2029年04月14日小行星2004 MN4撞击地球的概率已经上升到1/37

2004年12月27日更新的历表计算表明，这颗小行星将于北京时间2029年04月14日04时49分左右到达距离地球的
最近位置。

http://en.wikipedia.org/wiki/2004_MN4

2004 MN4
From Wikipedia, the free encyclopedia.

   The title given to this article is incorrect due to technical limit
ations. The correct title is 2004 MN4.

Current event This article or section is about a current event. Informa
tion may change rapidly.

2004 MN4 (also written 2004 MN4) is a Near-Earth asteroid first sighted
in June 2004 and the first object to be assessed at level four out of t
en on the Torino Impact Hazard Scale and 1.10 on the Palermo scale, scal
es scientists use to measure the danger of an asteroid hitting Earth. Ba
sed on the observations available up to December 27, 2004, the object ha
d an assessed 1 in 37 (2.7 percent) chance of collision with Earth on Fr
iday, April 13, 2029—Friday the 13th.

The asteroid is currently being tracked to improve predictions of its f
uture path. Scientists predict that, with a chance of over 97 percent, a
dditional data will allow for 2004 MN4 to be re-rated as a level zero (n
o threat) object.

2004 MN4 belongs to a group called the "Aten asteroids", asteroids with
an orbital semi-major axis less than one astronomical unit. The semi-ma
jor axis of an orbit's ellipse is one half of the major axis (the long a
xis) running from the center, through a focus. This particular asteroid
has an orbital period about the sun of 323 days, which brings it across
Earth's orbit twice on each passage around the sun.

Based upon the observed brightness, and assuming it reflects light in t
he way asteroids typically do, 2004 MN4's length is estimated at 390 m (
1280 feet). Its mass is estimated to be 7.9×1010 kg, assuming a typical
asteroid density of 2.6 g/cm3. Any potential impact would occur at a vel
ocity of 12.59 km/s.
Contents [showhide]
1 Possible impact effects
2 Discovery
3 History of estimates
4 See also
5 Sources
6 External links
[edit]

Possible impact effects

NASA estimates the energy that 2004 MN4 would release if it impacted Ea
rth as the equivalent of 1480 megatons of TNT. In contrast, the largest
man-made nuclear explosion, Tsar Bomba, had a yield of approximately 50
megatons. The nuclear bomb Little Boy, dropped by the United States on H
iroshima, Japan, had a yield of only about 0.013 megatons. The impacts w
hich created the Barringer Meteor Crater or caused the Tunguska event ar
e estimated to be in the 10-20 megaton range. The 1883 eruption of Kraka
toa was the equivalent of roughly 200 megatons.

The exact effects of any impact would vary based on the asteroid's comp
osition, and the location and angle of impact. Any impact would be extre
mely detrimental to an area of thousands of square kilometers, but would
be unlikely to have long-lasting global effects, such as the precipitat
ion of an impact winter (as posited in the 6th season episode (http://ww
w.westwingepguide.com/S6/Episodes/121_IW.html) of the television series
The West Wing, where such an asteroid impact—with only 48 hours warning
—was a subplot).

Based on the predicted time of impact (0.89 of a day, or about 21:21 UT
C) and the fact that the asteroid would be approaching the Earth from ou
tside of its orbit, any impact is likely to occur in the Eastern Hemisph
ere (time zones UTC +3 to UTC -10); however, because it will be moving a
t close to escape velocity, the path could be bent by Earth's gravity to
the point that it could impact on any part of a band wrapping around Ea
rth.
[edit]

Discovery

2004 MN4 was discovered on June 19, 2004, by Roy Tucker, David J. Thole
n, and Fabrizio Bernardi of the NASA-funded University of Hawaii Asteroi
d Survey from Kitt Peak National Observatory in Arizona. This group obse
rved for two nights.

On December 18, the object was rediscovered from Australia by Gordon Ga
rradd of the Siding Spring Survey, another NASA-funded NEA survey. Furth
er observations from around the globe over the next several days allowed
the Minor Planet Center to confirm the connection to the June discovery
.

At this point the possibility of impact in 2029 was realized by the aut
omatic SENTRY system of NASA's Near-Earth Object Program Office. NEODyS,
a similar automatic system at the University of Pisa, Italy and the Uni
versity of Valladolid, Spain also detected the impact possibility and pr
ovided similar predictions.
[edit]

History of estimates

   * The original NASA report on December 24 mentioned impact chances
of "around 1 in 300", which was widely reported in the media. The actual
NASA estimates at the time were 1 in 233; they resulted in the Torino s
cale rating of 2.
   * Later that day, based on a total of 64 observations, the NASA est
imates were changed to 1 in 62 (1.6 percent), resulting in an update to
the initial report and an upgrade to a Torino scale rating of 4.
   * On December 25, the chances were first reported as 1 in 42 (2.4 p
ercent) and later that day (based on 101 observations) as 1 in 45 (2.2 p
ercent). At the same time, the asteroid's estimated diameter was lowered
from 440 m to 390 m and its mass from 1.2×1011 kg to 8.3×1010 kg.
   * On December 26 (based on a total of 169 observations), the impact
probability was still estimated as 1 in 45 (2.2 percent), the diameter
as 380 m, and the mass as 7.5×1010 kg.
   * On December 27 (based on a total of 176 observations), the impact
probability has been raised to 1 in 37 (2.7 percent); diameter has incr
eased to 390 m, and mass 7.9×1010 kg.

NASA animation explaining how impact probablitiy is determined. (http:/
/en.wikipedia.org/wiki/Image:2004_MN4_animation.gif)
[edit]

See also

   * List of noteworthy asteroids
   * Asteroid deflection strategies

[edit]

Sources

   * Report from NASA (http://neo.jpl.nasa.gov/news/news146.html) - 23
December 2004, updated 24 December 2004
   * 2004 MN4 Impact Risk (http://neo.jpl.nasa.gov/risk/2004mn4.html),
continuously being updated as new observations are reported

   This article contains material and/or images that originally came f
rom a NASA website. All NASA information is in the public domain, with t
he exception of the usage-restricted NASA logo. For more information, pl
ease review NASA's use guidelines (http://www.jsc.nasa.gov/policies.html
#Guidelines).

[edit]

External links

   * 2004 MN4 status and info page (http://2004mn4.info)
   * Asteroid Watch: Odds of 2029 Collision Stuck at 1-in-40 (http://w
ww.space.com/scienceastronomy/asteroid_update_041227.html) (SPACE.com)
   * Worrisome Asteroid Underscores Planetary Defense Mission (http://
www.space.com/news/asteroid_defense_041227.html) (SPACE.com)
   * Risk estimate (http://newton.dm.unipi.it/cgi-bin/neodys/neoibo?ri
skpage:0;main) and orbital data (http://newton.dm.unipi.it/cgi-bin/neody
s/neoibo?info:0;main;jultab) from NEODyS
   * Impact Effects (http://www.lpl.arizona.edu/~marcus/cgi-bin/crater
.cgi?dist=5&distanceUnits=1&diam=390&diameterUnits=1&pde
ns=2600&pdens_select=0&vel=12.59&velocityUnits=1&theta=4
5&wdepth=&wdepthUnits=1&tdens=2500)


Retrieved from "http://en.wikipedia.org/wiki/2004_MN4"

Categories: Current event | Aten asteroids

大家赶快造飞船啊！逃！ :mrgreen:  :mrgreen:  :mrgreen:

赶快撞吧，我才不怕呢!

难道是世界末日吗 :?:  :

[quote]

Whew! Asteroid Won't Hit Earth in 2029, Scientists Now Say
科学家现在说, 小行星不会在2029年撞地球了
http://www.space.com/scienceastronomy/asteroid_update_B_041227.html

The giant space rock, named 2004 MN4, was said on Dec. 23 to have an outside shot at hitting the planet on April 13, 2029. The odds climbed as high as 1-in-37, or 2.7 percent, on Monday, Dec. 27.

Researchers had flagged the object as one to monitor very carefully. It was the first asteroid to be ranked 4 on the Torino Scale, a Richter-like measure for potentially threatening space rocks. The asteroid is about a quarter mile (400 meters) wide, large enough to cause considerable local or regional damage were it to hit the planet.

All along, scientists said additional observations would likely reduce the chance of impact to zero for the April 13 scenario, but they did not expect any significant new data to allow such a downgrading for days or weeks.

Instead, old observations provided the data necessary to rule out an impact.

Several groups were looking for the asteroid in past observations. Jeff Larsen and Anne Descour of the Spacewatch Observatory near Tucson, Arizona, found very faint images of asteroid 2004 MN4 on archival images dating to March 15 this year. Astronomers already had observations in June and from this month.

"An Earth impact on April 13, 2029 can now be ruled out," read a statement issued Monday evening by asteroid experts Don Yeomans, Steve Chesley and Paul Chodas at NASA's Jet Propulsion Laboratory.

It is not the first time a potentially threatening asteroid has been theoretically defused by looking into the past, pointed out Clark Chapman of the Southwest Research Institute. Most famously, a space rock catalogued as 1997 XF11 was said, in 1998, to be on a collision course before archived data showed it would pass harmlessly.

"ast observations can greatly extend the time baseline and strongly influence knowledge of the orbit," Chapman told SPACE.com. "At some level, we are 'lucky' that these earlier sightings were made since 2004 MN4 is usually too faint to be detected by near-Earth-object search telescopes."

The difficulty in predicting a precise path earlier in the game owes to knowing only a small section of an asteroid's orbit around the Sun. New observations -- or old ones -- make the known path longer and allow a better prediction of the full path, as well as where an asteroid will be years from now.

Orbits change slightly with time because of gravitational tugs by the Sun and planets, among other factors.

2004 MN4 circles the Sun, but unlike most asteroids that reside in a belt between Mars and Jupiter, the 323-day orbit of 2004 MN4 lies mostly within the orbit of Earth.

Scientists cannot say that the asteroid will never hit Earth, but there are no serious threats in the foreseeable future. "No subsequent Earth encounters in the 21st century are of any concern," the NASA statement read.

我要捡陨石！我要陨石！
落在哪？我去接着它，砸到花花草草不好。会污染环境的。

早就搬进博物馆了 :!:  :mrgreen:

怪不得有可能撞上.......2029年04月14日04时49分  一看时间一堆堆4.........

高唱JAY的世界末日吧.....

呵呵！这和数字有什么关系的。

[quote:75acf73e3d="lin-j-k"]呵呵！这和数字有什么关系的。[/quote]

嘿嘿~在科学时代允许我偶尔迷信一下啦~~

认真看了两个英文帖子，有点儿累！

继续关注中！