Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Scientists Solve Mystery Of Meteor Crater’s Missing Melted Rocks

10.03.2005


Scientists have discovered why there isn’t much impact-melted rock at Meteor Crater in northern Arizona. The iron meteorite that blasted out Meteor Crater almost 50,000 years ago was traveling much slower than has been assumed, University of Arizona Regents’ Professor H. Jay Melosh and Gareth Collins of the Imperial College London report in the cover article of Nature (March 10).

"Meteor Crater was the first terrestrial crater identified as a meteorite impact scar, and it’s probably the most studied impact crater on Earth," Melosh said. "We were astonished to discover something entirely unexpected about how it formed."

The meteorite smashed into the Colorado Plateau 40 miles east of where Flagstaff and 20 miles west of where Winslow have since been built, excavating a pit 570 feet deep and 4,100 feet across ­ enough room for 20 football fields.



Previous research supposed that the meteorite hit the surface at a velocity between about 34,000 mph and 44,000 mph (15 km/sec and 20 km/sec). Melosh and Collins used their sophisticated mathematical models in analyzing how the meteorite would have broken up and decelerated as it plummeted down through the atmosphere.

About half of the original 300,000 ton, 130-foot-diameter (40-meter-diameter) space rock would have fractured into pieces before it hit the ground, Melosh said. The other half would have remained intact and hit at about 26,800 mph (12 km/sec), he said. That velocity is almost four times faster than NASA’s experimental X-43A scramjet -- the fastest aircraft flown -- and ten times faster than a bullet fired from the highest-velocity rifle, a 0.220 Swift cartridge rifle. But it’s too slow to have melted much of the white Coconino formation in northern Arizona, solving a mystery that’s stumped researchers for years.

Scientists have tried to explain why there’s not more melted rock at the crater by theorizing that water in the target rocks vaporized on impact, dispersing the melted rock into tiny droplets in the process. Or they’ve theorized that carbonates in the target rock exploded, vaporizing into carbon dioxide. "If the consequences of atmospheric entry are properly taken into account, there is no melt discrepancy at all," the authors wrote in Nature. "Earth’s atmosphere is an effective but selective screen that prevents smaller meteoroids from hitting Earth’s surface," Melosh said.

When a meteorite hits the atmosphere, the pressure is like hitting a wall. Even strong iron meteorites, not just weaker stony meteorites, are affected. "Even though iron is very strong, the meteorite had probably been cracked from collisions in space," Melosh said. "The weakened pieces began to come apart and shower down from about eight-and-a-half miles (14 km) high. And as they came apart, atmospheric drag slowed them down, increasing the forces that crushed them so that they crumbled and slowed more."

Melosh noted that mining engineer Daniel M. Barringer (1860-1929), for whom Meteor Crater is named, mapped chunks of the iron space rock weighing between a pound and a thousand pounds in a 6-mile-diameter circle around the crater. Those treasures have long since been hauled off and stashed in museums or private collections. But Melosh has a copy of the obscure paper and map that Barringer presented to the National Academy of Sciences in 1909.

At about 3 miles (5 km) altitude, most of the mass of the meteorite was spread in a pancake shaped debris cloud roughly 650 feet (200 meters) across. The fragments released a total 6.5 megatons of energy between 9 miles (15 km) altitude and the surface, Melosh said, most of it in an airblast near the surface, much like the tree-flattening airblast created by a meteorite at Tunguska, Siberia, in 1908. The intact half of the Meteor Crater meteorite exploded with at least 2.5 megatons of energy on impact, or the equivalent of 2.5 tons of TNT.

Elisabetta Pierazzo and Natasha Artemieva of the Planetary Science Institute in Tucson, Ariz., have independently modeled the Meteor Crater impact using Artemieva’s Separated Fragment model. They find impact velocities similar to that which Melosh and Collins propose. Melosh and Collins began analyzing the Meteor Crater impact after running the numbers in their Web-based "impact effects" calculator, an online program they developed for the general public. The program tells users how an asteroid or comet collision will affect a particular location on Earth by calculating several environmental consequences of the impact. The program is online at http://www.lpl.arizona.edu/impacteffects

Lori Stiles | UA News Services
Further information:
http://uanews.org/science
http://www.lpl.arizona.edu/impacteffects

More articles from Earth Sciences:

nachricht In times of climate change: What a lake’s colour can tell about its condition
21.09.2017 | Leibniz-Institut für Gewässerökologie und Binnenfischerei (IGB)

nachricht Did marine sponges trigger the ‘Cambrian explosion’ through ‘ecosystem engineering’?
21.09.2017 | Helmholtz-Zentrum Potsdam - Deutsches GeoForschungsZentrum GFZ

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: LaserTAB: More efficient and precise contacts thanks to human-robot collaboration

At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.

Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...

Im Focus: The pyrenoid is a carbon-fixing liquid droplet

Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.

A warming planet

Im Focus: Highly precise wiring in the Cerebral Cortex

Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.

The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...

Im Focus: Tiny lasers from a gallery of whispers

New technique promises tunable laser devices

Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...

Im Focus: Ultrafast snapshots of relaxing electrons in solids

Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!

When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

“Lasers in Composites Symposium” in Aachen – from Science to Application

19.09.2017 | Event News

I-ESA 2018 – Call for Papers

12.09.2017 | Event News

EMBO at Basel Life, a new conference on current and emerging life science research

06.09.2017 | Event News

 
Latest News

Highest-energy cosmic rays have extragalactic origin

25.09.2017 | Physics and Astronomy

Two Group A Streptococcus genes linked to 'flesh-eating' bacterial infections

25.09.2017 | Life Sciences

NASA'S OSIRIS-REx spacecraft slingshots past Earth

25.09.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>