Tag Archives: meteors

Why do meteoroids explode in the atmosphere?

Why do meteoroids explode in the atmosphere?

Researchers identify new and previously overlooked mechanism for air penetration that helps explain why meteoroids explode.
Photographer Marat Ahmetvaleev was taking panoramic photos of the winter landscape when he captured this beautiful image of the Chelyabinsk meteoroid as it exploded over Russia in 2013. M. Ahmetvaleev/NASA APOD
On February 15, 2013, a near-Earth asteroid with a diameter of 66 feet (20 meters) entered Earth’s atmosphere traveling at around 40,000 miles per hour (60,0000 km/h). Within a few seconds, the cosmic projectile detonated 12 miles above the Chelyabinsk region of Russia, releasing as much energy as about 30 Hiroshima atomic bombs. This created a gigantic fireball — known as a superbolide — that caused shock waves to propagate outward for dozens of miles, damaging several thousand buildings and injuring 1,500 people.

Though the progenitor of the explosion had an initial mass of over 10,000 metric tons, only about 0.1 percent of that mass is believed to have reached the ground, indicating that something in the upper atmosphere not only caused the rock to explode, but also caused it to disintegrate much more than expected.

A relatively small meteor streaked through the sky and eventually exploded over the Chelyabinsk region of Russia on February 15, 2013. With a blast energy equivalent to roughly 500,000 tons of TNT, the explosion created shock waves that caused damage to thousands of buildings and injured nearly 1,500 people.

Today, a team of researchers published a study in Meteoritics & Planetary Science that proposes a new and previously overlooked mechanism for air penetration in meteoroids, which could help explain the powerful breakup of the Chelyabinsk meteoroid.

According to the paper, as a meteoroid hurtles through Earth’s atmosphere, high-pressure air in the front of the object infiltrates cracks and pores in the rock, which generates a great deal of internal pressure. This pressure is so great that it causes the object to effectively blow up from the inside out, even if the material in the meteoroid is strong enough to resist the intense external atmospheric pressures.

“There’s a big gradient between high-pressure air in front of the meteor and the vacuum of air behind it,” said the study’s co-author Jay Melosh, a professor of Earth, Atmospheric, and Planetary Sciences at Purdue University, in a press release. “If the air can move through the passages in the meteorite, it can easily get inside and blow off pieces.

These figures from the study show how two computer-generated meteoroids break up over time while flying through the atmosphere. The left half of each image is a meteoroid with 10% porosity (a measure of empty space), while the right half of each image is a meteoroid with 30% porosity. M.E. Tabetah/H.J. Melosh
According to the paper, “This process of pressure internalization, new to meteoritic studies, would not have been recognized without a two-material fluid dynamics code.” This unique computer code allowed researchers to generate models that let both air and solid material coexist in any part of the calculation.

“I’ve been looking for something like this for a while,” Melosh said. “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.”

Though this process of air penetration is a very effective way for our atmosphere to shield us from smaller meteoroids, larger and denser ones will likely not be as affected by it. However, the more we can learn about how different meteoritic materials explode, the more prepared we can be for the next Chelyabinsk.

Auroras, Taurids, Space Debris

Robot looks upFire in the sky!

From http://spaceweather.com
GEOMAGNETIC STORM WARNING: A high-speed stream of solar wind is about to hit Earth’s magnetic field, prompting NOAA forecasters to estimate an 85% to 90% chance of geomagnetic storms on Nov. 2-3. This is the same 800 km/s stream that lashed Earth’s magnetic field in early October, sparking strong geomagnetic storms and bright auroras over northern-tier US states. Visit http://spaceweather.com for more information and updates.

TAURID FIREBALLS: The annual Taurid meteor shower is underway and it is lighting up the midnight sky with bright fireballs. Taurid meteoroids are gravelly pieces of debris from Comet Encke that strike our planet’s atmosphere at 70,000 mph. They pose no danger to people on the ground as they disintegrate entirely high above Earth’s surface every few hours. If forecasters are correct, the display could continue until Nov. 10th. Tune into Space Weather Radio for live radar echoes.

From http://astronomy.com/  ASY_SpaceDebrisMILLIONS OF BITS OF SPACE JUNK — leftover fragments from spacecraft and related debris — orbit Earth, and the majority of these will eventually fall into Earth’s atmosphere and incinerate. Astronomers believe they have recently observed one of these pieces and, for the first time, they can predict when and where it will enter the atmosphere. Such forecasts could allow scientists the opportunity to observe these events to better understand what happens when space debris — manmade or natural — comes in contact with the atmosphere and determine which objects might be hazardous to humans.

“Artificial objects can have a coat of paint on their surfaces, and oftentimes that paint has titanium oxide in it. This does not occur naturally, so if the object’s spectrum indicates the presence of titanium oxide, we can know it’s definitively artificial.”

The Catalina Sky Survey (CSS), a project based near Tucson that searches the sky for comets and asteroids, particularly those that could potentially impact Earth, detected the object on October 3. Soon after this discovery, astronomers realized that the CSS had also imaged the object in 2013. Comparing the two observations allowed the scientists to determine its orbit, which looked much more like that of typical space junk than a natural body. They also concluded that it would enter Earth’s atmosphere on November 13 over the Indian Ocean, in the vicinity of Sri Lanka.

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