"خطر حقيقي".. ناسا تخشى على الأرض من "الكويكب القاتل"

"خطر حقيقي".. ناسا تخشى على الأرض من "الكويكب القاتل"


شدد مدير وكالة الفضاء الأميركية "ناسا"، جيم برايدنستاين، على ضرورة أخذ مخاطر اصطدام كويكبات قاتلة بالأرض على محمل الجد، وفق ما ذكر موقع "سكاي نيوز" البريطاني.
وحذر برايدنستاين من خطر اصطدام كويكبات قاتلة بالأرض في حال "لم يتم حماية كوكبنا بشكل أفضل وتقوية دفاعاته".

ويأتي هذا التحذير في وقت بدأت فيه وكالة الفضاء مشاركتها في مؤتمر الدفاع عن الكواكب بواشنطن، إذ يرتكز بالأساس على كشف المخاطر التي تشكلها الكويكبات على عالمنا.

وقال مدير "ناسا" إن التحذيرات المماثلة غالبا ما كانت تكون محط تسلية وسخرية، مضيفا "حان الوقت لأخذها على محمل الجد.. التهديدات حقيقية".

وتابع "يجب اتخاذ القرار الصحيح في الوقت الصحيح، من خلال تغيير مسار الكويكب الذي يشكل خطرا أو إخلاء المنطقة التي يمكن أن يقع فيها الاصطدام".

وأوضح "علينا أن نتأكد من أن الناس يدركون أن الأمر لا يتعلق بأفلام هوليوود.. يتعلق الأمر في نهاية المطاف بحماية الكوكب الوحيد الذي نعيش على متنه، وهو كوكب الأرض".

وأكد برايدنستاين أن على الجميع الاتحاد من أجل اتخاذ كافة الإجراءات الرامية إلى حماية الأرض، مضيفا "
يتعين علينا استخدام أنظمتنا وقدراتنا للحصول على المزيد من البيانات والمعلومات، وعلينا القيام بذلك بشكل أسرع".

ويقول الباحثون إن الصخور الصلبة قد تسبب أضرارا وخسائر أكبر، مشيرين إلى حادثة
"نيزك تشيليابنسك"، التي وقعت عام 2013 فوق جنوب الأورال الروسي.

وكان النيزك انفجر في الجو قبل اصطدامه بالأرض على ارتفاع نحو 25 كيلومترا فقط، وهو ما يبرز الخطر الكبير الذي كاد أن يشكله على البشر.

وعلى الرغم من أن هذه الأنواع من الأحداث تحدث مرة واحدة كل 60 عاما، إلا أن بريدنشتاين قال إنها حدثت ثلاث مرات خلال المئة عام الماضية.

Planetary defense is the term used to encompass all the capabilities needed to detect the possibility and warn of potential asteroid or comet impacts with Earth, and then either prevent them or mitigate their possible effects. Planetary defense involves:

• Finding and tracking near-Earth objects that pose of hazard of impacting Earth;
  
  
• Characterizing those objects to determine their orbit trajectory, size, shape, mass, composition, rotational dynamics and other parameters, so that experts can determine the severity of the potential impact event, warn of its timing and potential effects, and determine the means to mitigate the impact; and
  
  
• Planning and implementation of measures to deflect or disrupt an object on an impact course with Earth, or to mitigate the effects of an impact that cannot be prevented. Mitigation measures that can be taken on Earth to protect lives and property include evacuation of the impact area and movement of critical infrastructure.
  
  

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What does the Planetary Defense Coordination Office (PDCO) do?

A detailed description of what the PDCO does can be found on our "Overview" page.

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What does the Near Earth Object (NEO) Observations Program do?

A detailed description of what the NEO Observations Program does and what role it plays in planetary defense can be found on our "Overview" page.

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What is an asteroid?

A detailed description can be found on our "Asteroids" page.

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What is a comet?

A detailed description can be found on our "Comets" page.

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What are near-Earth objects (NEOs) and potentially hazardous objects (PHOs)?

A detailed description can be found on our "Did You Know" page.

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How many near-Earth asteroids have been discovered so far?

At the start of 2019, the number of discovered near-Earth asteroids totaled more than 19,000. An average of 30 new discoveries are added each week. The 15,000 milestone, reached on October 13, 2016, marked a 50 percent increase in the number of known near-Earth asteroids since 2013, when discoveries reached 10,000 in August of that year. More than 95 percent of these objects were discovered by NASA-funded surveys (primarily using ground-based telescopes) since 1998, when NASA initially established its Near-Earth Object Observations Program and began tracking and cataloguing them. The Jet Propulsion Laboratory’s Center for NEO Studies provides up-to-date asteroid discovery statistics.

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How good are we at finding and tracking NEOs?

Since 2015, observers discovered more than 1500 previously unknown NEOs each year (over 2000 in 2017). Roughly half of the known catalogue of NEOs are objects larger than about 460 feet (140 meters) in size. The estimated population of NEOs of this size is about 25,000. Current surveys are finding NEOs of this size at a rate of about 500 per year.

The 460-foot cutoff point was established by a NASA NEO survey science definition team (SDT) in 2003 and reaffirmed in 2017. The SDT determined that impacts from objects of that size would only produce regional effects, while larger objects would have corresponding wider effects such as large sub-global effects from impacts of a 984-foot (300-meter) object and global effects from 0.6 mile (1-kilometer) object impacts.

Ground-based telescopes alone have limitations - for instance, they can only survey the skies at night and in clear skies. Based on statistical population estimates, about two thirds of NEOs larger than 460 feet still remain to be discovered.

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What can be done to improve the NEO detection rate?

Studies of the NEO search techniques and technologies (see Supporting Documents page) point to a dedicated space-based infrared asteroid survey telescope in addition to larger ground-based telescopes to substantially increase the discovery rate and meet the goal in the NASA Authorization Act of 2005 to detect, track, catalogue, and characterize the physical characteristics of 90 percent of the NEO population down to 140 meters in size. NASA’s currently operating NEOWISE space-based survey was not designed for this purpose. NEOWISE is a repurposed astrophysics spacecraft, and while it has made significant contributions to NEO characterization and discovery, its capabilities are limited.

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How are NEOs characterized?

NEOs are characterized by using optical and radio telescopes to determine their size, shape, rotation, and physical composition. Most NEOs are characterized using ground-based and space-based photometric and spectroscopic measurements (visible and infrared “colors” indicating composition), light-curve measurements (brightness changes indicating shape and rotation), and long-arc high-precision astrometry (positions). Some of the most detailed characterization data is obtained for NEOs that approach Earth close enough to be observed with planetary radar, performed by radio telescopes at NASA’s Deep Space Network and the National Science Foundation’s Arecibo Observatory in Puerto Rico.

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How do NEO scientists assess asteroid impact risks?

The Jet Propulsion Laboratory’s Center for NEO Studies maintains an impact risk assessment Web page that describes this process, explaining how an asteroid’s orbit is calculated, how soon after discovery a search for potential collisions is initiated, and how uncertainties in initial calculations of an orbit are reduced over time.

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Does Bennu, the asteroid that will be studied by the OSIRIS-ReX spacecraft, pose an impact risk to Earth?

Asteroid Bennu orbits the sun every 1.2 years and makes a relatively close approach to Earth about every six years. Bennu has been measured by planetary radar and is roughly spherical with an equatorial bulge. Its average diameter is about 1,614 feet (492 meters).

By current definition, Bennu is a potentially hazardous asteroid (PHA). A PHA is an asteroid whose orbit is predicted to bring it within 0.05 Astronomical Units (just under 5 million miles, or 8 million kilometers) of Earth’s orbit; and of a size large enough to reach Earth’s surface – that is, greater than around 30 to 50 meters. (Smaller objects entering Earth’s atmosphere will likely disintegrate.) The potential for an asteroid to make a close approach to Earth does not mean that it will impact Earth. By monitoring PHAs and updating their orbits as new observations are made, observers can improve their predictions of the risk of impacting Earth. Sometimes the term potentially hazardous object, or PHO, is used to describe an asteroid, or comet, that meets these criteria.

The Jet Propulsion Laboratory’s Center for NEO Studies (CNEOS) has predicted the future orbital movements of Bennu based on 29 radar observations and 478 optical observations of the asteroid, conducted by trackers around the world between September 1999 and January 2011. CNEOS predicts that the next time Bennu will pass Earth within the Moon’s orbit will be in 2135. This particularly close approach will change Bennu’s orbit by a small amount, which is uncertain at this time and which may lead to a potential impact on Earth sometime between 2175 and 2199. CNEOS has calculated that the cumulative risk of impact by Bennu during this 24-year period is 0.037 percent or a 1 in 2,700 chance. That means there is a 99.963 percent probability that Bennu will not impact Earth during this quarter-century period.

Although there is some uncertainty in precisely predicting its orbital motion more than a century from now, future observations of Bennu – including those made by the OSIRIS-REx mission – will enable experts to update orbit predictions and revise the future impact probabilities.

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Is it likely that an asteroid will impact Earth in the near future?

Asteroid impacts are a continuously occurring natural process. Every day, 80 to 100 tons of material falls upon Earth from space in the form of dust and small meteorites (fragments of asteroids that disintegrate in Earth’s atmosphere). Over the past 20 years, U.S. government sensors have detected nearly 600 very small asteroids a few meters in size that have entered Earth’s atmosphere and created spectacular bolides (fireballs). Experts estimate that an impact of an object the size of the one that exploded over Chelyabinsk, Russia, in 2013 – approximately 55 feet (17 meters) in size – takes place once or twice a century. Impacts of larger objects are expected to be far less frequent (on the scale of centuries to millennia). However, given the current incompleteness of the NEO catalogue, an unpredicted impact – such as the Chelyabinsk event – could occur at any time.

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Would it be possible to shoot down an asteroid that is about to impact Earth?

An asteroid on a trajectory to impact Earth could not be shot down in the last few minutes or even hours before impact. No known weapon system could stop the mass because of the velocity at which it travels – an average of 12 miles per second.

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Why is it necessary to characterize a NEO that might impact Earth in order to develop a plan for an impact mitigation mission?

Research indicates that the best technique to use to divert an asteroid from its impact course with Earth is scenario-dependent. That is, the choice of method for impact mitigation depends on the orbit of the object and its composition, bulk properties, and relative velocity, as well as the probability of impact and the predicted impact location. Some NEOs could be in orbits that are especially hard to reach unless we find them many years to decades in advance of impact. Some asteroids are essentially rubble piles, making them difficult to “push on” without breaking them up, while others could be coherent monolithic bodies. Some are too small or fragile to reach the surface of Earth (for example, the asteroid that disintegrated over Chelyabinsk, Russia in 2013) and would not warrant a mitigation mission but rather emergency response planning. Prior to mounting a mitigation mission, it is especially important to adequately characterize the asteroid.

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What is the role of planetary radar in NEO observations?

Planetary radar observations contribute to the characterization of near-Earth objects by more precisely determining their orbits and by measuring their size, shape, body dynamics, and surface features if they approach close enough to the Earth. NASA’s Near-Earth Object Observations Program supports planetary radar observations of NEOs at the Arecibo Observatory in Puerto Rico and the Goldstone station of NASA’s Deep Space Network in California.

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Can planetary radar be used to search for near-Earth objects?

NEO search is feasible with optical telescopes that can survey large regions of the sky and detect light from the Sun that is reflected by an object, depending on its size and surface brightness. A space-based infrared telescope optimized for search could survey and detect the heat radiated by objects warmed by sunlight regardless of surface brightness.  However, no current radar is powerful enough to sweep vast areas of space even relatively near Earth and return enough signal to detect unknown NEOs. Nevertheless, ground-based radar can be used to more precisely track and determine orbits for NEOs discovered by optical telescopes and to determine their physical characteristics and body dynamics, when they approach within millions of miles of Earth.

Optical or infrared observations can only be used to indirectly determine distance to an asteroid ("range") or the speed at which it is moving, data that radar is uniquely useful in obtaining. Using radar tracking data, NEO observers can more precisely determine the orbital path of an asteroid and predict that path out years into the future. Observing an asteroid for less than an hour with radar will provide a more precise determination of the orbit than months of observations from an optical telescope.

Radar observations can reduce the uncertainly in position of an asteroid from the several thousands of kilometers provided by optical observations to just a few meters. The impact risk posed by a potentially hazardous asteroid can be relatively quickly resolved with radar observations, while it might otherwise remain uncertain for years if only optical observations are available. Such was the case with the asteroid Apophis, discovered in 2004 and initially thought to pose a risk of Earth impact in April 2029. Radar observations made by Arecibo Observatory in 2005 eliminated that possibility of impact.

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What is NASA’s Near-Earth Object Observations Program funding the Arecibo Observatory to do?

The Near-Earth Object Observations Program provides $4.5 million a year in funding to the Arecibo Observatory in Puerto Rico – about one third of the observatory’s yearly budget – to fund its planetary radar capability. The National Science Foundation is in the process of transitioning the Arecibo Observatory to the University of Central Florida and UCF’s proposed alternative funding avenues while reducing NSF’s own level of support. NASA has agreed to continue to fund planetary radar capability at Arecibo during this transition. NASA also uses planetary radar capability at its own Deep Space Network Goldstone station. However, Goldstone’s radar is not as powerful as Arecibo’s, so it does not have the same range into space, meaning that fewer NEOs could be characterized by radar.

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What is NASA’s role in the Large Synoptic Survey Telescope (LSST) project?

The LSST is a project of the National Science Foundation and Department of Energy, in partnership with the government of Chile (where the telescope will be located) and other international public-private partners. NASA is not directly involved in the construction of LSST. However, several individual NASA-supported scientists are members of the LSST Science Collaborations, which are contributing to plans for the operation of the telescope, and the LSST Science Advisory Committee.

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How will LSST contribute to finding, tracking, and characterizing near-Earth asteroids?

The current congressionally directed objective of the NEO Observations Program is to find, track, and catalogue at least 90 percent of the estimated population of NEOs that are equal to or greater than 460 feet (140 meters) in size by 2020 and to characterize a subset of those objects that is representative of the entire population. Roughly half of the known catalogue of NEOs are objects larger than 140 meters in size. The predicted population of NEOs of this size is about 25,000. Current surveys are finding NEOs of this size at a rate of about 500 per year.

LSST will survey the entire observable sky for 10 years, taking hundreds of images of individual fields every night. Under its current plan, LSST will return to each field, acquiring two images, approximately every third night. Combining the images will generate an unprecedentedly wide and deep picture of the universe. Comparing them against each other will reveal objects that change in brightness or color, or that move — including near-Earth objects (NEOs). Because LSST will be significantly larger than the telescopes currently used for NEO searches, scientists say LSST will be able to discover substantially more NEOs than are currently being found. They also have proposed that their project could help NASA meet its congressionally mandated detection goal but by well after 2020.

However, LSST is not designed specifically for NEO observations. The project’s scientific goals range from the study of the content of the solar system to understanding the evolution of the universe. In 2016 NASA’s Planetary Defense Coordination Office commissioned the Jet Propulsion Laboratory’s Center for NEO Studies to conduct an assessment study, in collaboration with the LSST Solar System Science Team, of LSST’s proposed performance in detecting and cataloging NEOs. The study results, published in 2017, show that, assuming 10 years of operations, currently scheduled to begin in 2022, and also assuming that LSST’s proposed multi-night observation linkage algorithms are successful, LSST could detect about 60 percent of NEOs 140 meters or larger in size. The study indicates that by the end of LSST’s 10-year survey period (ca. 2032), adding together LSST’s projected NEO detections and the projected results of all other ongoing NEO surveys, the catalog of 140 meter and larger NEOs could be 80 percent complete (plus or minus 5 percent).

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How are human-accessible asteroids identified?

NASA initiated a Near-Earth Object Human Space Flight Accessible Targets Study (NHATS) in September 2010. Its purpose was to identify any known NEOs that might be accessible by future human space flight missions. This study led NASA researchers to develop a process that automatically downloads orbital information on newly discovered NEAs from the Center for NEO Studies’ Small Bodies Database (SBDB) on a daily basis. Multiple trajectory calculations are made to determine which objects may meet NHATS accessibility parameters, such as minimum delta-V (the energy required to go from Earth to the object and return) and mission duration (typically less than 400 days). For objects found NHATS-compliant, future observation opportunities are identified, so that researchers can know when they may further characterize the objects.