Blogs / Bad Astronomy

Steve Newton of the wonderful National Center for Science Education has written another article promoting science in the Huffington Post, this time about asteroid impacts. And special bonus; he gives your loyal host here a shout-out.

Specifically, he mentions that I have said that the Hale-Bopp comet was larger than what wiped out the dinosaurs. It’s true: the object that created the Chicxulub crater off the coast of the Yucatan was something like 10 km (6 miles) across. The nucleus of Hale-Bopp was roughly 60 km (36 miles) across, meaning it would have had something like 100 times the mass of the dinosaur killer. I have vivid nightmares about asteroid impacts, and one 100x the size of the K-T extinction event is beyond scary.

Right now we lack the capability to stop such a comet impact; Hale-Bopp was discovered less than two years before it sailed by the Earth. It missed us by a huge margin, but had it been aimed at us things would look a lot different around here right now. We may be years away from being able to stop such an event, but as I’ve written before, people like Rusty Schweikart and Dan Durda are seriously considering what we can do, and have even started the B612 Foundation to look into it.

If we’re serious about such threats, were just a few years away from being able to prevent them. Given that statistically big impacts are very rare and only happen every few hundred thousand years or so, I’m rather liking where we stand right now. But that’s if we actually do something now. We need to start working on mitigation techniques, and rockets to carry them. I’m glad the B612 Foundation is working on it.

Related articles: A Pro-science article on HuffPo?

I’ve been posting sporadically on how sunspots are starting to come back to the Sun, and I’m glad to see a new group sprouted up recently… and it’s a monster:

These images are from SOHO, the Solar and Heliospheric Observatory. The orange one is in visible light, and the sunspots are pretty obvious. The green one shows the Sun in the far ultraviolet, and you can see the sunspots are pretty intense, blasting out high-energy light. Sunspots are indicators of magnetic activity, and the intense magnetic field can accelerate plasma (ionized gas) to high energies.

Just so’s you know, a hundred Earths could fit across this image, so that oughta give you an idea of just how big these blemishes are.

What this means is that the Sun is becoming active again. You can see it better in this video I put together using SOHO animations. These are real SOHO observations. Note that some of the data are missing so the Sun’s rotation is a bit jerky, and that you can see that data dropouts and other problems plague these sort of observations. Oh– actually, another group popped up on the Sun earlier, too, and you can see those in the visible light data.

You can actually see the plasma flowing along the magnetic field lines in the latter part of the video.

Right now, the Sun is struggling to climb back up to the peak of its magnetic cycle, which will probably occur in 2013 or later, given how slow this has been — which you might want to keep in mind if some crackpot or scammer is trying to sell you on the idea that solar activity will destroy the Earth in 2012. When the Sun is at its peak, the magnetic field is at its strongest, and we see the most sunspots. However, the strongest solar flares and other explosive events tend not to happen until well after the cycle peaks, so it’ll be late 2013 or 2014 before we see the most vigorous activity, if the Sun holds to its previous behavior.

Again, people selling you on 2012 disasters generally have a very tenuous grasp on science. The less you know the better for them.

I expect we’ll be seeing more and more sunspots now as time goes by. It’s nice to see this happening, as it adds to the activity seen in December, and ends a long period of minimal sunspots — heck, for a long time, there were none at all. Boring. Now we can look forward to some exciting action again… just in time for SDO to launch, too!

[P.S. If anyone can tell me why the first few frames of my uploaded videos turn gray sometimes, that would be nice. I don't know whether to curse iMovie, Flash, YouTube, or all three.]

Image credit: SOHO (ESA and NASA)

Apropos of my recent post showing a Hubble image of two asteroids colliding, the website Word Spy just happened to have a funny choice for their word of the day: cosmophobia, "the strong and irrational fear that in the near future the earth will be destroyed by some cosmic event."

Personally, I figured it’s really for people who don’t like vodka, triple sec, cranberry and lime juice all mixed together, which is silly. Unless it’s headed for you at 30 km/sec. Because that’ll give you a pretty wicked hangover.

Last week, the Lincoln Near-Earth Asteroid Research (LINEAR) sky survey program, designed to sweep the heavens looking for near-Earth asteroids, spotted something really weird; an elongated streak that looked as if two asteroids had collided. Just days later, Hubble was pointed at the object, and what it saw was really really weird:

[Click to armageddonate.]

This is a false-color image showing the object, called P/2010 A2, in visible light. The long tail of debris is obvious; this is probably dust being blown back by the solar wind, similar to the way a comet’s tail is blown back. What apparently has happened is that two small, previously-undiscovered asteroids collided, impacting with a speed of at least 5 km/sec (and possibly faster). The energy in such a collision is like setting off a nuclear bomb, or actually many nuclear bombs! The asteroids shattered, and much of the debris expanded outward as pulverized dust.

Now, let me just take a moment and say HOLY HALEAKALA WHAT WE’RE SEEING HERE IS THE COLLISION BETWEEN TWO PREVIOUSLY UNDISCOVERED ASTEROIDS THAT EXPLODED LIKE THERMONUCLEAR WEAPONS WHEN THEY IMPACTED!!!

Phew. OK, I feel better. I needed to get that off my chest.

First off, to be clear we’re in no danger from this event. It was really far away (in human terms; 140 million km or 90 million miles — the object’s orbit keeps it farther from the Sun than Mars — so we’re not about to get pummeled with debris. And while the explosion energy was quite large — certainly much larger than any weapon ever detonated on Earth — it wasn’t radioactive, in case you’re worried about that sort of thing. This was a kinetic explosion, caused by a high-speed collision, and not an actual detonation of any kind.

Looking at the image, the bright spot to the left is most likely what’s left of one of the two asteroids, a chunk of rock estimated to be a mere 140 meters (450 feet) across. In the press release they’re not clear about the curved line emanating to the right of the nucleus. It may be — and I’m spitballing here — dust blown back from a stream of chunks, since the tail is broad and appears to originate from that swept curve, and not from the nucleus itself. The other filament perpendicular to the curve is from yet another piece of debris.

Despite how much this looks like a comet, ground-based observations indicate no gas is present, meaning this was from asteroids colliding, not comets, which have significant amounts of ice which turn to gas near the Sun. The collision energy was high enough to produce a lot of gas if any were present. That clinches this being an asteroid impact.

Also, the orbit of the object indicates it’s an asteroid, and it appears to be part of a well-known group of asteroids called the Flora family, which share similar orbital characteristics, and are probably remnants themselves of an ancient breakup of a much larger parent asteroid.

Nothing like this has ever been seen before. Sure, Hubble and about a hundred other telescopes observed the comet Shoemaker-Levy 9 slam in to Jupiter in 1994, but that was different than seeing two asteroids hit. Asteroids are small, and very very far apart on average (don’t believe scenes like that in "Empire Strikes Back"), so a collision like this is extremely rare, and catching it from such a great vantage point rarer still. But we have a lot of eyes on the sky, and the more we watch the more we’ll see.

And we’d better. An object 140 meters across hitting the Earth would, to be technical, suck. Hard. Whatever caused Meteor Crater in Arizona, an impact scar over a kilometer across, was itself probably about 40 meters across. An object like 2010 A2, which is three times the diameter, would have 20 -30 times the mass, and do considerably more damage. I’m glad groups like LINEAR are out there patrolling the skies for such things. We need to learn as much as we can about these asteroids, so that we can prevent the next Meteor Crater from occurring.

While high over the grasslands of Kazakhstan, the Terra Earth-observing satellite saw something interesting… can you spot it in this image?

Not so easy, is it? But if you look just left of center you’ll see this:

See it there, right in the center? It’s the Chiyli impact crater, an ancient scar from a cosmic collision. The crater is roughly 1.5 km across (about a mile) — about the same size as Meteor Crater in Arizona — meaning the object that created it was something smaller than a football field, moving at perhaps 30 km/sec (20 miles/sec). It hit about 46 million years ago, give or take. Long after the dinosaurs, but long before us, too. Note that it’s a double-rimmed crater too, which sometimes form in large impacts depending on the conditions of the impactor and the ground.

This is a false-color image, at least part of which is in the infrared; vegetation appears red, water blue, and bare land is "earth tones" (browns and tans). This sort of imagery allows scientists to investigate how vegetation, land, and water change over time.

When I first saw this image, I didn’t see it as a crater, but more as a raised annulus, a ring in the ground. I knew immediately that this meant that in the picture, the sunlight was coming up from the bottom, and it turns out that’s correct. It’s a cool and optical illusion; when we see craters illuminated from below, they look like domes, and vice-versa. In the picture here, I flipped the image and now, to me at least, it looks more like the depression that it really is. The wide inner rim is more obvious, too.

Here’s an even better example:

Is it a dome…	… or a crater?

It just goes to show you that finding evidence of extra-terrestrial events on Earth can be tough, and even when you find them you can’t rest easy. They’re apt to fool you one way or another.

The Wide-field Infrared Satellite Explorer has detected its first near-Earth asteroid! Named 2010 AB78, it was discovered in mid-January by the orbiting observatory. Here’s an image of the rock:

AB78 is about a kilometer (0.6 miles) or so across, making it one of the bigger asteroids that can buzz the Earth. The orbital information on it isn’t perfect yet, but we already know its orbit doesn’t actually cross the Earth’s so it can’t hit us. At closest approach it’s still many million of kilometers away from us, and poses no threat.

However, I’ll be honest and say this discovery is mildly alarming (stressing the word mildly). One of the missions of WISE is to find such asteroids; some rocks are dark and therefore hard to detect using telescopes which search in visible light. However, AB78 is warm, so it glows in the infrared, making it an easy target for WISE. That’s why searching for such asteroids is one of WISE’s main goals.

The thing is, statistically speaking we should already know of almost all the kilometer-sized rocks that are in near-Earth orbits; given the rates and methods of finding them, our catalog should be about 90% complete. Finding an asteroid this size that eluded detection up until now is somewhat unsettling. How many more have we missed?

Let me be clear: this could be a statistical fluke; even if we know of 90% of all the NEAs out there, 10% still lurk out in the black. It could simply be that this first one found by WISE is somewhat on the hefty side, and the next 20 will be far smaller. Remember too, this one is bright in the IR (in the above picture, red is actually at a wavelength of 12 microns, 15 times longer what the human eye can see) and so it was easy to spot. Smaller ones are fainter, so they may not be as obvious and will take longer to detect. Also, AB78 is on a weird orbit, tipped substantially (about 33°) to the plane of the solar system, again making it more difficult to spot.

And in a way, this is good news! The more we know about these things, the better. AB78 may be a fluke, or there may be more rocks this size out there hiding, but either way I want as much info as we can get. Just knowing how many asteroids of a given size orbit the Sun and get near the Earth is an important piece of data, so that we can apply some statistics to them and try to figure out, on average, how often we get hit. That’s one of the things WISE will do over its 10-month-long mission, so in a year or so we’ll be in a better position to understand these orbiting worldlets.

Emily Lakdawalla at The Planetary Society has more info as well.

Image credit: NASA/JPL-Caltech/UCLA

A small meteorite, about the size of a tennis ball or so, crashed into a Lorton, Virginia doctor’s office on Monday, according to several reports including one in the Washington Post. No one was hurt, but there was some damage — not surprising, since it must have hit at a couple of hundred kilometers per hour (it’s a Hollywood myth that small rocks hit at huge speeds with flames drawn out behind them; they slow down to highway-like speeds while they are still dozens of kilometers off the ground). The Maryland Weather blog has a picture of the interplanetary interloper — there’s a clear fusion crust (the blackening of the surface from heat), which is a giveaway it’s a meteorite.

There were hundreds of eyewitness reports of the fireball reaching as far north as New Jersey, so the rock must have been traveling southward. There may be other pieces along the path, most likely near where this one hit. I wonder if there were other people who may have seen small debris hit but haven’t put the story together? If you live in that area (it’s actually near where I grew up, which is neither here nor there, but still makes me faintly jealous) then keep your eyes and ears open for any stories. It’s still pretty rare to be able to collect specimens from recent falls, making this a very valuable find– both scientifically and financially!

[Update: Nancy Atkinson has video on Universe Today, too.]

Tip o’ the Whipple Shield to Bill Smith.