Posted on by Nancy Atkinson

New Mineral Found in Meteorite is From Solar System’s Beginnings

Scientists have discovered a new mineral embedded in a meteorite that fell to Earth over 40 years ago, and it could be among the oldest minerals, formed in the early days of our solar system. The mineral is a type of titanium oxide and has been named panguite, after Pan Gu, the giant from ancient Chinese mythology who established the world by separating yin from yang to create the Earth and the sky.

“Panguite is an especially exciting discovery since it is not only a new mineral, but also a material previously unknown to science,” says Chi Ma, from Caltech and author of a new paper detailing the discovery.

The Allende meteorite arrived at Earth in 1969 as an exploding fireball in the skies over Mexico, scattering thousands of pieces of meteorites across the state of Chihuahua. The Allende meteorite is the largest carbonaceous chondrite—a diverse class of primitive meteorites—ever found on our planet and is considered by many the best-studied meteorite in history.

Ma has been leading nanomineralogy investigations of primitive meteorites, which looks at tiny particles of minerals, and has now found nine new minerals, including allendeite, hexamolybdenum, tistarite, kangite and now panguite.

“The intensive studies of objects in this meteorite have had a tremendous influence on current thinking about processes, timing, and chemistry in the primitive solar nebula and small planetary bodies,” said coauthor George Rossman, also from Caltech.

The team said the new mineral is likely among the first solid objects formed in our solar system and could date back to over 4 billion years ago, before the formation of Earth and the other planets.

According to Ma, studies of panguite and other newly discovered refractory minerals are continuing in an effort to learn more about the conditions under which they formed and subsequently evolved. “Such investigations are essential to understand the origins of our solar system,” he said.

The new mineral’s chemical name is Ti4+,Sc,Al,Mg,Zr,Ca, so it contains some unusual elements like zirconium and scandium.

The mineral and the mineral name have been approved by the International Mineralogical Association’s Commission on New Minerals, Nomenclature and Classification.

Image credit: Chi Ma/Caltech

Source: Caltech

Posted on by John Williams

Daylight Fireball Dazzles Colorado, Grounds Fire Tankers

Fireball Meteor
Credit: Pierre Martin of Arnprior, Ontario, Canada.

A dazzling daytime fireball zipped across New Mexico and Colorado yesterday creating a stir among law enforcement agencies, news organizations, radio stations and briefly grounded air tankers fighting wildfires west of Colorado Springs.

According to the Denver Post, Pueblo air-dispatch received reports of “balls of fire or something in the air.” As a precaution, officials grounded flights to ensure no aircraft were hit. Flights resumed 90 minutes later.

The event occurred between 12:35 and 12:40 MDT Wednesday afternoon. Witnesses say the fireball lasted about 3 seconds about 45 degrees above the ground, heading from the north to the south and ending near the horizon, with a tail color ranging from bright white to yellow and red. Some of the nearly 20 reports received by the American Meteor Society report that the brightness of the fireball was brighter than a full moon; some reporting it brighter than the Sun.

A fireball is a meteor that is larger and brighter than normal. Although typically visible after sunset, dramatic fireballs have been recorded during the daytime, such as the April 22, 2012 bright daytime meteor that was seen over California in the US. Usually meteors are smaller than a pebble and move very fast. As the object encounters increased friction from the air in the upper atmosphere, it begins to get hot and glow. Most meteors burn up before hitting the ground. But some survive to be picked up and put in museums. Scientists estimate that nearly 100 tons of space dust lands on Earth every day. Most of it lands in the ocean.

The North American Aerospace Defense Command (NORAD) based at Peterson Air Force Base near Colorado Springs told the Denver Post they were not tracking any man-made objects in the area.

The Denver Museum of Nature and Science has meteor cameras stationed around the state. Unfortunately, they are turned off during the day and no video or pictures have surfaced.

Astronomers and meteor/meteorite enthusiasts will certainly be interested in seeing any pictures or videos of the event, and so are we! If saw the event, or happened to capture it on a camera or surveillance video, you can send it to us or post it on our Flickr page.

Lead image caption: A Perseid fireball meteor. Credit: Pierre Martin of Arnprior, Ontario, Canada.

Posted on by Nancy Atkinson

Organics Found in Mars Meteorites, But Nothing Biological

Editor’s note: This guest post was written by Andy Tomaswick, an electrical engineer who follows space science and technology.

The search for biologically created organic molecules on Mars goes back at least to the 1970s with the Viking program. Those missions had famously mixed results, and so the search for carbon-based life on Mars continues to this day. Researchers keeping piling on more and more evidence to excite astrobiologists and new results published in a study by the Planetary Science Institute and the Carnegie Institute of Washington may heighten their enthusiasm.

The latest results come from a team led by Andrew Steele of the Carnegie Institution for Science who surveyed meteorites from Mars, which covered a 4.2 billion year time span of Martian geology. While it is no surprise that there are organics on Mars — that Martian meteorites contain carbon-based molecules has been known for years — the team confirmed those findings by detecting organics on ten of the eleven meteorites they examined. However, questions remained as to where exactly the meteorite-bound organic molecules came from and, if they were from Mars, what had created them?

The team set out to answer these questions and came to the conclusion that the molecules are indeed from Mars and not the result of some cross-contamination from Earth’s biosphere. However, they also found that the molecules were not created by any biological process. The organics actually formed in the chunks of rock that later became the meteorites that transported them to earth. Their formation was part of a volcanic process that traps carbon in crystal structures formed by cooling magma. Through a series of non-biological chemical reactions, the complex organics found in the meteorites are created using the carbon trapped in these crystals.

The team also casts doubt on another possible explanation: whether the organics might be caused by emissions from microbes that had migrated into the volcano via tectonic processes similar to those on Earth. They point out that Mars does not have the tectonic activity similar to Earth so there is very little likelihood that the molecules are created by microbial activity.

That might sound like a depressing result for the astrobiologists. But the important finding from this study is that Mars has been natively and naturally creating complex organic molecules for 4.2 billion years and may be still be doing so today. Since the creation of organic molecules on Earth was a precursor to life, scientists can still hold out hope that the same life-creating process might have already happened on the red planet.

Interestingly, one of the Martian meteorites that was studied was the famous ALH84001, the meteorite that some researchers claimed in 1996 might contain fossils from Mars. That claim was subsequently strongly challenged, and studies of the rock are ongoing. ALH84001 is a portion of a meteorite that was dislodged from Mars by a huge impact about 16 million years ago and that fell to Earth in Antarctica approximately 13,000 years ago. The meteorite was found in Allan Hills ice field in Antarctica.

Read the team’s abstract.

Lead image caption: ALH84001 is one of 10 rocks from Mars in which researchers have found organic carbon compounds that originated on Mars without involvement of life. Credit: NASA/JSC/Stanford University

Sources: Planetary Science Institute, LiveScience, NASA

Posted on by Nancy Atkinson

Video of California Daytime Fireball Surfaces

Dr. Peter Jenniskens take a closer look at the image from the AVS Cineflex HiDEF camera mounted on the nose of the Eureka Airship. Mike Coop, can be seen in the background checking the map, further back other flight members continue to look for potential impact sites. Image credit: NASA / Eric James

Video footage has finally surfaced of the daytime fireball that illuminated the sky over the Sierra Nevada Mountains in California back in April. NASA and the SETI Institute had asked the public to submit any amateur photos or video footage of the event, and previously a just few photos were taken of the event, even though it happened in broad daylight and created sonic booms that were heard over a wide area, back on Sunday, April 22, 2012 at 7:51 a.m. PDT. A few weeks later, Shon Bollock, who was making a time-lapse kayaking video just outside Kernville, California realized he had captured the bolide streaking through the air. This video shows the event several times, successively zooming in for a closer look. According to NASA it is the only footage of the meteor thus far.


Meteorite hunters have been successful in locating fragments of the meteor, now called the Sutter’s Mill meteor since the event occurred near the area famous for where gold was discovered back in 1848, creating the California gold rush.

NASA estimated fragments could be dispersed over a 16-km (10-mile) area.

Phil Plait says the video is being studied by astronomers and meteoriticists to try to calculate the trajectory, speed, and possible orbit of the object, which is difficult with just one video, so if anyone finds they have ‘accidently’ taken footage of the event, contact the NASA Lunar Science Institute at the NASA Ames Research Center.

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NASA used an airship to search for meteorites from this event. Noted meteorite expert Peter Jenniskens said the meteorites found so far from the fall are Carbonaceous Chondrites from the CM group of meteorites, “a rare type of primitive meteorite rich in organic compounds,”and scientists have precious few samples of this kind of material. The meteorites are very interesting to scientists from an astrobiology perspective, as they contain molecules related to how the building blocks for life on Earth may have been delivered from outer space. Scientist believe that this meteor could hold the answers to the origin of life on Earth and the universe. By studying the meteor, scientists also will learn more about the early solar system and the formation of our planets.

“This is among the most chemically primitive meteorites,” said NLSI Deputy Director Greg Schmidt. “It’s like asking ‘how did life on Earth begin?’ and then having a fossil fall right in your back yard. This is exciting stuff — who knows what’s inside? The Sutter’s Mill Meteorite could be the most profound sample collected in over 40 years.”

Via the Bad Astronomer

Posted on by Nancy Atkinson

Meteorites Could Provide New Explanation for Mars Methane

A Murchison meteorite specimen at the National Museum of Natural History in Washington DC.

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Where does the methane on Mars come from? That has been one of the biggest unanswered questions in planetary science since the discovery of large plumes of methane gas in the Martian atmosphere. Scientists have been trying to figure out how the planet’s environment or geology can keep replenishing this short-lived gas, and of course, in the back of everyone’s mind is whether the methane has any connection to possible life on Mars.

A new potential explanation squelches both the life and environment prospect and offers a unique answer. A group of researchers found that meteorites, which continually bombard the surface of Mars, may contain enough carbon compounds to generate methane when they are exposed to strong UV sunlight.

“Whether or not Mars is able to sustain life is not yet known, but future studies should take into account the role of sunlight and debris from meteorites in shaping the planet’s atmosphere,” said Dr. Andrew McLeod, of the University of Edinburgh, co-author of a new study published in Nature this week.

The group of European researchers looked at the famous Murchison meteorite, a carbonaceous chondrite meteorites that fell in Australia more than 40 years ago. Carbonaceous chondrites are very common meteorites, so they likely will be falling on Mars. The team exposed particles of the Murchison meteorite to levels of ultraviolet radiation equivalent to sunlight on Mars.

When the meteorite pieces were exposed to ample amounts of UV light the meteor fragments rapidly released methane. After the UV exposure was reduced, the amount of methane produced would lessen, but if there were other activities, such as heating, shaking or lowering the pressure on the meteorite, the amount of methane released would rise again.

With Mars thin atmosphere, UV light easily gets to the surface of the planet. The thin atmosphere also allows more meteorites to hit Mars than on Earth (estimates range from just a few thousands of metric tons to as much as 60,000 metric tons.) The team said that temperature changes on Mars, especially during the summertime when it gets warm, could account for a boost of methane release from meteorites, and seasonal dust storms could shake or move the meteorites.

However, while only small amounts of methane are present in the Martian atmosphere, it seems to be coming from very specific, localized sources. Meteorites would likely be falling across the planet.

Top: Map of methane concentrations in Autumn (first martian year observed). Peak emissions fall over Tharsis (home to the Solar System's largest volcano, Olympus Mons), the Arabia Terrae plains and the Elysium region, also the site of volcanos. Bottom: True colour map of Mars. Credit: NASA/Università del Salento

Additionally, levels of methane vary in the seasons, and are highest in autumn in the northern hemisphere, with localized peaks of 70 parts per billion. There is a sharp decrease in winter, with only a faint band of methane appearing in the atmosphere between 40-50 degrees north.

Methane was first detected in the Martian atmosphere by ground based telescopes in 2003 and confirmed a year later by ESA’s Mars Express spacecraft. In 2009, observations using ground based telescopes showed the first evidence of a seasonal cycle.

Other research has said that the methane in the Martian atmosphere lasts less than a year, making it a flitting – and difficult – feature to study.

Another issue is that the estimates for the amount of meteorites hitting Mars’ surface would likely not bring enough carbon to explain the amount of methane seen in the atmosphere.

The researchers said, however, that their findings give valuable insights into the planet’s atmosphere and these findings would be helpful for future robotic missions to Mars so scientists could fine-tune their experiments, potentially making their trips more valuable.

Read the team’s paper in Nature.

Posted on by Jason Major

A New Look at Apollo Samples Supports Ancient Impact Theory

Apollo 16 astronaut Charlie Duke collects lunar samples during EVA on April 23, 1972 (NASA)

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New investigations of lunar samples collected during the Apollo missions have revealed origins from beyond the Earth-Moon system, supporting a hypothesis of ancient cataclysmic bombardment for both worlds.

Samples of Apollo 16 breccia that contain chondritic material (JSC)

Using scanning electron microscopes, researchers at the Lunar-Planetary Institute and Johnson Space Center have re-examined breccia regolith samples returned from the Moon, chemically mapping the lunar rocks to discern more compositional detail than ever before.

What they discovered was that many of the rocks contain bits of material that is chondritic in origin — that is, it came from asteroids, and not from elsewhere on the Moon or Earth.

Chondrites are meteorites that originate from the oldest asteroids, formed during the development of the Solar System. They are composed of the initial material that made up the stellar disk, compressed into spherical chondrules. Chondrites are some of the rarest types of meteorites found on Earth today but it’s thought that at one time they rained down onto our planet… as well as our moon.

The Lunar Cataclysm Hypothesis suggests that there was a period of extremely active bombardment of the Moon’s surface by meteorite impacts around 3.9 billion years ago. Because very few large impact events — based on melt rock samples — seem to have taken place more than 3.85 billion years ago, scientists suspect such an event heated the Moon’s surface enough prior to that period to eradicate any older impact features — a literal resurfacing of the young Moon.

There’s also evidence that there was a common source for the impactors, based on composition of the chondrites. What event took place in the Solar System that sent so much material hurtling our way? Was there a massive collision between asteroids? Did a slew of comets come streaking into the inner solar system? Were we paid a brief, gravitationally-disruptive visit by some other rogue interstellar object? Whatever it was that occurred, it changed the face of our Moon forever.

Curiously enough, it was at just about that time that we find the first fossil evidence of life on Earth. If there’s indeed a correlation, then whatever happened to wipe out the Moon’s oldest craters may also have cleared the slate for life here — either by removing any initial biological development that may have occurred or by delivering organic materials necessary for life in large amounts… or perhaps a combination of both.

Timeline for the Lunar Cataclysm Hypothesis (LPI)

The new findings from the Apollo samples provide unambiguous evidence that a large-scale impact event was taking place during this period  on the Moon — and most likely on Earth too. Since the Moon lacks atmospheric weathering or water erosion processes it serves as a sort of “time capsule”, recording the evidence of cosmic events that take place around the Earth-Moon neighborhood. While evidence for any such impacts would have long been erased from Earth’s surface, on the Moon it’s just a matter of locating it.

In fact, due to the difference in surface area, Earth may have received up to ten times more impacts than the Moon during such a cosmic cataclysm. With over 1,700 craters over 20 km identified on the Moon dating to a period around 3.9 billion years ago, Earth should have  17,000 craters over 20 km… with some ranging over 1,000 km! Of course, that’s if the craters could had survived 3.9 billion years of erosion and tectonic activity, which they didn’t. Still, it would have been a major event for our planet and anything that may have managed to start eking out an existence on it. We might never know if life had gained a foothold on Earth prior to such a cataclysmic bombardment, but thanks to the Moon (and the Apollo missions!) we do have some evidence of the events that took place.

Sample of lunar impact melt breccia, showing exterior and chondrule-filled interior. (Click for sample report.) Source: JSC

The LPI-JSC team’s paper was submitted to the journal Science and accepted for publication on May 2. See the abstract here, and read more on the Lunar Science Institute’s website here.

And if you want to browse through the Apollo lunar samples you can do so in depth on the JSC Lunar Sample Compendum site.

Posted on by Jason Major

Fragments of Meteorite Worth Their Weight in Gold

Fragments collected from the April 22 fireball over central California. (Franck Marchis)

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Actually it’s more like 3.5 times their weight in gold, according to today’s market value… and meteorite experts from SETI and NASA’s Marshall Space Flight Center.

During the daylight hours of April 22, 2012, reports came in from all over the north central California area of an extremely bright fireball — described as a “glittering sparkler” — and accompanying loud explosion. It was soon determined that this was the result of a meteoroid about the size of a minivan entering the atmosphere and disintegrating. It was later estimated that the object weighed about 70 metric tons and detonated with a 5-kiloton force.

Read more about the California fireball event here.

Over a thousand meteorite hunters scrambled to the area, searching for any traces of the cosmic visitor’s remains. After a few days, several pieces of the meteorite were found and reported by five individuals, adding up to 46 grams in total.

Those pieces could be worth over $9,000 USD, according to Bill Cooke of NASA’s Meteoroid Environment Office at Marshall Space Flight Center.

Based on today’s market, that’s about 3.6 times the value of gold (about $1,660 per troy ounce — 31.1 grams).

The high value is due to the extreme rarity of the meteorite fragments. The California fireball is now known to have been created by a CM chondrite, a type of carbonaceous meteorite with material characteristics similar to comets.

SETI Institute's Franck Marchis and the chondrite fragments (F. Marchis)

According to Franck Marchis, Planetary Astronomer at the Carl Sagan Center of the SETI Institute and one of the coordinators of the meteorite reporting teams, CM chondrites appear to have been altered by water, and have deuterium-to-hydrogen ratios in line with what’s been measured in the tails of comets Halley and Hyakutake.

They also have been found to contain organic compounds and amino acids, lending to the hypothesis that such meteorites may have helped supply early Earth with the building blocks for life.

But due to their fragile composition, they are also incredibly rare. Only 1% of known meteorites are CM chondrites, making even the small handful of fragments found in California very valuable.

“This will be only the third observed CM fall in the US, after Crescent, OK, in 1936, (78 g) and Murray, KY, in 1950 (13 kg),” Marchis told Universe Today.

As far as what the finders will do with the fragments, that’s entirely up to them.

“They can sell them on eBay or they can lend them to the scientists… or make a donation.” Marchis said.

Just goes to show that all that glitters really isn’t gold — it could be even better.

Read more in an article by Sara Reardon on New Scientist, and read more on the comet/chondrite connection here. And the ongoing search for pieces of what’s now being referred to as the “Sutter’s Mill Meteorite” can be followed here and here.

The largest CM chondrite ever recovered was from a fall in Murchison, Australia on September 28, 1969. The total mass of its collected fragments weighed in at over 100 kg (220 lbs).

Posted on by Nancy Atkinson

Meteorite Hunters Find Fragments from the Recent ‘Daytime Fireball’ in California

Meteorite expert and researcher Peter Jenniskens with a fragment of the bolide seen over California on April 22, 2012. Image via Franck Marchis' Cosmic Diary blog.

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Meteorite hunters have been successful in locating fragments from the huge meteor visible in the daytime skies over California last weekend. One of the successful hunters was Peter Jenniskens, an expert in meteors and meteorites, perhaps best known for retrieving the fragments of asteroid 2008 TC3 which fell in Sudan in 2008. Astronomer Franck Marchis wrote in his Cosmic Diary blog that Jenniskens realized the size of the California meteor was very similar to 2008 TC3, and so fragments should have reached the surface, just like they did in 2008.

Jenniskens went out searching and found a four-gram fragment of the meteor in a parking lot in Lotus, California.

Update: NASA and the SETI Institute are asking the public to submit any amateur photos or video footage of the meteor that illuminated the sky over the Sierra Nevada mountains and created sonic booms that were heard over a wide area at 7:51 a.m. PDT Sunday, April 22, 2012.


Marchis wrote that several scientists from the Bay Area met at NASA Ames Research Center on April 24 to discuss a strategy for a search campaign, examining a radar data map which showed that dozens of fragments from the 100g to 1 kg range may have reached the ground.

Jenniskens said the fragment he found was a Carbonaceous Chondrites from the CM group of meteorites, “a rare type of primitive meteorite rich in organic compounds,” he said.

“We are very interested in this rare find,” said Greg Schmidt, deputy director of the NASA Lunar Science Institute. “With the public’s help, this could lead to a better understanding of these fascinating objects.”

Several other fragments were found, the first one by noted meteorite hunter Robert Ward.

“Getting fresh fragments of meteoroids, called meteorites, is key for astronomers to understand the composition of those remnants of the formation of the solar system,” Marchis wrote. “Fresh fragments are unaltered by the Earth’s weather and erosion processes, so they are pristine samples which can be used to detect organic materials for instance.”

Photos and video footage would help the scientists to better analyze the trajectory of the meteor and learn about its orbit in space. This information will also help scientists to locate the places along the meteor path where fragments may have fallen to the ground.

People who have photos or video of the meteorite are asked to contact Jenniskens at [email protected].

Marchis noted that a storm is heading towards the region and rain could alter the remaining fragments. So if you live nearby, consider heading out to take a look. Here is the radar map:

Radar map by Marc Fries showing the possible location of fragments (green area) of the meteor between Auburn and Placerville.

Marchis also said that if anyone has access to security camera footage taken on April 22, 2012 in the area of the fireball sighting, it may be useful to check them to see if the fireball was visible. “Astronomers could use them to pin down the site of the fall, maximizing the hunt for fragments,” he said.

Read more at the Cosmic Diary.

Posted on by Nancy Atkinson

Fireball Over California Exploded with Force of 5 Kilotons

Location of daylight (8 AM) fireball over California on April 22, 2012. Credit: NASA's Meteor Watch

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A daytime fireball over the skies of central/northern California on Sunday morning, April 22, 2012 caused a loud explosion and the event was also detected on several seismographs stations in the area. According to Bill Cooke, head of NASA’s Meteoroid Environments Office, the source of the blast was a meteoroid about the size of a minivan, weighing in at around 70 metric tons (154,300 pounds) and at the time of disintegration released energy equivalent to a 5-kiloton explosion.

For comparison, conventional bombs yield energy from less than 1 ton to 44 tons, and the approximate energy released when the Chicxulub impact caused the mass extinction 65 million years ago was estimated to be equal to 96 million megatons of TNT.

“This was a BIG event,” said Elizabeth Silber of the Meteor Group at the Western University in Ontario, Canada.

“Most meteors you see in the night’s sky are the size of tiny stones or even grains of sand and their trail lasts all of a second or two,” said Don Yeomans of NASA’s Near-Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena, Calif. “Fireballs you can see relatively easily in the daytime and are many times that size – anywhere from a baseball-sized object to something as big as a minivan.”

Silber estimates the location of its explosion in the upper atmosphere above California’s Central Valley. It is not known yet if any pieces of the space rock survived to land as meteorites, but the entire object was likely vaporized before hitting the ground. However, you can bet there are people out looking. (Silber said on the Meteorobs newsgroup that based on infrasonic data the approximate source coordinates are 37.6N, 120.5W).

Descriptions of the fireball range from a “silver flash” to like a “green glittering sparkler,” and one person said their sighting of the object was followed 4-5 minutes later by a loud sonic boom.

Unfortunately, since the huge fireball occurred during the day, all of NASA’s meteor-seeking cameras were turned off, so images of the event are sparse. You can see some at news station KTVN’s website.

This type of fireball is quite rare, and visual observations of them are even more rare. “An event of this size might happen about once a year,” said Yeomans. “But most of them occur over the ocean or an uninhabited area, so getting to see one is something special.”

That the fireball occurred during the Lyrid meteor shower is probably a coincidence, most experts are saying, as meteor shower meteors are generally small bits space dust that don’t produce large fireballs. However, another large fireball also occurred on April 20 in Brazil. See more information about that bolide here.

Posted on by Jason Major

Shaking Up Theories Of Earth’s Formation

Earth may not have formed quite like once thought (Image: NASA/Suomi NPP)

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Researchers from The Australian National University are suggesting that Earth didn’t form as previously thought, shaking up some long-standing hypotheses of our planet’s origins right down to the core — literally.

Ian Campbell and Hugh O’Neill, both professors at ANU’s Research School for Earth Sciences, have challenged the concept that Earth formed from the same material as the Sun — and thus has a “chondritic” composition — an idea that has been assumed accurate by planetary scientists for quite some time.

 

Chondrite meteorites are composed of spherical chondrules, which formed in the solar nebula before the asteroids. (NASA)

Chondrites are meteorites that were formed from the solar nebula that surrounded the Sun over 4.6 billion years ago. They are valuable to scientists because of their direct relationship with the early Solar System and the primordial material they contain.

“For decades it has been assumed that the Earth had the same composition as the Sun, as long the most volatile elements like hydrogen are excluded,” O’Neill said. “This theory is based on the idea that everything in the solar system in general has the same composition. Since the Sun comprises 99 per cent of the solar system, this composition is essentially that of the Sun.”

Instead, they propose that our planet was formed through the collision of larger planet-sized bodies, bodies that had already grown massive enough themselves to develop an outer shell.

This scenario is supported by over 20 years of research by Campbell on columns of hot rock that rise from Earth’s core, called mantle plumes. Campbell discovered no evidence for “hidden reservoirs” of heat-producing elements such as uranium and thorium that had been assumed to exist, had Earth actually formed from chondritic material.

“Mantle plumes simply don’t release enough heat for these reservoirs to exist. As a consequence the Earth simply does not have the same composition as chondrites or the Sun,” Campbell said.

The outer shell of early Earth, containing heat-producing elements obtained from the impacting smaller planets, would have been eroded away by all the collisions.

“This produced an Earth that has fewer heat producing elements than chondritic meteorites, which explains why the Earth doesn’t have the same chemical composition,” O’Neill said.

The team’s paper has been published in the journal Nature. Read the press release from The Australian National University here.