Near-Earth objects and close calls

A heads up.

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Asteroid hits Earth near California moments after being discovered on October 22

An asteroid hit Earth hours after being discovered on Oct 22. This is the third time this year that a space rock was found moments before impact. The asteroid was reported to be around three feet in diameter and was initially named A11dc6D. The...
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Asteroid hits Earth near California moments after being discovered

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© Shutterstock/Triff

An asteroid hit Earth hours after being discovered on Oct 22. This is the third time this year that a space rock was found moments before impact. The asteroid was reported to be around three feet in diameter and was initially named A11dc6D. The day after impact, it was officially called 2024 UQ.

It hit Earth's atmosphere over the Pacific Ocean, so there weren't any public sightings. After being briefly observed, the ATLAS survey kept a watch as the asteroid impacted the atmosphere causing no harm.

The space rock burst into a bright fireball about 1,000 km off the California coast. It was picked up by NASA's Center for Near Earth Object Studies (CNEOS). It reported that a fireball lit the skies at 3:54 am PT on October 22, 2024.

Last month, another such asteroid was spotted just a few hours before it hit Earth. It burst into a fireball over the Philippines on September 5, 2024. The energy released by the recent asteroid was likely a little less than that of the one that hit the Southeast Asian nation.

Peter Brown, a meteor scientist at Western University in Ontario, Canada, posted about the asteroid impact on X. He stated that this is the 10th time an asteroid impact was predicted in advance.

It is becoming increasingly common because of the efficiency of surveys like ATLAS, Catalina and Pan-Starra, he added.

Asteroid in the Philippines

The Philippines asteroid was 3-foot long, the European Space Agency (ESA) said at the time. It was named 2024 RW1 and was spotted by research technologist Jacqueline Fazekas using the NASA-funded Catalina Sky Survey, a NASA-funded observatory near Tucson, Arizona.

It turned into a green fireball after impact, and many people happened to watch it.


Comment: Moment asteroid hits Earth's atmosphere like a ball of fire over the Philippines on September 5 (local time) [Update: Calculated total impact energy 0.2 kt of TNT]

Meteorite in South Africa

In August, a meteorite fell in South Africa, the first time in nearly 51 years. The meteorite fall caused a sonic boom which was heard kilometres away. It also caused tremors and some parts of it fell into the ocean.

The last time South Africa reported a meteorite fall was in Lichtenburg in 1973. The country has recorded only 51 meteorites till now, and only 22 meteorite falls.
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Comet defence in the form of 'whiff of grapeshot' from the moon! Also provides a discussion of existing defence ideas.

theethicalskeptic.com

The Earth-Lunar Lagrange 1 Orbital Rapid Response Array (ELORA)

Elora is a name meaning ‘The laurel of victory’. Within this paper, The Ethical Skeptic has proposed for consideration a concept for an elegant, flexible, high delivery-mass, rapid resp…
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ELORA is an acronym for: Earth-Lunar Lagrange 1 (ELL-1) Orbital Rapid Response Array. ELORA is a proposed system to interdict and deflect Potential Hazardous Objects to Earth. It is a series of Lunar dust bags that each perform kinetically like shotgun pellets. They are bagged on the Moon and then individually launched to Earth-Lunar Lagrange point 1, in order to be assembled into massive single payloads of bound-but-separate dust bags – yielding a total of 1000 – 3000 kilotons of TNT (about 2.8 – 4.2 Petajoules) of direct kinetic energy per payload. Twelve of these 1728-bag/200,000 kilogram single payloads are to be assembled, which will station as Trojan ELL-1 payloads; ready to be rapid deployed to any Lunar orbit inclination in order to interdict large (>50 meters) and short notice Near Earth or Potential Hazardous Objects (NEO/PHO) from space. The array as a concept is easy to assemble and offers redundancy, power, and rapidity unparalleled by existing conceptual alternative interdiction approaches.
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The last screenshot of the CNEOS list was from this post, Aug 11, 2024. Here are those that have entered since then, including the last in July. The calculated total impact energy varies between 0.076 and 0.38 kt TNT, so as they appear in the list, the latest fireballs are quite small.
CNEOS list Aug to Dec 5 2024.png
It is not clear why there are several that do not have velocity components. It could relate to a lack of data. Another question is why they in such cases after all venture to estimate the total impact energy without knowing the speed. Either some information is withheld or the estimates are based on other parameters like colour and brightness, but if that is the case, the accuracy of the calculated total impact energy can not be given with the appearance of exactness, often ± 0.001 kt of TNT which is just one kg of TNT. Alternatively one could argue that probably there is also an inexactness connected with other figures.

Sometimes we observe bright fireballs that lighten up the sky, but do not show up on the list. Were they bright because the atmosphere was particularly clear? Did they not enter the list because they were in the border range of the minimum value which seems to be close to 0.076 kt of TNT? Are there cases where they do not have enough data to give even the velocity, but which would otherwise have made the list if they had had enough data points? Is there a statistical difference between the number of observations made during night and day time, as seen over the area of observation? Like that there are some questions one could ask.
 
The calculated Total Impact Energy is calculated directly from the Total Radiated Energy. It's basically the same information with a simple formula linking the two columns. These data are collected from different sources. Some are from satellites and some from ground-based stations. Earth-based stations can calculate the velocity and its components because they use triangulation (two synchronized cameras or more capture the entry from different places and the trajectory is calculated). I would imagine that it's difficult to calculate with satellites if the fireball was captured in one satellite, and even if it was captured by different satellites, the resolution wouldn't allow precise triangulation. OSIT
 
thorbiorn said:
± 0.001 kt of TNT which is just one kg of TNT
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This should read: ± 0.001 kt of TNT which is just one ton of TNT if a ton is 1000 kg, then 0.076 kt of TNT is 76 ton of TNT

To help provide a perspective of what 100 tons of explosive looks like when exploding, here is a video from Science Channel.

One difference between the energy released from explosives, as seen in the video, and what happens when an object from cosmic space hits and interacts with the atmosphere, is that the impact energy is released along the whole path of the entering object, rather from a small area.

Since the atmosphere extends tens of kilometers above the surface, the slowing down of the object and the transfer of energy to the surrounding gases begins high up. An article from the editors of earthsky.org, How high up are meteors when they begin to glow? posted October 21, 2023, writes:

Meteors light up almost as soon as they hit Earth’s atmosphere. So, on average, when you see a meteor, you’re looking at a piece of dust burning bright about 50 to 75 miles (80 to 120 km) in altitude above Earth’s surface.

But the height at which they entirely burn up in the atmosphere varies. Some meteors, such as the Perseids in August, burn up in the atmosphere at about 60 miles (100 km) above Earth’s surface. Other meteors, such as the Draconids in October, fall to about 40 miles (65 km) before they heat up enough to glow and vaporize.

The difference is that the Draconids are much slower meteors than the Perseids. The height in the atmosphere at which a meteor begins to glow depends on its arrival speed. Meteoroids dive into the atmosphere at speeds ranging from 25,000 to 160,000 miles per hour (40,200 to 257,500 km/h).
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