A Distant Asteroid Collision Gave Earthly Biodiversity An Ancient Boost

About 466 million years ago, there was an asteroid collision in the asteroid belt between Mars and Jupiter. The collision caused the breakup of a major asteroid, creating a shower of dust throughout the inner Solar System. That event is called the Ordovician Meteor Event, and its dust caused an ice age here on Earth.

That ice age contributed to an enormous boost in biodiversity on ancient Earth.

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Metallic Asteroids Might Have Had Volcanoes Erupting Molten Iron. That’s So Metal

Remember the asteroid Psyche? It’s the largest known asteroid in the asteroid belt between Mars and Jupiter. It’s been in the news because of its unusual properties, and because NASA plans to launch a mission to Psyche in 2022.

Psyche, aka 16 Psyche, is unusual because it’s quite different from other asteroids. Psyche appears to be the remnant, exposed nickel-iron core of an early planet. Because of that, Psyche is a building block left over from the early Solar System, when planets were still forming. It’s like a planet without a crust.

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Bright Fireball Explodes Over Ontario, Meteorite Fragments Might Have Reached the Ground

On Wednesday, July 24th, the people of the Great Lakes region were treated to a spectacular sight when a meteor streaked across the sky. The resulting fireball was observed by many onlookers, as well as the University of Western Ontario’s All-Sky Camera Network. This array runs across southern Ontario and Quebec and is maintained in collaboration with NASA’s Meteoroid Environment Office (MEO) at the Marshall Space Flight Center.

What is especially exciting about this event is the possibility that fragments of this meteorite fell to Earth and could be retrieved. This was the conclusion reached by Steven Ehlert at the MEO after he analyzed the video of the meteorite erupting like a fireball in the night sky. Examination of these fragments could tell astronomers a great deal about the formation and evolution of the Solar System.

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As Meteorites Slice Through the Atmosphere, They’re Sculpted Into Cones

Since it first formed roughly 4.5 billion years ago, planet Earth has been subject to impacts by asteroids and plenty of meteors. These impacts have played a significant role in the geological history of our planet and even played a role in species evolution. And while meteors come in many shapes and sizes, scientists have found that many become cone-shaped once they enter our atmosphere.

The reason for this has remained a mystery for some time. But thanks to a recent study conducted by a team of researchers from New York University’s Applied Mathematics Lab have figured out the physics that leads to this transformation. In essence, the process involves melting and erosion that ultimately turns meteorities into the ideal shape as they hurl through the atmosphere.

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Fossilized Clams Had Evidence of a Meteorite Impact Inside Them

When an extraterrestrial object slams into the Earth, it sends molten rock high into the atmosphere. That debris cools and re-crystallizes and falls back down to Earth. Tiny glass beads that form in this process are called microtektites, and researchers in Florida have found microtektites inside fossilized clams.

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This Meteorite is One of the Few Remnants from a Lost Planet that was Destroyed Long Ago

What if our Solar System had another generation of planets that formed before, or alongside, the planets we have today? A new study published in Nature Communications on April 17th 2018 presents evidence that says that’s what happened. The first-generation planets, or planet, would have been destroyed during collisions in the earlier days of the Solar System and much of the debris swept up in the formation of new bodies.

This is not a new theory, but a new study brings new evidence to support it.

The evidence is in the form of a meteorite that crashed into Sudan’s Nubian Desert in 2008. The meteorite is known as 2008 TC3, or the Almahata Sitta meteorite. Inside the meteorite are tiny crystals called nanodiamonds that, according to this study, could only have formed in the high-pressure conditions within the growth of a planet. This contrasts previous thinking around these meteorites which suggests they formed as a result of powerful shockwaves created in collisions between parent bodies.

“We demonstrate that these large diamonds cannot be the result of a shock but rather of growth that has taken place within a planet.” – study co-author Philippe Gillet

Models of planetary formation show that terrestrial planets are formed by the accretion of smaller bodies into larger and larger bodies. Follow the process long enough, and you end up with planets like Earth. The smaller bodies that join together are typically between the size of the Moon and Mars. But evidence of these smaller bodies is hard to find.

One type of unique and rare meteorite, called a ureilite, could provide the evidence to back up the models, and that’s what fell to Earth in the Nubian Desert in 2008. Ureilites are thought to be the remnants of a lost planet that was formed in the first 10 million years of the Solar System, and then was destroyed in a collision.

Ureilites are different than other stony meteorites. They have a higher component of carbon than other meteorites, mostly in the form of the aforementioned nanodiamonds. Researchers from Switzerland, France and Germany examined the diamonds inside 2008 TC3 and determined that they probably formed in a small proto-planet about 4.55 billion years ago.

Philippe Gillet, one of the study’s co-authors, had this to say in an interview with Associated Press: “We demonstrate that these large diamonds cannot be the result of a shock but rather of growth that has taken place within a planet.”

According to the research presented in this paper, these nanodiamonds were formed under pressures of 200,000 bar (2.9 million psi). This means the mystery parent-planet would have to have been as big as Mercury, or even Mars.

The key to the study is the size of the nanodiamonds. The team’s results show the presence of diamond crystals as large as 100 micrometers. Though the nanodiamonds have since been segmented by a process called graphitization, the team is confident that these larger crystals are there. And they could only have been formed by static high-pressure growth in the interior of a planet. A collision shock wave couldn’t have done it.

This is what’s called a High-Angle Annular Dark-Field (HAADF) Scanning Transmission Electron Microscopy (STEM) image. The image on the left shows diamond segments with similar crystal orientations. The image on the right is a magnification of the green square area. The orange lines highlight the inclusion trails, which match between the diamond segments. But those same trails are absent from the intersecting graphite. Image: Farhang Nabiei, Philippe Gillet, et. al.

But the parent body of the ureilite meteorite in the study would have to have been subject to collisions, otherwise where is it? In the case of this meteorite, a collision and resulting shock wave still played a role.

The study goes on to say that a collision took place some time after the parent body’s formation. And this collision would have produced the shock wave that caused the graphitization of the nanodiamonds.

The key evidence is in what are called High-Angle Annular Dark-Field (HAADF) Scanning Transmission Electron Microscopy (STEM) images, as seen above. The image is two images in one, with the one on the right being a magnification of a part of the image on the left. On the left, dotted yellow lines indicate areas of diamond crystals separate from areas of graphite. On the right is a magnification of the green square.

The inclusion trails are what’s important here. On the right, the inclusion trails are highlighted with the orange lines. They clearly indicate inclusion lines that match between adjacent diamond segments. But the inclusion lines aren’t present in the intervening graphite. In the study, the researchers say this is “undeniable morphological evidence that the inclusions existed in diamond before these were broken into smaller pieces by graphitization.”

To summarize, this supports the idea that a small planet between the size of Mercury and Mars was formed in the first 10 million years of the Solar System. Inside that body, large nanodiamonds were formed by high-pressure growth. Eventually, that parent body was involved in a collision, which produced a shock wave. The shock wave then caused the graphitization of the nanodiamonds.

It’s an intriguing piece of evidence, and fits with what we know about the formation and evolution of our Solar System.

Sources:

Meteors Explode from the Inside When They Reach the Atmosphere

Earth is no stranger to meteors. In fact, meteor showers are a regular occurrence, where small objects (meteoroids) enter the Earth’s atmosphere and radiate in the night sky. Since most of these objects are smaller than a grain of sand, they never reach the surface and simply burn up in the atmosphere. But every so often, a meteor of sufficient size will make it through and explode above the surface, where it can cause considerable damage.

A good example of this is the Chelyabinsk meteoroid, which exploded in the skies over Russia in February of 2013. This incident demonstrated just how much damage an air burst meteorite can do and highlighted the need for preparedness. Fortunately, a new study from Purdue University indicates that Earth’s atmosphere is actually a better shield against meteors than we gave it credit for.

Their study, which was conducted with the support of NASA’s Office of Planetary Defense, recently appeared in the scientific journal Meteoritics and Planetary Science – titled “Air Penetration Enhances Fragmentation of Entering Meteoroids. The study team consisted of Marshall Tabetah and Jay Melosh,  a postdoc research associate and a professor with the department of Earth, Atmospheric and Planetary Sciences (EAPS) at Purdue University, respectively.

In the past, researchers have understood that meteoroids often explode before reaching the surface, but they were at a loss when it came to explaining why. For the sake of their study, Tabetah and Melosh used the Chelyabinsk meteoroid as a case study to determine exactly how meteoroids break up when they hit our atmosphere. At the time, the explosion came as quite the a surprise, which was what allowed for such extensive damage.

When it entered the Earth’s atmosphere, the meteoroid created a bright fireball and exploded minutes later, generating the same amount of energy as a small nuclear weapon. The resulting shockwave blasted out windows, injuring almost 1500 people and causing millions of dollars in damages. It also sent fragments hurling towards the surface that were recovered, and some were even used to fashion medals for the 2014 Sochi Winter Games.

But what was also surprising was how much of the meteroid’s debris was recovered after the explosion. While the meteoroid itself weighed over 9000 metric tonnes (10,000 US tons), only about 1800 metric tonnes (2,000 US tons) of debris was ever recovered. This meant that something happened in the upper atmosphere that caused it to lose the majority of its mass.

Looking to solve this, Tabetah and Melosh began considering how high-air pressure in front of a meteor would seep into its pores and cracks, pushing the body of the meteor apart and causing it to explode. As Melosh explained in a Purdue University News press release:

“There’s a big gradient between high-pressure air in front of the meteor and the vacuum of air behind it. If the air can move through the passages in the meteorite, it can easily get inside and blow off pieces.”

The two main smoke trails left by the Russian meteorite as it passed over the city of Chelyabinsk. Credit: AP Photo/Chelyabinsk.ru

To solve the mystery of where the meteoroid’s mass went, Tabetah and Melosh constructed models that characterized the entry process of the Chelyabinsk meteoroid that also took into account its original mass and how it broke up upon entry. They then developed a unique computer code that allowed both solid material from the meteoroid’s body and air to exist in any part of the calculation. As Melosh indicated:

“I’ve been looking for something like this for a while. Most of the computer codes we use for simulating impacts can tolerate multiple materials in a cell, but they average everything together. Different materials in the cell use their individual identity, which is not appropriate for this kind of calculation.”

This new code allowed them to fully simulate the exchange of energy and momentum between the entering meteoroid and the interacting atmospheric air. During the simulations, air that was pushed into the meteoroid was allowed to percolate inside, which lowered the strength of the meteoroid significantly. In essence, air was able to reach the insides of the meteoroid and caused it to explode from the inside out.

This not only solved the mystery of where the Chelyabinsk meteoroid’s missing mass went, it was also consistent with the air burst effect that was observed in 2013. The study also indicates that when it comes to smaller meteroids, Earth’s best defense is its atmosphere. Combined with early warning procedures, which were lacking during the Chelyabinsk meteroid event, injuries can be avoided in the future.

This is certainly good news for people concerned about planetary protection, at least where small meteroids are concerned. Larger ones, however, are not likely to be affected by Earth’s atmosphere. Luckily, NASA and other space agencies make it a point to monitor these regularly so that the public can be alerted well in advance if any stray too close to Earth. They are also busy developing counter-measures in the event of a possible collision.

Further Reading: Purdue University, Meteoritics & Planetary Science

Meteorite Confirms 2 Billion Years of Volcanic Activity on Mars

Color Mosaic of Olympus Mons on Mars

Mars is renowned for having the largest volcano in our Solar System, Olympus Mons. New research shows that Mars also has the most long-lived volcanoes. The study of a Martian meteorite confirms that volcanoes on Mars were active for 2 billion years or longer.

A lot of what we know about the volcanoes on Mars we’ve learned from Martian meteorites that have made it to Earth. The meteorite in this study was found in Algeria in 2012. Dubbed Northwest Africa 7635 (NWA 7635), this meteorite was actually seen travelling through Earth’s atmosphere in July 2011.

A sample from the meteorite Northwest Africa 7635. Image: Mohammed Hmani
A sample from the meteorite Northwest Africa 7635. Image: Mohammed Hmani

The lead author of this study is Tom Lapen, a Geology Professor at the University of Houston. He says that his findings provide new insights into the evolution of the Red Planet and the history of volcanic activity there. NWA 7635 was compared with 11 other Martian meteorites, of a type called shergottites. Analysis of their chemical composition reveals the length of time they spent in space, how long they’ve been on Earth, their age, and their volcanic source. All 12 of them are from the same volcanic source.

Mars has much weaker gravity than Earth, so when something large enough slams into the Martian surface, pieces of rock are ejected into space. Some of these rocks eventually cross Earth’s path and are captured by gravity. Most burn up, but some make it to the surface of our planet. In the case of NWA 7635 and the other meteorites, they were ejected from Mars about 1 million years ago.

“We see that they came from a similar volcanic source,” Lapen said. “Given that they also have the same ejection time, we can conclude that these come from the same location on Mars.”

Taken together, the meteorites give us a snapshot of one location of the Martian surface. The other meteorites range from 327 million to 600 million years old. But NWA 7635 was formed 2.4 billion years ago. This means that its source was one of the longest lived volcanoes in our entire Solar System.

This false color X-ray of NWA 7635 shows the meteorite’s mineralogy mineral textures. O, olivine; P, plagioclase (maskelynite); C, clinopyroxene (augite). Chemical compositions: Fe (purple), Mg (green), Ca (blue), Ti (magenta), and S (yellow). Purple colors in the mesostasis represent Fe-rich augite. You’re welcome, mineral nerds. Image: Lapen et. al.

Volcanic activity on Mars is an important part of understanding the planet, and whether it ever harbored life. It’s possible that so-called super-volcanoes contributed to extinctions here on Earth. The same thing may have happened on Mars. Given the massive size of Olympus Mons, it could very well have been the Martian equivalent of a super-volcano.

The ESA’s Mars Express Orbiter sent back images of Olympus Mons that showed possible lava flows as recently as 2 million years ago. There are also lava flows on Mars that have a very small number of impact craters on them, indicating that they were formed recently. If that is the case, then it’s possible that Martian volcanoes will be visibly active again.

A colorized image of the surface of Mars taken by the Mars Reconnaissance Orbiter. The line of three volcanoes is the Tharsis Montes, with Olympus Mons to the northwest. Valles Marineris is to the east. Image: NASA/JPL-Caltech/ Arizona State University
A colorized image of the surface of Mars taken by the Mars Reconnaissance Orbiter. The line of three volcanoes is the Tharsis Montes, with Olympus Mons to the northwest. Valles Marineris is to the east. Image: NASA/JPL-Caltech/ Arizona State University

Continuing volcanic activity on Mars is highly speculative, with different researchers arguing for and against it. The relatively crater-free, smooth surfaces of some lava features on Mars could be explained by erosion, or even glaciation. In any case, if there is another eruption on Mars, we would have to be extremely lucky for one of our orbiters to see it.

But you never know.