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The Triple Asteroid (87) Sylvia

Cosmic Diary Marchis - June 15, 2016

Another beautiful simulation of the triple asteroid system (87) Sylvia and its two moons Romulus and Remus made in collaboration with the California Academy of Sciences.

(87) Sylvia was discovered in 1866 by N.R. Pogson, a British astronomer located in Madras, India. This main-belt asteroid is large with a diameter of ~150 km. That’s all we knew until recently.

In 2005, we discovered two moons around the asteroid that we baptized Romulus and Remus, sons of the Rhea Sylvia and founder of Rome. Both moons are very small with a diameter estimated to ~20 and ~7 km. The primary is irregular with a diameter of 193 x 129 x 124 km. Both moons orbit around the primary describing a coplanar and almost circular orbit.

From a long term study of their orbit we concluded that the primary is possibly differentiated, made of a dense core of ice. How the moons have formed is still unclear. They could be the product of a catastrophic disruption of a large asteroid early in the history of the  solar system.

The triple asteroid (87) Sylvia and its two moons Romulus and Remus from Franck Marchis on Vimeo.

(87) Sylvia is the first triple asteroid ever discovered. I have a fond memory of the day, I presented this discovery at the ACM conference in August 2005 at Buzios, Brazil, simultaneously with the publication in Nature. It was a very special moment in my career.

Today we know six  triple asteroids in the asteroid main-belt (45 Eugenia, 87 Sylvia, 93 Minerva, 130 Elektra, 216 Kleopatra, 3749 Balam)and there are probably more of them waiting to be discovered with the next generation of space-based and ground-based telescopes.

Clear Skies,

Franck M.


New craters and wind

Cosmic Diary by Lori Fenton - June 13, 2016

A Piece of Mars: The two small dark craters (2.25-2.4 m, or 7.4-7.8 ft across) are brand new, having appeared in CTX images sometime between May 2007 and April 2008. They punched through a layer of bright dust and threw up some darker material, which the wind carried downwind (near-surface winds blowing from the southwest, and higher winds blowing from the southeast). Application of an atmospheric model could further constrain the season and time of day when the impact happened, based on the prevailing wind direction. This picture from May 2016 shows the wind streaks are still there, having faded only a little in the 8-9 years since they formed. (HiRISE ESP_045798_1965, NASA/JPL/Univ. of Arizona)

Itty bitty changes: places where the wind barely moves sand

Cosmic Diary by Lori Fenton - June 06, 2016

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="http://www.uahirise.org/ESP_045785_1995"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)

Flying through the binary trojan asteroid system (617) Patroclus

Cosmic Diary Marchis - May 24, 2016

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.

In 2001, a group of astronomer discovered that the L5 Trojan asteroid (617) Patroclus is in fact made of two components. In 2006, using Laser Guide Star Adaptive Optics System at W.M. Keck Observatory, we showed that those two components orbit around the center of mass of the system in ~4 days at 680 km describing a circular orbit. We named the second component Menoetius, the argonaut father of Patroclus in the greek mythology.

From the estimate of the size (derived from various techniques including Spitzer observations of mutual events taken in 2010 and stellar occultation on October 2013), we found out that the components are less dense than icy water, with a grain density very close to satellites of giant planets (like Amalthea, moon of Jupiter).

The Binary Trojan Asteroid (617) Patroclus-Menoetius from Franck Marchis on Vimeo.

Because Patroclus has a different color and density than (624) Hektor, we speculated that it could be a captured Jupiter-Saturn asteroid which ended up in the gravitational well of the Sun-Jupiter system during the migration of the giant planets 3.7 Billion years ago. Its binary nature could be the result of tidal disruption when primitive asteroid had a close encounter with Jupiter before the capture.

Ultimately, we will need to send a spacecraft there to really understand this system. NASA has pre-selected the LUCY new discovery mission which could flyby this binary Trojan asteroid in 2033.

Clear Skies,

Franck M.

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

Cosmic Diary Marchis - May 23, 2016

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, …). 

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.

We will probably need to send a spacecraft over there to really understand this complex mini-geological world. The good news is that several space agencies, including JAXA and NASA, are thinking about that.


I would like to thank to my colleague Josef Durech,  Matija Ćuk, Julie Castillo, Frederic Vachier, Jerome Berthier and numerous more for their long-term contribution to this project. I also should include my sister Helene Marchis for making the first drawing of this system. Thanks as well to the California Academy of Sciences for making those great CGI videos and the director Ryan Wyatt for inviting me.

Clear skies,

Franck M.

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

Cosmic Diary by Lori Fenton - April 25, 2016

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)

Stripes by wind and gravity

Cosmic Diary by Lori Fenton - April 19, 2016

A Piece of Mars: This scene (800×450 m or 0.5×0.28 mi) is a steep slope, with high rocky outcrops on the upper right and both gullies and ripples heading downslope to the lower left. The wider, brighter stripes are gullies that were carved by stuff eroding from the outcrops and falling downhill, just like on Earth. Beneath that are some finer stripes: this time the straight lines are made by a combination of wind blowing sand into ripples (from upper left to lower right) and gravity elongating the ripples downslope (stretching them from upper right to lower left). (HiRISE ESP_044997_1755 NASA/JPL/Univ. of Arizona)

Windy windows

Cosmic Diary by Lori Fenton - April 11, 2016

A Piece of Mars: Here’s a tiny bit (0.69×0.39 km or 0.43×0.24 mi) of Jezero crater, one of the candidate landing sites for the Mars 2020 rover. On the bottom and left is high-standing volcanic terrain, former lava that flowed out on the crater floor. On the upper right is a much older deposit of stuff that piled up at the bottom of the lake that once, more than 3.5 billion years ago, filled the crater. Those lake deposits are so easy to erode that they’ve been worn down by the wind (see those bedforms there?) to the point that they’re now lower than the volcanic stuff. I wonder if they’ll eventually be completely covered by those ripples. (HiRISE ESP_037330_1990, NASA/JPL/Univ. of Arizona)

Schon, S. C., J. W. Head, and C. I. Fassett (2012), An overfilled lacustrine system and progradational delta in Jezero crater, Mars: Implications for Noachian climate, Planet. Space Sci., 67(1), 28–45, doi:10.1016/j.pss.2012.02.003.

The wind paints

Cosmic Diary by Lori Fenton - April 04, 2016

A Piece of Mars: For the last few billion years, the wind has (by far) moved more sediment around on Mars than any other geological process. Not tectonics, volcanism, fluvial activity, or impact cratering (although a case has been made for glacial activity). Here’s yet one more swipe at the ground, scouring off bright dust to reveal darker terrain underneath. (HiRISE ESP_044511_2005, NASA/JPL/Univ. of Arizona)

Three types of windblown piles of stuff

Cosmic Diary by Lori Fenton - March 28, 2016

A Piece of Mars: The wind blows different sorts of sediment in different ways. Ultimately they pile up because some oddity in nature makes one spot accumulate more sediment than other spots, allowing that windblown pile of stuff to grow. Sometimes it’s because of the wind interacting with the shape of the pile, and sometimes it’s because of the trajectories of moving grains as the wind blows them along the ground. Here’s an example of three types adjacent to each other: 1) a big dune on the left (migrating towards the right), which is covered in 2) smaller ripples, and downwind of the big dune are 3) brighter intermediate-scale piles (that are surrounded by larger and, presumably, better-developed versions of the “smaller ripples”). (HiRISE ESP_044515_1620, NASA/JPL/Univ. of Arizona)

Dune shadows

Cosmic Diary by Lori Fenton - March 16, 2016

A Piece of Mars: Normally I post in color, but sometimes you need to back out to the grayscale images to see the big awesome things. This scene is 4.6×2.6 km (2.8×1.6 mi); the conical hill is 1.4 km (0.89 mi) wide. Sand-laden wind from the right is blowing streamers of dunes around the hill, which leaves a wake that stretches downwind. Some of the luckier hills on Mars have lovely dunes scarves like this, slowly shifting over the centuries as the wind brings in more sand. (HiRISE ESP_044258_1715 NASA/JPL/Univ. of Arizona)

How far does the wind blow stuff?

Cosmic Diary by Lori Fenton - March 07, 2016

A Piece of Mars: Hargrave crater has an amazing array of colorful surfaces, each of which reflects a different type of rock (this scene is 480×270 m or 0.3×0.17 mi). I like the ripples sitting on top of it all; I’ve long thought that much of the material in those ripples hasn’t moved very far from where it originated. Here’s a good example of why. The ripples on the greenish surface have incorporated some local greenish material. The same is true of the tan ripples in the lower left. I’d bet most of this stuff has only moved as far as it took to make the ripple it’s in. (HiRISE ESP_044161_2005 NASA/JPL/Univ. of Arizona)

What the Hack

ENCORE  A computer virus that bombards you with pop-up ads is one thing. A computer virus that shuts down a city’s electric grid is another. Welcome to the new generation of cybercrime. Discover what it will take to protect our power, communication and transportation systems as scientists try to stay ahead of hackers in an ever-escalating game of cat and mouse.

The expert who helped decipher the centrifuge-destroying Stuxnet virus tells us what he thinks is next. Also convenience vs. vulnerability as we connect to the Internet of Everything. And, the journalist who wrote that Google was “making us stupid,” says automation is extracting an even higher toll: we’re losing basic skills. Such as how to fly airplanes.


•   Ray Sims – Computer Technician, Computer Courage, Berkeley, California

•   Eric Chien – Technical Director of Security Technology and Response, Symantec

•   Paul Jacobs – Chairman and CEO of Qualcomm

•   Shankar Sastry – Dean of the College of Engineering, University of California, Berkeley, director of TRUST

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•   Nicholas Carr – Author of The Shallows: What the Internet Is Doing to Our Brains and the forthcoming “The Glass Cage”. His article, “The Great Forgetting,” is in the November 2013 issue of The Atlantic.


First released November 11, 2013.

Skeptic Check: Evolutionary Arms Race

ENCORE It’s hard to imagine the twists and turns of evolution that gave rise to Homo Sapiens. After all, it required geologic time, and the existence of many long-gone species that were once close relatives. That may be one reason why – according to a recent poll – one-third of all Americans reject the theory of evolution. They prefer to believe that humans and other living organisms have existed in their current form since the beginning of time.

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But if you’ve ever been sick, you’ve been the victim of evolution on a very observable time scale. Nasty viruses and bacteria take full advantage of evolutionary forces to adapt to new hosts. And they can do it quickly.

Discover how comparing the deadly 1918 flu virus with variants today may help us prevent the next pandemic. Also, while antibiotic resistance is threatening to become a major health crisis, better understanding of how bacteria evolve their defenses against our drugs may help us out.

And the geneticist who sequenced the Neanderthal genome says yes, our hirsute neighbors co-mingled with humans.

It’s Skeptic Check … but don’t take our word for it!


•   Svante Pääbo – Evolutionary geneticist, Max Planck Institute for Evolutionary Anthropology, author of Neanderthal Man: In Search of Lost Genomes

•   Ann Reid – – Molecular biologist, executive director of the National Center for Science Education, Oakland, California

•   Martin Blaser – Microbiologist, New York University School of Medicine, member of the National Academy of Sciences, author of Missing Microbes: How the Overuse of Antibiotics Is Fueling Our Modern Plagues

•   Gautam Dantas – Pathologist, immunologist, Center for Genome Sciences and Systems Biology, Washington University, Saint Louis

First released March 31, 2014.

It's All Relative

A century ago, Albert Einstein rewrote our understanding of physics with his Theory of General Relativity. Our intuitive ideas about space, time, mass, and gravity turned out to be wrong.

Find out how this masterwork changed our understanding of how the universe works and why you can thank Einstein whenever you turn on your GPS.

Also, high-profile experiments looking for gravitational waves and for black holes will put the theories of the German genius to the test – will they pass?

And why the story of a box, a Geiger counter, and a zombie cat made Einstein and his friend Erwin Schrödinger uneasy about the quantum physics revolution.


•   Jeffrey Bennett – Astronomer, author of What Is Relativity?: An Intuitive Introduction to Einstein’s Ideas, and Why They Matter

•   Beverly Berger – Theoretical physicist and the Secretary for the International Society on General Relativity and Gravitation

•   Hiawatha Bray – Technology reporter, Boston Globe, author of You Are Here: From the Compass to GPS, the History and Future of How We Find Ourselves

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•  Paul Halpern – Physicist at the University of the Sciences in Philadelphia, author of Einstein’s Dice and Schrödinger’s Cat: How Two Great Minds Battled Quantum Randomness to Create a Unified Theory of Physics


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