Latest Posts

Itty bitty changes: places where the wind barely moves sand

A Piece of Mars: Not all dunes on Mars are moving at a measurable pace. This 0.96×0.45 km (0.6×0.28 mi) scene looks a lot like one I posted 3 years ago called Martian Sports. This image shows the same dunes 9.5 years apart (that’s 5 Mars Years). There are a few places where patches of sand have appeared or been removed, but it would take some detailed work to figure out whether the bulk of the dunes has shifted much. In the first post I guessed that the upper dune would crash into its topographic hurdle in 20 years, but after nearly 10 years of relative inactivity, I’ll have to revise that estimate upwards to perhaps 100 years. (HiRISE <a href=""ESP_045785_1995 NASA/JPL/Univ. of Arizona)

Neverending dust

A Piece of Mars: Some parts of Mars, like this one, are very dusty. This 1.92×1.1 km (1.2×0.67 mi) area has built up a thick deposit of dust that slowly buries the impact craters until they’re mere ghosts of the deep bowls they once were. If you knew the dust fallout rate, you could date the age of the craters. Or if you knew the age of the craters, you could estimate the mean dust fallout rate. (HiRISE ESP_044884_2050, NASA/JPL/Univ. of Arizona)

GPIES May 2016 Observing Run: Women in Astronomy

Hello GPI fans! We are just wrapping up our cloudy, snowy May 2016 GPIES observing run. While the weather wasn’t the best, we accomplished what we could in between the clouds. We also enjoyed the fact that this was the first all-woman run that any of the 5 of us had ever been on. It was a celebration of women in astronomy! EDIT: To clarify, for myself, I often spend 4-6 weeks at a time at the telescope, and I am often the ONLY woman there. So it was quite a novel experience for me!

Winter in Chile means snow in the high mountains to the East, as well as a chance of snow at the slightly lower telescope mountains. Here is a wintery view out my window on the plane ride in:

View out the airplane window from Santiago to La Serena


Flying through the binary trojan asteroid system (617) Patroclus

Another day, another video!

This time I am posting a video of the binary L5 Trojan Asteroid (617) Patroclus-Menoetius. In collaboration, with the team at the California Academy of Sciences, we have created a model of this interesting binary asteroid system which shares its orbit with Jupiter.



Dune cannibals II

A Piece of Mars: This 0.96×0.54 km (0.60×0.34 mi) scene shows two sets of bedforms (dunes), each aligned in different directions. The more closely-spaced set has sharper crests, and it’s superposed on top of (and it is therefore younger than) the more widely-spaced set. Like a previous post I wrote, the younger set has cannibalized sediment from the older set (although in aeolian geology we say it has “reworked” the sediment). If you click on the image, you might be able to convince yourself that some internal bedding from the older set is being exposed by erosion, but it’s hard to tell for sure at this resolution (maybe we could tell if we had a full resolution HiRISE image to work with here – hmm, maybe I’ll go request one). (HiRISE ESP_045299_1545 NASA/JPL/Univ. of Arizona)

Visiting the L4 Trojan Asteroid (624) Hektor

I finally started uploading some of the animations of the talk that I gave last month at the California Academy of Sciences. Today let’s watch (624) Hektor, the binary and bilobed largest Jupiter-Trojan asteroids. This is a puzzling multiple asteroid system with a lot of mysteries (eccentric and inclined orbit of the moon, complex shape and structure for the primary, …). 

Screen Shot 2016-05-23 at 9.50.49 AM

Our study based on AO observations collected over 8 years was published in 2014. The conclusion of our work is that 624 Hektor is probably a captured Kuiper-belt object and the moon formed a long time ago from the slow velocity encounter of the components.

The Largest Jupiter Trojan: 624 Hektor and its moon from Franck Marchis on Vimeo.


Wind shadow

A Piece of Mars: There’s a dune field migrating past a 230 m (755 ft) diameter crater, creating a 1.6 km (1 mi) long “shadow” that’s empty of dunes. Why? The rim of the crater pokes up just enough to affect the wind, like pebbles in a stream. Either the sand is diverted around the crater, or the rim produces turbulence that increases erosion (or possibly both at different times). I like the dunes that are disrupted as they migrate into the crater. (HiRISE ESP_037948_1645, NASA/JPL/Univ. of Arizona)

Craters and wind

A Piece of Mars: This 90 m (295 ft) crater impacted into a windy, cratered plain. It’s now partly filled with dark sand, but where did that sand come from? Looking closely you’ll see that many of the boulders that were flung out during the impact have little “tails”. These tails show that wind from the upper right blows sediment toward the lower left: some of it gets trapped behind the boulders (and other topographic projections), and some of it is the dark sand that got trapped inside the crater. (HiRISE ESP_045397_1885, NASA/JPL/Univ. of Arizona)

Giant “combs” on Mars

A Piece of Mars: This 480×270 m (0.3×0.17 mi) scene shows a herd of 100-300 m fine-toothed combs grazing on the surface of Mars. Wait, what? No, it’s not really combs. This is actually a landscape covered by two sets of windblown bedforms. The larger ones (the “comb” shafts) are very old, now inactive windblown features. The smaller ones (the “comb” teeth) are ~2 m apart, and they extend downwind (eastward) from the older bedforms, which effectively serve as filters that block winds from the west (left to right), allowing only the northerly or southerly components of most winds to shape the ripples on their lee sides. Beyond the influence of the larger bedforms, the small ripples merge with those on the surrounding sand sheet, which show the influence of several different winds (HiRISE ESP_045166_1690, NASA/JPL/Univ. of Arizona)

Old ripples

A Piece of Mars: In this 480×270 m scene (0.3×0.17 mi), there are a bunch of “ripples” spaced by 5-20 m (the quotes are because we don’t know yet if these are ripples, dunes, or some other new kind of bedform). They’re old: they’re eroded by winds blowing from the bottom to the top of the frame (exposing layers on the upwind side), and if you look carefully you’ll see some craters superposed on them. The craters don’t have any obvious ejecta blankets, which suggests they’re not that young either, so there’s been enough time for the ejecta to erode away. (HiRISE ESP_017766_1535, NASA/JPL/Univ. of Arizona)