Blogs / Bad Astronomy

Speaking of HiRISE and Mars…

The Phoenix Mars Lander is sitting at the Martian north pole, its mission complete. Designed to study the history of water on Mars and investigate potential human habitability, it touched down in May 2008. It dug trenches and examined the surface soil of Mars for months, but the Martian winter was inexorable. Eventually, the intense cold forced engineers to shut Phoenix down (as planned), and there it still sits.

The HiRISE camera on the Mars Reconnaissance Orbiter took images of Phoenix last year while its mission was still active, in June 2008. Here’s that image:

Phoenix is pretty obvious! The surface there was relatively free of frost at that time. But scientists on Earth decided to get more images, this time during the winter. In July of this year they found Phoenix once again, but the picture is a little different!

First off, the green is not real; this is a false color image. So don’t go thinking they found moss bogs or anything like that. What you’re seeing is the same field as in the first picture, but this time its covered with carbon dioxide frost! Even Phoenix appears to have CO₂ over it, making it pretty difficult to see. I imagine that if they hadn’t taken the earlier picture, it would’ve been a lot harder to pick the lander out from the background.

Spring sprung on the northern hemisphere of Mars a couple of weeks ago, and in another few months scientists will try to contact Phoenix and see if they can wake it up after its lengthy hibernation. It’s a bit of a long shot — the mission wasn’t designed for it — but one thing we’ve learned about the probes we’ve sent to Mars is that they can be incredibly hardy: the two rovers are still operating years after the initial design lifetime. So maybe Phoenix will live again, and get back to work (expect other news sources to say it will rise from its ashes; a bad metaphor given that it’s covered in frost). And if it does, images like the ones above from HiRISE will help us back here on Earth interpret what it’s seeing. The more eyes we have on Mars, the better.

Mars is weird. It’s small, and cold, and has a thin atmosphere that’s almost entirely carbon dioxide, and what isn’t CO₂ is nitrogen and, bizarrely, argon.

So you expect to see weird landscapes. But even so, Mars has the potential to be really, really weird. Check this out:

That slightly disturbing image (click to embiggen) is not a microscopic picture of a scientist’s colon (at least, not as far as you know). It’s actually a region near the Martian south pole. It was taken with the HiRISE camera on the Mars Reconnaissance Orbiter, and the area shown is roughly 700 meters across (about 0.4 miles).

What you’re seeing are layers of the polar ice cap. The ice is mostly CO₂. Mars is so cold that a lot of the cap persists throughout the year, and is called the residual cap. Some of it does sublimate, though, which means it goes right from a solid to a gas. Underneath that layer is something more solid, perhaps water ice, that does not sublimate. As the upper layer partially goes away, it leaves these weird Swiss-cheese-like patterns, revealing the smooth layer below.

This image only shows a small portion of a much larger area where this occurs. Here’s the "context image", a zoom out if you will:

I marked the rough outline of the zoomed image in this one (it’s rotated about 90 degrees counterclockwise in the zoom). You can see that this odd terrain (aresain?) goes on for kilometers. It really does look like some sort of bacterial colony. But it’s actually the result of millennia, maybe millions of years, of constant annual atmospheric deposition and sublimation.

And just as a reminder — because I love to point this out — Mars was 250 million kilometers (150 million miles) away from Earth on August 20, 2009, when this image was obtained. Yet MRO was only 250 km above its target, yielding this fine imagery at a resolution of 25 centimeters (10 inches) per pixel. Got a ruler handy? Pick it up, hold it in your hand, and think on the fact that we have spacecraft orbiting Mars, an alien world, that can take pictures of objects on its surface about the size of that ruler.

Man. I love this stuff.

[P.S. If you like this image, the HiRISE page has wallpaper versions of it; the links are at the lower right at that link.]

1) The new Carnival of Space is up at Lab Lemming’s tent, and it’s a BIG tent.

2) Emily has news that Phobos is a bit lighter than previously thought. What a pile.

3) Emily also has some nifty new MESSENGER images explained. I’ve been too lazy to deal with that.

4) Tom notes that HiRISE spotted Spirit on Mars. Massively embiggenated version is here.

4) This is dumb. So why did it make me smile so much? Oh right: I’m a dork.

The instant I saw the avalanche image from the HiRISE camera on-board MRO orbiting Mars, I knew I would have a contender for my Top Ten Astronomy Pictures of 2008.

But then they released this one at the same time:

Yeah, that’s us. That’s home. We were 192 million kilometers (115 million miles) from Mars when HiRISE turned around and took this picture. Right away I could tell that was South America’s west coastline… which is incredible. I also was just starting to wonder about the Moon in the image when I read that it had been brightened artificially to make it easier to see; in general the Earth is 3-4 times more reflective than the Moon, so it’s a lot brighter.

The Mars-Earth-Sun angle was just about 90 degrees when this was taken, which is why the Earth and Moon are half-full. Note that in reality, the Moon is about 30 Earth-diameters away from the Earth, so we’re seeing some perspective here. The Moon was a day before third quarter when this was taken, so it was actually a bit closer to Mars than the Earth was when HiRISE snapped this picture.

Beautiful.

This is TOTALLY HAWESOME: an avalanche on Mars was caught in the act by the HiRISE camera.

This picture shows the billowing dust cloud from an avalanche of ice and dust along scarps — sheer cliffs — near the north pole of Mars. To give you a sense of scale, the cloud is about 180 meters across, and about the same distance from the base of the cliff.

Holy cow.

You can see the cliff in the middle of the picture. It’s 700 meters high (2300 feet!) and slopes at about 60 degrees; that’s pretty close to vertical. To the left you can see white carbon-dioxide frost (which is evaporating as spring ensues in the Martian northern hemisphere) at the top of the cliff.

If my (very) rough calculations are accurate, it would take a rock about 20 seconds to fall from the top of the cliff, and would hit the bottom at about 70 meters/second, or about 150 miles per hour. Look out below!

You can read lots more about this on the HiRISE page.

Sidenote: after the disappointing news from HiRISE this weekend, I feel a lot better about this. Totally amazing. I might even say ground breaking.

Update: The HiRISE blog has a more personal take on this as well.