The easiest way to tell is to look for both craters and dunes, like what's shown here in this 640x360 m (0.4x0.22 mi) scene. Not all martian landscapes have either feature, and there are some other worlds that do have both (Earth, Titan, maybe Pluto, and probably Venus but we need better data...), but it's a pretty good bet that if you see both features together, you're looking at Mars. Anyway, in this lovely view, the dark gray terrain (you'll see boulders if you look closely enough!) is being eroded away slowly, revealing a much older, brighter surface beneath it. Unfortunately for those who would study ancient terrains on Mars, much of that older, lower surface is covered in dunes. But I like the dunes - they give... read more ❯

Mars' giant sweaters
Published 1/23/2017 in Lori Fenton's Blog Author lfenton
A Piece of Mars: Sometimes in the floors of small craters, the wind blows in from several directions to produce odd polygon-shaped dunes that look like crochet (maybe Mars is making sweaters for its craters - it is, after all, a cold place). This "sweater" segment is 480x270 m (0.3x0.17 mi) in size (the "stitches" are ~20 m, or 66 ft, across). The smaller interior lines are younger windblown features, that are superposed on the larger structures - their alignment is strongly controlled by the topography of the larger polygonal "stitches". (HiRISE ESP_017833_1975, NASA/JPL/Univ. of Arizona) read more ❯

Mid-infrared light reveals a contaminated crust around Ceres
Published 1/19/2017 in Franck Marchis Blog Author Franck Marchis
Using a combination of space telescope data, as well as recent data acquired with the SOFIA Airborne telescope and lab experiments, a team of astronomers including researchers from the SETI Institute and Jet Propulsion Laboratory  have revealed the presence of dust of exogenic origin at the surface of dwarf planet Ceres. This contamination likely stems from a dust cloud formed in the outer part of the main belt of asteroids following a collision in recent times. That study challenges the relationship proposed between Ceres and asteroids in the C spectral class and instead suggests an origin of this dwarf planet in the transneptunian region. This study was published on January  19 2017 in Astronomical Journal. Interplanetary dust particles (IDPs), which form meteors when they cross Earth’s atmosphere, represent the largest fraction of extraterrestrial material accreted on Earth. A team led by Pierre Vernazza, research scientist CNRS in the Laboratoire d’Astrophysique de Marseille... read more ❯

Dunes carving up rock (3D)
Published 1/16/2017 in Lori Fenton's Blog Author lfenton
A Piece of Mars: Get out your 3D blue/red glasses (or look here for a 2D version if you can't find them). This is a 3.2x1.8 km (2x1.13 mi) scene showing dark dunes carving lanes 50-70 m (165-230 ft) deep into a stack of brighter sedimentary layers. Over time, the sand wears down the rock into yardangs, the elongated remnants of rock the sand didn't manage to reach. Here we see the process ongoing; perhaps in a few million years there will be nothing left but a few streamlined peaks. Those murdering basterds [sic]. (HiRISE ESP_034419_2015, NASA/JPL/Univ. of Arizona) read more ❯

Tortoise and hare
Published 1/12/2017 in Lori Fenton's Blog Author lfenton
A Piece of Mars: There's a lot of evidence for both fast and slow movement in this 480x270 m (0.3x0.17 mi) scene. The tortoise: The rippled surface at the top is high ground: the top of a dune. Wind pushes the ripples toward a steep sunlit slope, creating long thin, dark avalanches that slowly inch the slipface forward. At the bottom of the slope, which is shielded from winds blowing from the top, ripples have been formed by wind blowing from the left. The hare: Oblivious to both the slow progression of ripples and dunes, 5-25 m wide dust devils have blazed on by, leaving behind erratic trails. (HiRISE ESP_048592_2070, NASA/JPL/Univ. of Arizona) read more ❯

Crater ejecta on old ripples
Published 1/3/2017 in Lori Fenton's Blog Author lfenton
A Piece of Mars: Mars rarely does anything without drama. Long ago in this 0.96x0.54 km (0.6x0.34 mi) scene, large ripples formed and then, presumably, lithified (turned into rock). Some time after that, an impact formed the crater in the center, throwing debris into an ejecta blanket that covered the lithified ripples. That ejecta blanket sat around long enough to acquire some smaller impact craters of its own. Since then, most of that ejecta blanket has eroded away, exposing the ripples to view once again. (HiRISE ESP_011699_1910, NASA/JPL/Univ. of Arizona) read more ❯

Steno's principles, or "how to make sense of pretty landscapes"
Published 12/26/2016 in Lori Fenton's Blog Author lfenton
A Piece of Mars: Nicholas Steno was a 19th century geologist, who came up with some principles that are still used today to guide interpretation of exposed sedimentary rocks. The principles seem a bit obvious, but then some of the most profound principles can be like that. Emily Lakdawalla of the Planetary Society describes them in more detail here, with really good examples. You can use these principles to do forensics on a landscape, to see what happened and when. You can see all three principles at work in this image. #1: Stuff makes horizontal layers. (This isn't always true, e.g., dunes and deltas make tilted layers, but most sediments pile up into flat, horizontal layers.) You can see that at work here: A thick layer of dark gray stuff once piled up on a flat surface of brighter stuff. Some of the dark gray stuff has since eroded away, but... read more ❯

The trail of a dune
Published 12/19/2016 in Lori Fenton's Blog Author lfenton
A Piece of Mars: A low, broad dune occupies the center of this 800x450 m (0.5x0.28 mi) scene, blown by a dominant wind towards the lower left. The slip face on the lee side has several small avalanches, formed as the slope oversteepens (this is how dunes crawl along the surface). Upwind, among other fainter lines, is a prominent bright line: it is a former slip face of this dune, possibly formed from a thick accumulation of bright dust (maybe there was a big dust storm that year). Farther upwind, another dune slowly approaches. (HiRISE ESP_033955_2065, NASA/JPL/Univ. of Arizona) read more ❯

An AGU 2016 Session on Solar System Small Bodies
Published 12/14/2016 in Franck Marchis Blog Author kchris
I co-organized a session for the AGU 2016 meeting entitled "P42A: Solar System Small Bodies: Asteroids, Satellites, Comets, Pluto, and Charon". Below the info on the session and the schedule. We have three invited talks that will describe the New Horizons data of Charon, color of Kuiper Belt Object from a ground-based survey and a theoretical study of the formation of the asteroid belt. Abstract: The composition and physical properties of Small Solar System Bodies (SSSBs), asteroids and dwarf planets, remnants of the formation of planets, are key to better understand our solar system. Increased knowledge of their surface properties and their potential as resources are also necessary to prepare for robotic and human exploration. Hints about the internal structure and composition of SSSBs have been acquired recently thanks to flyby/rendezvous data from space missions, study of complex multiple asteroid systems, or close encounter between asteroids. In this session we will discuss results bringing information on the internal... read more ❯

Them that make ripples and them that don't
Published 12/12/2016 in Lori Fenton's Blog Author lfenton
A Piece of Mars: Higher ground is to the left. You're seeing a tan layer sandwiched between two gray layers in this 0.96x0.54 km (0.6x0.34 mi) scene. Large ripples have accumulated in the lowest area to the right, which is the floor of an old river channel. Ripples have also formed on the gray upper layer. But not the middle tan layer - maybe it's too fine-grained to erode into sand grains, or maybe it erodes too slowly to allow any eroded sand grains to pile into ripples before they're blown away. (HiRISE ESP_048196_1995, NASA/JPL/Univ. of Arizona) read more ❯

Fall AGU meeting: Detection and Direct Imaging of Habitable Exoplanets
Published 12/11/2016 in Franck Marchis Blog Author kchris
AGU Fall meeting is starting tomorrow. I co-organized a session entitled "Detection and Direct Imaging of Habitable Exoplanets: Progress and Future" to discuss the potential of new and future facilities and modeling efforts designed to detect, image and characterize habitable exoplanets, studying their formation, evolution and also the existence of possible biospheres.  Topics that are covered in this session include signs of exoplanet habitability and global biosignatures that can be sought with upcoming instrumentation; instrument requirements and technologies to detect these markers; strategies for target selection and prioritization; and impacts of planetary system properties, ground-based and space telescope architectures. We have two invited talks, one by George Ricker on TESS and a second one by Shawn D Domagal-Goldman on HabEx, two NASA missions that could play a major role on identification and characterization of Earth-Like exoplanets. Conveners & Chairs: Franck Marchis SETI Institute Mountain View Ramses M Ramirez Cornell University Douglas A. Caldwell SETI Institute Mountain View Location: Room 2020 - Moscone West Schedule... read more ❯

Martian spiders
Published 12/5/2016 in Lori Fenton's Blog Author lfenton
A Piece of Mars: Martian spiders, or araneiforms, are geological structures found at high latitudes on Mars. The dark splotch with branching arms in this 0.48x0.27 km (0.3x0.17 mi) scene is a good example. They form in the springtime, when bright frost still covers a darker sandy soil, but some sunlight filters through the frost to warm the underlying surface. Sublimation of gas (under the frost but just above the soil) creates enough pressure that little explosions occur like dry geysers, punching through the frost and blowing up sand that then falls back to the surface as a dark splotch. If the wind is blowing when this happens, then the dark splotch is carried a ways downwind, but that hasn't happened in this case. (HiRISE ESP_048189_0985, NASA/JPL/Univ. of Arizona) read more ❯

Grainfall
Published 11/28/2016 in Lori Fenton's Blog Author lfenton
A Piece of Mars: The dunes climbing over a rocky surface in this 0.96x0.54 km (0.6x0.34 mi) scene are mostly yellow because they're covered (and therefore kept immobile) by dust. The crest of one dune, though, shows recent activity: dark sand has been pushed by the wind up the lower right side, and then shot (cannonball-style) over the brink, where it slowly piles up on the upper left side. This pileup is called grainfall, because that's what the sand grains have done here (rather than sliding downhill, avalanche-style, which is called grainflow). There's a dune on the left side of the image that hasn't experienced this activity, maybe because it's a little more sheltered from the wind. (HiRISE ESP_047779_1655, NASA/JPL/Univ. of Arizona) read more ❯

Bedforms on crater rims
Published 11/21/2016 in Lori Fenton's Blog Author lfenton
A Piece of Mars: Dunes and ripples most commonly form in topographic lows. But not in this 0.96x0.54 km (0.6x0.34 mi) scene. Here, and in other places on Mars, these bedforms (called TARs) form on plains, and sometimes appear to cling to the rims of craters - which are topographic highs, not lows. It's not clear how this happens: Does the topography of the crater rim provide a wind shadow that allows windblown sediment to accumulate there? Or was there simply more loose material on the crater rims to begin with, allowing these things to form in place? I'm open to suggestions. (HiRISE ESP_047787_1910 NASA/JPL/Univ. of Arizona) read more ❯

Shadows behind boulders
Published 11/14/2016 in Lori Fenton's Blog Author lfenton
A Piece of Mars: Bright material (either dust or sand) has accumulated in the lee of wagon- to car-sized boulders in this 0.96x0.54 km (0.6x0.34 mi) scene. It's perhaps something like the Rocknest sand shadow that Curiosity visited a few years back. The wind blows from lower right to upper left, carrying along sediment that occasionally gets trapped in the protected areas behind the boulders. These sand shadows aren't very thick, as the underlying texture (polygonal terrain!) is visible through them. (HiRISE ESP_047798_1150, NASA/JPL/Univ. of Arizona) read more ❯