I know I just posted a MESSENGER photo of craters, but this one is different and spectacular enough that I figure, why not? I love a big, splashy, wide-angle shot of a rayed crater! So here’s the lovely, 80-km wide impact crater Debussy on the surface of Mercury:

[Click to haphaestenate.]

Craters make rays when the ejected material blasted out forms long plumes which fall across the surface. On airless worlds, those trajectories are ballistic, heading straight out from the center of the impact. Deeper material tends to be a lighter shade than surface material, so the interior of the crater and the rays are lighter than surrounding surface stuff. You can also see what’s called the apron, the layer of material that falls immediately around the crater, surrounding it (that’s more clear in an earlier image of the crater looking more straight down on it).

Rayed craters are common (even on our Moon; take a look at Tycho!), and usually indicate the impact was recent (geologically), since the rays eventually get eroded by the solar wind, cosmic rays, and subsequent meteorite impacts. Debussy is therefore one of the younger features on Mercury. It still has that youthful shine.

Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

The MESSENGER spacecraft, orbiting Mercury for nearly a year now, took this pretty nifty shot of the tiniest planet’s south polar region, showing deep, dark craters in the Goethe basin:

This region is about 300 km (180 miles) from the true south pole of the planet. On Earth that might be a cold spot, but on Mercury, cold spots are hard to come by.

… however, see how dark those craters are? Since they’re near the pole, the Sun never gets far above the horizon for them, and the crater floors are shrouded in perpetual darkness. That does make them cold! Well below the freezing point of water, it’s thought. Interestingly, radar observations of Mercury have indicated something in the crater floors is highly reflective, and water ice fits that bill. It’s not at all confirmed, but it’s entirely possible Mercury — a planet hot enough in the open Sun where zinc can exist as liquid lakes on the surface — might have frozen lakes of ice locked in crater bottoms near its poles!

While gazing idly at this picture, another thought popped into my head. (more…)

We live in an era of wonder, where people send robots to other worlds and view them close up. These machines get bathed in radiation, searing heat, bitter cold, suffocating vacuum, and they keep running. Moreover, they send their data back digitally, which can then be stored in a database and, if permissions are given, accessed by the public. And a subset of that public is educated in the ways of digital media, able to stitch together pictures, carefully aligning them, balancing them, coordinating borders and overlap regions.

The result? This:

Yegads. That is Mercury as seen by the MESSENGER spacecraft in 2008, as it flew by the planet for the first time. It would do so again before finally entering orbit in March 2011. But as it left the smallest planet, it snapped a series of wide angle and high-resolution images.

Gordon Ugarkovic is a Croatian software developer. He’s also an amateur image processor… for a sufficiently wide definition of "amateur". He takes space images and works his prowess on them, creating dramatic and beautiful images like this one of Mercury.

Click the picture to embiggen it, or you can also download a vast 5000 x 5000 pixel version that is, frankly, spectacular. Gordon used over 30 of the high-res frames from MESSENGER’s Narrow Angle Camera to make this mosaic, and then used images from the Wide Angle Camera to balance the color.

The 25 megapixel image is nothing short of amazing. Scrolling across it is like flying across the planet. I see features there I hadn’t noticed before, like a pale dark streak just south of Mercury’s equator, sharp cliffs called scarps that litter the surface, craters with bright rays of ejected material streaming out of them. It’s breathtaking.

Gordon has also done images of Saturn, Jupiter, and moons galore. You can follow his work at the Unmanned Spaceflight forum, or peruse his Flickr stream. But be warned: better have a lot of time handy. You’ll be spending it there.

Image used with permission. Tip o’ the heat shield to Dan Durda for tipping me off to the picture.

When an asteroid or comet impacts a planet, the explosion ejects huge amounts of material, sending it flying in all directions. But there are also plumes of material, long fingers of rock and dust that stream out as well. The boulders and such inside this plume then fall back to the ground, making linear chains of secondary craters. We see lots of these on our Moon, moons in the outer solar system, and Mercury, too.

If these features are long enough, it’s inevitable two chains from two different primary craters would cross somewhere. And it turns out this has been seen… but where?

Well, X marks the spot!

This MESSENGER image of Mercury shows exactly that: two crater chains from two separate impacts crossing over each other (and a third, shorter chain is at the bottom, too). They’re almost exactly perpendicular to each other, which is cool, and the intersection happens to lie in a big, shallow crater about 120 km (72 miles) across that fills this image. Unfortunately, MESSENGER hasn’t been orbiting Mercury long enough to have surveyed the whole planet yet, so I wasn’t able to find the source craters of these two chains.

Interestingly, both chains have elongated craters at their ends, one on the upper left and the other at the top. That indicates a very low-angle impact; anything hitting the ground from an angle above about 10° tends to make a circular crater. However, the one on the left appears to be right on the big crater’s rim, so the elongation may be due to the ground angle changing. The other may be coincidence; both are far too small to have been the source craters for the chains.

I’m not sure there’s any real scientific value in knowing these crater chains intersect or examining the intersection in detail. Still. They’re fun to look at, fun to explore, and they’re just seriously nifty.

UNLESS… hmmm.

NASA has just released more images of Mercury as seen by the MESSENGER spacecraft, and they’re pretty cool:

This first one is something of a repeat, showing the same region as the picture they released yesterday, but now it’s in color! Mercury is not exactly the most beautifully hued planet, but it does have some color to it. This composite was taken in the infrared (shown red in the image), red (shown as green in the image) and blue (shown as blue), and has a maximum resolution of about 2.7 kilometers (1.6 miles) per pixel. While most of the surface looks gray, look again: some of the craters do show subtle color variations. This is most likely due to the material excavated on impact — composition, particle size, and other factors change the way these features reflect light. This image only uses three colors, but the wide angle camera has eight 11 filters, which will allow planetary scientists to map the planet very effectively and learn about the composition and history of the surface.
(more…)

The MESSENGER spacecraft settled into orbit around Mercury earlier this month, and engineers have been busy making sure it’s functioning well. Now, the first pictures are coming in from the solar system’s innermost world, and as expected, wow!

Cooool! Or rather, hot. I mean, duh, it’s Mercury. [Click to ensmallestplanetate.]

The picture is dominated by the crater Debussy (named after the composer, who wrote "Clair de Lune", apropos of nothing, I suppose^*), an impact crater about 80 kilometers (50 miles) across. It’s a rayed crater, with plumes of ejecta leaving those long, linear features across the planet.

This image is the first ever returned from a spacecraft orbiting Mercury, but MESSENGER has already taken hundreds more, and thousands are planned during this commissioning phase (when the various instruments and spacecraft are checked out). The real science observations begin April 4.

Tomorrow, NASA will have a press conference and more images. I’ll have more info and more amazing pictures from Mercury to show you then!

Image credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

^* Oh, duh. After posting this article I realized he also wrote "Trois Scènes au Crépuscule". Why is that appropriate? Because Debussy is a rayed crater.

Just a quick note to y’all, since I’m in the middle of about eight things all demanding my full attention: the MESSENGER spacecraft will enter orbit around Mercury tonight at 9:00 p.m. EDT, after a tortuous 7-year journey. Once safely circling the planet, engineers will be focusing on making sure the probe is safe and sound, so it’ll be a while (days) before we start getting images.

I’m quite sure my pal Emily Lakdawalla will be poised for attack on every tidbit of news that comes in, so follow her on Twitter and on her blog at the Planetary Society.