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All posts for the month June, 2011

Asteroid Flys By, Earth is Still Here

This image of Asteroid 2011 MD was shot by Marco Langbroek five hours before the closest approach, using a "remote" telescope, the 0.61-meter F/10 Cassegrain of Sierra Stars Observatory (G68) in California. The CCD image is a 30-second exposure. The fast moving asteroid has tracked a clear bright trail on the image during these 30 seconds. Field center is approximately RA 15h35m57s, dec. +19.441 degrees. Image from 08:32:00 to 08:32:30 UTC (June 27th 2011).

While you were doing your daily thing a little while ago, a little chunk of rock flew by our planet at a distance of 12,000 kilometers (7,500 miles).  It was Asteroid 2011 MD, an Earth-grazing object that is about ten meters (about 30 feet) wide and tumbling through space on its way over our atmosphere and through our flock of artificial satellites.

As NASA scientists predicted, the rock didn’t pose any danger to the planet. But, this is yet another reminder that we live in a solar system populated with stuff that also orbits the Sun, stuff that we don’t always see until the last minute. And, every so often, we do spot something that comes uncomfortably close to our planet. This is perfectly normal in solar system asteroid populations and their orbital dynamics, and is usually nothing to worry about. Until it is.

So far, we’ve been lucky, but let’s put this into perspective. The last really huge bash into our planet made life miserable for the dinosaurs some 65 million years ago, but it wasn’t made by a ten-meter-wide rock. That object was more like 10 kilometers (16 miles) across. Meteor Crater in Arizona was dug out by something about 50 meters (about 150 feet) across, and that impact probably made life miserable for whatever animals (woolly mammoths, maybe) that happened to be ranging around that formerly grassy and temperate plain on that fateful day some 50,000 years ago.

A lot has been made about the fact that we need some sort of “asteroid early warning system” to keep us apprised of such close flybys. We seem to have one now, since this one was discovered on June 22, 2011. But, I think what the community really wants is better detectors to find these things earlier. The little rocks,which are harder to spot, aren’t quite so much a danger as the big rocks — which we should be able to spot sooner than a few days before they get close enough.

What should we do with that information? Just what we do now. We note the approach, the speed at which the object is traveling, and its size and rotation rate, and astronomers around the world (both amateur and professional) arrange to get images of the thing. In fact, for this one, images and movies are already starting to stream in to places like Spaceweather.com. More will show up as astronomers track its passage.

What if a newly discovered rock is bigger than these little guys, and headed straight for us? Well, that’s the scenario that worries scientists and makes the press salivate and write about each asteroid as if it were “the” one. Such a press frenzy for every little rock chunk  is not scientific, but it does sell click-throughs and page views. Believe me, if the big one were on the way, it’d be hard to keep scientists quiet about it, and I can just imagine the über-frenzy the press would lapse into.

Not only would scientists want to study it all the way in (I mean, come on — the opportunity to study an asteroid both visually and spectroscopically as it plunges through our atmosphere is at once an interesting scientific study and a sociological phenomenon), but every politico, evangelist, and wannabe commentator would have their own take on what it “means”. I don’t know about you, but I’d far rather see rational scientific discussion rather than uninformed ranting… but perhaps I’m damning the pundits unfairly ahead of time.

Nah.

In the meantime, we should embrace the science that’s being done on the little guys that rush past. Each one tells us a bit more about our near-Earth orbital environment, and sometimes we even learn more about the kinds of debris chunks that flash past in the night.

A Star?  A Planet?  What?

Back when I used to work at the planetarium, we’d get phone calls from people — or they’d walk up to the console after a star talk and show — asking about a bright object they saw in the sky one night. Usually, the “thing” turned out to be a planet (if it wasn’t moving during the course of several minutes), or if it wasn’t that — then we’d have a chat about airplanes, helicopters, etc.  They never got confused by the Moon, although there were always questions about things they thought they saw ON the Moon’s surface whilst gazing through binoculars or a telescope.

This was in the days before the International Space Station, but there were still plenty of other satellites — “space birds” — to be seen, and we’d talk about those, too, because people would see them and wonder “Just what is THAT?” Nowadays, we can go online and find a whole listing of space bird sighting opportunities, plus predictions for ISS passes, and using that information, be ready to spot something besides a planet, high-flying jet, or flock of birds.

The view of Spica and Saturn to the west-southwest around 10 p.m. from latitude 40 degrees northin late June, 2011. Click to embiggen. Done using Stellarium.

People are always surprised when I tell them that they can see the ISS from their backyards. No doubt many people HAVE seen ISS and didn’t know that’s what they were looking at.  There’s something pretty cool about stepping outside at the right time (and you can find out when and where in the sky it will next appear over YOUR house by going to Spaceweather.com’s “Flybys” page and plugging in your zip code (if you’re in the U.S. or Canada), or here at www.Heavens-above.com.)

For folks in the northern hemisphere, these summery nights are great times to get out and check out the stars and planets (and flyover spacecraft). Actually, southern hemisphere viewers should bundle up warmly (if it’s cold in the evenings in your locale), and check out the sky, too.

I’ve given you some links to check out possible ISS and satellite passes, and if you need a star chart, check out the website at SkyandTelescope.com or go here to Skymaps.com for either a northern or southern hemisphere star chart).  These nights, Saturn is in the west-southwest after sunset.  That’s definitely a planet. It’s not far from the bright star Spica, and if you look at it through binoculars, you should be able to make out the star Porrima, right next to it.

There’s a lot of stuff out there to find in the sky. Sometimes it’s natural… sometimes it’s a human construct passing by. Whatever it is, get out there and check it out!  The skies provide free entertainment and have for as long as people have been looking up!

A Cloudy Precursor to a Violent Stellar End

You can’t see it in the evening skies right now, but the bright, old star Betelgeuse that makes up one of the shoulders of Orion, the Hunter (visible beginning late in the year), is giving up more of its secrets even as it continues down the road of old age and eventual disruption by a supernova explosion. Betelgeuse is a red supergiant star.  It’s so big that if you placed it in our solar system in place of the Sun, its “surface” would be out at the orbit of Jupiter.  But, Betelgeuse’s influences stretches far out beyond that.  Why?  You have to understand something about this big old star. It’s big. It’s old. And when big, old stars get older, they shed much of their material out to space in an intense stellar wind. In the final step of aging, such stars can lose as much as one solar mass (that is, the amount of mass it takes to make the Sun) in just about 10,000 years.

For Betelgeuse, scientists describe this mass loss as two processes:  the first occurred when huge plumes of gas began to snake their way out from the star into nearby space; the second one involves giant bubbles in the star’s atmosphere. Those bubbles move up and down through the atmosphere quite vigorously, similar to boiling water in a pan.

This picture of the dramatic nebula around the bright red supergiant star Betelgeuse was created from images taken with the VISIR infrared camera on ESO’s Very Large Telescope (VLT). This structure, resembling flames emanating from the star, forms because the behemoth is shedding its material into space. The earlier NACO observations of the plumes are reproduced in the central disc. The small red circle in the middle has a diameter about four and half times that of the Earth’s orbit and represents the location of Betelgeuse’s visible surface. The black disc corresponds to a very bright part of the image that was masked to allow the fainter nebula to be seen. Courtesy ESO/P. Kervella.

How do we know that this is what Betelgeuse is doing?  For one thing, astronomers have been able to image the plumes of material blowing away from the star. They used an instrument called VISIR (an infrared-sensitive camera) attached to the European Southern Observatory’s Very Large Telescope in Chile to measure the extent of the clouds of material coming off Betelgeuse. They found an interesting structure to the clouds (see picture at left). It almost looks like flames licking out from the star.  They’re not fire, but warm streams of  “star stuff” blowing away from Betelgeuse.

The astronomers’ observations show the plumes that are close to the star are probably connected to structures in the outer nebula now imaged in the infrared with VISIR. The nebula cannot be seen in visible light, as the very bright Betelgeuse completely outshines it.

Notice that the clouds of material are irregularly shaped, not symmetrical. This also tells astronomers that Betelgeuse hasn’t been losing its material at the same rate in all directions. In other words, the loss is not symmetrical.  This is indirect evidence that the bubbles in the atmosphere and their plumes are responsible for the nebula’s appearance.

So, what is this material that’s flowing away from Betelgeuse?

Based on the observations, it’s most likely that this stellar stuff is composed of silicate and alumina dust. This is the same material that forms most of the crust of the Earth and other rocky planets.

This is kind of interesting. Think about it.  It means that at some time in the distant past, the silicates that make up Earth were formed by a massive (and now extinct) star similar to Betelgeuse. It’s interesting to see evidence for that now, but in a star that is at least several hundred light-years away from us (possibly farther).

Now, you’re probably wondering when Betelgeuse will finally go supernova.  A good question. In cosmic timekeeping, it could be anytime, meaning anytime in the next million years. Stars die on lengthy timelines.  And, its distance will keep us from knowing that it happened until a few hundred years after the initial explosion. So, if Betelgeuse is, oh, say 500 light-years away (and we don’t know for sure how far away it is, so I’m using that number as an example), and it blows up tomorrow, we won’t see that flash in our skies until the year 2511.  We’ll probably see an influx of neutrinos before that, emanating from the direction of Betelgeuse. Eventually, sky observers will see it start to get very large and bright in the sky, and once the initial flash dies out, they’d start to see a colorful, glowing nebula where Betelgeuse used to be.  It would be a bright source in radio and x-rays, a new “thing” to study in the annals of violent star death.

For now, however, astronomers are marking the progression of Betelgeuse’s “change of life” events by observing it as much as they can, in as many regimes of light as they can. Those continue to tell the story of this star’s inevitable death march.