Tag: impact

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Finnish team found out the composition of asteroid Phaethon

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The asteroid that causes the Geminid shooting star swarm has also puzzled researchers with its comet-like tail. The infrared spectrum of rare meteorites helped to determine the composition of the asteroid.

Postdoctoral Researcher Eric MacLennan holds in his hands a very rare type of meteorite, the so-called CY carbonaceous chondrite. Only six specimens of the same type are known. The sample is on loan from the Natural History Museum in London. (Image: Susan Heikkinen)
Asteroid Phaethon, which is five kilometers in diameter, has been puzzling researchers for a long time. A comet-like tail is visible for a few days when the asteroid passes closest to the Sun during its orbit.
However, the tails of comets are usually formed by vaporizing ice and carbon dioxide, which cannot explain this tail. The tail should be visible already at Jupiter’s distance from the Sun.
When the surface layer of an asteroid breaks up, the detached gravel and dust continue to travel in the same orbit and give birth to a cluster of shooting stars when it encounters the Earth. Phaethon causes the Geminid meteor shower, which also appears in the skies of Finland every year around mid-December. At least according to the prevailing hypothesis because that’s when the Earth crosses the asteroid’s path.
Until now, theories about what happens on Phaethon’s surface near the Sun have remained purely hypothetical. What comes off the asteroid? How? The answer to the riddle was found by understanding the composition of Phaethon.
A rare meteorite group consisting of six known meteorites
In a recent study published in the journal Nature Astronomy by researchers from the University of Helsinki, the infrared spectrum of Phaethon previously measured by NASA’s Spitzer space telescope is re-analyzed and compared to infrared spectra of meteorites measured in laboratories.
The researchers found that Phaethon’s spectrum corresponds exactly to a certain type of meteorite, the so-called CY carbonaceous chondrite. It is a very rare type of meteorite, of which only six specimens are known.
Asteroids can also be studied by retrieving samples from space, but meteorites can be studied without expensive space missions. Asteroids Ryugu and Bennu, the targets of recent JAXA and NASA sample-return missions, belong to CI and CM meteorites.
All three types of meteorites originate from the birth of the Solar System, and partially resemble each other, but only the CY group shows signs of drying and thermal decomposition due to recent heating.
All three groups show signs of a change that occurred during the early evolution of the Solar System, where water combines with other molecules to form phyllosilicate and carbonate minerals. However, CY-type meteorites differ from others due to their high iron sulfide content, which suggests their own origin.
Phaethon’s spectrum match the spectra of CY carbonaceous chondrites
Analysis of Phaethon’s infrared spectrum showed that the asteroid was composed of at least olivine, carbonates, iron sulfides, and oxide minerals. All of these minerals supported the connection to the CY meteorites, especially iron sulfide. The carbonates suggested changes in water content that fit the primitive composition, while the olivine is a product of thermal decomposition of phyllosilicates at extreme temperatures.
In the research, it was possible to show with thermal modeling what temperatures prevail on the surface of the asteroid and when certain minerals break down and release gases. When Phaethon passes close to the Sun, its surface temperature rises to about 800°C. The CY meteorite group fits this well. At similar temperatures, carbonates produce carbon dioxide, phyllosilicates release water vapor and sulfides sulfur gas.
According to the study, all the minerals identified on Phaethon appear to correspond to the minerals of CY-type meteorites. The only exceptions were the oxides portlandite and brucite, which were not detected in the meteorites. However, these minerals can form when carbonates are heated and destroyed in the presence of water vapor.
The tail and the meteor shower get an explanation
Asteroid composition and temperature explained the formation of gas near the Sun, but do they also explain the dust and gravel forming the Geminid meteors? Did the asteroid have enough pressure to lift dust and rock from the surface of the asteroid?
The researchers used experimental data from other studies in conjunction with their thermal models, and, based on them, it was estimated that when the asteroid passes closest to the Sun, gas is released from the mineral structure of the asteroid, which can cause the rock to break down. In addition, the pressure produces by carbon dioxide and water vapor is high enough to lift small dust particles from the surface of the asteroid.
“Sodium emission can explain the weak tail we observe near the Sun, and thermal decomposition can explain how dust and gravel are released from Phaethon,” says the study’s lead author, postdoctoral researcher Eric MacLennan from the University of Helsinki.
“It was great to see how each one of the discovered minerals seemed to fall into place and also explain the behavior of the asteroid,” sums up associate professor Mikael Granvik from the University of Helsinki.

AR #87

Russians Warn of Asteroid Hit in 2036

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Asteroid Impact Prediction Getting Better

On 19 November, asteroid 2022 WJ1 became one of the many small asteroids to strike Earth, but only the sixth we ever saw coming. For the second time this year, humankind predicted an asteroid impact. The ~1-m rock caused no harm and burnt up in the sky above Toronto as a striking fireball. The detection, warning and advance observations of this asteroid illustrate our rapidly increasing ability to warn of asteroid impacts, however small.

The new asteroid was first imaged by Catalina’s 1.5-m Mt. Lemmon telescope, and once four observations were made it was reported to the Minor Planet Center (MPC), 38 minutes after initial detection, at 05:31 UTC.

These four observations were enough to map out the asteroid’s path in the sky, and within a few minutes of this ‘astrometry’ being published, ESA’s own internal monitoring software reported that the object had a ~20% chance of Earth impact, possibly hitting somewhere in North America in the next two to three hours. A few minutes later, other impact monitoring programs also sent alerts outlining a similar scenario.

Following the potential impact notifications, observers at Catalina and elsewhere across the US got follow-up observations of the new asteroid. Less than 30 minutes from the initial trigger, the impact was confirmed with excellent precision: the small asteroid, likely less than a meter in diameter, was going to impact somewhere between Lake Erie and Lake Ontario, near the US-Canada border, around 08:27 UTC (09:27 CET).

At exactly the predicted time, a ~1-m asteroid struck the atmosphere becoming a brilliant fireball above the expected location. Find out more about this event at ESA’s Near-Earth Object Coordination Centre (NEOCC) web portal.
Because of how the Solar System formed, small objects are in the majority in terms of their total population. It is estimated there are 40-50 million little asteroids and ‘just’ 1 000 of the biggest, giant ‘planet-killers’. The rest fall somewhere in between.

We currently know of more than 1.1 million asteroids, although many more are out there. Of those discovered, about 30 600 travel in an orbit that brings them near Earth’s own. These are the ‘near-Earth asteroids’ (NEAs).
The reassuring news is that almost all the giant asteroids have been found – more than 95% – and none are of concern for the next hundred years. Astronomers are tirelessly searching for every last one.

Small, meter-sized asteroids strike Earth every couple of weeks. They add to our understanding of asteroid populations, of fireballs and their makeup, but they aren’t a big priority when it comes to Planetary Defense because they pose no real danger.

The objects we are most concerned about are those ‘goldilocks asteroids’ that are large enough to do harm if they impact, and there are enough of them out there that we know, at some point, they will. The infamous Chelyabinsk impact in February 2013 and the Tunguska impact in June 1908 fall into this category, and when it comes to discovering these asteroids, there’s still a lot of work to be done.

That’s why ESA’s Planetary Defence Office is planning new telescopes on the ground and missions in space to improve our asteroid detection abilities, sending the Hera mission to the Dimorphos asteroid struck by NASA’s DART mission to test asteroid deflection, as well as working with the international community to prepare for the scenario in which a bigger asteroid is discovered on a collision course.

Pictures & Captions
https://www.esa.int/Space_Safety/Planetary_Defence/The_sixth_asteroid_impact_we_saw_coming

AR #87

Russians Warn of Asteroid Hit in 2036

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Giant Ancient Impact Left Two-Faced Moon

South Pole Hit Caused Big Differences Between Near and Far Side

The face that the Moon shows to Earth looks far different from the one it hides on its far side. The nearside is dominated by the lunar mare — the vast, dark-colored remnants of ancient lava flows. The crater-pocked far side, on the other hand, is virtually devoid of large-scale mare features. Why the two sides are so different is one of the Moon’s most enduring mysteries.
Now, researchers have a new explanation for the two-faced Moon — one that relates to a giant impact billions of years ago near the Moon’s south pole.
A new study published in the journal Science Advances shows that the impact that formed the Moon’s giant South Pole–Aitken (SPA) basin would have created a massive plume of heat that propagated through the lunar interior. That plume would have carried certain materials — a suite of rare-Earth and heat-producing elements — to the Moon’s nearside. That concentration of elements would have contributed to the volcanism that created the nearside volcanic plains.
“We know that big impacts like the one that formed SPA would create a lot of heat,” said Matt Jones, a Ph.D. candidate at Brown University and the study’s lead author. “The question is how that heat affects the Moon’s interior dynamics. What we show is that under any plausible conditions at the time that SPA formed, it ends up concentrating these heat-producing elements on the nearside. We expect that this contributed to the mantle melting that produced the lava flows we see on the surface.”
The study was a collaboration between Jones and his advisor Alexander Evans, an assistant professor at Brown, along with researchers from Purdue University, the Lunar and Planetary Science Laboratory in Arizona, Stanford University and NASA’s Jet Propulsion Laboratory.
The Moon’s nearside (left) is dominated by vast volcanic deposits, while the far side (right) has far fewer). Why the two sides are so different is an enduring lunar mystery.
The differences between the near and far sides of the Moon were first revealed in the 1960s by the Soviet Luna missions and the U.S. Apollo program. While the differences in volcanic deposits are plain to see, future missions would reveal differences in the geochemical composition as well.
Some scientists have suspected a connection between the PKT and the nearside lava flows, but the question of why that suite of elements was concentrated on the nearside remained. For the study, the researchers conducted computer simulations of how heat generated by a giant impact would alter patterns of convection in the Moon’s interior, and how that might redistribute KREEP material in the lunar mantle. KREEP is thought to represent the last part of the mantle to solidify after the Moon’s formation. As such, it likely formed the outermost layer of mantle, just beneath the lunar crust. Models of the lunar interior suggest that it should have been more or less evenly distributed beneath the surface. But this new model shows that the uniform distribution would be disrupted by the heat plume from the SPA impact. 

AR #58 “Mixing Apples & Moons,”

Peter Bros