Geminid meteor shower: why spectacular light show puzzles scientists

By Pete Spotts, Staff writer / December 13, 2011

Gemenid meteor shower watchers can’t figure out where all the material in the event comes from. Asteroid 3200 Phaethon, the apparent source of the Gemenid meteor shower, doesn’t seem to shed enough rock and dust to account for the shower’s intensity.

The Gemenid meteor shower lights up the sky over the Mexican volcano Popocatepetl. Daniel Aguilar/REUTERS/File

The Geminid meteor shower peaks tonight. Don’t miss it!
Geminid meteor shower gets rave reviews as best of 2010
By now you’ve probably heard that tonight’s the night for what is arguably one of the most spectacular meteor showers of the year, the Geminids.

The shower earns its name from its apparent point of origin, or radiant, in the constellation Gemini.

But where many meteor showers represent Earth’s encounter with dust from a comet, the Geminids appear to have an odd duck of a source: an asteroid that some now call a rock comet.

And it’s not clear from recent observations whether the object, known as 3200 Phaethon, is kicking off enough material to account for the intensity of the meteor shower Earth encounters.

A team of astronomers identified the debris gap in a paper published in the Astronomical Journal in November 2010. And researchers are still puzzling over it.

Although the first recorded observations of the Geminids don’t appear until the early 1860s, modeling studies of the debris’ orbit suggests that the stream is anywhere from 200 to 6,000 years old.

3200 Phaethon was discovered by NASA’s Infrared Astronomical Satellite in 1983. Once scientists determined its orbit, the orbit closely matched with the orbit of the debris stream.

One of the asteroid’s key features is its proximity to the sun at closest approach. It comes nearer the sun than any known asteroid, well inside the orbit of Mercury. This allows surface temperatures to reach 1,400 degrees Fahrenheit.

In their 2010 paper, David Jewitt and Jing Li at the University of California at Los Angeles looked at images from one of a pair of NASA sun-watching satellites taken of 3200 Phaethon during its close approach to the sun. Its brightness increased suddenly, indicating that it was shedding material, just as a comet might.

Given the asteroid’s rocky makeup, the team posited that the object’s relatively quick swing into and out of this hot zone leads to rock fracturing when heated. Comets, on the other hand, shed material when the ices they contain heat and shift directly from solid to gas. In the process, a comet also ejects dust and rock bound up with the ices.

To account for the intensity of the Geminid stream, the duo calculated, the 30-mile-wide 3200 Phaethon would have to repeat the shedding process 10 times per orbit, something no one has observed.

Dr. Jewitt allows in an e-mail exchange that their mass estimate could be off, and that additional outbursts during each orbit could emerge with more-systematic observations.

But for now, the grit gap remains.

So, bundle up, grab a chaise lounge, a Thermos of hot chocolate, and head out to see the show overnight tonight or even Wednesday night. The peak actually is expected to occur at about 2 p.m. Eastern Standard Time Wednesday.

But the shower, which typically produces more than 100 meteors an hour during its peak under dark skies, will be a bit less spectacular than it otherwise might be. Blame the bright, if waning, moon. Moonlight will wash out the dimmer meteor streaks.

Geminid meteor shower: why spectacular light show puzzles scientists – CSMonitor.com.

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New Tunguska Crater Found?

Jul 05, 2007

A team of Italian scientists has announced seismic evidence of what could be meteor fragments beneath Lake Cheko in Siberia–the first “solid evidence” of a Tunguska asteroid.


Lake Cheko in the Siberian region of Tunguska has recently emerged as a candidate for an “impact site” linked to the famous Tunguska explosion of 1908. Credit: www-th.bo.infn.it/tunguska / University of Bologna

On June 30, 1908, a massive explosion detonated in the skies over Tunguska in northern Siberia. The resulting shock wave flattened some 60 million trees across 2000 square kilometers. The blast was heard hundreds of miles away and the cloud of dust colored the skies of the Northern Hemisphere for months afterwards.

The first expedition to investigate the region could not locate any sign of an impact event, nor did it recover any meteoric fragments. A later expedition, however, did uncover magnetite globules and various forms of silicate globules embedded in the earth and in the trees.

Most scientists eventually settled on either an icy comet explosively vaporized before reaching the surface, or a small rocky asteroid exploding in the atmosphere and leaving no appreciable fragments. But the absence of definitive evidence for an impact invited many exotic theories–ranging from “mirror-matter” or a tiny “quantum black hole,” to an exploding alien craft or a Nikola Tesla experiment gone awry.

In past discussions of the Tunguska event, our Picture of the Day editors have suggested electric discharge between a small comet or asteroid and the Earth. That suggestion was based on a wide variety of recorded physical effects and the testimony of human witnesses.

More recently, however, a team of Italian researchers has suggested that the 164-foot deep Lake Cheko, five miles northwest of the epicenter of the blast, could be the site of an impact by a meteor or a fragment of the body responsible for the devastating Tunguska event.

The team reported that 3D sonar images of the lake’s bottom indicate that it is funnel-shaped, something that might be expected of both an impactor and an electric discharge. Using seismic detectors, the University of Bologna scientists discovered an area of greater density beneath the lake, noting that this could indicate the remains of a meteor. “When we looked at the bottom of the lake, we measured seismic waves reflecting off of something,” said Giuseppe Longo, a physicist at the University of Bologna in Italy and co-author of the study. “Nobody has found this before. We can only explain that and the shape of the lake as a low-velocity impact crater.”

According to a report on the Space.com web site, however, some physicists are skeptical about the small size of the Lake Cheko crater. “We know from the entry physics that the largest and most energetic objects penetrate deepest,” said David Morrison, an astronomer with NASA’s Ames Research Center. Morrison wondered aloud why only a fragment of the main explosion would reach the ground to make a relatively small crater, while the greater portion would not create a larger main crater.

But Alan Harris, a planetary scientist at the Space Science Institute, points out that, in 1947, the Russian Sikhote-Alin meteorite created 100 small craters. Some were 20 meters (66 feet) across. A site in Poland also exists, he explained, where a large meteor exploded and created a series of small lakes. “If the fragment was traveling slowly enough, there’s actually a good chance [the Italian team) will unearth some meteorite material,” Harris said.

The researchers will return to Tunguska this summer with plans to drill beneath the bottom of Lake Cheko, hoping to find a meteorite. From an Electric Universe perspective, if the Tunguska explosion was the result of an electric discharge, a meteor fragment may indeed be found, pointing to the source of the discharge. But more likely, the increased density beneath the lake could be the signature of the electric arc that excavated the depression, producing the fused sands and soils of a fulgurite.

By Stephen Smith

New Tunguska Crater Found?.

Asteroid 2011 AG5 Earth Impact Threat Should Be Studied More

by Leonard David, SPACE.com’s Space Insider Columnist
Date: 12 March 2012 Time: 05:47 PM ET

An artist’s illustration of asteroids, or near-Earth objects, that highlight the need for a complete Space Situational Awareness system. CREDIT: ESA – P.Carril

A massive asteroid that may be on a collision course with Earth should be studied in more detail, according to a former Apollo astronaut who specializes in monitoring potentially hazardous space rocks.

Asteroid 2011 AG5 has been the object of attention because scientists say it may swing close to our planet in the year 2040.

The big space rock is on NASA’s impact hazards list, but more definitive tracking of the object is still needed, scientists say. In fact, some near-Earth object (NEO) experts say it’s time to start hammering out a plan in case the asteroid needs to be deflected.

Former Apollo astronaut Russell Schweickart is calling upon NASA to undertake a detailed engineering and mission planning analysis of 2011 AG5.

In a March 3 open letter to NASA administrator Charles Bolden, Schweickart spotlighted what he sees as the potential deflection challenges posed by asteroid 2011 AG5, should the object happen to be headed for a so-called keyhole in 2023, setting up a possible impact with Earth in 2040.

Keyholes are small regions in space near Earth through which a passing NEO may be perturbed — due to gravitational forces — placing it onto a path that would strike Earth.

In this most recent communiqué, Schweickart questioned a view held by Bolden from an earlier exchange of letters between the two that a Deep Impact-like intercept of asteroid 2011 AG5 could be staged in enough time to derail a space rock from hitting Earth.

NASA’s Deep Impact probe was purposely crashed into comet Tempel 1 on July 4, 2005.

A more daunting challenge

While Deep Impact was a very successful mission, it is a poor analogy for the potential deflection challenges presented by 2011 AG5, Schweickart noted. To depend on such an impact mission to justify waiting until after the next tracking opportunities — before doing any further engineering analysis — is ill advised, he said.

Schweickart contends that a 2011 AG5 deflection campaign requires two missions, not one, as was used on Deep Impact. In addition, intercepting and impacting 2011 AG5 presents far more daunting challenges than was posed by comet Tempel 1.

In his open letter, Schweickart told Bolden that, “neither you nor I would have risked our lives without solid engineering having gone into our respective missions. In this instance again, there are potentially lives at stake, and I know you take that responsibility seriously, as do I.”

“To be clear, what I am asking for is specific engineering and mission planning analysis to be performed now in order to insure that we fully understand the timeline requirements, in the unlikely event that AG5 should be headed for the 2023 keyhole,” Schweickart wrote.

“We all realize it is highly likely that AG5 is not headed for an impact. But we must also hedge against the possibility that this will not be the case by being prepared to act, and not find ourselves awkwardly beyond the point where deflection remains an option,” Schweickart concluded in his open letter to the NASA chief.

NASA’s response

In response to the letter, Schweickart told SPACE.com that a NASA-organized teleconference was held on March 8 involving himself, as well as John Grunsfeld, NASA’s Associate Administrator for the Science Mission Directorate, Jim Green, Director of Planetary Science, and Lindley Johnson, NEO Observations Program Executive.

“It was a very constructive discussion and as a result we will be getting together in the next few weeks to discuss the various issues and options which would apply to a variety of future scenarios regarding 2011 AG5,” Schweickart said. “I’m looking forward to these substantive discussions and I commend John Grunsfeld and NASA for this positive response.”

Schweickart’s new letter to Bolden, “presents points we at NASA have considered in looking at the 2011 AG5 scenario,” Lindley Johnson told SPACE.com.

“A big concern with any mission analysis is that they are only as good the initial input conditions. The results you obtain are always dependent on those conditions,” he said.

Johnson said that if 2011 AG5’s orbit model in hand now turns out to be a good representation of where the NEO will be in the future, then a mission analysis could be done now, and such work would be worthwhile.

But, if the asteroid’s orbit isn’t that well defined, then a mission analysis would need to be mostly re-done after a better orbit is ascertained, he said.

“We are certain we will have a higher confidence model after observations are collected in another orbit of AG5,” Johnson said, “and we are confident we will have more than sufficient time to do both the mission analysis and undertake any response still necessary after that observation opportunity.”

“However, we will continue to study the AG5 situation, as we do continuously for all objects on the impact hazards list,” Johnson concluded.

Tools to monitor 2011 AG5

“There are logical reasons to start really planning to do something really soon … and analyzing AG5 really soon,” said Clark Chapman, a noted specialist in asteroids and a planetary scientist at the Southwest Research Institute in Boulder, Colo.

It has been generally thought that 2011 AG5 can’t be observed again until September of 2013, Chapman told SPACE.com. “That’s not true. We can see it again in August of this year.”

What’s needed is one of the largest ground-based telescopes on Earth, or the Hubble Space Telescope, Chapman advised. Doing so wouldn’t be too easy, “but in all probability could be done.”

For one, the asteroid is very faint and ground-based telescopes would need to slew toward the horizon in a really dark sky.

“Telescopes are sort of designed to look more or less up … rather than over,” Chapman noted. In the case of the Hubble Space Telescope, caution is the rule as it would be necessary to point the scope 42 degrees away from the sun to observe 2011 AG5, “but exceptions have been made in the past.”

Odds of an impact

Still, whether using these tools to eye the asteroid will improve our understanding of the asteroid’s track isn’t a given.

“We simply don’t know whether observations in August can make that much of a difference … but that’s another arena in which studies should be done in the very near term,” Chapman said.

In the meantime, more information about 2011 AG5 is needed, Chapman said.

“We don’t know how big this thing is,” he said. “And if it’s on the big side, it would be hard to move it away from the keyhole with only a few years planning. And if it’s really big, it’s hard to move it away from the Earth if it goes through the keyhole.”

Chapman stressed that the most probable result of more tracking of the asteroid is that the 2040 impact of Earth probability will drop to zero.

“I’m of the view that you can’t say, ‘let’s just wait and the odds are likely to go to zero.’ Yes, the odds are likely to go to zero…but suppose they don’t,” Chapman said.

Leonard David has been reporting on the space industry for more than five decades. He is a winner of last year’s National Space Club Press Award and a past editor-in-chief of the National Space Society’s Ad Astra and Space World magazines. He has written for SPACE.com since 1999.

Asteroid 2011 AG5 Earth Impact Threat Should Be Studied More | Near-Earth Objects | Space.com.