Enter A Chemical Formula For The Following Molecular Model The Strange Mystery Of The Missing Asteroids

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The Strange Mystery Of The Missing Asteroids

Near Earth Objects (NEOs) are Solar System bodies that are small in size, but very dangerous. This is because NEOs sport orbits that carry them too close to Earth for comfort, and have a closest approach to our Star (perihelion) of less than 1.3 astronomical units (AU). One AU is equal to the average distance between Earth and Sun, which is 93,000,000 miles. Great in number, NEOs include about thirteen thousand near-Earth asteroids (NEAs), more than one hundred near-Earth comets (NECs), and a population of small solar-orbiting spacecraft and meteoroids that are nevertheless large enough to be tracked in space before crashing down on our unlucky planet. Ever since astronomers came to the realization that asteroid and comet impacts are a true danger to the survival of life on our planet, it has been thought that most of these wayward, worrisome bodies wind up ending their existence in a final farewell plunge into the furious fires of our roiling Sun. However, in February 2016, it was announced that a new study published in the journal Nature shows that most of those wandering objects are destroyed in a long, slow, searing-hot fizzle, much farther from our Star than astronomers had previously thought–ending not with a bang, but with a whimper.

Indeed, this surprising new study explains several mysterious observations that have been reported in recent years.

An international team of astronomers from Finland, France, the United States, and the Czech Republic, set out originally to construct a sophisticated model of the NEO population necessary for planning future asteroid surveys and spacecraft missions. The model describes the orbit distribution of the NEOs, as well as estimates of the number of NEOs of different sizes.

Most NEOs originate in the Main Asteroid Belt between the planets Mars and Jupiter, but were unceremoniously evicted from their home as a result of the gravitational bullying of nearby planets, only to wander into treacherous orbits that carried them too close to Earth. These primitive, primeval rocky and metallic wanderers from the Main Asteroid Belt, are all that remains of what was once an ancient, vast population of planetary building blocks, called planetesimals. The rocky planetesimals went into the construction of the four rocky, inner terrestrial worlds of our Sun’s family–Mercury, Venus, our Earth, and Mars–when our Sun was a burning baby of a Star, still in the process of forming. The comets, on the other hand, are the icy, dirty planetesimals that went into the construction of the four giant gaseous planets of the outer Solar System–Jupiter, Saturn, Uranus, and Neptune.

The orbit of a Main Belt asteroid slowly evolves as time goes by, as it is pushed around by the uneven release of excess heat emanating from its own surface. Ultimately, the asteroid’s orbit slowly begins to do a dance with the orbital motion of the gas-giant duo, Jupiter and Saturn, that alters its trajectory bringing the asteroid too close to our own planet.

The team of astronomers used the properties of almost 9,000 NEOs that had been spotted in about 100,000 images obtained over an eight year span by the Catalina Sky Survey (CSS) near Tucson, Arizona. The scientists did this in order to construct the new population model. One of the most difficult problems for the team was computing which asteroids they could actually detect. This is because an asteroid shows itself as a traveling point of light moving against a sparkling background of fixed stars, but spotting it on an image depends on how bright it is and how speedily it seems to be traveling through space. If the telescope isn’t peering at the correct location at exactly the right time–when an asteroid is bright enough and lazy enough to be spotted–it may never be found at all.

Falling From The Sky

As primitive, ancient building blocks from our Solar System’s formation about 4.56 billion years ago, asteroids and comets provide precious clues about the composition of the chemical stew from which the planets emerged. If astronomers want to understand the composition of the ancient soup from which the planets formed, they need to determine the chemical composition of the relic debris left behind. This is because it can reveal the long-lost story of this primordial process.

Made up mainly of water ice, heavily splattered with dust, comets were born in the frigid outer reaches of our Solar System. In contrast, the majority of rocky, metallic asteroids originated in the warmer, golden inner region, much closer to our fiery Star. Because they have changed little since our Solar System’s ancient formation, asteroids and comets can be used as time capsules that can reveal some very ancient, long-lost secrets about how our Solar System came to be.

Our Solar System emerged from the swirling, undulating depths of a beautiful, enormous, frigid and dark molecular cloud. It emerged when a relatively small, dense glob, embedded like a black pearl within the cloud’s billowing folds, collapsed under the squeeze of its own gravity. Most of the collapsing glob gathered at the center, and ultimately caught raging fire as a result of the process of nuclear fusion–and our Star, the Sun was born. All stars are born this way! The remaining mass flattened out around our Sun, and became what is called a protoplanetary accretion disk. The planets, their moons, the asteroids, the comets, all ultimately were born from this primordial protoplanetary accretion disk. Protoplanetary accretion disks serve a nurturing formula of gas and dust to hungry baby stars, or protostars.

Ultimately, tiny and inherently “sticky” dust motes, swirling around within this gaseous disk, bumped into each other and merged, creating ever larger and larger bodies within the crowded, dense environment of the disk. The tiny grains of dust formed objects up to several centimeters in size, and these then went on to merge together to form the planetesimals–the asteroids and comets of our Sun’s family. Planetesimals can grow to be 1 kilometer across, and even larger. Planetesimals represented a large population within the disk environment, and they zipped around in this primordial structure. Some of these ancient objects can survive long enough to linger around and serve as tattle-tale relics billions of years after the formation of a mature planetary system, such as our own.

But there is a dark side to all of this. While the rocky and metallic asteroids served as the precious ancient building blocks of our planet, they can wreak havoc if they crash into our planet now! It is generally accepted that blasts in the past played a starring role in shaping the geological and biological history of Earth. In fact, NEOs have become objects of growing interest and concern since the 1980s, as a result of an increase in our scientific understanding of the potential threat that some of these wayward wanderers pose to our planet. As a result of this increased awareness, in January 2016, NASA announced the Planetary Defense Coordination Office designed to keep a wary eye on–and track–dangerous NEOs that are larger than 30 to 50 meters in diameter, and coordinate an effective threat response and mitigation effort if necessary.

NEAs sport orbits situated between 0.983 and 1.3 AU from our Star. When astronomers spot a wayward NEA, their discovery is promptly submitted to the International Astronomical Union’s (IAU) Minor Planet Center for cataloging. The United States, the European Union, and other nations are now searching the skies for wayward NEOs in an effort called Spaceguard.

In the United States, NASA has a congressional mandate to catalogue every NEO that is at least 1 kilometer wide. This is because such relatively large impactors can hit our planet with disastrous results. As of June 2015, 872 NEAs larger that 1 kilometer had been discovered, out of which 153 were determined to be potentially hazardous. A decade ago, astronomers estimated that about 20% of the mandated objects had not yet been detected. In 2011, as a result of NEOWISE, it was estimated that about 93% of the NEAs bigger that 1 kilometer had been found, and that only approximately 70 yet remained to be detected. However, the inventory is far less complete for smaller potential impactors, which have the ability to cause widespread damage.

The NEOWISE project is an asteroid-hunting part of the Wide-field Infrared Survey Explorer (WISE) mission. NEOWISE was developed to obtain necessary measurements of asteroids and comets that had been revealed in the original WISE images, and it provides a valuable archive to aid in this scientific hunt for Solar System objects. Launched in December 2009, WISE scanned the entire sky in infrared bands. In September 2010, when the supply of frozen hydrogen necessary to cool the telescope had finally run out, the survey was reborn as NEOWISE.

Humans tend to perceive NEOs as either harmless objects of great interest–or as murderous objects with highly destructive potential.

The Strange Mystery Of The Missing Asteroids

Dr. Robert Jedicke, an astronomer at the University of Hawaii Institute for Astronomy (IFA), developed the software necessary to determine the probability that asteroids, traveling on different orbits, had been detected by the Catalina Sky Survey. This calculation demanded a detailed understanding of the operations of the telescope and detector systems, as well as an enormous amount of computing time–even with the newly-developed, and very fast, mathematical techniques. The team then produced the best-ever model of the NEO population by combining this information with the CSS data and theoretical models of the orbit distributions of NEOs that come from different portions of the Main Asteroid Belt.

However, the scientists discovered that their model had a problem–it predicted that there should be almost 10 times more objects on orbits that carry them close to our Star. The team then spent a year veryifying their calculations before they came to the realization that the problem was not in their analysis, but in their assumption about how our Solar System operates.

Dr. Mikael Granvik, a research scientist at the University of Helsinki in Finland, and lead author of the new Nature paper, noted in a February 17, 2016 IFA Press Release that his team’s model would match their NEO observations better if the wayward NEOs are destroyed when they are close to our Sun–but long before an actual collision occurs. The team went on to test this theory and found an excellent agreement between this model and the observed population of NEOs–when they elimated asteroids that lingered too long within about 10 solar diameters of our Star. “The discovery that asteroids must be breaking up when they approach too close to the Sun was surprising and that’s why we spent so much time verifying our calculations,” Dr. Jedicke noted in the same IFA Press Release.

This new discovery also helps to explain some important and nagging discrepancies. There are several conflicts that exist between observations and predictions in respect to the distribution of smaller objects inhabiting our Solar System. Shooting stars (meteors) are small tidbits composed of dust and rock that have been shot out from the surfaces of asteroids and comets that then perish by burning up as they enter Earth’s atmosphere–when they appear as bright flashes of dazzling light zipping around rapidly in the night sky. The shooting stars wander around in streams that follow the path of the parent-object from which they were ejected. However, astronomers have not been successful in their attempts to match the majority of meteor streams with any known parent-object. This new research indicates that the parent-objects completely disintegrated when they wandered too close to the raging fires and melting heat of our roiling, glaring Sun–leaving behind only the tattle-tale streams of shooting stars, but no parent NEOs, to tell the tragic story. The astronomers also found that darker asteroids are destroyed when they are farther away from our searing-hot Star than brighter ones. This observation explains a previous discovery suggesting that NEOs, that wander closer to our Sun, are brighter than those that remain more distant. The fact that darker objects are more readily destroyed than brighter ones implies that dark and bright asteroids have different internal compositions and structure.

Dr. Granvik explained in the February 17, 2016 IFA Press Release that their discovery that asteroids can disintegrate before a catastrophic collision blasts them into our fiery Sun, enables planetary scientists to understand a variety of recent observations from a new perspective–and also leads to a profound advance in asteroid science. “Perhaps the most intriguing outcome of this study is that it is now possible to test models of asteroid interiors simply by keeping track of their orbits and sizes. This is truly remarkable and was completely unexpected when we first started constructing the new NEO model,” Dr. Granvik commented.

The paper presenting this research, titled Super-catastrophic Disruption of Asteroids at Small Perihelion Distances, has been accepted for publication in volume 530 of the journal Nature. The authors of this paper are Mikael Granvik, Alessandro Morbidelli, Robert Jedicke, Bryce Bolin, William F. Bottke, Edward Beshore, David Vokrouhlicky, Marco Delbo, and Patrick Michel.

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