It makes for a good movie: 12,900 years ago, a comet slams into Earth, igniting forest fires across North America and sending the planet into a thousand cold years, killing off mammoths, giant sloths, and a bunch of other big mammals. But scientists have fiercely debated whether such a movie, about the cause of the planet-wide cooling period called the Younger Dryas, should be documentary or science fiction. According to a paper recently published in the Geophysical Research Letters, new evidence–or refuted, old evidence–points to science fiction.
Those that think a comet hit the planet cite “carbonaceous spherules” and nanodiamonds found in sediment from the period of the suspected impact. They argue that these particles formed from the intense heat of the collision.
Lead author of this new study, Andrew Scott of the University of London in Egham suspects those spherules are not from a comet collision, but are bug poop, fungal spores, or charcoal pellets.
From a test that measures how much light the spherules reflect, Scott’s team has determined that the spherules were slow-roasted in a low-intensity heat (perhaps from natural wildfires) instead of in intense, comet impact heat. As shown in the figure, the researchers compare the charred spherules to fungal sclerotia, emergency cell balls created by stressed fungi that can germinate after a bad growing period is over, and saw a striking similarity.
Some of the more elongate particles are “certainly fecal pellets, probably from termites,” says Scott…. “There’s certainly no evidence [that any of these particles are] related to intense fire from a comet impact,” says Scott. Part of the problem, he says, is that “there was nobody [among impact proponents] who ever worked on charcoal deposits, modern or ancient. If you’re not familiar with the material, you can make mistakes.” [Science Now]
When you saw the Hale-Bopp comet, you may have seen material from a distant star passing by. In a new study, a team of astronomers argues that most of the comets that streak through our solar system were actually born in other solar systems.
Given their eccentric orbits and infrequent visits, comets seem like worthy candidates for an exotic origin. But the prevailing thinking said no, they are rather ordinary. Researchers thought most of the comets that pay us a visit initially formed from the sun’s protoplanetary disk—the same swirling mass that formed our own planet—and came to reside in the weird Oort cloud region at the periphery of our solar system. From there, the gravitational bullying of larger bodies can dislodge a few like Halley’s Comet or Hale-Bopp, which swerve into an orbit that sees them visit the inner solar system now and then.
In a study in Science this week, researchers led by Harold Levison posit a different idea: Many of the comets hanging around our solar system are stolen. It goes like this:
Like most stars, the sun may very well have been created in a tightly nestled birth cluster, a stellar nursery with tens, hundreds or possibly even thousands of stars. During millions of years of intimate infancy, the newborn stars could have exchanged vast numbers of comets from the fringes of their disks, each of them winding up with an ensemble of hand-me-downs from their stellar siblings [Scientific American].
Its doom was sealed six years ago.
In 2004, UC Berkeley researchers say, this comet was tugged by Jupiter’s gravity into a path bound for destruction in the cauldron of the sun. And when its end finally came this March, astronomers captured the comet plunging deep into the sun on video (see below), watching it go farther into the light than any suicide comet seen before.
Seeing comets and other small objects approach the sun is difficult because the objects are overwhelmed by the sun’s brightness. Scientists were able to track this one closer to the sun than ever, before it it burned up in the sun’s lower atmosphere [Wired.com].
Since NASA’s Stardust mission returned in 2006 from its trip of billions of miles collecting the dust of a comet called Wild2 and dropped it samples down to Earth in the Utah desert, the samples have raised all sorts of questions about how comets formed and what the early solar system was like. In a study this week in Science, there’s a new surprise. Scientists say that the comet sample contains chemicals that must have formed in our home turf, the inner solar system.
Lead researcher Jennifer Matzel studies a tiny particle taken from Stardust’s sample, a piece just five micrometers across. In it her team found the mark of materials that would have formed under high temperatures. Matzel, who specializes in using the decay rates of radioactive chemical elements to assess ancient dates, determined that the Stardust particle must have crystallized just 1.7 million years after the oldest solid rocks in the solar system were forming [San Francisco Chronicle]. After that, the researchers says, the particle must have been flung out to the Kuiper Belt, the region of icy comets revolving around the sun at a distance far past Neptune.
While Jupiter’s two largest moons, Ganymede and Callisto, are nearly the same size, they’re far from identical twins. Now, in a Nature Geoscience study, Amy Barr and her team might have figured out this tale of two similar moons with very different histories.
Voyager and Galileo mission images showed Ganymede, seen here on the right, to be a geologically active place, with a surface that scientists think changes through tectonic processes like those that we have here on the Earth. Callisto, seen on the left, looks totally different: Its rock and ice have not mixed in the same way, and it doesn’t seem to have such active geology, despite being approximately the same size as Ganymede. For 30 years, researchers have wondered what process could have got enough heat into Ganymede to drive its geological evolution without setting off Callisto as well [ScienceNOW Daily News].
Stars and other astronomical phenomena radiate across the electromagnetic spectrum, on both sides of the puny band of visible light that the human eye can pick up. NASA‘s newest toy, set for a Friday launch into space, will map the infrared portion of that radiation—and do it across the entire sky.
The Wide-Field Infrared Survey Explorer, or WISE, has been under construction since 2006. The satellite will spend six months mapping the entire sky in the infrared, after which it will make a second, three-month pass to further refine the mapping [Universe Today]. Stars, galaxies, comets, and other objects will fall under the explorer’s purview.
In the wee hours of Tuesday morning, 2009’s edition of the Leonid meteor shower will reach peak viewing time for sky-watchers in North America. Star gazers who lift their eyes to the heavens between 2 a.m. and 4 a.m. will likely be rewarded with a good show of “shooting stars.” A second, briefer, but very intense outburst is expected about 12 hours later — during the early-morning hours of November 18th in Asia [Sky & Telescope]. But that probably won’t last long enough for North Americans to see it when night returns here.
Like other meteor showers, such as the Perseids and the Orionids, the Leonids happen when Earth plows through a trail of debris left in the wake of a comet orbiting the sun [National Geographic News]. This comet, called Tempel-Tuttle, swings through the inner solar system about every 33 years, and last did so in 1998.
On special occasions we’ll pass directly through an unusually concentrated dust trail, or filament, which can spark a meteor storm resulting in thousands of meteors per hour. That indeed is what transpired in 1999, 2001 and 2002 [MSNBC]. This year won’t supply such a bonanza, astronomers predict, but we will see more meteors than average: probably 30 to 300 per hour, depending on where you are.
To get the most spectacular views, of course, you’ll have to venture away from city lights. But you won’t need to haul a telescope. For meteor showers, the naked eye is enough to enjoy the show.
Bad Astronomy: Will the Leonids Roar in 2009?
Bad Astronomy: Leonids ROCK! (Check out the link to the amazing Mt. Hopkins video of a Leonid shower)
80beats: Tonight’s Orionid Meteor Shower Should Be a Beauty, from October
80beats: Study: 20-Million-Year Meteor Shower Turned Earth Warm & Wet
This dazzling picture of our planet, all dark but the cerulean sliver of the South Pole, was a long time coming.
Rosetta, a European Space Agency craft, captured this view of the crescent Earth from about 400,000 miles away. The unmanned probe, which is busy chasing comets, was making its third flypast since it was launched in 2004. The close approach gave it a speed boost to send it on its mission to Comet Churyumov-Gerasimenko [Scientific American].
This will be Rosetta’s final visit to its home planet, having already executed a flyby of the asteroid Steins, a gravity assist with Mars, and two previous swoops past the Earth, gathering images all the way. Now it’s off to the comet.
Rosetta is carrying a fridge-sized lab, Philae, that it will send down to the comet. Anchored by tiny hooks, Philae will look for clues about the Solar System’s primal past, exploring a theory that comets are primitive rubble left over from the making of the Solar System [AFP].
While we bid safe travels to Rosetta, it could tell us something about the Earth itself on this final pass. Scientists notice unexpected behavior in spacecraft that make gravitational assists with our planet: Rosetta itself behaved exactly as expected in 2007 flyby but picked up an extra speed boost of 1.8 millimeters per second on its initial maneuver in 2005, leading some mission scientists to speculate that the Earth’s rotation might be distorting space-time more than they thought. “Some studies have looked for answers in new interpretations of current physics. If this proves correct, it would be absolutely groundbreaking news” [MSNBC], says Rosetta flight dynamics specialist Trevor Morley.
Bad Astronomy: Rosetta Takes Some Home Pictures
Bad Astronomy: Earth From Rosetta, from its 2007 flyby.
Bad Astronomy: Rosetta Swings By Mars!
DISCOVER: To Catch a Comet, which anticipated Rosetta, Stardust, and other comet-chasing missions.
Tonight, in the wee hours, dedicated star watchers and people just looking for a good celestial show will turn their faces up to the heavens to watch the annual Orionid meteor shower. The Orionids are so named because the meteors appear to radiate from near the constellation Orion, aka the Hunter. This easily spotted constellation “kind of looks like an hourglass with a very recognizable belt of stars,” said astronomer Mark Hammergren [National Geographic News].
The “shooting stars” are really tiny fragments of debris left behind in space by Halley’s Comet, which loops through the inner solar system every 76 years and leaves a trail of dust in its wake. Most fragments are tiny, only about the size of a grain of sand–but they still go out in a blaze of glory as they vaporize in the Earth’s upper atmosphere. The best time to watch will be between 1 a.m. and dawn local time Wednesday morning, regardless of your location. That’s when the patch of Earth you are standing on is barreling headlong into space on Earth’s orbital track, and meteors get scooped up like bugs on a windshield [SPACE.com]. Tonight’s star gazers will benefit from a dark, moonless sky.
NASA scientist Bill Cooke says the Orionids have been strong in recent years. “Since 2006, the Orionids have been one of the best showers of the year, with counts of 60 or more meteors per hour” [SPACE.com].
80beats: For the World’s Best Stargazing, Head to Antarctica
80beats: Perseid Meteor Shower Should Dazzle Despite a Bright Moon
DISCOVER: 20 Things You Didn’t Know About… Meteors
According to a theory proposed in 2007, the explosion of a comet over North America killed off the Clovis people and many of the continent’s largest mammals nearly 13,000 years ago. Not so fast, says a new study published in the Proceedings of the National Academy of Sciences, fueling a WWE-style stare down between the opposing camps.
The new report explains that archaeologists have examined sediments at seven Clovis-age sites across the United States, and found that the concentration of magnetic debris was insufficient to confirm an extraterrestrial impact at that time [Nature News]. The original theory’s evidence came from magnetic microspherules, or cosmic debris, discovered in sediments at 25 locations. However, one of the new study’s authors, Todd Surovell, said that even after 18 months of sedimentary analysis and hundreds of hours peering into a microscope, he could find no evidence of microspherules to support the the exploding comet theory. Snap.