Blogs / Bad Astronomy

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.]

Today (as I write this), the Cassini spacecraft passed just a hair under 100 km (62 miles) from the surface of Enceladus, an icy moon of Saturn. This little moon is scientifically incredibly interesting; there are geysers at the south pole that are spewing out water! The images are just now coming in, and have not been calibrated or processed yet, but they are still breathtaking. I particularly like this one:

[Click to embiggen, as usual.]

That, me droogs, is high art. Enceladus was about 190,000 km (118,000 miles) away from Cassini when that shot was taken, a little under half the distance of the Earth to the Moon. From this angle, Enceladus is lit in a gorgeous thin crescent, but we can see detail on the dark side, I suspect due to light reflecting off Saturn onto the moon. You can see ridges in the surface; the moon has a thick crust of ice presumably floating on an undersurface ocean of water (though there have been arguments about that), so the surface is a bit of a mess, looking for all the world(s) like ice floes seen at our own north pole.

The geysers are obvious too, blasts of light at the top of the moon’s limb as the water erupting from the south pole is lit by the Sun. Thumbing through the raw images is a delight (once there, set the target for Enceladus, choose both narrow and wide angle, and put in dates of October 30 through November 3 to narrow the search). You’ll see dramatic images of the moon, its limb, the geysers, and everything.

Stunning, and wondrous. And there’s better to come: as Carolyn Porco herself mentions on Twitter, the primary purpose of this flyby was not to get images; November 21st is the imaging flyby where we’ll see lots of spectacular shots of the moon. So stay tuned!

Image credit: NASA/JPL/Space Science Institute

Clearly, the artist behind The Stonemaker Argument is after my heart. And his daughter is an awful lot like mine…

[Click to see the whole thing...]

The link to this cartoon was left in the comments to an earlier post of mine, but deserves its on post, so tip o’ the Treknobabble to Andrew.

What is the source of cosmic rays?

Seems like an easy enough question. Cosmic rays are little subatomic particles zipping across the Universe. We’ve known about them for decades, and just about any astronomer who has used a space telescope knows and loathes them; cosmic rays zap our detectors, leaving bright streaks in the images which need to be tediously cleaned out before we can do any real science. I spent a large fraction of my time with Hubble doing just that.

But what’s generating them? They seem to come from all directions in the sky, making it difficult to pin down their source. They’re moving at fantastic speeds, so they must have a huge energy source behind them. For years, astronomers have suspected that they are accelerated to high velocities in supernovae explosions as well as in the fierce solar winds from massive stars. Recent evidence has been making that supposition seem more likely.

And now new results from the VERITAS gamma-ray telescope array have added fuel to that fire. VERITAS stands for Very Energetic Radiation Imaging Telescope Array System, and it’s located atop a mountain in Arizona. When energetic gamma rays (a form of light) hit the Earth’s air, they create a shower of subatomic particle that rains down and can be detected by the telescopes.

If cosmic rays come from supernovae and massive stars, then we should see more of them coming from galaxies that have a lot of stars being born. That’s because massive stars don’t live long. A nearby galaxy vigorously cranking out baby stars will therefore have lots of massive stars making cosmic rays. As a happy by-product, those same massive stars are the ones that blow up as supernovae, giving us a two-fer as far as cosmic ray production goes.

Such a galaxy exists: M82, a weird-looking one located a mere 12 million light years away (it’s close enough to see in binoculars, in fact). The image above is M82 as seen by Hubble, Chandra, and Spitzer. Astronomers trained VERITAS on M82 and took a very, very long exposure. What they found is that is is a weak source of gamma rays, but definitely above the background level. The amount detected is consistent with cosmic rays being generated in the violent environment of the galaxy which then slam into the gas surrounding the stars, generating gamma rays. Another process, called inverse Compton scattering, is probably behind this as well: when a low energy particle of light called a photon hits a cosmic ray, its energy is pumped waaaay up, and it becomes a gamma ray. Think of it like gently throwing a rubber ball in front of a speeding truck on the highway; the ball suddenly and violently finds itself with a lot more energy.

This all may not seem like a big deal, but it is. For one thing, there are a lot of cosmic rays flitting about out there, so knowing what they are and how they formed is clearly a big piece of understanding the high-energy Universe. Also, these cosmic rays may have an effect here on Earth. Scientists have been studying how they may interact with the Earth… and while the effect, if any, is incredibly small (people still argue over whether there is anything to this at all, like cloud formation and such) it’s worth investigating.

And I want to add something that makes me smile. The cosmic rays (which, remember, are subatomic particles) from M82 were detected because while still inside that galaxy they make gamma rays, a form of light, which then travel straight to Earth. But once those gamma rays hit our air they create subatomic particles once again, which are what VERITAS detects. So there are several steps to this process, with cosmic and gamma rays going back and forth until we actually detect their effect. It goes to show that sometimes the key to our understanding the Universe can involve subtle processes piled one atop the other, and it’s up to us to carefully peel back those layers to get to the underlying processes underneath.

If you’re anywhere near southern Florida on Saturday, November 7, then you need to get yourself over to the Broward College, which is holding the very first celebration of Carl Sagan Day!

It’s in honor of Sagan’s birthday, which is on November 9th. He would’ve been 75 this year. Sagan inspired a generation of astronomers, and in reality a whole generation of people to look at the sky and appreciate the — yes, I’ll say it — cosmos.

Celebrating his life is a great idea, and the folks at BCCC have a full day planned (the schedule is online in PDF and Word formats). A lot of good speakers will be giving talks, including my friend Jeffrey Bennett (who wrote Max goes to the Moon series of kids’ books), skeptic and "Point of Inquiry" podcast host D. J. Grothe, and NASA astrobiologist and impact expert David Morrison (via satellite). I’ll be giving my Death from the Skies! talk at 4:00 (with David there, I’ll have to be on my toes). They’ll be showing "Cosmos" continuously in one room, with kids’ activities in another. There’s a planetarium show in the evening, too.

And this will be very special: James Randi will be there, talking about Sagan. The two were friends. Randi has a lot of personal insight on the man and will have wonderful things to say. This is a don’t-miss opportunity, folks. I think I’m looking forward to that part most of all.

For more info, there’s contact info on the Carl Sagan Day website. Also, there’s a writeup in the Broward/Palm Beach New Times.

This really will be a fun and wonderful tribute to Sagan. I’m very pleased and honored to be a part of this great day for a great man.

Regular readers know that Saturday Morning Breakfast Cereal is one of my favorite web comics. This morning, he had an astronomy-themed bit of snark:

I’ve blocked out the woman’s reply, so you’ll have to click through to see the punch line.

And I love Zach, the artist, I really do, but…

SPOILER for the joke:

Meteorites are after they hit the ground. Meteors are when they are still in the air and glowing, and the solid part is called a meteoroid. There is no semantic definition of when a meteoroid is is big enough to be called an asteroid, but given the size depicted in the cartoon, I’d say that one counts.

See? This is why you shouldn’t date an astronomer. Unless you like that sort of thing. Oh baby! Talk cosmic to me!

Tip o’ the Whipple Shield to Brian Carroll who tweeted the link to Rebecca at Skepchick, who is in turn technically correct in her title since I’m married and Mrs. BA can kick anyone else’s asteroid herself.

As promised, Brian Cox was on The Colbert Report last night, and hit it out of the park. The whole show was better than average (which is saying a lot) but Brian truly rocked!

If you missed it (and live in the States) the whole episode is online (Brian’s segment is about 13:50 into the episode). Comedy Central won’t allow embedding the whole show (sigh), and Brian’s segment isn’t separated out on the CC site, but right before he was on Colbert ragged on physics and the LHC:

In the full segment, they talk about Brian’s book Why E=mc², which was excellent. I’ll try to write a review of it as soon as I can. In the meantime, I do have to praise Colbert for his insight; as Brian points out he was correct in his ideas! I was cheering along with the segment. It still cracks me up that the smartest and most insightful commentary on TV is not from any of the "real" news stations, but from satirical shows like Colbert and The Daily Show. They have better science coverage than CNN, MSNBC and anyone else combined.