A penetrating, double-ringed crater on Mars

By Phil Plait | September 27, 2012 6:55 am

Mars is weird. Right? I mean, it’s a whole other planet. So you expect it to be weird.

But then I see pictures like this one from the Mars Reconnaissance Orbiter’s HiRISE camera, and I am reminded just how weird it is:

[Click to chicxulubenate.]

Most craters you see are pretty simple: something impacts the ground at high speed, BOOM!, and you get a crater like a dish tossed into soft sand. But this one has two rings, one inside the other. That can happen with huge impacts producing craters hundreds of kilometers across, but this one is small, only 230 meters from side to side – an American football stadium would just fit inside this crater.

The most likely explanation for the double ring is that the Martian landscape here is layered. There’s rock and sand on the surface, but underneath that is a layer of ice. The big rim is from the displaced rock, and the inner, smaller ring is from the impactor plowing through the ice. Each layer has a different strength – rock is harder than ice – so it’s as if two craters were formed, one inside the other. Radar observations of Mars from orbit have indicated there’s ice under the surface in this region, so that fits.

Similar double-ringed craters have been seen on Mars – though the structure and history is by no means well understood! – and some have been found on the Earth’s Moon as well. Those tend to be big, as I mentioned, though they don’t have to be.

By the way, the image above is color enhanced to show details. The blue may be from carbon dioxide frost, which can be seen in similar color-enhanced HiRISE images. The ripples in the center are sand dunes, sculpted into parallel waves by the ceaseless Martian wind.

Craters this small on Earth are extremely unlikely to form; the impactor would be maybe 20 meters or so across, and objects that size tend to break up when they ram through our thick atmosphere at high speed. Mars has much thinner air, so rocks that size can hit intact. Studying craters on Mars is a chance to see what these hypervelocity impacts are like under very different conditions, which helps us understand them. The physics of extremely high-speed collisions is hard to study experimentally – accelerating large objects to that kind of speed is both difficult and more than slightly dangerous – so it’s nice to have a lab like Mars where we can observe these effects.

Tip o’ the lens cap to HiRISE on Twitter. Image credit: NASA/JPL/University of Arizona.

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- Mars craters are sublime
- Desktop Project Part 1: A weird Moon crater
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- A fresh Martian impact

CATEGORIZED UNDER: Cool stuff, Pretty pictures

Curiosity's looking a little blue

By Phil Plait | August 14, 2012 12:54 pm

We have a fleet of spacecraft at Mars right now, including the amazing Mars Reconnaissance Orbiter and its equally amazing HiRISE camera, capable of taking very high-res pictures of the planet below.

The folks managing HiRISE just released a new picture of Mars showing the location of Curiosity, and it’ll wow you for sure:

Wow!* [Click to enaresenate.]

The colors have been enhanced in this image – which actually makes things very interesting. As I’ve pointed out before, most of Mars is covered in basalt, a blue-gray rock. When you hear about sand on Mars, it’s usually coarse-grained stuff made up of eroded basalt. However, there’s also much finer-grained dust which is high in iron oxide – rust – and it’s that which gives Mars its characteristic ruddy color.

That fine dust covers everything, making the planet red/orange/ochre. But there’s wind on Mars, and it can blow the dust around, revealing the grayer basalt underneath (like the dust devils do). And if there’s no natural wind, why, the thrusters from the rockets of a sky crane hovering over the surface as it lowers a one-ton rover to the ground will do just fine.

That part is actually pretty obvious in the picture. The thrusters blew around the dust, revealing the rock underneath, giving the landing site a bluer cast in the image (remember, it’s color enhanced). In the first images from the rover you can see that as well, but not as clearly as here. In fact, in the high-res version you can see the streaks from the individual rockets under the sky crane immediately around the rover, which then fanned out to produce the larger region of disturbed dust.

And as an added bonus, the rover itself can be seen sitting pretty right in the middle!

Note that this is a small, small portion of a vastly huger picture from HiRISE showing an incredible slice of Mars. The colors and landscape in that (also enhanced) picture are jaw-dropping, and you should take a look.

Wanna see more? I created a gallery of my favorite images of and from Curiosity from its first week on Mars.

Image credit: NASA/JPL/University of Arizona

* See?

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CATEGORIZED UNDER: Cool stuff, NASA, Pretty pictures

Gallery – Curiosity's triumphant first week on Mars

By Phil Plait | August 13, 2012 7:00 am

Curiosity landing site: the whole mess

By Phil Plait | August 8, 2012 7:00 am

A new picture returned from the HiRISE camera on the Mars Reconnaissance Orbiter shows an overview of the Mars Curiosity rover landing site, showing all the hardware that took it safely to the surface!

Coooool. Click to barsoomenate.

It’s like an episode of CSI: Gale Crater. You can see the Curiosity rover itself (labeled MSL for Mars Science Laboratory, the official name), sitting in a circle of dust disturbed by the landing rockets in the sky crane at final moments of descent. The sky crane impact site is to the upper left, several hundred meters away. The crane lowered the rover to the surface, disconnected the cables, then flew off to a safe distance. Note the plume of disturbed material pointing away from the direction to the rover, indicating the crane hit the ground at a low angle and not straight down (in which case the splash pattern would be more circular).

The parachute and backshell are off to the left. The backshell was literally that: a protective shell on the back of the rover and crane assembly to which the parachute was attached. That disconnected while the crane and rover were still well off the surface, to avoid getting tangled.

Finally, the heat shield is off to the lower right. That was the blunt capsule under the whole package that protected it from the heat of atmospheric entry; you can see it detach and fall to the ground in the descent video I posted recently.

These images are cool, but serve a solid purpose: they provide the engineers and scientists here on Earth evidence of precisely how the hardware performed. By looking at locations, dust patterns, and more, they can determine how well these devices did versus what was predicted. That’s important info for planning future missions, especially given how complex this landing sequence was. It really is a bit of forensics.

But it also says something else: we have hardware that made it to Mars! And we have photographic evidence of it!

The future. We are in you.

Image credit: NASA/JPL/University of Arizona

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- VIDEO of Curiosity’s descent… from the rover cam itself!
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CATEGORIZED UNDER: Cool stuff, NASA, Pretty pictures

Mars orbiter catches pic of Curiosity on its way down!

By Phil Plait | August 6, 2012 10:12 am

This is truly astonishing: the HiRISE camera on the Mars Reconnaissance Orbiter snapped what may turn out to be the Space Picture of the Year: Curiosity descending to Mars under its parachutes!

Holy. Haleakala.

The rover is safely tucked inside the backshell, suspended underneath its huge parachute. This image was taken just moments after Curiosity’s speed had dropped from thousands of kilometers per hour to just hundreds. Shortly after that, rockets underneath took over the job of slowing it further, so that the sky crane could lower Curiosity safely to the Martian surface.

This took incredible skills in calculations, engineering, and a just a wee pinch of good timing. Engineers here on Earth knew just where and when Curiosity would be coming down, so they were able to aim HiRISE at the right place at the right time. It strongly reminds me of a similar picture taken in 2008 by the same camera as the Phoenix lander descended to the surface of Mars. I suspect MRO was closer to Curiosity than it was to Phoenix, allowing higher resolution. [Update (16:40 UTC): More info about the picture can be found on the MRO HiRISE wesbite.]

The simple and sheer amazingness of this picture cannot be overstated. Here we have a picture taken by a camera on board a space probe that’s been orbiting Mars for six years, reset and re-aimed by programmers hundreds of millions of kilometers away using math and science pioneered centuries ago, so that it could catch the fleeting view of another machine we humans flung across space, traveling hundreds of million of kilometers to another world at mind-bending speeds, only to gently – and perfectly – touch down on the surface mere minutes later.

The news these days is filled with polarization, with hate, with fear, with ignorance. But while these feelings are a part of us, and always will be, they neither dominate nor define us. Not if we don’t let them. When we reach, when we explore, when we’re curious – that’s when we’re at our best. We can learn about the world around us, the Universe around us. It doesn’t divide us, or separate us, or create artificial and wholly made-up barriers between us. As we saw on Twitter, at New York Times Square where hundreds of people watched the landing live, and all over the world: science and exploration bind us together. Science makes the world a better place, and it makes us better people.

It’s what we can do, and what we must do.

Image credit: NASA/JPL/University of Arizona

Related Posts:

- Humans send their Curiosity to Mars!
- Best. Image. Ever.
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Mars craters are sublime

By Phil Plait | May 24, 2012 7:00 am

Someday, Mars will stop surprising me.

Today is not that day.

The image below was taken by the HiRISE camera on the Mars Reconnaissance Orbiter, which has been taking devastatingly high-res pictures of the Red Planet for many years. While passing over the edge of the Tharsis Shield — a huge uplifted region of Mars home to its four gigantic volcanoes –it saw this bizarre fieldof craters:

[Click to hephaestenate.]

First, you may think these are mounds and not craters, but that’s an illusion. Our brain uses illumination to gauge up and down in pictures like these, and assumes the sunlight is coming from above. However, these really are craters, but the illumination is coming from below — north is roughly toward the top of the picture and the crater field is at a northern latitude of about 50°. Flip the picture over if it helps (I’ll be honest, even doing that makes it hard for me to see these as other than mounds; confounded brain!). You can see more examples of this illusion here, here, and here.

But that’s not the weirdest thing about these craters. What’s really odd is they aren’t circular! Impacts are generally round unless 1) the impact is at a very shallow angle, b) the terrain suddenly goes from one kind of material to another, creating a discontinuity, or γ) something happened after the crater was formed to distort it.

A shallow-angle impact is almost certainly not the case here, since there are so many craters spread out over the region that an incoming object would’ve had to break up into a gazillion pieces, all of which came in at that angle. Not impossible, but it seems unlikely.

The changing terrain idea doesn’t work, since again the craters are spread out over the area. You might see one crater with a sudden break in its rim or change in shape, but dozens? Spread out in all directions? Nope.

That leaves after effects, and in this case we have two more clues. Read More

Desktop Project Part 17: Sculpting Martian dunes

By Phil Plait | April 11, 2012 6:30 am

[I have a lot of astronomy pictures I've saved to my computer's desktop, so I've pledged to post one every day in an attempt to regain control of my machine. I call this my Desktop Project.]

Speaking of Martian winds…

Mars is a pretty interesting place. A lot of the surface is covered in dust and sand, and while the air there is very thin, it can move with terrific speed. That gives it enough momentum to push that solid material around. The small-grained dust is far easier to pick up and get blown around by that wind, and we see lots of clear (and gorgeous) evidence of that in pictures from Mars. But the bigger, heavier basaltic sand is harder to move. Until recently there was no evidence of bulk dune motion at all on Mars*!

But the fantastic HiRISE camera on board the Mars Reconnaissance Orbiter has found that evidence: the motion of a Martian sand dune that took nearly two years to see:

[Click to barsoomenate.]

The animation shows the barchan (horseshoe-shaped) dune on June 25, 2008 and May 21, 2010. During that time, the sand was blown a few meters, and you can see the difference. It’s most obvious in the crescent-shaped part, but if you look closely (especially at the embiggened picture) you’ll see the rippling has moved as well, sculpted by the moving Martian air.

This fantastic image brings home (so to speak) an important point. There are, broadly speaking, two kinds of planetary missions: ones that fly past their target, like when New Horizons will blow past Pluto in 2015; and ones that go to their destination and stay. Flybys give us a great opportunity to see other worlds, and aren’t as expensive — you don’t need to bring all that fuel to slow down (like Cassini did) or pack parachutes and a lander. But as great and important as they are, we only get a fleeting glimpse of the target.

But when we go to stay, we get a long, long view. Long enough, in most cases, to see change. Mars is a dynamic, ever-evolving planet. And sometimes that change is slow, so we need the time to see it. And when we do, we see dust devils, landslides, meteorite impacts, and the march of dunes across the Red Planet’s surface.

It’s more expensive, and it’s harder, but it’s worth it to go someplace and settle in. Otherwise, you might miss something really cool.

* There’s evidence that the ripples on dunes have moved, but not that the dunes themselves have been moving as wind pushes them.

Image credit: Image credit: NASA/JPL-Caltech/Univ. of Ariz./JHUAPL

Related Posts:

- Between the Devil and the deep Red Planet
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- Martian dunes under the microscope

MORE ABOUT: dunes, dust, HiRISE, MRO, sand

A monster Martian vortex

By Phil Plait | April 10, 2012 9:45 am

In March, I wrote about a dust devil on Mars spotted by the Mars Reconnaissance Orbiter. It was 800 meters high, which I said was "huge".

Yeah. A week later, MRO spotted another dust devil… that was 20 kilometers high!

[Click to vortexenate.]


Dust devils form when air blows over warmer air rising off of the plains. If conditions are right, a vortex forms, becomes vertical, and you get a dust devil. It happens all the time on both Earth and Mars, and is common in the spring. It’s spring in the Martian northern hemisphere now, so there you go.

The folks at MRO put together a cool video to show what this monster would have looked like from the ground, and how it moved. Mind you, this is based on the image: shadows and sun angle give the height, and the shape of the shadow tells you the shape of the funnel. [You may have to refresh the page if you don't see the video directly below.]

What a sight! I’ve seen dozens of dust devils, including some that were clearly hundreds of meters high, and they’re mesmerizing and eerie. This picture is a reminder that as different as Mars is from Earth, there are also some striking similarities. And that just because Mars is smaller and has a thinner atmosphere, not everything it does is on a smaller scale than here.

Related Posts:

- Between the Devil and the deep Red Planet
- The artwork of the Martian landscape
- Martian dunes under the microscope
- A tornado made of fire. Seriously.
- The devil is in the details

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: dust devil, HiRISE, Mars, MRO

Between the Devil and the deep Red Planet

By Phil Plait | March 7, 2012 10:45 am

Mars is a pretty incredible place. It’s way too easy to easy to think of it as a cold, dry, dead world, but that’s not really true: it has an atmosphere (though thin), it has seasons, and it even has weather.

Circling the Red Planet is the Mars Reconnaissance Orbiter, and with its HiRISE camera it has a fantastic view of the changing face of the planet. And it so happens that sometimes MRO is looking at just the right place, at just the right time, to capture astonishing events… like this magnificent twisting dust devil towering over the landscape:

Holy wow! [Click to barsoomenate.]

This picture is just amazing. Dust devils are wind vortices, like tornadoes, but generally not as violent. They form when sunlight warms the surface of Mars. The air just above it gets warmer and rises. If there is a crosswind, it can blow across the rising air and start it spinning like waves breaking on a beach. But since the air is rising, it can lift up vertically while still spinning, forming a dust devil.

I’ve seen them here on Earth all the time; driving across the American southwest one day I saw dozens, including one that was easily a hundred meters across. And so it happens on Mars too. But I’ve never seen one like this! Given the shadow and height of the Sun when this shot was taken, the devil must have been 800 meters high — a half a mile! That’s huge.

The dust devil actually was relatively vertical until a height of about 250 meters above the ground, where the wind caught it and swept it back into that serpentine shape. The path of the dust devil was actually fairly straight; it’s just the plume being whipped around that makes it look wavy (the shadow on the surface adds a wonderful depth to it as well).

Devils usually commonly leave behind interesting tracks on the ground as well as they sweep away dust, which can be phenomenally beautiful and intricate. That’s not easily apparent in this closeup, but I’ve included a shot here that shows a much larger area — you can see the dust devil at the bottom for scale — and there are bright tracks all over the place, where earlier devils have swept up surface material.

As the folks at HiRISE point out, it’s interesting that these tracks are bright and not dark as usual. The area seen here has thick dust that is too heavy to be picked up by the devil’s winds, but there is lighter dust scattered around on top of the thicker material. It’s likely that after the dust devil moves, the lighter, brighter material swirls and settles behind the vortex, forming those tracks.

Dust devils are most common in the spring, when atmospheric conditions are best for them, and it happens to be late spring in this location on Mars. And having seen dust devils like this on Earth — where they are mesmerizing and fascinating — I have to wonder. Will my descendants someday put on a pressure suit and protective gear, walk out an airlock into a rusty landscape and butterscotch sky, and see a phenomenon like this towering above them?

I hope so. I surely do.

Related Posts:

- The artwork of the Martian landscape
- Martian dunes under the microscope
- A tornado made of fire. Seriously.
- The devil is in the details

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: dust devil, HiRISE, Mars, MRO

Frosty blue dunes on Mars

By Phil Plait | February 27, 2012 7:00 am

It’s been a while since I’ve posted a jaw-dropping high-res picture from Mars, so how about this one: a gorgeous shot of frost coating dunes on the surface of the Red Planet?

[Oh yes, you want to click that to enaresenate.]

This picture was taken by the HiRISE camera on board the Mars Reconnaissance Orbiter, which takes extremely detailed images of the surface of the planet. It shows wind-driven sand dunes on Mars, rippling in a similar way as on Earth. The sunlight is coming from the upper left direction, and where the light hits the surface you can see the familiar reddish cast; that’s actually from very fine-grain dust laden with iron oxide — rust!

But the shadows, where the Sun doesn’t reach, it’s cold enough that carbon dioxide in the Martian air freezes out, forming a thin layer of dry ice on the surface. In this image — where the colors have been enhanced so you can see the effects better — this shades the dunes blue. You can see the frost not just covering the dunes in general, but hiding in the troughs of the ripples too (which I think is why the sunward facing parts of the dunes can look blue; that’s from the ripple shadows). The non-color-enhanced version showing the entire dune region can be found here — and is stunning in its own right.

These dunes fascinate me. The sand on Mars is actually basaltic, making it look grey to the eye. Those grains are big enough that they don’t move as easily as the finer dust, and they pile up to form the big dunes, with the redder dust coating them. The color can change when frost forms, as in the picture above, but you also get incredibly dramatic and simply stunning patterns when dust devils — tornado-like vortices that form when wind blows over warm air rising off the surface — lift up the red dust and expose the grey basalt underneath. The swirling patterns are intricate and incredible, as you can see in this picture here (click to embiggen and get more details).

Pictures like this remind me viscerally that these objects we see in the sky are not just some distant lights, they are whole worlds. They have fantastic details and are as diverse and have complex interactive systems as any we find on Earth. This makes their study important, fascinating… and of course, astonishingly beautiful.

Image credit: NASA/JPL/University of Arizona. Tip o’ the heat shield to HiRISE on Twitter.

Related posts:

- The artwork of the Martian landscape
- Martian dunes under the microscope
- The Devil is in the details
- Happy first day of spring… Mars!

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures

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