天文學家估計一顆10米小行星在印尼上空爆炸

C.L.Chan

請看2009 October  29日的
http://spaceweather.com/
報導未在提及找到隕石,十米直徑的天體爆到粉身碎骨,不留半點殘骸?
看天上的餘跡,可能太小了,不像十米天體的全部物質.
直徑十米的天體,體積為523.6立方米.拿密度為 5克/立方厘米來算,
質量有2.6x10^6公斤,即二千六百公頓.若全部變成塵埃,場面不只這樣簡單.
實覺有點誇大了.
這次的爆炸機理值得查究.會否是彗星隕落呢?猶如西伯利亞的通古斯大爆炸.

mca

(我的意見)

設十米隕星的質量 = 2.6 x 10^6 kg，闖入速度 = 20 km/s，
它的動能 = 1/2‧質量‧速度平方
= 1/2 (2.6 x 10^6 kg) (20,000 m/s)^2
= 5.2 x 10^14 joules
= 6 個炸長崎的原子彈

這個能量級可使隕星在大氣層迅速生熱，完全蒸發而不留半點殘骸。

C.L.Chan

流星一般出現在90公里高的大氣層,消失在那一個高度就決定於它的體積及質量,
看書提過一般閃一閃的2到3等流星,體積小如針頭.
沙粒大的流星體已可做成光度負數的流星.
電話般大的流星體走完90公里也消耗不盡,會產生隕石.
10米的小行星一定要深入大氣層一段長距離才有足夠長的時間去摩擦生熱令其爆炸.
假設走了一半,即45公里.
有6個原子彈在你頭上45公里爆炸,你還可以拿相機去看它的餘跡?
我想情況會像通古斯大爆炸一樣,全部物件向外傾倒,甚至發生大火.
故此,一個可能是過份估計該流星體的直徑,二則是該天體為彗星.

mca

先看 spaceweather 怎樣報導這件事:

Picture this:  A 10-meter wide asteroid hits Earth and explodes in the atmosphere with the energy of a small atomic bomb. Frightened by thunderous sounds and shaking walls, people rush out of their homes, thinking that an earthquake is in progress. All they see is a twisting trail of debris in the mid-day sky.

This really happened on Oct. 8th around 11 am local time in the coastal town of Bone, Indonesia. The Earth-shaking blast received remarkably little coverage in Western press, but meteor scientists have given it their full attention. "The explosion triggered infrasound sensors of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) more than 10,000 km away," report researchers Elizabeth Silber and Peter Brown of the Univ. of Western Ontario in an Oct. 19th press release. Their analysis of the infrasound data revealed an explosion at coordinates 4.5S, 120E (close to Bone) with a yield of about 50 kton of TNT. That's two to three times more powerful than World War II-era atomic bombs.
The asteroid that caused the blast was not known before it hit and took astronomers completely by surprise. According to statistical studies of the near-Earth asteroid population, such objects are expected to collide with Earth on average every 2 to 12 years. "Follow-on observations from other instruments or ground recovery efforts would be very valuable in further refining this unique event," say Silber and Brown.

如果科學家在一萬公里外也探測到聲爆的經緯度 (4.5S, 120E) 和 infrasound data ，闖入者不似是小隕星，科學家一定有其道理才公開說闖入者是十米左右小行星，我的個人計算也說明十米大的闖入者等於幾個原子彈能量，爆炸後有無殘骸實在非我和你可以斷定。

流星行跡不是你說那樣直覺，小行星可以斜角進入100公里厚的大氣層，但其實己衝行了數百公里後才生光，人耳或儀器聽到聲爆時，闖入者早在幾秒前解體了 (因為聲音速度比光線速度低很多倍)，人眼見到的空中煙幕只是後期解體而已，更早期的解體痕跡 (例如高溫蒸發) 肉眼未必見到。這些影響因素，研究人員不會忽略，所以我仍然相信 spaceweather 沒有誇大報導。

AC