Example of a lunar flash, photographed in 1953. Credit: Leon Stuart/Columbia University Department of Astronomy
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For hundreds of years, people have seen tiny flashes of light on the surface of the Moon. Very brief, but bright enough to be seen from Earth, these odd flashes still hadn’t been adequately explained up until now. Also known as Transient Lunar Phenomena (TLPs), they’ve been observed on many occasions, but rarely photographed. On Earth, meteorites burning up in the atmosphere can produce similar flashes, but the Moon has no atmosphere for anything to burn up in, so what could be causing them? As it turns out, according to a new study, the answer is still meteorites, but for a slightly different reason.
The lights don’t result from burning up as on Earth, but rather are hot blobs of material produced by the impact itself. The impacts were calculated to be powerful enough to melt the meteorites, producing super hot liquid droplets, called melt droplets, that produced light as they formed and then began to cool afterwards. The meteorites themselves can be tiny, but still cause an impact that could be seen from Earth.
Sylvain Bouley, a planetary scientist at the Paris Observatory and co-author of the study, explains: “You have just a small piece of cometary material or asteroid, about 10 centimeters, that can do a very bright flash visible from the Earth.”
Fellow planetary scientist Carolyn Ernst of Johns Hopkins University’s Applied Physics Laboratory, adds: “Something is melting, and because it’s so hot, it radiates in the visible wavelength until it cools down.”
The study included observations from 1999 – 2007, for which the brightness of the flashes and sizes and speeds of the meteorites were calculated.
The impacts have also been replicated at the Meteoroid Environment Office at the Marshall Space Flight Center, where tiny aluminum spheres were shot into simulated lunar dirt. The results were similar, helping to confirm the other team’s findings.
Other previous possible explanations included reflections on the Moon by tumbling satellites or even volcanic activity. There may still be debate though, as an earlier report in 2007 had attributed the flashes to outgassing on the Moon’s surface.
The paper will be published in the March 2012 issue of Icarus.
Scientists studying life on Mars got a late Christmas present this year: confirmation that meteorites found in Morocco in December are of Martian origin. It’s a significant discovery; Martian meteorites fall to Earth only about once every 50 years making this a once-in-a-lifetime, and for many a once-in-a-career, event. The Mars rocks are worth more than their weight in gold, but what they can tell us could be even more valuable.
Astronomers suspect that the meteorite has been wandering around the solar system for millions of years, ever since something big smashed into the red planet and sent debris flying all directions. One of those pieces has wandered its way towards Earth and plunged through the atmosphere.
ALH 84001, the meteorite found in Antarctica in 1984. Evidence of fossilized life inside the rock sparked a search for life on Mars. Image credit: NASA/ JSC
This is only the fifth time scientists have chemically confirmed the Martian origin of meteorites. Rocks found in France in 1815, in India in 1865, in Egypt in 1911, and in Nigeria in 1962 have all been positively identified as being from Mars.
The chemical signature of the Moroccan rocks and the Martian air match said Tony Irving of the University of Washington who did the scientific analysis. But this discovery is different. The rocks weren’t just found, they were seen streaking through the sky in July 2011, which makes them extremely valuable.
These rocks have only had six months to accumulate Earth-based materials and traces of life; typically Martian meteorites found on Earth have been here anywhere from decades to millennia, giving them ample time to become tainted.
These new rocks, while still contaminated because they have been on Earth for months, are relatively pure. “It’s incredibly fresh. It’s highly valuable for that reason,” said Carl Agee, director of the Institute of Meteoritics and curator at the University of New Mexico.
It’s also a rare find. This new sample, about 15 pounds of rocks, brings the total weight of all Martian samples on Earth to just 240 pounds.
Meteorite dealer Darryl Pitt is cashing in on the rocks’ rarity and selling pieces for $11,000 to $22,500 an ounce and has sold most of his supply already. At that price, the Martian meteorite costs about 10 times as much as gold.
An artist's conception of early Mars being hit by an asteroid wider than Texas. Scientists believe the impact melted the planet's crust in its northern hemisphere, flung crust into space, and sent shock wave through the planet's molten core (inset). This explains why Mars' crust is thinner in the northern hemisphere, according to three new studies. Image courtesy Jeff Andrews-Hanna; inset courtesy Francis Nimmo.
Cornell University astronomer Steve Squyres, the principal investigator for NASA’s Mars Exploration Rover Program, is less excited. The rocks, he said, are not the kind scientists are most hoping for. They are hard, igneous or volcanic rock. A softer kind of rock capable of holding water or life would be better. But he also points that these rocks aren’t likely to come streaking through the atmosphere. Any soft rock would be unlikely to survive the fiery entry through Earth’s atmosphere.
Former NASA sciences chief Alan Stern, director of the Florida Space Institute at the University of Central Florida, takes a brighter outlook. “It’s nice to have Mars sending samples to Earth,” he said, “particularly when our pockets are too empty to go get them ourselves.”
Until we manage a sample return mission from Mars, this is the best shot scientists have to study the red planet up close.
A unique type of crystal appears to have its origins in meteorites, according to a new study. Quasicrystals are an unusual type of crystalline structure that were initially thought to have only occurred in artificial conditions in labs, and impossible in nature, until they were found by geologists in the Koryak mountains in Russia in 2009. Their origin was unknown, but now new evidence indicates that they most likely came from space in meteorites, dating back to the early stages of the formation of the solar system.
Regular crystals, such as diamonds, snowflakes and salt, are symmetrical, ordered and repeating geometrical arrangements of atoms that extend in all three spatial dimensions (at both microscopic and macroscopic scales); they are commonly found in different types of rock. Quasicrystals are different however, with variations from the standard structure and composition.
When the newly found quasicrystals were studied, they were found to be composed primarily of copper and aluminum, similar to carbonaceous meteorites. The clincher came when the isotope measurements (ratios of oxygen atoms) indicated an extraterrestrial origin.
From the paper:
“Our evidence indicates that quasicrystals can form naturally under astrophysical conditions and remain stable over cosmic timescales.”
“The rock sample was first identified for study as a result of a decade-long systematic search for a natural quasicrystal (4). Quasicrystals are solids whose atomic arrangement exhibits quasi-periodic rather than periodic translational order and rotational symmetries that are impossible for ordinary crystals (5) such as fivefold symmetry in two-dimensions and icosahedral symmetry in three-dimensions. Until recently, the only known examples were synthetic materials produced by melting precise ratios of selected elemental components and quenching under controlled conditions (6–8). The search consisted of applying a set of metrics for recognizing quasicrystals to a database of powder diffraction data (4) and examining minerals outside the database with elemental compositions related to those of known synthetic quasicrystals.”
“What is clear, however, is that this meteoritic fragment is not ordinary. Resolving the remarkable puzzles posed by this sample will not only further clarify the origin of the quasicrystal phase but also shed light on previously unobserved early solar system processes. Fitting all these clues together in a consistent theory of formation and evolution of the meteorite is the subject of an ongoing investigation.”
The report has been published in the January 2 issue of Proceedings of the National Academy of Science. The article (PDF) is here. More detailed information about quasicrystals is also available here and here.
Holiday Greetings from an Alien Snowman on Vesta - to all inhabitants of the Galaxy
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Celebrate the winter holiday season in the company of an ‘Alien Snowman’ on the asteroid Vesta, someone we didn’t even have a clue about until six months ago.
Vesta and the Snowman have been transformed into the beautiful banner above – sent to me courtesy of the Dawn mission team to share with the readers of Universe Today.
Now you can be a creative artist and use the striking new images of Vesta to fashion your own greeting cards (see below) and send seasonal tidings of winter holiday cheer not possible before – all thanks to the remarkably insightful discoveries of Dawn’s international science team.
Vesta Greeting Card created by Joe W - From Dawn website
The Dawn spacecraft orbiting the giant asteroid Vesta is one of NASA’s crowning scientific accomplishments of 2011 because it’s cameras and spectrometers have unveiled a mysteriously diverse world that has no match elsewhere in our solar system.
The more we explore the unknown the more we are enlightened as to just how limited our view of the Universe is from within the narrow confines of our miniscule abode.
Vesta Greeting Card created by Judy C - From Dawn website
Hey, Let's go skiing at the South Pole !
The Kepler Space Telescopes latest discoveries of Earth-sized worlds are just the latest examples guiding us to a clearer understanding of our place in the Universe.
Vesta Greeting Card created by Jillian S - From Dawn website
Here are just a few of the Vestan images you can masterfully decorate – the Snowman, The Mount Everest of Vesta and the cataclysmically bombarded South Pole.
Alien Snowman on Vesta
An impact structure on asteroid Vesta resembling a snowman. Credit: NASA
So, let you imaginations run wild with wintery scenes to match the majesty of this matchless world. The Dawn Education and Public Outreach (EPO) team has created several templates which you can access here
Of course you can also use any of the images posted at the Dawn mission website.
The Mount Everest of Vesta
Image of asteroid Vesta calculated from a shape model, showing a tilted view of the topography of the south polar region. This perspective shows the topography, but removes the overall curvature of Vesta, as if the giant asteroid were flat and not rounded. Credit: NASAShattered South Pole of Vesta
This Dawn framing camera image shows scarps, hummocky (eg. wavy/ undulating) terrain and impacts in Vesta's south polar region. Credit: NASA
And feel free to post your inspired creations here at Universe Today.
Vesta is the second most massive object in the main Asteroid Belt between Mars and Jupiter.
Dawn arrived in orbit at Vesta in July 2011 for the first ever close up studies of the shattered celestial body. Dawn will spend a year investigating Vesta before spiraling out towards Ceres, the largest asteroid.
Artist's conception of an asteroid impact on Mars. (Image painted by William K. Hartmann, co-founder of the Planetary Science Institute, Tucson, Ariz.)
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They are headed toward the surface like a speeding freight train… and running ahead of them is a shockwave. Just like a loud sound can trigger a snow avalanche here on Earth, the shockwave of a meteorite crashing through the Martian atmosphere could trigger dust avalanches on the surface before an actual impact.
According to a study led by University of Arizona undergraduate student, Kaylan Burleigh, there is sufficient photographic evidence to prove that incoming meteorites are producing enough energy to impact the surface environment just as much as the strike. Mars’ thin atmosphere also contributes, since the lesser density means most meteorites survive the trip to the surface. “We expected that some of the streaks of dust that we see on slopes are caused by seismic shaking during impact,” said Burleigh. “We were surprised to find that it rather looks like shockwaves in the air trigger the avalanches even before the impact.”
HiRISE image of the study area showing the central crater with two dagger-like features extending at an angle (red and blue arrows). Called scimitars, these features most likely resulted from shockwave interference just before impact. (Image: NASA/JPL-Caltech/The University of Arizona)Spotting new craters happens frequently. Thanks to the HiRISE camera on board NASA’s Mars Reconnaissance Orbiter, researchers find up to twenty newly formed craters that measure between 1 and 50 meters (3 to 165 feet) each year. To perform their study, the team focused their attention on a grouping of five craters which formed at the same time. This quintuplet is located near the Martian equator, about 825 kilometers (512 miles) south of the boundary scarp of Olympus Mons. Earlier investigations of the area had revealed dark streaks which were surmised at the time to be landslides, but no one thought to credit them to an impact theory. The largest crater in the cluster measures 22 meters, or 72 feet across and the multiple formation is thought to have occurred due to a shattering of the meteor just ahead of final impact.
“The dark streaks represent the material exposed by the avalanches, as induced by the airblast from the impact,” Burleigh said. “I counted more than 100,000 avalanches and, after repeated counts and deleting duplicates, arrived at 64,948.”
As Burleigh took a closer look at the distribution of avalanches around the impact site, he noticed a lot of relative things, but the most important was a curved formation described as scimitars. This was a major clue as to how they were formed. “Those scimitars tipped us off that something other than seismic shaking must be causing the dust avalanches,” Burleigh said.
Just as a freight train sends a rumble before it arrives, so does the incoming meteor. By using computer modeling, the team was able to simulate how a shockwave could form and match the scimatar patterns to the HiRISE images. “We think the interference among different pressure waves lifts up the dust and sets avalanches in motion. These interference regions, and the avalanches, occur in a reproducible pattern,” Burleigh said. “We checked other impact sites and realized that when we see avalanches, we usually see two scimitars, not just one, and they both tend to be at a certain angle to each other. This pattern would be difficult to explain by seismic shaking.”
Because there are no plate tectonics, nor water erosion issues, these types of findings are very important to understanding how many Martian surface features are formed. “This is one part of a larger story about current surface activity on Mars, which we are realizing is very different than previously believed,” said Alfred McEwen, principal investigator of the HiRISE project and one of the co-authors of the study. “We must understand how Mars works today before we can correctly interpret what may have happened when the climate was different, and before we can draw comparisons to Earth.”
The huge fireball event as seen from a remote camera in Orangeville, Ontario. Credit: University of Western Ontario
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In newly released footage from the University of Western Ontario, a bright, slow-moving fireball was captured in the skies near Toronto, Canada on December 12, 2011 by remote cameras watching for meteors. Although this meteor looks huge as it burns up in Earth’s atmosphere, astronomers estimate the rock to have been no bigger than a basketball. Footage reveals it entered the atmosphere at a shallow angle of 25 degrees, moving about 14 km per second. It first became visible over Lake Erie then moved toward the north-northeast.
See below for the video.
But in a meteorite-hunter alert, Peter Brown, the Director of Western’s Centre for Planetary & Space Exploration said that data garnered from the remote cameras suggest that surviving fragments of the rock are likely, with a mass that may total as much as a few kilograms, likely in the form of many fragments in one gram to hundreds of a gram size range.
“Finding a meteorite from a fireball captured by video is equivalent to a planetary sample return mission,” said Brown. “We know where the object comes from in our solar system and can study it in the lab. Only about a dozen previous meteorite falls have had their orbits measured by cameras so each new event adds significantly to our understanding of the small bodies in the solar system. In essence, each new recovered meteorite is adding to our understanding of the formation and evolution of our own solar system.”
Brown and his team are interested in hearing from anyone who may have witnessed or recorded this event, or who may have found fragments of the freshly fallen meteorite. See UWO’s website for contact information.
Another camera view of the meteor:
Western Meteor Group’s Southern Ontario Meteor Network sensor suite has seven all-sky video systems designed to automatically detect bright fireballs.
At 6:04 p.m. on December 12, six of the seven cameras of Western’s Southern Ontario Meteor Network recorded this meteor. In a press release, UWO said the fireball’s burned out at an altitude of 31 km just south of the town of Selwyn, Ontario. It is likely to have dropped small meteorites in a region to the east of Selwyn near the eastern end of Upper Stony Lake. See the map of the projected path below.
Although this bright fireball occurred near the peak of the annual Geminid meteor shower, the astronomers say it is unrelated to that shower.
Estimated flight path of the Dec. 12, 2011 meteor seen near Toronto, Canada. Credit University of Wester Ontario.
'Rainbow-Colored Palette' of Southern Hemisphere of Asteroid Vesta from NASA Dawn Orbiter. This mosaic using color data obtained by the framing camera aboard NASA's Dawn spacecraft shows Vesta's southern hemisphere in false color, centered on the Rheasilvia impact basin, about 290 miles (467 kilometers) in diameter with a central mound reaching about 14 miles (23 kilometers) high. The black hole in the middle is data that have been omitted due to the angle between the sun, Vesta and the spacecraft. The green areas suggest the presence of the iron-rich mineral pyroxene or large-sized particles. This mosaic was assembled using images obtained during Dawn's approach to Vesta, at a resolution of 480 meters per pixel. The German Aerospace Center and the Max Planck Institute for Solar System Research provided the Framing Camera instrument and funding as international partners on the mission team. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
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The giant Asteroid Vesta is among the most colorful bodies in our entire solar system and it appears to be much more like a terrestrial planet than a mere asteroid, say scientists deciphering stunning new images and measurements of Vesta received from NASA’s revolutionary Dawn spacecraft. The space probe only recently began circling about the huge asteroid in July after a four year interplanetary journey.
Vesta is a heavily battered and rugged world that’s littered with craters and mysterious grooves and troughs. It is the second most massive object in the Asteroid Belt and formed at nearly the same time as the Solar System some 4.5 Billion years ago.
“The framing cameras show Vesta is one of the most colorful objects in the solar system,” said mission scientist Vishnu Reddy of the Max Planck Institute for Solar System Research in Katlenburg-Lindau, Germany. “Vesta is unlike any other asteroid we have visited so far.”
Scientists presented the new images and findings from Dawn at the American Geophysical Union meeting this week in San Francisco.
Comparative View of Terrains on Vesta - Oppia Crater
This image of Oppia Crater combines two separate views of the giant asteroid Vesta obtained by Dawn's framing camera. The far-left image uses near-infrared filters where red is used to represent 750 nanometers, green represents 920 nanometers and blue represents 980 nanometers. The image on the right is an image with colors assigned by scientists, representing different rock or mineral types on Vesta. The data reveal a world of many varied, well-separated layers and ingredients. The reddish color suggests a steep visible spectral slope, and areas of fresh landslides in the inner walls of the crater show deeper green colors. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
“Vesta is a transitional body between a small asteroid and a planet and is unique in many ways,” Reddy said. “We do not know why Vesta is so special.”
Although many asteroids look like potatoes, Reddy said Vesta reminds him more of an avocado.
Asteroid Vesta is revealed as a ‘rainbow-colored palette’ in a new image mosaic (above) showcasing this alien world of highly diverse rock and mineral types of many well-separated layers and ingredients.
Researchers assigned different colors as markers to represent different rock compositions in the stunning new mosaic of the asteroid’s southern hemisphere.
The green areas in the mosaic suggest the presence of the iron-rich mineral pyroxene or large-sized particles, according to Eleonora Ammannito, from the Visible and Infrared (VIR) spectrometer team of the Italian Space Agency. The ragged surface materials are a mixture of rapidly cooled surface rocks and a deeper layer that cooled more slowly.
What could the other colors represent?
“The surface is very much consistent with the variability in the HED (Howardite-Eucritic-Diogenite) meteorites,” Prof. Chris Russell, Dawn Principal Investigator (UCLA) told Universe Today in an exclusive interview.
“There is Diogenite in varying amounts.”
“The different colors represent in part different ratios of Diogenite to Eucritic material. Other color variation may be due to particle sizes and to aging,” Russell told me.
No evidence of volcanic materials has been detected so far, said David Williams, Dawn participating scientist of Arizona State University, Tucson. Fresh Impact Craters on Asteroid Vesta
The fresh impact craters in this view are located in the south polar region, which has been partly covered by landslides from the adjacent crater. This would suggest that a layer of loose material covers the Vesta surface. This image combines two separate views of the giant asteroid Vesta obtained by Dawn’s framing camera. The far-left image uses near-infrared filters where red is used to represent 750 nanometers, green represents 920 nanometers and blue represents 980 nanometers. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Before Dawn arrived, researchers expected to observe indications of volcanic activity. So, the lack of findings of volcanism is somewhat surprising. Williams said that past volcanic activity may be masked due to the extensive battering and resultant mixing of the surface regolith.
“More than 10,000 high resolution images of Vesta have been snapped to date by the framing cameras on Dawn,” Dr. Marc Rayman told Universe Today. Rayman is Dawn’s Chief Engineer from NASA’s Jet Propulsion Lab (JPL) in Pasadena, Calif.
Dawn will spend a year in orbit at Vesta and investigate the asteroid at different altitudes with three on-board science instruments from the US, Germany and Italy.
The probe will soon finish spiraling down to her lowest mapping orbit known as LAMO (Low Altitude Mapping Orbit), approximately 130 miles (210 kilometers) above Vesta’s surface.
“Dawn remains on course to begin its scientific observations in LAMO on December 12,” said Rayman.
The German Aerospace Center and the Max Planck Institute for Solar System Research provided the Framing Camera instrument and funding as international partners on the mission team. The Visible and Infrared Mapping camera was provided by the Italian Space Agency.
In July 2012, Rayman and the engineering team will fire up Dawn’s ion propulsion system, break orbit and head to Ceres, the largest asteroid and what a number of scientists consider to be a planet itself.
Ceres is believed to harbor thick caches of water ice and therefore could be a potential candidate for life.
Southern Hemisphere of Vesta -Rheasilvia and Older Basin
Colorized shaded-relief map showing location of 375-kilometer-wide Older impact basin that is overlapping with the more recent 500 km (300 mi) wide Rheasilvia impact structure at asteroid Vesta’s South Pole. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDAAsteroid Vesta from Dawn - Exquisite Clarity from a formerly Fuzzy Blob
NASA's Dawn spacecraft obtained this image of the giant asteroid Vesta with its framing camera on July 24, 2011. It was taken from a distance of about 3,200 miles (5,200 kilometers). Before Dawn, Vesta was just a fuzzy blob in the most powerful telescopes. Dawn entered orbit around Vesta on July 15, and will spend a year orbiting the body before firing up the ion propulsion system to break orbit and speed to Ceres, the largest Asteroid. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Read continuing features about Dawn by Ken Kremer starting here:
This image of the unusual asteroid Lutetia was taken by ESA’s Rosetta probe during its closest approach in July 2010. Lutetia, which is about 100 kilometres across, seems to be a leftover fragment of the same original material that formed the Earth, Venus and Mercury. It is now part of the main asteroid belt, between the orbits of Mars and Jupiter, but its composition suggests that it was originally much closer to the Sun. Credit: ESA 2010 MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA
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According to data received from ESA’s Rosetta spacecraft, ESO’s New Technology Telescope, and NASA telescopes, strange asteroid Lutetia could be a real piece of the rock… the original material that formed the Earth, Venus and Mercury! By examining precious meteors which may have formed at the time of the inner Solar System, scientists have found matching properties which indicate a relationship. Independent Lutetia must have just moved its way out to join in the main asteroid belt…
A team of astronomers from French and North American universities have been hard at work studying asteroid Lutetia spectroscopically. Data sets from the OSIRIS camera on ESA’s Rosetta spacecraft, ESO’s New Technology Telescope (NTT) at the La Silla Observatory in Chile, and NASA’s Infrared Telescope Facility in Hawaii and Spitzer Space Telescope have been combined to give us a multi-wavelength look at this very different space rock. What they found was a very specific type of meteorite called an enstatite chondrite displayed similar content which matched Lutetia… and what is theorized as the material which dates back to the early Solar System. Chances are very good that enstatite chondrites are the same “stuff” which formed the rocky planets – Earth, Mars and Venus.
“But how did Lutetia escape from the inner Solar System and reach the main asteroid belt?” asks Pierre Vernazza (ESO), the lead author of the paper.
It’s a very good question considering that an estimated less than 2% of the material which formed in the same region of Earth migrated to the main asteroid belt. Within a few million years of formation, this type of “debris” had either been incorporated into the gelling planets or else larger pieces had escaped to a safer, more distant orbit from the Sun. At about 100 kilometers across, Lutetia may have been gravitationally influenced by a close pass to the rocky planets and then further affected by a young Jupiter.
“We think that such an ejection must have happened to Lutetia. It ended up as an interloper in the main asteroid belt and it has been preserved there for four billion years,” continues Pierre Vernazza.
Asteroid Lutetia is a “real looker” and has long been a source of speculation due to its unusual color and surface properties. Only 1% of the asteroids located in the main belt share its rare characteristics.
“Lutetia seems to be the largest, and one of the very few, remnants of such material in the main asteroid belt. For this reason, asteroids like Lutetia represent ideal targets for future sample return missions. We could then study in detail the origin of the rocky planets, including our Earth,” concludes Pierre Vernazza.
Dr. Randy Korotev at Washington University with the Conception Junction meteorite.
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Meteorite hunter Karl Aston finds meteorites not by digging in the ground, but by placing ads in local newspapers. He asked people who found unusual rocks to contact him. Most responses were bum leads, but in 2009 Aston heard from a farmer in the northwestern Missouri of Conception Junction, who found something interesting: An unusually heavy stone buried in a hillside. The overall size was similar to that of a basketball and had a mass of 17 kilograms (37 pounds). Its rusty exterior hid its true nature. When the farmer had sawed off one end, olive-green crystals embedded in a shining metal shone forth. It was one of the rarest types of meteorites, a pallasite, of which only 61 samples are currently known. Recently, scientists at Washington University in St. Louis have gotten involved in an attempt to discover the meteorite’s history.
Pallasites and other meteorites are relics of the formation of the solar system. The most commonly accepted story for their formation is that they represent a boundary region inside larger asteroids where the heat from formation melted the iron and nickel metal which sunk to the core. The lighter crystals would float, and near this transition, there would be some mixing which, when broken apart due to later impacts, would form the pallasites. These asteroids formed in the asteroid belt between Mars and Jupiter and similar layers would likely be found in larger asteroids still present as well as in planets like the Earth. An alternative theory is that the materials formed independently and were mixed more recently due to large impacts.
The rusting fusion crust on the outside of the Conception Junction meteorite disguises it as just another rock, but one glimpse of the interior gives the game away. The olive-green crystals set in lustrous metal are unique to pallasites. Image credit: Dave Gheesling
Within the United States, 20 pallasite meteorites have been discovered. The majority of them belong to a single family of “main group” pallasites due to a similar chemical composition of their olivine crystals. When compared to other samples, the Conception Junction meteorite was unique. Because of this, the sample was given a unique designation this past August, named after the location of discovery. Before the Meteoritical Society recognizes a designation, it is required that a museum or other institutional collection houses a “type specimen” which will make the material available for scholarly research. As such a portion of the sample will be housed at UCLA where the chemical analysis on the metal was performed (the olivine was examined at Washington University).
The rarity of pallasite meteorites makes them uncommonly valuable. Some slices of the Conception Junction meteorite are still available for sale or trade, but don’t expect it to be an impulse buy. While more common stony meteorites sell for a few dollars per gram, pallasite meteorites sell for a few hundred dollars per gram. The overall price is also determined by the condition (some are unstable in Earth’s atmosphere) and whether or not it has a unique history. Meteorites for which the fall was observed are especially prized.
Wondering if the discovered meteorite was part of a larger body, Aston and other meteorite collectors including Robert Ward and Dave Gheesling conducted an extensive search of the region. They looked for 16 months in concentric circles centered on the original discovery location, but did not find any other specimens.
The time evolution of case I. Color coded is the density at t = 0 kyr, t = 4.16 kyr and t = 8.33 kyr. The length scale is given in units of the radius of the initial cold core (R0 = 0.21 pc). Credit: M. Gritschneder (et al)
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Away in space some 4.57 billion years ago, in a galaxy yet to be called the Milky Way, a hydrogen molecular cloud collapsed. From it was born a G-type main sequence star and around it swirled a solar nebula which eventually gelled into a solar system. But just what caused the collapse of the molecular cloud? Astronomers have theorized it may have been triggered by a nearby supernova event… And now new computer modeling confirms that our Solar System was born from the ashes a dead star.
While this may seem like a cold case file, there are still some very active clues – one of which is the study of isoptopes contained within the structure of meteorites. As we are well aware, many meteorites could very well be bits of our primordial solar nebula, left virtually untouched since they formed. This means their isotopic signature could spell out the conditions that existed within the molecular cloud at the time of its collapse. One strong factor in this composition is the amount of aluminium-26 – an element with a radioactive half-life of 700,000 years. In effect, this means it only takes a relatively minor period of time for the ratio between Al-26 and Al-24 to change.
“The time-scale for the formation events of our Solar System can be derived from the decay products of radioactive elements found in meteorites. Short lived radionuclides (SLRs) such as 26Al , 41Ca, 53Mn and 60Fe can be employed as high-precision and high-resolution chronometers due to their short half-lives.” says M. Gritschneder (et al). “These SLRs are found in a wide variety of Solar System materials, including calcium-aluminium-rich inclusions (CAIs) in primitive chondrites.”
However, it would seem that a class of carbonaceous chondrite meteorites known CV-chondrites, have a bit more than their fair share of Al-26 in their structure. Is it the smoking gun of an event which may have enriched the cloud that formed it? Isotope measurements are also indicative of time – and here we have two examples of meteorites which formed within 20,000 years of each other – yet are significantly different. What could have caused the abundance of Al-26 and caused fast formation?
“The general picture we adopt here is that a certain amount of Al-26 is injected in the nascent solar nebula and then gets incorporated into the earliest formed CAIs as soon as the temperature drops below the condensation temperature of CAI minerals. Therefore, the CAIs found in chondrites represent the first known solid objects that crystalized within our Solar System and can be used as an anchor point to determine the formation time-scale of our Solar System.” explains Gritschneder. “The extremely small time-span together with the highly homogeneous mixing of isotopes poses a severe challenge for theoretical models on the formation of our Solar System. Various theoretical scenarios for the formation of the Solar System have been discussed. Shortly after the discovery of SLRs, it was proposed that they were injected by a nearby massive star. This can happen either via a supernova explosion or by the strong winds of a Wolf-Rayet star.”
While these two theories are great, only one problem remains… Distinguishing the difference between the two events. So Matthias Gritschneder of Peking University in Beijing and his colleagues set to work designing a computer simulation. Biased towards the supernova event, the model demonstrates what happens when a shockwave encounters a molecular cloud. The results are an appropriate proportion of Al-26 – and a resultant solar system formation.
“After discussing various scenarios including X-winds, AGB stars and Wolf-Rayet stars, we come to the conclusion that triggering the collapse of a cold cloud core by a nearby supernova is the most promising scenario. We then narrow down the vast parameter space by considering the pre-explosion survivability of such a clump as well as the cross-section necessary for sufficient enrichment.” says Gritschneder. “We employ numerical simulations to address the mixing of the radioactively enriched SN gas with the pre-existing gas and the forced collapse within 20 kyr. We show that a cold clump at a distance of 5 pc can be sufficiently enriched in Al-26 and triggered into collapse fast enough – within 18 kyr after encountering the supernova shock – for a range of different metallicities and progenitor masses, even if the enriched material is assumed to be distributed homogeneously in the entire supernova bubble. In summary, we show that the triggered collapse and formation of the Solar System as well as the required enrichment with radioactive 26Al are possible in this scenario.”
While there are still other isotope ratios yet to be explained and further modeling done, it’s a step toward the future understanding of how solar systems form.
