see url They vary, depending on where you are and what you're doing in the water. But the National Aquarium in Baltimore says the odds of being killed by a shark are one in 3. You're much more in danger of succumbing to the flu a one in 63 chance ; a car accident one in 90 ; a fall one in ; a lightning strike one in , ; or even an asteroid one in 1. University of Florida shark experts say you're times more likely to die in a boating accident than to suffer a fatal shark attack, and times more likely to drown at the beach. Surfers tend to suffer the most attacks. Last year, nearly six in 10 U.
Experts say that's probably because surfers spend a lot of time in the "surf zone" where waves are breaking — an area sharks also tend to frequent. They urge bathers and others to avoid places where seals, a favorite prey for white sharks, congregate. Swimmers and waders accounted for one in three attacks.
Snorkelers and people using flotation gear figured into a combined 8. Massachusetts' last attack was in , when a white shark bit a bodysurfing man on his legs. Even so, perspective is everything: A Stanford University study concluded that scuba divers are nearly 7, times more likely to be hospitalized for decompression sickness than for shark bites. Biologists tracking them in Massachusetts say they've identified individuals over the past three years, most along Cape Cod's outer Atlantic-facing coastline.
Increasingly, though, they've been straying into Cape Cod Bay. Earlier this month, an 8-foot-long juvenile nicknamed Cisco, for the popular brewery on Nantucket, was detected in the bay near Barnstable. More are expected in July, August and September — the peak months on the Cape. If the odds are so minuscule, why are we so scared of sharks? Is it some kind of primal fear? Humans, he notes, have evolved an acutely tuned sense of survival that alerts us to potential threats.
Despite the fact that any interaction between a person and a shark is highly improbable — particularly a deadly one — "there's a deep-seated fear in all humans of being bitten by some animal, either on land or in the sea," Skomal says. It embellishes that fear. Follow Bill Kole on Twitter at https: His work can be found at https: Are you afraid of sharks? Spacewatch , which uses a 90 centimeter telescope sited at the Kitt Peak Observatory in Arizona, updated with automatic pointing, imaging, and analysis equipment to search the skies for intruders, was set up in by Tom Gehrels and Robert S.
The Spacewatch project has acquired a 1. The Asteroid Terrestrial-impact Last Alert System , now in operation, conducts frequent scans of the sky with a view to later-stage detection on the collision stretch of the asteroid orbit. Those would be much too late for deflection, but still in time for evacuation and preparation of the affected Earth region.
Their aim is to provide test mission designs for feasible NEO mitigation concepts. The project particularly emphasises on two aspects. The B Foundation is a private nonprofit foundation with headquarters in the United States, dedicated to protecting the Earth from asteroid strikes. As a non-governmental organization it has conducted two lines of related research to help detect NEOs that could one day strike the Earth, and find the technological means to divert their path to avoid such collisions. The foundation's current goal is to design and build a privately financed asteroid-finding space telescope , Sentinel , to be launched in — Data gathered by Sentinel will help identify asteroids and other NEOs that pose a risk of collision with Earth, by being forwarded to scientific data-sharing networks, including NASA and academic institutions such as the Minor Planet Center.
Orbit home intends to provide distributed computing resources to optimize search strategy. On February 16, , the project was halted due to lack of grant funding. As of July 13, , the project is offline according to its website. The Large Synoptic Survey Telescope , currently under construction, is expected to perform a comprehensive, high-resolution survey starting in the early s. WISE surveyed the sky in the infrared band at a very high sensitivity. Asteroids that absorb solar radiation can be observed through the infrared band.
It was used to detect NEOs, in addition to performing its science goals. Research published in the March 26, issue of the journal Nature , describes how scientists were able to identify an asteroid in space before it entered Earth's atmosphere, enabling computers to determine its area of origin in the Solar System as well as predict the arrival time and location on Earth of its shattered surviving parts.
The four-meter-diameter asteroid, called TC 3 , was initially sighted by the automated Catalina Sky Survey telescope, on October 6, Computations correctly predicted that it would impact 19 hours after discovery and in the Nubian Desert of northern Sudan. Additional observations revised this probability down to zero. The ellipses in the diagram on the right show the predicted position of an example asteroid at closest Earth approach. At first, with only a few asteroid observations, the error ellipse is very large and includes the Earth.
Further observations shrink the error ellipse, but it still includes the Earth. This raises the predicted impact probability, since the Earth now covers a larger fraction of the error region. Finally, yet more observations often radar observations, or discovery of a previous sighting of the same asteroid on archival images shrink the ellipse revealing that the Earth is outside the error region, and the impact probability is near zero. For asteroids that are actually on track to hit Earth the predicted probability of impact continues to increase as more observations are made. This very similar pattern makes it difficult to differentiate between asteroids which will only come close to Earth and those which will actually hit it.
This in turn makes it difficult to decide when to raise an alarm as gaining more certainty takes time, which reduces the time available to react to a predicted impact.
However raising the alarm too soon has the danger of causing a false alarm and creating a Boy Who Cried Wolf effect if the asteroid in fact misses Earth. Various collision avoidance techniques have different trade-offs with respect to metrics such as overall performance, cost, operations, and technology readiness. Strategies fall into two basic sets: Delay exploits the fact that both the Earth and the impactor are in orbit. An impact occurs when both reach the same point in space at the same time, or more correctly when some point on Earth's surface intersects the impactor's orbit when the impactor arrives.
Delaying, or advancing the impactor's arrival by times of this magnitude can, depending on the exact geometry of the impact, cause it to miss the Earth. Collision avoidance strategies can also be seen as either direct, or indirect and in how rapidly they transfer energy to the object. The direct methods, such as nuclear explosives, or kinetic impactors, rapidly intercept the bolide's path.
Direct methods are preferred because they are generally less costly in time and money. Their effects may be immediate, thus saving precious time.
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These methods would work for short-notice, and long-notice threats, and are most effective against solid objects that can be directly pushed, but in the case of kinetic impactors, they are not very effective against large loosely aggregated rubble piles. The indirect methods, such as gravity tractors , attaching rockets or mass drivers, are much slower and require traveling to the object, time to change course up to degrees to fly alongside it, and then take much more time to change the asteroid's path just enough so it will miss Earth.
Many NEOs are thought to be "flying rubble piles " only loosely held together by gravity, and a typical spacecraft sized kinetic-impactor deflection attempt might just break up the object or fragment it without sufficiently adjusting its course. Tracking the thousands of buckshot -like fragments that could result from such an explosion would be a very daunting task, although fragmentation would be preferable to doing nothing and allowing the originally larger rubble body, which is analogous to a shot and wax slug , to impact the Earth.
In Cielo simulations conducted in —, in which the rate and quantity of energy delivery were sufficiently high and matched to the size of the rubble pile, such as following a tailored nuclear explosion, results indicated that any asteroid fragments, created after the pulse of energy is delivered, would not pose a threat of re- coalescing including for those with the shape of asteroid Itokawa but instead would rapidly achieve escape velocity from their parent body which for Itokawa is about 0.
Initiating a nuclear explosive device above , on , or slightly beneath , the surface of a threatening celestial body is a potential deflection option, with the optimal detonation height dependent upon the composition and size of the object. In the case of an inbound threat from a "rubble pile," the stand off , or detonation height above the surface configuration, has been put forth as a means to prevent the potential fracturing of the rubble pile.
If the object is very large but is still a loosely held together rubble pile, a solution is to detonate one or a series of nuclear explosive devices alongside the asteroid, at a meter or greater stand-off height above its surface, so as not to fracture the potentially loosely held together object.
Providing this stand-off strategy was done far enough in advance, the force from a sufficient number of nuclear blasts would be enough to alter the object's trajectory to avoid an impact, according to computer simulations and experimental evidence from meteorites exposed to the thermal X-ray pulses of the Z-machine. The book Islands in Space calculates that the nuclear megatonnage necessary for several deflection scenarios exists. This would have used a number of modified Saturn V rockets sent on interception courses and the creation of a handful of nuclear explosive devices in the megaton energy range—coincidentally, the maximum yield of the Soviets' 27 metric-tonne mass, Tsar Bomba if a uranium tamper had been used—as each rocket vehicle's payload.
A NASA analysis of deflection alternatives, conducted in , stated: Nuclear standoff explosions are assessed to be 10— times more effective than the non-nuclear alternatives analyzed in this study. Other techniques involving the surface or subsurface use of nuclear explosives may be more efficient, but they run an increased risk of fracturing the target NEO.
They also carry higher development and operations risks. Under these hypothetical conditions, the report determines that a "Cradle spacecraft" would be sufficient to deflect it from Earth impact. This conceptual spacecraft contains six B83 physics packages, each set for their maximum 1.
The results of this study indicated that a single employment of this "option can deflect NEOs of [m diameter] two years before impact, and larger NEOs with at least five years warning". The director of the Asteroid Deflection Research Center at Iowa State University , Wie, who had published kinetic impactor deflection studies in the past,  began in to study strategies that could deal with 50 to meter diameter objects when the time to Earth impact was under a year or so.
He concluded that to provide the required energy, a nuclear explosion or other events that could deliver the same power, are the only methods that can work against a very large asteroid within these time constraints. This work resulted in the creation of a conceptual Hypervelocity Asteroid Intercept Vehicle HAIV , which combines a kinetic impactor to create an initial crater for a follow-up subsurface nuclear detonation within that initial crater, which would generate a high degree of efficiency in the conversion of the nuclear energy that is released in the detonation into propulsion energy to the asteroid.
Another proposed approach along similar lines is the use of a surface detonating nuclear device, in place of the prior mentioned kinetic impactor, in order to create the initial crater, with the resulting crater that forms then again being used as a rocket nozzle to channel succeeding nuclear detonations. In , the related National Laboratories of the US and Russia signed a deal that includes an intent to cooperate on defense from asteroids. An April GAO report notes that the NNSA is retaining canned subassemblies CSAs " in an indeterminate state pending a senior-level government evaluation of their use in planetary defense against earthbound asteroids.
The use of nuclear explosive devices is an international issue and will need to be addressed by the United Nations Committee on the Peaceful Uses of Outer Space. However it is unlikely that a nuclear explosive device, fuzed to be detonated only upon interception with a threatening celestial object,  with the sole intent of preventing that celestial body from impacting Earth would be regarded as an un-peaceful use of space, or that the explosive device sent to mitigate an Earth impact, explicitly designed to prevent harm to come to life would fall under the classification of a " weapon ".
The impact of a massive object, such as a spacecraft or even another near-Earth object, is another possible solution to a pending NEO impact. An object with a high mass close to the Earth could be sent out into a collision course with the asteroid, knocking it off course. When the asteroid is still far from the Earth, a means of deflecting the asteroid is to directly alter its momentum by colliding a spacecraft with the asteroid. ESA's Advanced Concepts Team has also demonstrated theoretically that a deflection of Apophis could be achieved by sending a simple spacecraft [ when?
During a trade-off study one of the leading researchers [ who? The principle of the kinetic impactor mitigation method is that the NEO or Asteroid is deflected following an impact from an impactor spacecraft.
The mass and velocity of the impactor the momentum are transferred to the NEO, causing a change in velocity and therefore making it deviate from its course slightly. As of mid, the AIDA mission has been partly approved. The goal os to impact the m asteroidal moon of Near-Earth Asteroid Didymos , nicknamed Didymoon.
While slow, this method has the advantage of working irrespective of the asteroid composition or spin rate — rubble pile asteroids would be difficult to deflect by means of nuclear detonations while a pushing device would be hard or inefficient to mount on a fast rotating asteroid. Set up My libraries How do I set up "My libraries"? British National Space Center. Pill Reminder - All in One. The m-wide Apophis had been tracked on and off since its discovery in June In , there were 53 unprovoked shark attacks in the U.
The impact will occur in October when Didymos is relatively close to Earth, allowing Earth-based telescopes and planetary radar to observe the event. The result of the impact will be to change the orbital velocity and hence orbital period of Didymoon, by a large enough amount that it can be measured from Earth. If approved, it would reach the Didymos system in and measure both the mass of Didymoon and the precise effect of the impact on that body, allowing much better extrapolation of the AIDA mission to other targets. One more alternative to explosive deflection is to move the asteroid slowly over a time.
Tiny constant thrust accumulates to deviate an object sufficiently from its predicted course. Lu and Stanley G. Love have proposed using a large heavy unmanned spacecraft hovering over an asteroid to gravitationally pull the latter into a non-threatening orbit. The spacecraft and the asteroid mutually attract one another. If the spacecraft counters the force towards the asteroid by, e. While slow, this method has the advantage of working irrespective of the asteroid composition or spin rate — rubble pile asteroids would be difficult to deflect by means of nuclear detonations while a pushing device would be hard or inefficient to mount on a fast rotating asteroid.
A gravity tractor would likely have to spend several years beside the asteroid to be effective. Another "contactless" asteroid deflection technique has been recently proposed by C. The method involves the use of a low divergence ion thruster pointed at the asteroid from a nearby hovering spacecraft. The momentum transmitted by the ions reaching the asteroid surface produces a slow but continuous force that can deflect the asteroid in a similar way as done by the gravity tractor but with a lighter spacecraft.
Jay Melosh proposed deflecting an asteroid or comet by focusing solar energy onto its surface to create thrust from the resulting vaporization of material, or to amplify the Yarkovsky effect. Over a span of months or years enough solar radiation can be directed onto the object to deflect it. This method would first require the construction of a space station with a system of gigantic lenses. Then the station would be transported toward the Sun. A mass driver is an automated system on the asteroid to eject material into space thus giving the object a slow steady push and decreasing its mass.
A mass driver is designed to work as a very low specific impulse system, which in general uses a lot of propellant, but very little power. The idea is that when using local material as propellant, the amount of propellant is not as important as the amount of power, which is likely to be limited. Another possibility is to use a mass driver on the Moon aimed at the NEO to take advantage of the Moon's orbital velocity and inexhaustible supply of "rock bullets". Attaching any spacecraft propulsion device would have a similar effect of giving a push, possibly forcing the asteroid onto a trajectory that takes it away from Earth.
Chapman, Durda, and Gold's white paper  calculates deflections using existing chemical rockets delivered to the asteroid. Such direct force rocket engines are typically proposed to use highly-efficient electrically powered spacecraft propulsion , such as ion thrusters or VASIMR. This concept, called asteroid laser ablation was articulated in the SpaceCast  white paper "Preparing for Planetary Defense",  and the Air Force  white paper "Planetary Defense: Catastrophic Health Insurance for Planet Earth".
Campbell's monograph "Using Lasers in Space: Carl Sagan , in his book Pale Blue Dot , expressed concern about deflection technology that any method capable of deflecting impactors away from Earth could also be abused to divert non-threatening bodies toward the planet.
Considering the history of genocidal political leaders and the possibility of the bureaucratic obscuring of any such project's true goals to most of its scientific participants, he judged the Earth at greater risk from a man-made impact than a natural one. Sagan instead suggested that deflection technology be developed only in an actual emergency situation.
All low-energy delivery deflection technologies have inherent fine control and steering capability, making it possible to add just the right amount of energy to steer an asteroid originally destined for a mere close approach toward a specific Earth target. According to Rusty Schweickart , the gravitational tractor method is controversial because, during the process of changing an asteroid's trajectory, the point on the Earth where it could most likely hit would be slowly shifted across different countries.
Thus, the threat for the entire planet would be minimized at the cost of some specific states' security. In Schweickart's opinion, choosing the way the asteroid should be "dragged" would be a tough diplomatic decision. Analysis of the uncertainty involved in nuclear deflection shows that the ability to protect the planet does not imply the ability to target the planet. However, if the uncertainty of the velocity change was more than a few percent, there would be no chance of directing the asteroid to a particular target.
Asteroid or comet impacts are a common subgenre of disaster fiction , and such stories typically feature some attempt—successful or unsuccessful—to prevent the catastrophe.
Most involve trying to destroy or explosively redirect an object. See also Asteroids in fiction —Collisions with Earth. From Wikipedia, the free encyclopedia.
For defending against alien invasion in fiction, see Alien invasion. B Foundation and Sentinel Space Telescope.