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2018 LA
2018 LA-orbit.png
지구와 충돌하기 30일 전의 2018 LA 궤도 및 위치 지도.
발견
발견자마운트 렘몬 탐사팀 (G96)
리차드 코발스키[1][2][3]
발견일2018년 6월 2일
명칭
임시 이름2018 LA
다른 이름ZLAF9B2 (NEOCP)
궤도 성질
(역기점 2018년 6월 2일 (JD 2458271.5))
궤도 긴반지름(a)1.3764 AU
근일점(q)0.7820 AU
원일점(Q)1.9709 AU
공전 주기(P)1.61 yr (590 d)
궤도 경사(i)4.2975°
궤도 이심률(e)0.4319
승교점 경도(Ω)71.870°
근일점 편각(ω)256.05°
평균 근점 이각(M)326.73°
물리적 성질
평균 지름1.6-5.2m
(0.05–0.3 추정)
2.6-3.8m
(충돌 에너지 추정)
질량25–35 t
반사율0.15–0.30 (충돌구 크기에서 추정)
겉보기등급18.3 (발견 당시)
절대등급30.554[4]
30.6[2]

2018 LA 또는 ZLAF9B2은 2018년 6월 2일 남아프리카 공화국보츠와나 국경 지점에 충돌한 직경 2.6-3.8m 가량의 아폴로 소행성군 지구 접근 소행성이다. 이 소행성은 지구에 충돌하기 불과 8시간 전 마운트 렘몬 탐사대가 발견하였으며 1시간 30분 가량의 관측에 기초하여 지구에 추락할 확률이 85%이며[5] 대략 호주와 마다가스카르 사이에 충돌할 것이라고 추정했다. 1시간 후 미국유성학회에 보츠와나에서 매우 밝은 화구(fireball)을 관측했다는 보고가 들어왔다. 충돌 후 소행성 지상충돌 최종 경보 시스템(ATLAS)에서는 2시간의 관측 후 소행성이 지구를 스쳐가는 경로를 따라가다 화구를 관측한 곳 인근에서 지구에 충돌했다는 것을 확인했다는 보고를 발표하였다. 이 유성체의 충돌사전진화 예비분석에서는 동적 집단의 일부일 수 있다고 결론내렸다.[6][7][8]

관측[편집]

2018년 6월 2일 UTC 08:22(현지 시각 01:22) 경, 마운트 렘몬 관측팀은 배경별을 뒤로 두고 매우 빠른 속도로 움직이는 겉보기등급 대략 18 정도의 소행성을 관측하였다. The object was observed over the course of 15 minutes and submitted to the Minor Planet Center, and was followed up by the same survey for the next hour or so, resulting in an Observation arc of 1 hour and 17 minutes. The asteroid was soon identified as having a chance of impacting Earth (identified by JPL's scout program as 30% odds, calculated by Bill Gray as 82%) and one precovery observation was found just 7 minutes prior to its discovery observation, resulting in a final observation arc of 85 minutes before the asteroid was widely considered lost.

Entry and ATLAS observations[편집]

JPL estimated final trajectory and timing
Animation of 2018 LA틀:'s orbit from 2 June 2016 to 2 June 2018
       2018 LA ·       Venus ·       Earth ·       Mars

Several hours later, at 16:44 UTC, a report arrived from southern Botswana to the American Meteor Society that an exceptionally bright fireball had been spotted. Although this was further west than projected based on the initial observations, the timing and location were consistent, although substantiated by just one observer.

Confirmation that the asteroid had indeed impacted Earth, rather than simply a near approach, came when two observations by the Asteroid Terrestrial-impact Last Alert System (ATLAS) arrived later the same day and extended the observation arc from 85 minutes to 3 hours and 47 minutes, significantly improving the orbital parameters.[2] The 4 hour observation arc better constrained the line of variations and showed that the asteroid was virtually certain to impact Earth, and based only on the sky observations, projected to have impacted in Namibia instead. This proves consistent with the fireball report.

The bolide was also detected by infrasound at station I47 in South Africa and registered about 0.4 kt.[9] The asteroid was several meters in diameter and impacted the atmosphere going about 17 km/s (38,000 mph). Based on its velocity and energy, the asteroid was likely 2.6-3.8 meters in diameter.

Asteroids in the range of several meters in diameter are very hard to detect as they are too small to reflect much sunlight. For example, on 24 May 2018, the asteroid was still 0.069 AU (10,300,000 km; 6,400,000 mi) from Earth and only had an apparent magnitude of 25.5, much dimmer than any major modern surveys can detect using rapid-fire 30 second snapshots meant to cover as much of the sky as possible.[10]

Fragment recovery[편집]

Scientists promptly looked for a meteorite strewn field, hoping to recover fragments of the asteroid before they had a chance to weather too much. Fragments can achieve dark flight after deceleration to terminal velocity. Dark flight starts when fragments decelerate to about 2–4 km/s. Larger fragments will fall further down the strewn field.

Assuming a similar fraction of 2018 LA survived as of 2008 TC3, several kilograms of meteorites were expected to have reached the ground and be recoverable. 2018 LA was estimated to only be about 40% as massive as 2008 TC3.

On June 23, three weeks after the asteroid entered Earth's atmosphere, the first meteorite fragments were recovered by scientists. The physical characteristics of the meteorites are not yet known.[11]

더 보기[편집]

각주[편집]

  1. “Tiny Asteroid Discovered Saturday Disintegrates Hours Later Over Southern Africa”. 《NASA/JPL》 (Jet Propulsion Laboratory). 2018년 6월 4일에 확인함. 
  2. “2018 LA”. 《Minor Planet Center》. 2018년 6월 14일에 확인함. 
  3. “MPEC 2018-L04 : 2018 LA”. Minor Planet Center. 2018년 6월 3일. 2018년 6월 3일에 확인함.  (K18L00)
  4. “JPL Small-Body Database Browser: (2018 LA)” (2018-06-02 last obs.). Jet Propulsion Laboratory. 2018년 6월 14일에 확인함. 
  5. Gray, Bill. “Re: {MPML} Re: [neo_followup] Further on ZLAF9B2”. 《MPML》. 2018년 6월 3일에 확인함. 
  6. de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (2018년 6월 18일). “On the Pre-impact Orbital Evolution of 2018 LA, Parent Body of the Bright Fireball Observed Over Botswana on 2018 June 2”. 《Research Notes of the AAS2 (2): 57. Bibcode:2018RNAAS...2b..57D. arXiv:1806.05164. doi:10.3847/2515-5172/aacc71. 
  7. de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (2018년 7월 26일). “Pre-airburst Orbital Evolution of Earth's Impactor 2018 LA: An Update”. 《Research Notes of the AAS2 (3): 131. Bibcode:2018RNAAS...2c.131D. arXiv:1807.08322. doi:10.3847/2515-5172/aad551. 
  8. de la Fuente Marcos, C.; de la Fuente Marcos, R. (2019). “Waiting to make an impact: A probable excess of near-Earth asteroids in 2018 LA-like orbits”. 《Astronomy and Astrophysics621: A137. Bibcode:2018arXiv181111845D. arXiv:1811.11845. doi:10.1051/0004-6361/201834313. 
  9. Brown, Peter. “Strong infrasound detection of a bolide at station I47 in South Africa”. 2018년 6월 3일에 확인함. 
  10. Stolte, Daniel. “What it Takes to Discover Small Rocks in Space”. 《University of Arizona News》. 2018년 6월 8일에 확인함. 
  11. First Fragment Of Shattered Asteroid Recovered In Botswana July 6, 2018, Bob King
인용 오류: <references> 안에 정의된 "projectplutoneocp"이라는 이름을 가진 <ref> 태그가 위에서 사용되고 있지 않습니다.

외부 링크[편집]