The meteor explosion over Russia in February 2013 raised concerns that even small asteroid impactors may wreak some havoc given our heavily populated cities. A new study by NASA scientists aims to improve our understanding of such asteroids that are lurking in Earth’s vicinity. The team, led by Amy Mainzer, noted that only a mere fraction of asteroids comparable in size to the object that exploded over Russia have been discovered, and their physical properties are poorly characterized.
The team derived fundamental properties for over a hundred near-Earth objects, and determined that many are smaller than 100 meters. Indeed, the team notes that, “In general … [asteroids] smaller than 100-m are only detected when they are quite close … and the smallest … were detected when they were only 2-3 lunar distances away from Earth.”
Essentially, a large fraction of these bodies may go undetected until they strike Earth, analogous to the case of the asteroid that exploded over Russia in February.
The team’s results rely partly on observations from the Wide-field Infrared Survey Explorer (WISE), which is a space-based telescope that mapped the entire sky in the mid-infrared. Observations taken in the infrared, in concert with those taken in the optical, can be used to infer the fundamental properties of asteroids (e.g., their diameter and chemical composition).
On a somewhat positive note, Mainzer remarks that 90% of near-Earth asteroids larger than 1-km are known, and those potential impactors are most worrisome as they may cause widespread fatalities. The dinosaurs suffered a mass-extinction owing, at least in large part, to a 10-km impactor that struck Earth 65 million years ago. However, Mainzer notes that the survey completeness drops to 25% for nearby 100-m asteroids, and it is likely to be less than 1% for 20-m asteroids like that which exploded over Russia (Chelyabinsk). The Tunguska event (see the image below) is likewise speculated to have been on the order of that latter size.
The team highlights that approximately 10,000 near-Earth objects have been discovered to date, 900 of which are 1-km or larger, and 3500 objects appear to be 100-m or smaller. “Because their small sizes usually make them undetectable until they are very nearby the Earth, it is often difficult for the current suite of asteroid surveys and follow-up telescopes to track them for very long.
Consequently, the fraction of the total population at small sizes that has been discovered to date remains very low,” noted Mainzer.
In closing, Mainzer emphasizes that, “It is, however, clear that much work remains to be done to discover and characterize the population of very small NEOs [near-Earth objects].”
The Mainzer et al. 2013 findings have been accepted for publication in the Astrophysical Journal (ApJ), and a preprint is available on arXiv. Coauthors on the study are J. Bauer, T. Grav, J. Masiero, R. M. Cutri, E. L. Wright, C. R. Nugent, R. Stevenson, E. Clyne, G. Cukrov, and F. Masci.
Scientists and meteorites hunters have been on a quest to find bits of rock from the asteroid which exploded over the city of Chelyabinsk in Russia on February 15. More than 100 fragments have been found so far that appear to be from the space rock, and now scientists from Russia’s Urals Federal University have discovered the biggest chunk so far, a meteorite fragment weighing more than one kilogram (2.2 lbs).
The asteroid has been estimated to be about 15 meters (50 feet) in diameter when it struck Earth’s atmosphere, traveling several times the speed of sound, and exploded into a fireball, sending a shockwave to the city below, which broke windows and caused other damage to buildings, injuring about 1,500 people.
Fragments of the meteorite have been found along a 50 kilometer (30 mile) trail under the meteorite’s flight path. Small meteorites have also been found in an eight-meter (25 feet) wide crater in the region’s Lake Chebarkul, scientists said earlier this week. Viktor Grokhovsky from the Urals University believes there are more to be found, including a possible biggest chunk that he says may lie at the bottom of Lake Chebarkul. It could be up to 60cm in diameter, he estimated.
This video from NASA explains more:
Please note that while many pieces have been found, and if you are looking to buy a chunk of this famous meteorite, you need to approach this with a lot of skepticism. There have been some reports of people trying to sell pieces that they claim to be from the Ural/Russian meteorite, but they likely are not. Be careful and do your research on the seller before you buy.
Just a week after a huge fireball streaked across the skies of the Chelyabinsk region of Russia, astronomers published a paper that reconstructs the orbit and determines the origins of the space rock that exploded about 14-20 km (8-12.5 miles) above Earth’s surface, producing a shockwave that damaged buildings and broke windows.
Researchers Jorge Zuluaga and Ignacio Ferrin at the University of Antioquia in Medellin, Colombia used a resource not always available in meteorite falls: the numerous dashboard and security cameras that captured the huge fireball. Using the trajectories shown in videos posted on YouTube, the researchers were able to calculate the trajectory of the meteorite as it fell to Earth and use it to reconstruct the orbit in space of the meteoroid before its violent encounter with our planet.
The results are preliminary, Zuluaga told Universe Today, and they are already working on getting more precise results. “We are working hard to produce an updated and more precise reconstruction of the orbit using different pieces of evidence,” he said via email.
But through their calculations, Zuluaga and Ferrin determined the rock originated from the Apollo class of asteroids.
Using triangulation, the researchers used two videos specifically: one from a camera located in the Revolutionary Square in Chelyabinsk and one video recorded in the a nearby city of Korkino, along with the location of a hole in the ice in Lake Chebarkul, 70km west of Chelyabinsk. The hole is thought to have come from the meteorite that fell on February 15.
Zuluaga and Ferrin were inspired to use the videos by Stefen Geens, who writes the Ogle Earth blog and who pointed out that the numerous dashcam and security videos may have gathered data about the trajectory and speed of the meteorite. He used this data and Google Earth to reconstruct the path of the rock as it entered the atmosphere and showed that it matched an image of the trajectory taken by the geostationary Meteosat-9 weather satellite.
But due to variations in time and date stamps on several of the videos — some which differed by several minutes — they decided to choose two videos from different locations that seemed to be the most reliable.
From triangulation, they were able to determine height, speed and position of the meteorite as it fell to Earth.
This video is a virtual exploration of the preliminary orbit computed by Zuluaga & Ferrin
But figuring out the meteroid’s orbit around the Sun was more difficult as well as less precise. They needed six critical parameters, all which they had to estimate from the data using Monte Carlo methods to “calculate the most probable orbital parameters and their dispersion,” they wrote in their paper. Most of the parameters are related to the “brightening point” – where the meteorite becomes bright enough to cast a noticeable shadow in the videos. This helped determine the meteorite’s height, elevation and azimuth at the brightening point as well as the longitude, latitude on the Earth’s surface below and also the velocity of the rock.
“According to our estimations, the Chelyabinski meteor started to brighten up when it was between 32 and 47 km up in the atmosphere,” the team wrote. “The velocity of the body predicted by our analysis was between 13 and 19 km/s (relative to the Earth) which encloses the preferred figure of 18 km/s assumed by other researchers.”
They then used software developed by the US Naval Observatory called NOVAS, the Naval Observatory Vector Astrometry to calculate the likely orbit. They concluded that the Chelyabinsk meteorite is from the Apollo asteroids, a well-known class of rocks that cross Earth’s orbit.
According to The Technology Review blog, astronomers have seen over 240 Apollo asteroids that are larger than 1 km but believe there must be more than 2,000 others that size.
However, astronomers also estimate there might be about 80 million out there that are about same size as the one that fell over Chelyabinsk: about 15 meters (50 feet) in diameter, with a weight of 7,000 metric tons.
In their ongoing calculations, the research team has decided to make future calculations not using Lake Chebarkul as one of their triangulation points.
“We are acquainted with the skepticism that the holes in the icesheet of the lake have been produced artificially,” Zuluaga told Universe Today via email. “However I have also read some reports indicating that pieces of the meteoroid have been found in the area. So, we are working hard to produce an updated and more precise reconstruction of the orbit using different pieces of evidence.”
Many have asked why this space rock was not detected before, and Zuluaga said determining why it was missed is one of the goals of their efforts.
“Regretfully knowing the family at which the asteroid belongs is not enough,” he said. “The question can only be answered having a very precise orbit we can integrate backwards at least 50 years. Once you have an orbit, that orbit can predict the precise position of the body in the sky and then we can look for archive images and see if the asteroid was overlooked. This is our next move!”
A little more than week ago a 7,000 ton, 50-foot (15-meter) wide meteoroid made an unexpected visit over Russia to become the biggest space rock to enter the atmosphere since the Tunguska impact in 1908. While scientists still debate whether it was asteroid or comet that sent a tree-flattening shockwave over the Tunguska River valley, we know exactly what fell last Friday.
Now is a fitting time to get more familiar with these extraterrestrial rocks that drop from out of nowhere.
The Russian meteoroid – the name given an asteroid fragment before it enters the atmosphere – became a brilliant meteor during its passage through the air. If a cosmic rock is big enough to withstand the searing heat and pressure of entry, fragments survive and fall to the ground as meteorites. Most of the meteors or “shooting stars” we see on a clear night are bits of rock the size of apple seeds. When they strike the upper atmosphere at tens of thousands of miles an hour, they vaporize in a flash of light. Case closed. But the one that boomed over the city of Chelyabinsk was big enough to to survive its last trip around the Sun and sprinkle the ground with meteorites.
Ah, but the Russian fireball didn’t get off the hook that easy. The overwhelming air pressure at those speeds combined with re-entry temperatures around 3,000 degrees F (1,650 C) shattered the original space rock into many pieces. You can see the dual trails created by two of the larger hunks in the photo above.
Scientists at Urals Federal University in Yekaterinburg examined 53 small meteorite fragments deposited around a hole in ice-covered Chebarkul Lake 48 miles (77 km) west of Chelyabinsk the following day. Chemical analysis revealed the stones contained 10% iron-nickel metal along with other minerals commonly found in stony meteorites. Since then, hundreds of fragments have been dug out of the snow by people in surrounding villages. As specimens continue to be recovered and analyzed, here’s an overview — and a look at what we know — of these space rocks that pay us a visit from time to time.
How many times has a meteor taken your breath away? A brilliant fireball streaking across the night sky ranks among the most memorable astronomical sights most of us will ever see. Like objects in your side view mirror, meteors appear closer than they really are. And it’s all the more true when they’re exceptionally bright. Studies show however that meteors burn up at least 50 miles (80 km) overhead. If big enough to remain intact and land on the ground, the fragments go completely dark 5-12 miles (8-19 km) high during the “dark flight” phase. A meteor passing overhead would be at the minimum distance of about 50 miles (80 km) from the observer.
Since most sightings are well off toward one direction or another, you have to add your horizontal distance to the meteor’s height to get a true distance. While some meteors are bright enough to trick us into thinking they landed just over the next hill, nearly all are many miles away. Even the Russian meteor, which put on a grand show and blasted the city of Chelyabinsk with a powerful shock wave, dropped fragments dozens of miles to the west. We lack the context to appreciate meteor distances, perhaps unconsciously comparing what we see to an aerial fireworks display.
Very cute Youtube video of Sasha Zarezina, 8, who lives in a small Siberian village, as she hunts for meteorite fragments in the snow after Friday’s meteor over Russia. Credit: Ben Solomon/New York Times
An estimated 1,000 tons (907 metric tons) to more than 10,000 tons (9,070 MT) of material from outer space lands on Earth every day delivered free of charge from the main Asteroid Belt. Crack-ups between asteroids in the distant past are nudged by Jupiter into orbits that cross that of Earth’s. Most of the stuff rains down as micrometeoroids, bits of grit so small they’re barely touched by heating as they gently waft their way to the ground. Many larger pieces – genuine meteorites – make it to Earth but are missed by human eyes because they fall in remote mountains, deserts and oceans. Since over 70% of Earth’s surface’s is water, think of all the space rocks that must sink out of sight forever.
About 6-8 times a year however, a meteorite-producing fireball streaks over a populated area of the world. Using eyewitness reports of time, direction of travel along with more modern tools like video surveillance cameras and Doppler weather radar, which can ping the tracks of falling meteorites, scientists and meteorite hunters have a great many clues on where to look for space rocks.
Since most meteorites break into pieces in mid-air, the fragments are dispersed over the ground in a large oval called the strewnfield. The little pieces fall first and land at the near end of the oval; the bigger chunks travel farthest and fall at the opposite end.
When a new potential meteorite falls, scientists are eager to get a hold of pieces as soon as possible. Back in the lab, they measure short-lived elements called radionuclides created when high-energy cosmic rays in space alter elements in the rock. Once the rock lands on Earth, creation of these altered elements stops. The proportions of radionuclides tell us how long the rock traveled through space after it was ejected by impact from its mother asteroid. If a meteorite could write a journal, this would be it.
Other tests that examine the decay of radioactive elements like uranium into lead tells us the age of the meteorite. Most are 4.57 billion years old. Hold a meteorite and you’ll be whisked back to a time before the planets even existed. Imagine no Earth, no Jupiter.
Many meteorites are jam-packed with tiny rocky spheres called chondrules. While their origin is still a topic of debate, chondrules (KON-drools) likely formed when blots of dust in the solar nebula were flash-heated by the young sun or perhaps by powerful bolts of static electricity. Sudden heating melted the motes into chondrules which quickly solidified. Later, chondrules agglomerated into larger bodies that ultimately grew into planets through mutual gravitational attraction. You can always count on gravity to get the job done. Oh, just so you know, meteorites are no more radioactive than many common Earth rocks. Both contain trace amounts of radioactive elements at trifling levels.
Meteorites fall into three broad categories – irons (mostly metallic iron with smaller amounts of nickel), stones (composed of rocky silicates like olivine, pyroxene and plagioclase and iron-nickel metal in form of tiny flakes) and stony-irons (a mix of iron-nickel metal and silicates). The stony-irons are broadly subdivided into mesosiderites, chunky mixes of metal and rock, and pallasites.
Pallasites are the beauty queens of the meteorite world. They contain a mix of pure olivine crystals, better known as the semi-precious gemstone peridot, in a matrix of iron-nickel metal. Sliced and polished to a gleaming finish, a pallasite wouldn’t look out of place dangling from the neck of an Oscar winner. About 95% of all found or seen-to-fall meteorites are the stony variety, 4.4% are irons and 1% stony-irons.
Earth’s atmosphere is no friend to space rocks. Collecting them early prevents damage by the two things most responsible for keeping us alive: water and oxygen. Unless a meteorite lands in a dry desert environment like the Sahara or the “cold desert” of Antarctica, most are easy prey to the elements. I’ve seen meteorites collected and sliced open within a week after a fall that already show brown stains from rusting nickel-iron. Antarctica is off-limits to all but professional scientists, but thanks to amateur collectors’ efforts in the Sahara Desert, Oman and other regions, thousands of meteorites including some of the rarest types, have come to light in recent years.
Hunters share their finds with museums, universities and through outreach efforts in the schools. A portion of the material is sold to other collectors to finance future expeditions, pay for plane tickets and sit down to a good meal after the hunt. Finding a meteorite of your own is hard but rewarding work. If you’d like to have a go at it, here’s a basic checklist of qualities that separate space rocks from Earth rocks:
* Attracts a magnet. Most meteorites – even stony ones – contain iron.
* Most are covered with a matt-black, slightly bumpy fusion crust that colors dark brown with age. Look for hints of rounded chondrules or tiny bits of metal sticking up through the crust.
* Aerodynamic shape from its flight through the atmosphere, but be wary of stream-eroded rocks which appear superficially similar
* Some are dimpled with small thumbprint-like depressions called regmaglypts. These form when softer materials melt and stream away during atmospheric entry. Some meteorites also display hairline-thin, melted-rock flow lines rippling across their exteriors.
Should your rock passes the above tests, file off an edge and look inside. If the interior is pale with shining flecks of pure metal (not mineral crystals), your chances are looking better. But the only way to be certain of your find is to send off a piece to a meteorite expert or lab that does meteorite analysis. Industrial slag with its bubbly crust and dark, smooth volcanic rocks called basalts are the most commonly found meteor-wrongs. We imagine that meteorites must have bubbly crust like a cheese pizza; after all, they’ve been oven-baked by the atmosphere, right? Nope. Heating only happens in the outer millimeter or two and crusts are generally quite smooth.
Stony meteorites are further subdivided into two broad types – chondrites, like the Russian fall, and achondrites, so-called because they lack chondrules. Achondrites are igneous rocks formed from magma deep within an asteroid’s crust and lava flows on the surface. Some eucrites (YOU-crites), the most common type of achondrite, likely originated as fragments shot into space from impacts on Vesta. Measurements by NASA’s Dawn space mission, which orbited the asteroid from July 2011 to September 2012, have found great similarities between parts of Vesta’s crust and eucrites found on Earth.
We also have meteorites from Mars and the Moon. They got here the same way the rest of them did; long-ago impacts excavated crustal rocks and sent them flying into space. Since we’ve studied moon rocks brought back by the Apollo missions and sampled Mars atmosphere with a variety of landers, we can compare minerals and gases found inside potential moon and Mars meteorites to confirm their identity.
Scientists study space rocks for clues of the Solar System’s origin and evolution. For the many of us, they provide a refreshing “big picture” perspective on our place in the Universe. I love to watch eyes light up with I pass around meteorites in my community education astronomy classes. Meteorites are one of the few ways students can “touch” outer space and feel the awesome span of time that separates the origin of the Solar System and present day life.
Planetary Defense is a concept very few people heard of or took seriously – that is until last week’s humongous and totally unexpected meteor explosion over Russia sent millions of frightened residents ducking for cover, followed just hours later by Earth’s uncomfortably close shave with the 45 meter (150 ft) wide asteroid named 2012 DA14.
This ‘Cosmic Coincidence’ of potentially catastrophic space rocks zooming around Earth is a wakeup call that underscores the need to learn much more about the ever present threat from the vast array of unknown celestial debris in close proximity to Earth and get serious about Planetary Defense from asteroid impacts.
The European Space Agency’s (ESA) proposed Asteroid Impact and Deflection Assessment mission, or AIDA, could significantly bolster both our basic knowledge about asteroids in our neighborhood and perhaps even begin testing Planetary Defense concepts and deflection strategies.
After two years of work, research teams from the US and Europe have selected the mission’s target – a so called ‘binary asteroid’ named Didymos – that AIDA will intercept and smash into at about the time of its closest approach to Earth in 2022 when it is just 11 million kilometers away.
“AIDA is not just an asteroid mission, it is also meant as a research platform open to all different mission users,” says Andres Galvez, ESA studies manager.
Asteroid Didymos could provide a great platform for a wide variety of research endeavors because it’s actually a complex two body system with a moon – and they orbit each other. The larger body is roughly 800 meters across, while the smaller one is about 150 meters wide.
So the smaller body is some 15 times bigger than the Russian meteor and 3 times the size of Asteroid 2012 DA14 which flew just 27,700 km (17,200 mi) above Earth’s surface on Feb. 15, 2013.
The low cost AIDA mission would be comprised of two spacecraft – a mother ship and a collider. Two ships for two targets.
The US collider is named the Double Asteroid Redirection Test, or DART and would smash into the smaller body at about 6.25 km per second. The impact should change the pace at which the objects spin around each other.
ESA’s mothership is named Asteroid Impact Monitor, or AIM, and would carry out a detailed science survey of Didymos both before and after the violent collision.
“The project has value in many areas,” says Andy Cheng, AIDA lead at Johns Hopkins’ Applied Physics Laboratory, “from applied science and exploration to asteroid resource utilisation.” Cheng was a key member of NASA’s NEAR mission that first orbited and later landed on the near Earth Asteroid named Eros back in 2001.
Recall that back in 2005, NASA’s Deep Impact mission successfully lobbed a projectile into Comet Tempel 1 that unleashed a fiery explosion and spewing out vast quantities of material from the comet’s interior, including water and organics.
ESA has invited researchers to submit AIDA experiment proposals on a range of ideas including anything that deals with hypervelocity impacts, planetary science, planetary defense, human exploration or innovation in spacecraft operations. The deadline is 15 March.
“It is an exciting opportunity to do world-leading research of all kinds on a problem that is out of this world,” says Stephan Ulamec from the DLR German Aerospace Center. “And it helps us learn how to work together in international missions tackling the asteroid impact hazard.”
The Russian meteor exploded without warning in mid air with a force of nearly 500 kilotons of TNT, the equivalent of about 20–30 times the atomic bombs detonated at Hiroshima and Nagasaki.
Over 1200 people were injured in Russia’s Chelyabinsk region and some 4000 buildings were damaged at a cost exceeding tens of millions of dollars. A ground impact would have decimated cities like New York, Moscow or Beijing with millions likely killed.
ESA’s AIDA mission concept and NASA’s approved Osiris-REx asteroid sample return mission will begin the path to bolster our basic knowledge about asteroids and hopefully inform us on asteroid deflection and Planetary Defense strategies.