When the first episode of Bad Universe aired, my Aussie friends complained about us choosing Sydney as the impact site of a small asteroid. We chose it because most other major cities have already been wiped out in TVs and movies, and the Sydney Opera House was so iconic we knew it would make a great visual (it did).

But as much as my friends complained, they had it easy. Check out this impact site just a few thousand kilometers west of Sydney:

[Click to impactenate.]

That’s Shoemaker (formerly Teague) Crater, an old impact crater about 30 km (19 miles) or so across. It’s a bit tough to see, but it’s the oddly wobbly circular shape right in the middle of this photo. Craters this big are hard to see from the ground, and are easier to identify from space; this shot was taken by an astronaut on the International Space Station. Like many large craters, it has multiple rings around it, probably formed as massive shock waves from the gigantic impact slammed through the ground. There’s a ridge at the bottom of the high-res photo that’s part of a heavily eroded outer ring. This crater is in the Outback, with mostly brown rock punctuated by colorful salty lakes.

I knew it was old just by glancing at it. Young craters look young: fresh, sharp rims, obvious outlines, sometimes surrounded by rays (long, straight features pointing away from the center of the crater, formed when plumes of ejected material collapse). This one is sloppy, vague, faded. Estimates of its age vary. It may be as young as 570 million years, or as old as 1.3 billion years! Some estimates put it even farther back along Earth’s timeline. Australia itself is ancient, with some parts having been around for 4 billion years. This crater dates back to the Precambrian age, when the most sophisticated lifeforms on Earth were soft multi-cellular microscopic creatures; the first true fossils of hard-shelled life were still millions of years in the future, even for the younger age range of the crater.

It’s hard to imagine that our lush green and blue Earth was once covered with craters like this. Heck, a few billion years ago this one would’ve been considered small! But two things have changed that: for one, the solar system had a lot more rocks to toss at us back then. Things have thinned out considerably in the past few billion years. Plus, the Earth isn’t static: it’s dynamic, with erosion and continental drift wiping out really old craters. Only a few survive now, the ones that happened to be in very stable locations like this one. Studying them is like having a direct line to the past, though muffled by time and change. Still, it’s an amazing look into what things were like before life took hold on land all those eons ago.

Oh, one more thing: if the name is familiar, it should be. It’s named after Eugene Shoemaker, a geologist who was a pioneer in studying and identifying impact craters like this one. He died in 1997 in a car accident in Australia, so it’s fitting a crater there was named in his memory.

Image credit: NASA

- Raising an impact in Africa
- New study finds giant impacts aren’t periodic
- "Amateur" geologist finds a South American crater
- Deforestation reveals an old scar
- Terra spots an impact on, um, Terra
- Impact
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NASA’s Earth Observatory site just put up this amazing picture. I have to say, this is one of the cooler pictures from the International Space Station that I’ve seen. Not for it’s beauty or anything like that — though it is starkly lovely — but because of what it shows:

[Click to dicraternate.]

Obviously, that’s a volcano on the right: Emi Koussi, in northern Africa. But look to the left, almost at the edge of the picture. See that faded ring? That’s Aorounga — an impact crater, some 10 – 15 km wide, formed when a chunk of cosmic debris hit the Earth about 300 million years ago! So these are two craters, one formed from processes happening deep below the Earth, and one from events from far above. Yet both can be seen at the same time, from one vantage point: orbiting our planet somewhere above the surface but beneath the rest of the Universe.

Image credit: NASA

What would sunset look like if you were on the planet HD209458b, a gas giant orbiting a star 150 light years away? According to exoplanetary scientist Frédéric Pont, it looks like this:

Isn’t that pretty? And there’s quite a bit of science in that, too.

First things first: HD209458 is a star pretty similar to our Sun. It was one of the first stars determined to have a planet orbiting it (way back in 1999) — the aforementioned HD209458b, nicknamed Osiris — and it turns out the planet’s orbit is so close to edge-on as seen from Earth that we see that planet passing directly in between us and that star once per orbit. When the planet transits that star the amount of light we see dips a little bit. From that we can get the period of the orbit and the size of the planet (a bigger planet blocks more light).

But we can get more, too. There’s a camera on board Hubble called the Space Telescope Imaging Spectrograph, or STIS. It can take the light from an object and break it up into thousands of separate narrowly sliced colors, called a spectrum. By analyzing that spectrum we can find out an astonishing amount of things about astronomical objects: their temperature, rotation, even their composition!

Shortly after HD209458b was discovered to be a transiting exoplanet, STIS was pointed at the star. The camera took hundreds of very short exposures during a transit in the hope of being able to detect the atmosphere of the planet. Osiris was known to be massive, about 70% as massive as Jupiter, so it most likely has a thick atmosphere. It also orbits so close to its parent star — 6.7 million km (4 million miles), much closer than Mercury orbits the Sun — that the heat from the star puffs the atmosphere up, making it easier to see.

In fact, the spectra did reveal the presence of an atmosphere; the first time the atmosphere of an alien planet was ever observed. Different elements and molecules absorb light at different colors, so in the spectrum there are dark spots where the planet’s air absorbs the light from the star behind it during a transit, and how dark that spot gets tells you how much light is absorbed.

It’s this information Prof. Pont used to create the image above (inspired by investigation and an animation done by Alain Lecavelier des Etangs). By knowing the color of the star itself, and using the way the planet’s atmosphere absorbs light, he created this image of the star using sophisticated computer modeling. (more…)

Never tell me the odds!

Yegads. I saw this while I was outside the other day; that’s a lenticular cloud, shaped by winds blowing over the Rocky Mountains. We see a lot of them around Boulder, but this one looked really familiar. I suddenly realized: it’s a ship from Star Wars!

I thought it looked a lot like Queen Amidala’s ship. But I couldn’t be sure, so I sent a note to my pal Bonnie Burton, aka BonnieGrrl, the proprietor of grrl.com, and major Star Wars dork. She concurred with my conclusion of the cloud looking like a Naboo Royal Starship (I was careful not to bias her by suggesting it; she mentioned it herself). And Bonnie should know: she literally wrote the book on Star Wars crafts!

Still, it looked like another ship from Star Wars, too… maybe even one that might be carrying Vader himself. If that’s the case, I know which cloud I could really use now!

Moisture and updrafts matter not. Look at me. Judge me by my convection do you? Hmm? Hmmm?

Carolyn Porco, the leader of the Cassini spacecraft imaging team, tweeted about this picture last night, and it’s simply overwhelming:

This is a stunning portrait of Saturn taken by the Cassini spacecraft in December. Its beauty and fantastic — in the literal sense of being like a fantasy — cloudscape are so overwhelming you might not even notice the moon Tethys hanging just under the knife-edged rings. To give you an idea of how immense Saturn is, "tiny" Tethys is over a thousand kilometers across.

This picture was taken using an infrared filter, where details in the clouds come out. That, plus the shadow of the rings on the southern hemisphere, make this one of my favorite pictures of Saturn I’ve seen in quite some time.

Astronomical imagery is a tricky business. Different objects behave differently, emitting light in different ways. So, for example, a cool dinky star might give off very little blue light — through a blue filter it virtually disappears — while a hot, massive star blasts out blue light. Your choice of filter can drastically change the way an object looks.

Having said that, I recognized right away that this image is the core of the nearby galaxy M82… but it still looks funny to me:

[Click to galactinate, or grab the huge 12.5 Mb image.]

One reason this new image from Hubble looks funny to me is that there aren’t as many stars in it as I expect. M82, also called the Cigar Galaxy due to its elongated shape, is pretty close as galaxies go, about 12 million light years away. It’s one of the closest large galaxies in the Universe, and a Hubble image usually shows it littered with stars, so closely packed they form a bluish background glow in most pictures.

And while that background of stars is there, it’s more diminished than usual because in this image astronomers used a series of filters that accentuate the light emitted by gas. While stars put out this kind of light as well, these filters downplay starlight and crank up the volume on, um, gaslight. Specifically, blue and green are from oxygen, red is from sulfur, and teal is hydrogen. The dark material is dust: long-chain molecules that absorb starlight. They also tend to redden light coming from behind them, similar to the way haze in the air makes sunsets look red.

Clearly, M82 is lousy with gas and dust in its core. (more…)

I am fascinated by junk floating around stars. And no, not paparazzi, har har. I mean circumstellar material, literally gas and dust orbiting other stars. We see it around stars that are dying, we see it around stars being born, and we see it even after stars are well into their youth.

One such young’un is the bright and shiny HR4796, a star 240 light years away, with about twice the mass of the Sun. It’s known to be less than 10 million years old — compare that to the Sun’s age of 4.56 billion years; we’re 450 times older! — and has also been known for some time to have material around it in the shape of a ring. New observations by Japan’s huge 8.2 meter Subaru telescope have provided some of the sharpest views of this ring ever taken, and revealed some surprises.

Isn’t that lovely? [Click to enannulusenate.]

This picture is in the infrared, well outside what the human eye can see. The star itself is so bright it’s saturated, overexposed. That part of the picture is blocked out to make it easier to see details around it, but the star’s position is marked with a dot. The tendril-like structures radiating outward are not real, but are artifacts of the image processing techniques. You can ignore them.

The important thing is the ring itself, which is easy to spot. It’s almost certainly a circle, but we’re seeing it at an angle (about 13° from edge-on) so it looks like an ellipse. It’s huge; 22 billion km (14 billion miles) across, more than twice as wide as our entire solar system.

Again, the ring has been known for some time; for example it was seen in Hubble observations back in 2009 [NOTE: as astronomer (and my friend) Glenn Scheider points out in the comments below, HR 4706's ring was seen long before 2009. I wasn't clear when I wrote the previous statement; I was only alluding to one particular earlier observation, but it wound up sounding like it was the earliest such observation. My apologies for any confusion.]. But there is some new stuff here. For one, if you look along the long axis of the ring, you can see it looks fuzzy. That’s real! The ring is made of dust grains of various sizes, probably the result of bigger clumps colliding with each other and grinding themselves up into ever-smaller pieces (the authors of this reasearch (PDF) call this a "collisional cascade", my new favorite phrase for 2012). These grains of dust orbit the star, and the smaller ones get blown away from the star due to the pressure of its fierce light. Bigger grains are less affected, so they tend to stay in place.

So the main ring is made of bigger grains, while the smaller ones are blown back, forming a larger, extended ring. That fuzzier outer ring is fainter and harder to see, but we see it more easily along the long axis because of geometric effects (similar to why soap bubbles and giant shells of cosmic gas look like circles in space). So even though we only see a part of this outer ring, the fact that we only see it in those two spots is what makes it clear we’re seeing a ring at all! Funny how that works.

(more…)