Posted on by David Dickinson

Remembering the Great Meteor Procession of 1860

Painting of The Meteor of 1860 by Hudson River School artist Frederic Church. (Credit: Frederic Church courtesy of Judith Filenbaum Hernstadt).

“Year of meteors! Brooding year!”

 -Walt Whitman

July 20th is a red letter date in space history. Apollo 11, the first crewed landing on the Moon, took place on this day in 1969. Viking 1 also made the first successful landing on Mars, seven years later to the day in 1976.

A remarkable astronomical event also occurred over the northeastern United States 153 years ago today on the night of July 20th, known as the Great Meteor Procession of 1860. And with it came a mystery of poetry, art and astronomy that was only recently solved in 2010.

A meteor procession occurs when an incoming meteor breaks up upon reentry into our atmosphere at an oblique angle. The result can be a spectacular display, leaving a brilliant glowing train in its wake. Unlike early morning meteors that are more frequent and run into the Earth head-on as it plows along in its orbit, evening meteors are rarer and have to approach the Earth from behind. In contrast, these often leave slow and stately trains as they move across the evening sky, struggling to keep up with the Earth.

The Great Meteor Procession of 1860 also became the key to unlock a 19th century puzzle as well. In 2010, researchers from Texas University San Marcos linked the event to the writings of one of the greatest American poets of the day.

Whitman...
Photograph of Walt Whitman taken by Mathew Brady circa 1860 (Library of Congress image in the Public Domain)..

Walt Whitman described a “strange, huge meteor-procession” in a poem entitled “Year of Meteors (1859-60)” published in his landmark work Leaves of Grass.

English professor Marilynn S. Olson and student Ava G. Pope teamed up with Texas state physics professors Russell Doescher & Donald Olsen to publish their findings in the July 2010 issue of Sky & Telescope.

As a seasoned observer, Whitman had touched on the astronomical in his writings before.

The event had previously been attributed over the years to the Great Leonid Storm of 1833, which a young Whitman would’ve witnessed as a teenager working in Brooklyn, New York as a printer’s apprentice.

Researchers noted, however, some problems with this assertion.

The stanza of contention reads;

Nor forget I sing of the wonder, the ship as she swam up my bay,

Well-shaped and stately, the Great Eastern swam up my bay, she was 600 feet long,

Her moving swiftly surrounded by myriads of small craft I forget not to sing;

Nor the comet that came unannounced out of the north flaring in heaven,

Nor the strange huge meteor-procession dazzling and clear shooting over our heads.

(A moment, a moment long, it sail’d its balls of earthly light over our heads,

Then departed, dropt in the night, and was gone.)

In the poem, the sage refers to the arrival of the Prince of Wales in New York City on October 1860. The election of Abraham Lincoln in November of that same year is also referred to earlier in the work.  Whitman almost seems to be making a cosmic connection similar to Shakespeare’s along the lines of “When beggars die, no comets are seen…”

Path of the Meteor Procession of 1860 as depicted in the newspapers of the day. (From the collection of Don Olson).
Path of the Meteor Procession of 1860 as depicted in the newspapers of the day. (From the collection of Don Olson).

The “comet that came unannounced” is easily identified as the Great Comet of 1860. Also referred to as Comet 1860 III, this comet was discovered on June 18th of that year and reached +1st magnitude that summer as it headed southward. The late 19th century was rife with “great comets,” and northern hemisphere observers could look forward to another great cometary showing on the very next year in 1861.

The Great Comet of 1861 as drawn by G. Williams on June 30th, 1861. (From Descriptive Astronomy by George Chambers, 1877)
The Great Comet of 1861 as drawn by G. Williams on June 30th, 1861. (From Descriptive Astronomy by George Chambers, 1877)

There are some problems, however with the tenuous connection between the stanza and the Leonids.

The 1833 Leonids were one of the most phenomenal astronomical events ever witnessed, with estimates of thousands of meteors per second being seen up and down the U.S. Eastern Seaboard the morning of November 13th. Whitman himself described the event as producing;

“…myriads in all directions, some with long shining white trains, some falling over each other like falling water…”

Keep in mind, many startled townsfolk assumed their village was on fire on that terrifying morning in 1833, as Leonid bolides cast moving shadows into pre-dawn bedrooms. Churches filled up, as many thought that Judgment Day was nigh. The 1833 Leonids may have even played a factor in sparking many of the religious fundamentalist movements of the 1830s. We witnessed the 1998 Leonids from Kuwait, and can agree that this meteor shower can be a stunning sight at its peak.

But Whitman’s poem describes a singular event, a “meteor-procession” very different from a meteor shower.

Various sources have tried over the years to link the stanza to a return of the Leonids in 1858. A note from Whitman mentions a “meteor-shower, wondrous and dazzling (on the) 12th-13th, 11th month, year 58 of the States…” but keep in mind, “year 1” by this reckoning is 1776.

A lucky break came for researchers via the discovery of a painting by Frederic Church entitled “The Meteor of 1860.” This painting and several newspaper articles of the day, including an entry in the Harpers Weekly, collaborate a bright meteor procession seen across the northeastern U.S. from New York and Pennsylvania across to Wisconsin.

Such a bright meteor entered the atmosphere at a shallow angle, fragmented, and most likely skipped back out into space. Similar meteor processions have been observed over the years over the English Channel on August 18th, 1783 & across the U.S. Eastern Seaboard and Canada on February 9th, 1913.

On August 10th, 1972, a similar bright daylight fireball was recorded over the Grand Tetons in the western United States. Had the Great Meteor Procession of 1860 come in at a slightly sharper angle, it may have triggered a powerful airburst such as witnessed earlier this year over Chelyabinsk, Russia the day after Valentine’s Day.

The 1860 Meteor Procession is a great tale of art, astronomy, and mystery. Kudos to the team of researchers who sleuthed out this astronomical mystery… I wonder how many other unknown stories of historical astronomy are out there, waiting to be told?

Posted on by David Dickinson

Did a Piece of Mir Really Land in Massachusetts?

Screenshot closeup of the Amesbury Mass. find.

We love a good space debris mystery. Hey, who doesn’t, right?  Regular readers of Universe Today know that it’s a shooting gallery out there, from meteor fireballs caught on dashboard cams to rogue space junk reentries lighting up our skies. 

But an unusual story that made its rounds across the internet this past weekend caught our attention. What at first glance was a simple “Man finds space rock” story morphed into an extraordinary claim, which, in the words of the late great Carl Sagan, “demand extraordinary evidence.”

The find was made by Phil Green of Amesbury, Massachusetts. Mr. Green was searching the local riverbed for arrowheads when he came across the unusual find. The black pitted rock immediately struck him as something bizarre.  It didn’t register as metallic to his metal detector, but Mr. Green kept it in his backyard for about five years until it was noticed by a friend.

“I didn’t really think much of it, and then a fellow came over, saw it and said that’s a meteor,” Green told local reporters.

From here, the story takes a strange turn. Green told local reporters that the rock was sent off for analysis, only to be returned to him just a few weeks ago. The analysis confirmed that the rock was indeed from space… sort of. It also stated that the vitreous material “shows a composition similar to that used in ballast by the Soviet space program starting in the mid-1980s.”

And the word was out. The media quickly ran with the “Man finds a piece of Mir” story.

There are just a few problems with the tale. Mir reentered in 2001, six years before the 2007. A few articles do bother to note this, mentioning that Mir ended its career in the “so-called spacecraft cemetery of the southern Pacific Ocean,” about as far away from Massachusetts as you can get.

A few articles do also mention the possibility of a reentry of a Progress resupply vehicle being a potential source, or perhaps an unrelated Russian space vehicle.

But there seems to be a potential problem of the certification. Several articles state that the piece of debris coming from Mir was “confirmed by NASA.” However, Universe Today contacted NASA Chief Scientist for Orbital Debris Nicholas L. Johnson and NASA Headquarters official Joshua Buck, who both told us that no such NASA validation exists. Mr. Johnson went on to tell Universe Today that, “The NASA Orbital Debris Program Office has not been presented with any claim regarding debris from the Mir space station,” adding “I can tell you that it is not possible for debris from the Mir reentry to have landed in the U.S.”

A name that occasionally turns up in reports online as validating the find (withheld by request) also tells Universe Today that they had nothing to do with the discovery. Mr. Green or the original validation source  have thus far been unavailable for comment.

We did uncover two documented reentries that occurred over the general region over the last few decades. One is the reentry of Mir-R 1986-017B (The rocket booster that launched the core module of Mir) seen from a trans-Atlantic airliner on February 24th 1986 about 500 kilometres off of the east coast of Newfoundland. Another possible suspect is the June 26/27th 2004 reentry of a SL-12 auxiliary rocket motor with the NORAD ID 1992-088E, seen to the west from New Jersey to Ontario.

Like the International Space Station, Mir was placed in a 51.6° inclined orbit. This made it accessible from the Baikonur Cosmodrome as well as visits from the U.S. Space Shuttle. Payloads going to and from the station would cover an identical ground track ranging from 51.6° north to south latitude.

The story is also reminiscent of the reentry of debris from Sputnik 4, which struck a small town in Wisconsin in 1962. This was analyzed by mineralogist Ursula Marvin and confirmed to be of Russian origin.

A Progress spacecraft inbound for docking with the International Space Station. (Credit: NASA).
A Progress spacecraft inbound for docking with the International Space Station. (Credit: NASA).

Probably the biggest question in our minds is: what links the object back to an errant Russian spacecraft? What do they use for ballast, anyhow? How did they arrive at the often quoted “85% certainty?” of the object’s origin?

Still, the find does look like something interesting. The pitting and the melted fusion crust are all reminiscent of reentry. We’ll keep researching this story, and for the time being we’ll leave it up to you, the diligent and insightful readers of Universe Today, to make up your own minds on this strange and interesting tale.

Posted on by Nancy Atkinson

Possible Meteorite Fragments from 1908 Tunguska Explosion Found

Image of potential meteorite fragments from the Tunguska event, from a paper by Andrei E. Zlobin, 'Discovery of probably Tunguska meteorites at the bottom of Khushmo river's shoal.'

The 1908 explosion over the Tunguska region in Siberia has always been an enigma. While the leading theories of what caused the mid-air explosion are that an asteroid or comet shattered in an airburst event, no reliable trace of such a body has ever been found. But a newly published paper reveals three different potential meteorite fragments found in the sandbars in a body of water in the area, the Khushmo River. While the fragments have all the earmarks of being meteorites from the event – which could potentially solve the 100-year old mystery — the only oddity is that the researcher actually found the fragments 25 years ago, and only recently has published his findings.

Like the recent Chelyabinsk airburst event, the Tunguska event likely also produced a shower of fragments from the exploding parent body, scientists have thought. But no convincing evidence has ever been found from the June 30, 1908 explosion that occurred over the Tunguska region. The explosion flattened trees in a 2,000 square kilometer area. Luckily, that region was largely uninhabited, but reportedly one person was killed and there were very few people that reported the explosion. Forensic-like research has determined the blast was 1,000 times more powerful than a nuclear bomb explosion, and it registered 5 on the Richter scale.

Previous expeditions to the region turned up empty as far as finding meteorites; however one expedition in 1939 by Russian mineralogist Leonid Kulik found a sample of melted glassy rock containing bubbles, which was considered evidence of an impact event. But the sample was somehow lost and has never undergone modern analysis.

The expedition in 1998 by Andrei Zlobin from the Russian Academy of Sciences was initially unsuccessful in finding meteorites or evidence of impacts. He made several drill holes in the peat bogs in the area and while he found evidence of the explosion, he didn’t find any meteorites. He then decided to look in the nearby river shoal.

Zlobin gathered about 100 samples of rocks that had features of potential meteorites, but further examination produced just three rocks with tell-tale features like melting and regmalypts – the , thumblike impressions found on the surface of meteorites which are caused by ablation as the hot rock falls through the atmosphere at high speed.

Zlobin writes that “After the expedition the author focused his efforts on experimental investigation of thermal processes and mathematical modeling of the Tunguska impact [Zlobin, 2007],” and he used tree ring evidence to estimate the temperatures from the event, and concluded that rocks already on the ground would not have been changed or melted from the blast, and therefore any rocks having evidence of melting should be from the impactor itself.

Zlobin says he has not yet carried out a detailed chemical analysis of the rocks, which would reveal their chemical and isotopic composition. But he does say the stony fragments do not rule out a comet since the nucleus could easily contain rock fragments. However, he has calculated the density of the impactor must have been about 0.6 grams per cubic centimeter, which is about the same as nucleus of Halley’s comet. Zlobin says that initially, the evidence seems “excellent confirmation of cometary origin of the Tunguska impact.”

While there is nothing definitive yet from Zlobin’s new paper – and there is the question of why he waited so long to conduct his study – his work provides hope for a better explanation of the Tunguska event as opposed to some rather off-the-wall ideas that have been proposed, such as a Tesla death-ray or an explosion of methane gas from the bogs.

The Technology Review blog writes that “clearly there is more work to be done here, particularly the chemical analysis perhaps with international cooperation and corroboration.”

Read Zlobin’s paper, Discovery of probably Tunguska meteorites at the bottom of Khushmo river’s shoal

Source: MIT Technology Review

Posted on by Nancy Atkinson

Cassini Watches as Meteors Hit Saturn’s Rings

ive images of Saturn's rings, taken by NASA's Cassini spacecraft between 2009 and 2012, show clouds of material ejected from impacts of small objects into the rings. Image Credit: NASA/JPL-Caltech/Space Science Institute/Cornell.

From tell-tale evidence, we know that Earth, our Moon and other bodies in our Solar System are constantly barraged with both small meteoroids and larger asteroids or comets. And sometimes – like in the case of seeing meteors fling across our sky, or flashes on the Moon or Jupiter getting hit by Comet Shoemaker-Levy 9 — we even get to watch as it happens. Now, for the first time the Cassini spacecraft has provided direct evidence of small meteoroids crashing into Saturn’s rings.

Researchers say that studying the impact rate of meteoroids from outside the Saturnian system helps scientists understand how different planet systems in our solar system formed.

Saturn’s rings act as very effective detectors of many kinds of surrounding phenomena, including the interior structure of the planet and the orbits of its moons. For example, a subtle but extensive corrugation that ripples 12,000 miles (19,000 kilometers) across the innermost rings tells of a very large meteoroid impact in 1983.

“These new results imply the current-day impact rates for small particles at Saturn are about the same as those at Earth — two very different neighborhoods in our solar system — and this is exciting to see,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “It took Saturn’s rings acting like a giant meteoroid detector — 100 times the surface area of the Earth — and Cassini’s long-term tour of the Saturn system to address this question.”

The Saturnian equinox in summer 2009 was an especially good time to see the debris left by meteoroid impacts. The very shallow sun angle on the rings caused the clouds of debris to look bright against the darkened rings in pictures from Cassini’s imaging science subsystem.

This animation depicts the shearing of an initially circular cloud of debris as a result of the particles in the cloud having differing orbital speeds around Saturn. Image credit: NASA/Cornell

“We knew these little impacts were constantly occurring, but we didn’t know how big or how frequent they might be, and we didn’t necessarily expect them to take the form of spectacular shearing clouds,” said Matt Tiscareno, lead author of the paper and a Cassini participating scientist at Cornell University in Ithaca, N.Y. “The sunlight shining edge-on to the rings at the Saturnian equinox acted like an anti-cloaking device, so these usually invisible features became plain to see.”

Tiscareno and his colleagues now think meteoroids of this size probably break up on a first encounter with the rings, creating smaller, slower pieces that then enter into orbit around Saturn. The impact into the rings of these secondary meteoroid bits kicks up the clouds. The tiny particles forming these clouds have a range of orbital speeds around Saturn. The clouds they form soon are pulled into diagonal, extended bright streaks.

“Saturn’s rings are unusually bright and clean, leading some to suggest that the rings are actually much younger than Saturn,” said Jeff Cuzzi, a co-author of the paper and a Cassini interdisciplinary scientist specializing in planetary rings and dust at NASA’s Ames Research Center in Moffett Field, Calif. “To assess this dramatic claim, we must know more about the rate at which outside material is bombarding the rings. This latest analysis helps fill in that story with detection of impactors of a size that we weren’t previously able to detect directly.”

Source: JPL

Posted on by Nancy Atkinson

Bright Meteor Rocks Argentina Rock Concert

Talk about a light show! A massive bolide was captured on video during a middle-of-the-night rock concert in Argentina on April 21, 2013. The band, Los Tekis performed at an outdoor concert venue and in perfect timing, right after the band concluded a song, the person who shot the video panned out so that the sky was visible — just as the bolide lit up the sky.
Continue reading “Bright Meteor Rocks Argentina Rock Concert”

Posted on by David Dickinson

The Curious History of the Lyrid Meteor Shower

The 2013 Lyrid meteors as seen from Windy Point Vista on Mt. Lemmon, Tucson Arizona. (Credit & copyright Sean Parker Photography. In the Universe Today flickr gallery).

Today we residents of planet Earth meet up with a meteor stream with a strange and bizarre past.

The Lyrid meteors occur annually right around April 21st to the 23rd. A moderate meteor shower, observers in the northern hemisphere can expect to see about 20 meteors in the early morning hours under optimal conditions. Such has been the case for recent years past, and this year’s presence of a waxing gibbous Moon has lowered prospects for this April shower considerably in 2013.

But this has not always been the case with this meteor stream. In fact, we have records of the Lyrids stretching back over the past 2,600 years, farther back than any other meteor shower documented.

The earliest account of this shower comes from a record made by Chinese astronomers in 687 BC, stating that “at midnight, stars dropped down like rain.” Keep in mind that this now famous assertion that is generally attributed to the Lyrids was made by mathematician Johann Gottfried Galle in 1867. It was Galle along with Edmond Weiss who noticed the link between the Lyrids and Comet C/1861 G1 Thatcher discovered six years earlier.

Comet Thatcher was discovered on April 5th, 15 days before it reached perihelion about a third of an astronomical unit (A.U.) from the Earth. Comet Thatcher a periodic comet on a 415 year long orbital period.

But in the early to mid-19th century, the very idea that meteor showers were linked to comets or even non-atmospheric phenomena was still hotly contested.

One singular event more than any other triggered this realization. The Leonid meteor storm of 1833 in the early morning hours of November 13th was a stunning and terrifying spectacle for residents of the U.S eastern seaboard. This shower produces mighty outbursts, often topping a Zenithal Hourly Rate (ZHR) of over a 1,000 once every 33 to 34 years. I witnessed a fine outburst of the Leonids from Kuwait in 1998, and we may be in for a repeat performance from this shower around 2032 or 2033.

There is substantial evidence that the Lyrids may also do the same at an undetermined interval. On April 20th 1803, one of the most famous accounts of a “Lyrid meteor storm” was observed up and down the United States east coast. For example, one letter to the Virginia Gazette states;

“From one until three, those starry meteors seemed to fall from every point in the sky heavens, in such numbers as to resemble a shower of sky rockets.”

Another account published in the Raleigh, North Carolina Register states that:

“The whole hemisphere as far as the extension of the horizon seemed illuminated; the meteors kept no particular direction but appeared to move in every way.”

A study of the 1803 Lyrid outburst by W.J. Fisher cites over a dozen accounts of the event and is a fascinating read. Viewers were also primed for the event by the dramatic Leonid storm of 1799 four years earlier.

Interestingly, the Moon was only one day from New phase on the night of the 1803 Lyrids. Prime meteor watching conditions.

An unrelated meteorite fall would also occur four years later over Weston, Connecticut on December 14th, 1807 as recounted by Kathryn Prince in A Professor, A President, and a Meteor. These events would place Yankee politics at odds with the origin of meteors and rocks from the sky.

An apocryphal quote is often attributed to President Thomas Jefferson that highlights the controversy of the day, saying that “I would more easily believe that two Yankee professors would lie than that stones would fall from heaven.”

While both are of cosmogenous origin, no meteorite fall has ever been linked to a meteor shower, which is spawned by dust debris from comets. For example, many in the media erroneously speculated that the Sutter’s Mill meteorite that fell to Earth on the morning of April 22nd, 2012 was in fact a Lyrid meteor.

But a Lyrid may be implicated in another unusual 19th century observation. On April 24th 1874, a professor Scharfarik of Prague, Czechoslovakia was observing the daytime First Quarter Moon with his 4” refractor. The good professor was surprised by an “Apparition on the disc of the Moon of a dazzling white star,” which was “quite sharp and without a perceptible diameter.” Possible suspects are a telescopic meteor moving towards or along the observers’ line of sight or perhaps a Lyrid impacting the dark limb of the Moon.

Moving into the 20th century, rates for the Lyrids have stayed in the ZHR=20 range, with notable peaks of 100+ per hour noted by Japanese observers in 1922 and 100 per hour noted by U.S. observers in 1982.

It should also be noted that another less understood shower radiates from the constellation Lyra in mid-June. First noted Stan Dvorak while hiking in the San Bernardino Mountains in 1966, the June Lyrids produce about 8-10 meteors per hour from June 10 to the 21st. The source of this newly discovered shower is thought to be Comet C/1915 C1 Mellish.

A June Lyrid may have even made its way into modern fiction. As recounted in a July 2004 issue of Sky & Telescope, researchers Marilynn & Donald Olson note the following line from James Joyce’s Ulysses:

“A star, precipitated with great apparent velocity across the firmament from Vega in the Lyre above the zenith.”

Joyce seems to be describing a June Lyrid decades before the shower was officially recognized. The constellation Lyra rides high in the early morning sky for mid-northern latitudes in the early summer months.

All interesting concepts to ponder as we keep an early morning vigil for the Lyrids this week. Could there be more Lyrid storms in the far off future, as Comet Thatcher reaches perihelion once again in the late 23rd century? Could more historical clues of the untold history of this and other showers be awaiting discovery?

Somewhat closer to us in time and space, Paul Wiegert of the University of Ontario has also recently speculated that Comet 2012 S1 ISON may provoke a meteor shower on January 12th, 2014. Regardless of whether ISON turns out to be the “Comet of the Century,” this could be one to watch out for!

  

Posted on by Jason Major

Friday Night Lights: Fireball Lights Up the U.S. East Coast

Visibility map of the Manhattan meteor (American Meteor Society)

Last night a bright meteor was spotted up and down the northern mid-Atlantic United States from Maryland to Manhattan to Massachusetts. Streaking across the sky just before 8 p.m. EDT, the fireball was witnessed by thousands — the American Meteor Society alone has so far received over 630 reports on its website from the event. (Update 3/25: The AMS has received now over 1170 reports of the meteor.)

While many false images of the meteor quickly began circulating online, the video above is real — captured from a security camera in Thurmont, MD and uploaded to YouTube by Kim Fox (courtesy of Alan Boyle’s article on NBC News’ Cosmic Log.)

So what’s up with all these meteors lately?

According to NASA meteor specialist Bill Cooke, Friday’s fireball — which has become known as the “Manhattan meteor” — was likely caused by a boulder-sized asteroid about 3 feet (0.9 meters) wide entering Earth’s atmosphere. While bolides of this size sometimes result in meteorites that land on the ground, the last reports of the Manhattan meteor have it miles over the Atlantic… any pieces that survived entry and disintegration probably ended up in the ocean.

Here’s another video of the event from a Massachusetts news station.

And if you’re concerned about an apparent increase in the rate of meteors being spotted around the world, don’t be alarmed. Remember — spring is fireball season, after all.

“We’ve known about this phenomenon for more than 30 years. It’s not only fireballs that are affected. Meteorite falls–space rocks that actually hit the ground–are more common in spring as well.”

– Bill Cooke,  NASA’s Meteoroid Environment Center

So keep an eye on the sky over the next few weeks — you never know when we’ll be treated to another show!

Posted on by Dan Majaess

Russian Asteroid Explosion and Past Impactors Paint a Potentially Grim Future for Earth

Impactors strike during the reign of the dinosaurs (image credit: MasPix/devianart)

The recent meteor explosion over Chelyabinsk brought to the forefront a topic that has worried astronomers for years, namely that an impactor from space could cause widespread human fatalities.  Indeed, the thousand+ injured recently in Russia was a wake-up call. Should humanity be worried about impactors? “Hell yes!” replied astronomer Neil deGrasse Tyson to CNN’s F. Zakharia .

The geological and biological records attest to the fact that some impactors have played a major role in altering the evolution of life on Earth, particularly when the underlying terrestrial material at the impact site contains large amounts of carbonates and sulphates. The dating of certain large impact craters (50 km and greater) found on Earth have matched events such as the extinction of the Dinosaurs (Hildebrand 1993, however see also G. Keller’s alternative hypothesis).  Ironically, one could argue that humanity owes its emergence in part to the impactor that killed the Dinosaurs.

The Manicouagan impact crater in Quebec, Canada (image credit: NASA)
More than a dozen known impactors created 50 km sized craters (and larger) on Earth. One such example is the Manicouagan crater in Quebec, Canada.  The crater is 215 million years old, and exhibits an 85 km diameter (image credit: NASA).

Only rather recently did scientists begin to widely acknowledge that sizable impactors from space strike Earth.

“It was extremely important in that first intellectual step to recognize that, yes, indeed, very large objects do fall out of the sky and make holes in the ground,” said Eugene Shoemaker. Shoemaker was a co-discoverer of Shoemaker-Levy 9, which was a fragmented comet that hit Jupiter in 1994 (see video below).

Hildebrand 1993 likewise noted that, “the hypothesis that catastrophic impacts cause mass extinctions has been unpopular with many geologists … some geologists still regard the existence of ~140 known impact craters on the Earth as unproven despite compelling evidence to the contrary.”

Beyond the asteroid that struck Mexico 65 million years ago and helped end the reign of the dinosaurs, there are numerous lesser-known terrestrial impactors that also appear destructive given their size. For example, at least three sizable impactors struck Earth ~35 million years ago, one of which left a 90 km crater in Siberia (Popigai). At least two large impactors occurred near the Jurassic-Cretaceous boundary (Morokweng and Mjolnir), and the latter may have been the catalyst for a tsunami that dwarfed the recent event in Japan (see also the simulation for the tsunami generated by the Chicxulub impactor below).

Glimsdal et al. 2007 note, “it is clear that both the geological consequences and the tsunami of an impact of a large asteroid are orders off magnitude larger than those of even the largest earthquakes recorded.”

However, in the CNN interview Neil deGrasse Tyson remarked that we’ll presumably identify the larger impactors ahead of time, giving humanity the opportunity to enact a plan to (hopefully) deal with the matter.   Yet he added that often we’re unable to identify smaller objects in advance, and that is problematic.  The meteor that exploded over the Urals a few weeks ago is an example.

Sketch of the ensuing Tsunami caused by an impactor from Space (image credit: binouse49/devianart).
An artist’s sketch of a tsunami which can be potentially generated by an asteroid/comet impactor (image credit: binouse49/deviantart).

In recent human history the Tunguska event, and the asteroid that recently exploded over Chelyabinsk, are reminders of the havoc that even smaller-sized objects can cause. The Tunguska event is presumed to be a meteor that exploded in 1908 over a remote forested area in Siberia, and was sufficiently powerful to topple millions of trees (see image below).  Had the event occurred over a city it may have caused numerous fatalities.

Mark Boslough, a scientist who studied Tunguska noted, “That such a small object can do this kind of destruction suggests that smaller asteroids are something to consider … such collisions are not as improbable as we believed. We should be making more efforts at detecting the smaller ones than we have till now.” 

Neil deGrasse Tyson hinted that humanity was rather lucky that the recent Russian fireball exploded about 20 miles up in the atmosphere, as its energy content was about 30 times larger than the Hiroshima explosion.  It should be noted that the potential negative outcome from smaller impactors increases in concert with an increasing human population.

The Tungunska impactor is thought to have felled millions of trees in Siberia in 1908 (image credit: Kulik).
In 1908 the Tunguska impactor toppled millions of trees in a rather remote part of Siberia (image credit: Kulik).  Had the object exploded over a city, the effects may have been catastrophic.

So how often do large bodies strike Earth, and is the next catastrophic impactor eminent? Do such events happen on a periodic basis? Scientists have been debating those questions and no consensus has emerged. Certain researchers advocate that large impactors (leaving craters greater than 35 km) strike Earth with a period of approximately 26-35 million years.

The putative periodicity  (i.e., the Shiva hypothesis) is often linked to the Sun’s vertical oscillations through the plane of the Milky Way as it revolves around the Galaxy, although that scenario is likewise debated (as is many of the assertions put forth in this article). The Sun’s motion through the denser part of the Galactic plane is believed to trigger a comet shower from the Oort Cloud. The Oort Cloud is theorized to be a halo of loosely-bound comets that encompasses the periphery of the Solar System. Essentially, there exists a main belt of asteroids between Mars and Jupiter, a belt of comets and icy bodies located beyond Neptune called the Kuiper belt, and then the Oort Cloud.  A lower-mass companion to the Sun was likewise considered as a perturbing source of Oort Cloud comets (“The Nemesis Affair” by D. Raup).

A belt of comets called the Oort Cloud is theorized to encircle the Solar system (image credit: NASA/JPL).
A halo of comets designated the Oort Cloud is theorized to encircle the periphery of the Solar System, and reputedly acts as a reservoir for objects that may become terrestrial impactors (image credit: NASA/JPL).

The aforementioned theory pertains principally to periodic comets showers, however, what mechanism can explain how asteroids exit their otherwise benign orbits in the belt and enter the inner solar system as Earth-crossers? One potential (stochastic) scenario is that asteroids are ejected from the belt via interactions with the planets through orbital resonances.  Evidence for that scenario is present in the image below, which shows that regions in the belt coincident with certain resonances are nearly depleted of asteroids.  A similar trend is seen in the distribution of icy bodies in the Kuiper belt, where Neptune (rather than say Mars or Jupiter) may be the principal scattering body.  Note that even asteroids/comets not initially near a resonance can migrate into one by various means (e.g., the Yarkovsky effect).

Indeed, if an asteroid in the belt were to breakup (e.g., collision) near a resonance, it would send numerous projectiles streaming into the inner solar system.  That may help partly explain the potential presence of asteroid showers (e.g., the Boltysh and Chicxulub craters both date to near 65 million years ago).   In 2007, a team argued that the asteroid which helped end the reign of the Dinosaurs 65 million years ago entered an Earth-crossing orbit via resonances. Furthermore, they noted that asteroid 298 Baptistina is a fragment of that Dinosaur exterminator, and it can be viewed in the present orbiting ~2 AU from the Sun.  The team’s specific assertions are being debated, however perhaps more importantly: the underlying transport mechanism that delivers asteroids from the belt into Earth-crossing orbits appears well-supported by the evidence.

Kirkwood Gaps, histogram of asteroids as a function of their average distance from the Sun. Regions deplete of asteroids are called Kirkwood Gaps, and those bodies may have been escavated from the main belt owing to orbital resonances (image credit: Alan Chamberlain, JPL/Caltech).
A histogram featuring the number of asteroids as a function of their average distance from the Sun. Regions depleted of asteroids are often coincident with orbital resonances, the latter being a mechanism by which objects in the belt can be scattered into enter Earth-crossing orbits (image credit: Alan Chamberlain, JPL/Caltech).

Thus it appears that the terrestrial impact record may be tied to periodic and random phenomena, and comet/asteroid showers can stem from both.  However, reconstructing that terrestrial impact record is rather difficult as Earth is geologically active (by comparison to the present Moon where craters from the past are typically well preserved).  Thus smaller and older impactors are undersampled.  The impact record is also incomplete since a sizable fraction of impactors strike the ocean.  Nevertheless, an estimated frequency curve for terrestrial impacts as deduced by Rampino and Haggerty 1996 is reproduced below.  Note that there is considerable uncertainty in such determinations, and the y-axis in the figure highlights the “Typical Impact Interval”.

Estimated frequency of impacts as a function of age, diameter, and energy yield. Results assume an impact speed of 20 km/s and density of 3 g/cm^3 (image credit: Fig. 2 from Rampino & Haggerty 1996, NASA ADS/Springer).
Estimated frequency of impactors as a function of diameter, energy yield, and typical impact interval. Results assume an impact speed of 20 km/s and density of 3 g/cm^3 (image credit: Fig. 2 from Rampino and Haggerty 1996, NASA ADS/Springer).

In sum, as noted by Eugene Shoemaker, large objects do indeed fall out of the sky and cause damage. It is unclear when in the near or distant future humanity will be forced to rise to the challenge and counter an incoming larger impactor, or again deal with the consequences of a smaller impactor that went undetected and caused human injuries (the estimated probabilities aren’t reassuring given their uncertainty and what’s in jeopardy).  Humanity’s technological progress and scientific research must continue unabated (and even accelerated), thereby affording us the tools to better tackle the described situation when it arises.

Is discussion of this topic fear mongering and alarmist in nature? The answer should be obvious given the fireball explosion that happened recently over the Ural mountains, the Tunguska event, and past impactors.  Given the stakes excessive vigilance is warranted.

Fareed Zakharia’s discussion with Neil deGrasse Tyson is below.

The interested reader desiring additional information will find the following pertinent: the Earth Impact Database, Hildebrand 1993, Rampino and Haggerty 1996, Stothers et al. 2006, Glimsdal et al. 2007, Bottke et al. 2007, Jetsu 2011, G. Keller’s discussion concerning the end of the Dinosaurs, “T. rex and the Crater of Doom” by W. Alvarez, “The Nemesis Affair” by D. Raup, “Collision Earth! The Threat from Outer Space” by P. Grego.  **Note that there is a diverse spectrum of opinions on nearly all the topics discussed here, and our understanding is constantly evolving.  There is much research to be done.

Posted on by David Dickinson

Giant Ancient Impact Crater Confirmed in Iowa

3-D perspective map of the Decorah impact feature looking northward. (Credit: USGS/Adam Kiel graphic/Northeast Iowa RC&D).

A monster lurks under northeastern Iowa. That monster is in the form of a giant buried basin, the result of a meteorite impact in central North America over 470 million years ago.

A recent aerial survey conducted by the state of Minnesota Geological Survey and the United States Geological Survey (USGS) confirms the existence of an impact structure long suspected near the eastern edge of the town of Decorah, Iowa. The goal of the 60 day survey was a routine look at possible mineral and water resources in the region, but the confirmation of the crater was an added plus. Continue reading “Giant Ancient Impact Crater Confirmed in Iowa”

Posted on by Nancy Atkinson

Big Meteorite Chunk Found in Russia’s Ural Mountains

Lecturer at Ural Federal University's Institute of Physics and Technology Viktor Grokhovsky with meteorite fragment found during an expedition in the Chelyabinsk region on February 25, 2013. Credit: RIA Novosti / Pavel Lysizin.

Scientists and meteorites hunters have been on a quest to find bits of rock from the asteroid which exploded over the city of Chelyabinsk in Russia on February 15. More than 100 fragments have been found so far that appear to be from the space rock, and now scientists from Russia’s Urals Federal University have discovered the biggest chunk so far, a meteorite fragment weighing more than one kilogram (2.2 lbs).

The asteroid has been estimated to be about 15 meters (50 feet) in diameter when it struck Earth’s atmosphere, traveling several times the speed of sound, and exploded into a fireball, sending a shockwave to the city below, which broke windows and caused other damage to buildings, injuring about 1,500 people.

A hole in Chebarkul Lake made by meteorite debris. Photo by Chebarkul town head Andrey Orlov.Via RT.com
A hole in Chebarkul Lake made by meteorite debris. Photo by Chebarkul town head Andrey Orlov. Via RT.com

Fragments of the meteorite have been found along a 50 kilometer (30 mile) trail under the meteorite’s flight path. Small meteorites have also been found in an eight-meter (25 feet) wide crater in the region’s Lake Chebarkul, scientists said earlier this week. Viktor Grokhovsky from the Urals University believes there are more to be found, including a possible biggest chunk that he says may lie at the bottom of Lake Chebarkul. It could be up to 60cm in diameter, he estimated.

This video from NASA explains more:

Please note that while many pieces have been found, and if you are looking to buy a chunk of this famous meteorite, you need to approach this with a lot of skepticism. There have been some reports of people trying to sell pieces that they claim to be from the Ural/Russian meteorite, but they likely are not. Be careful and do your research on the seller before you buy.

Source: RT.com