June 27, 2011 at 11:21 am | Leave a Comment
Asteroid Flys By, Earth is Still Here
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.
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.
June 26, 2011 at 11:41 am | Leave a Comment
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.
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!
June 23, 2011 at 12:54 pm | Leave a Comment
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.
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.
June 22, 2011 at 12:25 pm | Leave a Comment
Cassini Probes Subsurface Oceans of Enceladus
Take a look at that moon. It’s called Enceladus and it orbits the planet Saturn. It looks all serene and quiet, in this view. And, probably looks cold and lifeless.
But, in reality, this little world has a hidden ocean beneath that icy surface. And, as on Earth, when we we think “ocean”, we often think “life”.
How can such a cold-looking place support an ocean? Doesn’t it have to be… um… warm? Well, as it turns out, a confluence of gravitational forces (between Saturn, Enceladus and neighboring moons) keep the subsurface water just warm enough to exist as in a liquid-slushy state. Couple that with tectonic actions that crack the surface and allow water under pressure to escape out to space, and suddenly Enceladus is way more than a quiet, icy world. It’s a place that spouts plumes of ice crystals out to space.
And, since the Cassini Solstice mission spacecraft is there studying those worlds, and occasionally sails through these plumes, we get an instant sample of the interior saltwater reservoirs of Enceladus after it has sprayed out to space. The plumes originate from the ‘tiger stripe’ surface fractures at the moon’s south pole, and create the faint E-ring, which traces the orbit of Enceladus around Saturn.
Today, NASA and ESA released information about the sampling runs that the Cassini spacecraft has been making through the icy plumes that the spacecraft first discovered in 2005. During three passes, done in 2008 and 2009, the mission’s Cosmic Dust Analyzer measured the composition of icy grains that had just been ejected from Enceladus. Close to the moon, the plume particles are large and rich in salt. In fact, about 99 percent of the total mass of solid material ejected through these plumes is very salty — but most of it falls back to the surface of this icy world.
So, how salty are we talking about? It appears that the particles that are the saltiest have what scientists call an “ocean-like” composition. That tells us most of the ice that gets shot out in the plumes comes from liquid salt water inside Enceladus.
Scientists studying these plumes have come up with this scenario to explain the plumes: deep underneath Enceladus’ surface, perhaps 80 km down, there is a layer of water between the rocky core and the icy mantle (structural layers). It is kept liquid by tidal forces generated by Saturn and some neighboring moons, as well as by the heat generated by radioactive decay (from elements that exist inside the moon and have been there since it formed).
Salt in the rock dissolves into the water, which accumulates in liquid reservoirs beneath the icy crust. When the outermost layer cracks open, the reservoir is exposed to space. The drop in pressure causes the liquid to evaporate, with some of it flash-freezing into salty ice grains: together these create the plumes.
Roughly 200 kg of water vapor gets lost every second as these plumes stream out to space. According to the team’s calculations, the water reservoirs must have large evaporating surfaces, otherwise they would easily freeze over, and that would stop the plume action dead.
This is one of those findings that simply amazes me about what we are able to learn from our science missions in space. If I walked up to you on the street and asked you, “How can we figure out whether or not a frozen world out near Saturn has subsurface oceans, and how much salt would they have, if they exist?” you would look at me blankly. It’s not on your daily radar, but that doesn’t make such a discovery unimportant. If you stop to think about why we’d even want to know such a thing, it wouldn’t take long to make a connection between water, salt water, warm salt water and… life. And, finding out places in our solar system where life could survive (and this is NOT a story about whether or not life exists there — that’s a whole other issue), tells us a lot about places where it DOES survive and exist. Mainly, here on Earth. We know of extreme places on Earth that have similar environments to Enceladus — and life exists in those Earthly habitats. So, now we know of at least one other place in the outer solar system where the conditions to harbor life mimic those on Earth. Kinda makes Enceladus seem all warm, fuzzy, and neighborly, all of a sudden. Not that life is there… but, the cradle of life is possible there.
June 20, 2011 at 14:40 pm | Leave a Comment
Exploring an Ice World
I took a week off from writing (everybody needs a short vacation, right?) and am now back in front of the screen, going through the latest astro-news.
What caught my eye first thing today was the ongoing Cassini Solstice mission. It’s the little spacecraft that just keeps going and going. While her older sisters Voyager and Pioneer are out exploring the outer limits of our solar system, and her little sister New Horizons is headed to Pluto, Cassini keeps sending back images and data about the Saturnian system. The latest views are of a little moon called Helene.
It’s an icy world, which is why I tuned into the story. Today, June 20, we woke up to snow (which has since turned to rain). Seems rather incongruous the day before summer solstice (for the northern hemisphere). But, the snow outside reminded me of the snow “out there” – orbiting Saturn like a lopsided iceberg.
It doesn’t take a very close inspection of the image to see the mottled, serrated-looking surface of this little world and to figure out that it looks just plain cold. As to be expected, since temperatures of ice worlds are far, far colder than the conditions we experience here on Earth. Helene is really an irregularly shaped chunk of ice that orbits Saturn in the same orbital path as another moon, Dione. It appears to have been beat up by collisions with other debris in Saturn’s orbit.
Spotting Another Ice Chunk in Space
The distant solar system contains many icy bodies, including these chunky worlds orbiting the gas and ice giant planets. But, there are icy chunks out there that aren’t gravitationally bound to any planets — and astronomers using the Pan-STARRS telescope on Haleakala in Hawai’i spotted one of them just outside the orbit of Jupiter. It’s a comet, called C/2001 L4 (PANSTARRS). A preliminary orbit computed by the Minor Planet Center in Cambridge, Mass., shows that the comet will come within about 30 million miles (50 million km) of the sun in early 2013, about the same distance as Mercury. The comet will pose no danger to Earth.
The good news about this find is that as it gets closer to the Sun, astronomers have excellent chances to study this comet and figure out just how bright it will appear to be in our skies. If conditions are right, once the comet gets close enough to Earth (say, within the orbit of Mars), it should start to sprout a plasma tail. That’s the tail of ionized gases that streams out from a comet when it gets close enough to the Sun for solar radiation to heat up the gases (and cause them to glow).
It’s tough to know right now just what the composition of the comet is — certainly it’s made of ice. But, how much dust is embedded in that ice? What kind of ice is it? Astronomers should be able to tell as they study the comet’s tail with spectrographs (instruments that break up the light from an object into its component wavelengths — and each gas gives off a specific “fingerprint” in the spectrum).
Astronomers think that this comet could be on its first trip around the Sun. It mostly like comes from the Oort Cloud, that collection of icy objects left over from the formation of the Sun and planets, some 4.5 billion years ago. This cloud lies at the very fringes of the solar system and is a treasure trove of objects that can tell us what conditions were like ‘way back when.
Keep an eye out for this comet in a couple of years. It probably won’t be easy to spot, but if you do see it, you’ll be seeing an object that harks back to a time when our Sun was still forming and the planets were still a work in progress.
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Copyright 2013, Carolyn Collins Petersen
Image of Horsehead Nebula: T.A.Rector (NOAO/AURA/NSF) and Hubble Heritage Team (STScI/AURA/NASA)
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