Планетарная защита

[ronatu]

Near-Earth Object
Survey and Defintion
Analysis of Alternvatives

Report to Congress
March 2007

http://neo.jpl.nasa.gov/neo/report2007.html



Currently, NASA carries out the "Spaceguard Survey" to find NEOs greater than 1 kilometer in diameter, and this program is currently budgeted at $4.1 million per year for FY 2006 through FY 2012.

http://impact.arc.nasa.gov/downloads/spacesurvey.pdf

Throughout Its history, the Earth has been impacted by countless
asteroids and comets. Smaller debris continually strike Earth's upper
atmosphere where they burn due to friction with the air; meteors
(which are typically no larger than a pea and have masses of about a
gram) can be seen every night from a dark location if the sky is clear.
Thousands of meteorites (typically a few kilograms in mass) penetrate
the atmosphere and fall harmlessly to the ground each year. On rare
occasions, a meteorite penetrates the roof of a building, although to
date there are no fully documented human fatalities.
A much larger event, however, occurred in 1908 when a cosmic fragment
disintegrated in the atmosphere over Tunguska, Siberia, with an
explosive energy of more than 10 megatons TNT. But even the
Tunguska impactor was merely one of the smallest of Earth's
neighbors in space. Of primary concern are the larger objects, at least
one kilometer in diameter. Although very rare, the impacts of these
larger objects are capable of severely damaging the Earth's
ecosystem with a resultant massive loss of life...

[ronatu]

Indeed, during our lifetime, there is a small but non-zero chance (very roughly 1 in 10,000) that the Earth will be struck by an object large enough to destroy food crops on a global scale and possibly end civilization as we know it (Shoemaker and others 1990)....

Particularly uncertain is the significance of hard-to-detect
long-period or new comets, which would generally strike at higher
velocities than other NEO's (Olsson-Steel 1987), although asteroids
(including dead comets) are believed to dominate the flux. However,
the resulting environmental consequences of the impacts of these
objects are much less well understood. The greatest uncertainty in
comparing the impact hazard with other natural hazards relates to the
economic and social consequences of impacts.

[ronatu]

The hazard can be conveniently divided into three broad
categories that depend on the size or kinetic energy of the impactor:

1. Impacting body generally is disrupted before it reaches the
surface; most of its kinetic energy is dissipated in the
atmosphere, resulting in chiefly local effects.

2. Impacting body reaches ground sufficiently intact to make a
crater; effects are still chiefly local, although nitric oxide and
dust can be carried large distances, and there will be a tsunami
if the impact is in the ocean.

3. Large crater-forming impact generates sufficient globally
dispersed dust to produce a significant, short-term change in
climate, in addition to devastating blast effects in the region of
impact.

[ronatu]

Category 1: 10-m to 100-m diameter impactors

Bodies near the small end (10m) of this size range intercept Earth every
decade (10 years).

Bodies about 100 m diameter and larger strike, on average, several times per millennium.

The kinetic energy of a 10-m projectile traveling at a typical atmospheric entry velocity of 20 km/s is about 100 kilotons TNT equivalent, equal to several Hiroshima-size bombs.

The kinetic energy of a 100-m diameter body is equivalent to the
explosive energy of about 100 megatons, comparable to the yield of
the very largest thermonuclear devices.

[ronatu]

Category 2: 100-m to 1-km diameter impactors

Incoming asteroids of stony or metallic composition that are larger
than 100 m in diameter may reach the ground intact and produce a
crater. The threshold size depends on the density of the impactor and
its speed and angle of entry into the atmosphere. Evidence from the
geologic record of impact craters as well as theory suggests that, in
the average case, stony objects greater than 150 m in diameter form
craters. They strike the Earth about once per 5000 years and -- if
impacting on land -- produce craters about 3 km in diameter. A
continuous blanket of material ejected from such craters covers an
area about 10 km in diameter. The zone of destruction extends well
beyond this area, where buildings would be damaged or flattened by
the atmospheric shock, and along particular directions (rays) by flying
debris. The total area of destruction is not, however, necessarily
greater than in the case of atmospheric disruption of somewhat
smaller objects, because much of the energy of the impactor is
absorbed by the ground during crater formation. Thus the effects of
small crater-forming events are still chiefly local.

Toward the upper end of this size range (1km), the megaton equivalent
energy would so vastly exceed what has been studied in nuclear war
scenarios that it is difficult to be certain of the effects. Extrapolation
from smaller yields suggests that the "local" zones of damage from
the impact of a 1-km object could envelop whole states or countries,
with fatalities of tens of millions in a densely populated region. There
would also begin to be noticeable global consequences, including
alterations in atmospheric chemistry and cooling due to atmospheric
dust -- perhaps analogous to the "year without a summer" in 1817,
following the explosion of the volcano Tambora.

[ronatu]

Category 3: 1 km to 5 km diameter impactors

At these larger sizes, a threshold is finally reached at which the
impact has serious global consequences, although much work
remains to be done to fully understand the physical and chemical
effects of material injected into the atmosphere. In general, the crater
produced by these impacts has 10 to 15 times the diameter of the
projectile; i.e., 10-15 km diameter for a 1-km asteroid. Such craters
are formed on the continents about once per 300,000 years. At
impactor sizes greater than 1 km, the primary hazard derives from the
global veil of dust injected into the stratosphere. The severity of the
global effects of large impacts increases with the size of the impactor
and the resulting quantity of injected dust.
At some size, an impact would lead to massive world-wide crop failures and might threaten the survival of civilization. At still larger sizes, even the survival of the human species would be put at risk.

etc................

[VK]

Ронату нашел неисчерпаемый источник ...  :lol:

[ronatu]

Источников как грязи... и единого мнения тут не наблюдается...

ТУРИНСКАЯ ШКАЛА АСТЕРОИДНОЙ ОПАСНОСТИ. 0 Вероятность столкновения равна нулю или ниже вероятности столкновения Земли с неизвестным небесным телом того же размера в течение нескольких десятилетий. Эту же оценку получают небольшие небесные тела, которые даже в случае столкновения не смогут достичь поверхности вследствие разрушения в атмосфере Земли.

1. Вероятность столкновения чрезвычайно низка или равна вероятности столкновения Земли с неизвестным небесным телом того же размера в течение нескольких десятилетий.
2. Небесное тело совершит сближение с Землей, однако столкновение при этом маловероятно.
3. Тесное сближение с Землей с вероятностью столкновения 1% и более. В случае столкновения возможны локальные разрушения.
4. Тесное сближение с Землей с вероятностью столкновения 1% и более. В случае столкновения возможны региональные разрушения.
5. Тесное сближение с Землей с серьезной вероятностью столкновения, которое может вызвать региональные " разрушения.
6. Тесное сближение с Землей с серьезной вероятностью столкновения, которое может вызвать глобальную катастрофу.
7. Тесное сближение с Землей с очень высокой вероятностью столкновения, которое может вызвать глобальную катастрофу.
8. Столкновение, способное вызвать местные разрушения (подобные события происходят раз в 1000 лет)
9. Столкновение, способное вызвать глобальные разрушения (подобные события происходят раз в 1000-100000 лет)
10. Столкновение, способное вызвать глобальную катастрофу (подобные события происходят раз в 100000 лет и более).

http://www.astrogalaxy.ru/097.html

[ronatu]

И под конец парa слов о масштабе явления:

Характеристика энергетического процесса и явления

Ашхабадское землетрясение 1948 г.      1,0 • 10^16 Дж

Взрыв 5-мегатонной водородной бомбы   5,7 • 10^16 Дж

Ежегодное (среднее) выделение сейсмической энергии на Земле   1,0 • 10^19 Дж

Взрыв вулкана Безымянный на Камчатке в 1956 г.  4,0 • 10^19 Дж

Взрыв вулкана Кракатау в 1883 г.              1,8 • 10^22 Дж

Ежегодное поглощение земной поверхностью солнечной энергии 5,2 • 10^24 Дж

Образование метеоритного кратера:
--- диаметром около 1 км     ~1 • 10^18 Дж
--- диаметром около 30 км   ~1 • 10^22 Дж
--- диаметром около 70 км.  ~1 • 10^23 Дж.

[Corvine]

Извиняюсь, а вот этот ядреный гамма-лазер "от Крикалева" уже обсуждался где-нибудь?
http://www.rufund.ru/index.php?PAGE=projects&CONTENT=laser

http://www.novosti-kosmonavtiki.ru/phpBB2/viewtopic.php?t=5946