2018 LA

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2018 LA
2018 LA-orbit.png
Orbit and positions of 2018 LA, 30 days before collision
Discovery [2][3]
Discovered byMount Lemmon Srvy.
Richard Kowalski[1]
Discovery siteMount Lemmon Obs.
Discovery date2 June 2018
Designations
MPC designation2018 LA
ZLAF9B2 (NEOCP)
NEO · Apollo[2][4]
Orbital characteristics[4][5]
Epoch 2 June 2018 (JD 2458271.5)
Uncertainty parameter 8[4] · 6[2]
Observation arc3.8 hours (14 obs.)
Aphelion1.9709 AU
Perihelion0.7820 AU
1.3764 AU
Eccentricity0.4319
1.61 yr (590 d)
326.73°
0° 36m 37.08s / day
Inclination4.2975°
71.870°
256.05°
Earth MOID< 5000 km
Venus MOID0.0557 AU
Mars MOID0.0191 AU
Physical characteristics
Mean diameter
1.6–5.2 m (5.2–17.1 ft)
(est. 0.05–0.3)
2.6–3.8 m (8.5–12.5 ft)
(est. impact energy)
Mass25–35 t
(55,000–77,000 lbs.)
0.15–0.30 (est. impact size)
18.3 (at discovery)
30.554[4]
30.6[2]

2018 LA, also known as ZLAF9B2, was a small Apollo near-Earth asteroid approximately 2.6–3.8 m (9–12 ft) in diameter that impacted Earth at roughly 16:44 UTC (18:44 local time) on 2 June 2018 near the border of Botswana and South Africa. It was discovered only 8 hours prior by the Mount Lemmon Survey, and based on an hour and a half of observations, it was calculated to have a roughly 85% chance of impacting Earth,[6] likely somewhere between Australia and Madagascar. Hours later, a report arrived to the American Meteor Society that an observer from Botswana had seen a bright fireball. After the impact, the Asteroid Terrestrial-impact Last Alert System (ATLAS) released observations roughly 2 hours after the other reported observations which confirmed that the asteroid had indeed impacted Earth on a grazing path and near the location of the fireball. A preliminary analysis of the pre-impact evolution of this meteoroid suggests that it may be part of a dynamical grouping.[7][8][9]

Discovery[edit]

On 2 June 2018, at roughly 08:22 UTC (01:22 local time), the Mount Lemmon Survey picked up an 18th magnitude asteroid moving quickly against the background stars. 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[edit]

JPL estimated final trajectory and timing
Animation of 2018 LA'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.[10] 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.[11]

Fragment recovery[edit]

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.[12]

See also[edit]

References[edit]

  1. ^ "Tiny Asteroid Discovered Saturday Disintegrates Hours Later Over Southern Africa". NASA/JPL. Jet Propulsion Laboratory. Retrieved 4 June 2018.
  2. ^ a b c d e "2018 LA". Minor Planet Center. Retrieved 14 June 2018.
  3. ^ "MPEC 2018-L04 : 2018 LA". Minor Planet Center. 2018-06-03. Retrieved 2018-06-03. (K18L00)
  4. ^ a b c d "JPL Small-Body Database Browser: (2018 LA)" (2018-06-02 last obs.). Jet Propulsion Laboratory. Retrieved 14 June 2018.
  5. ^ Gray, Bill. "Pseudo-MPEC for ZLAF9B2". Project Pluto. Archived from the original on 2 June 2018. Retrieved 3 June 2018.
  6. ^ Gray, Bill. "Re: {MPML} Re: [neo_followup] Further on ZLAF9B2". MPML. Retrieved 3 June 2018.
  7. ^ de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (18 June 2018). "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 AAS. 2 (2): 57. arXiv:1806.05164. Bibcode:2018RNAAS...2b..57D. doi:10.3847/2515-5172/aacc71.
  8. ^ de la Fuente Marcos, Carlos; de la Fuente Marcos, Raúl (26 July 2018). "Pre-airburst Orbital Evolution of Earth's Impactor 2018 LA: An Update". Research Notes of the AAS. 2 (3): 131. arXiv:1807.08322. Bibcode:2018RNAAS...2c.131D. doi:10.3847/2515-5172/aad551.
  9. ^ 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 Astrophysics. arXiv:1811.11845. Bibcode:2018arXiv181111845D. doi:10.1051/0004-6361/.
  10. ^ Brown, Peter. "Strong infrasound detection of a bolide at station I47 in South Africa". Retrieved 3 June 2018.
  11. ^ Stolte, Daniel. "What it Takes to Discover Small Rocks in Space". University of Arizona News. Retrieved 8 June 2018.
  12. ^ First Fragment Of Shattered Asteroid Recovered In Botswana July 6, 2018, Bob King

External links[edit]