Near-Earth objects and close calls

Out of the approximately 30-40 large fireballs that yearly have entered the CNEOS list for the last decade, there are for 2024 already four that have been widely videoed:
Some viewers of the videos may wonder how these impact energies are calculated. Below are abstracts of research papers that mention the considerations and methods involved:

How do scientists calculate the total impact energy? - A few related studies.
arXiv:2408.04078v1 [astro-ph.EP] 07 Aug 2024
A Comparison of Fireball Luminous Efficiency Models using Acoustic Records
Luke McFadden lmcfadd6@uwo.ca
Peter G. Brown
Denis Vida
Department of Physics and Astronomy, University of Western Ontario, London, Ontario, N6A 3K7, Canada

Abstract

The total energy of a fireball is commonly obtained from optical measurements with an assumed value for luminous efficiency. Acoustic energy measurements offer an independent means of energy estimation. Here we combine optical and acoustic methods to validate the luminous efficiency model of Borovička et al. [2020]. Our goal is to compare these models with acoustic measurements of meteoroid energy deposition. Employing theoretical blast scaling laws following the approach of McFadden et al. [2021], we determine explosive yields for both fireball fragmentation events and cylindrical shocks for four different bright fireballs. We model fireballs using the MetSim software [Vida et al., 2023] and find that the Borovička et al. [2020] model produces agreement better than a factor of two for our three chondritic fireball case studies. The major exception is an iron meteorite-producing fireball where the luminous efficiency is an order of magnitude higher than model predictions calibrated with stony fireballs. We suggest that large disparities between optical and acoustic energies could be a signature of iron fireballs and hence useful as a discriminant of that population.
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Energy signature of ton TNT-class impacts: analysis of the 22 December 2018 fireball over Western Pyrenees
  • October 2021
  • Monthly Notices of the Royal Astronomical Society 508(4)
  • 508(4)
DOI:10.1093/mnras/stab2968
Authors:
S Anghel,
Esther Drolshagen, - Carl von Ossietzky Universität Oldenburg
Theresa Ott, Carl von Ossietzky Universität Oldenburg
M. Birlan, Observatoire de Paris
Show all 31 authors

Abstract
The increase in detector sensitivity and availability in the past three decades has allowed us to derive knowledge of the meteoroid flux and impact energy into the Earth’s atmosphere. We present the multi-instrument detected 22 December 2018 fireball over Western Pyrenees, and compare several techniques aiming to obtain a reliable method to be used when measuring impacts of similar scale. From trajectory data alone, we found a bulk density of 3.5 g/cm3 to be the most likely value for the Pyrenean meteoroid. This allowed to further constrain the dynamic mass, which translated into a kinetic energy of 1 ton TNT (4.184 · 109 J). For the second energy derivation, via the fireball’s corrected optical radiation, we obtained a more accurate empirical relation measuring well studied bolides. The result approximates to 1.1 ton TNT, which is notably close to the nominal dynamic result, and agrees with the lower margin of the seismic-based energy estimation, yet way lower than the infrasound estimate. Based on the relation derived in this study, we consider the nominal estimate from both the dynamic and photometric methods to be the most accurate value of deposited energy (1 ton TNT). We show that the combination of these two methods can be used to infer the meteoroid density. Among the methods presented in this paper, we found that the optical energy is the most reliable predictor of impact energy near the ton TNT-scale.
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And much earlier in 2003:
The luminosity and heat-transfer efficiencies in fireballs as a problem of the hypersonic gas dynamics
  • March 2003
  • Kinematika i fizika nebesnyh tel 19:159-171
  • 19:159-171
Authors: V. V. Kalenichenko
Abstract

The coefficient of transformation of the kinetic energy flow of air particles into the luminous flow is obtained from fireball observational data. The coefficient is dependent only on the fireball velocity over a wide range of fireball parameters. The coefficient values cannot explain the observed ablation of fireball-generating bodies for velocities under 20 km/s. The flow of air particles is probably the main source of the heating of the body in this case. For velocities over 40 km/s the fireball radiation flow to the body is substantially less than the flow to the outside space. The evaluation of the classical fireball luminous efficiency is still largely an indefinite procedure on account of the body fragmentation.
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Have the questions and problems from 2003 been solved since?

The above examples illustrate some of the problems involved in making estimates, which may also explain the variation between them, as when different studies were attempting to assess the total impact energy of the Chelyabinsk meteorite., which may serve as an introduction to the last study which addresses the impact energy of a fireball from the effect it creates on windows.
The frequency of window damage caused by bolide airbursts: A quarter century case study
Nayeob Gi, Peter Brown, Michael Aftosmis
First published: 10 April 2018

https://doi.org/10.1111/maps.13085
Citations: 7

Abstract
We have empirically estimated how often fireball shocks produce overpressure (∆P) at the ground sufficient to damage windows. Our study used a numerical entry model to estimate the energy deposition and shock production for a suite of 23 energetic fireballs reported by U.S. Government sensors over the last quarter century. For each of these events, we estimated the peak ∆P on the ground and the ground area above ∆P thresholds of 200 and 500 Pa where light and heavy window damage, respectively, are expected. Our results suggest that at the highest ∆P, it is the rare, large fireballs (such as the Chelyabinsk fireball) which dominate the long-term areal ground footprints for heavy window damage. The height at the fireball peak brightness and the fireball entry angle contribute to the variance in ground ∆P, with lower heights and shallower angles producing larger ground footprints and more potential damage. The effective threshold energy for fireballs to produce heavy window damage is ~5–10 kT; such fireballs occur globally once every 1–2 years. These largest annual bolide events, should they occur over a major urban center with large numbers of windows, can be expected to produce economically significant window damage. However, the mean frequency of heavy window damage (∆P above 500 Pa) from fireball shock waves occurring over urban areas is estimated to be approximately once every 5000 yr. Light window damage (∆P above 200 Pa) is expected every ~600 yr.
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The February 15, 2013 airburst proximal to the city of Chelyabinsk in Russia was the first recorded impact producing an air blast leading to widespread window damage (Brown et al. 2013) in an urban area. The shock wave impacting the city caused damage in excess of $60 M, mostly through breakage or cracking of windows (Popova et al. 2013).
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The above writers would have us think something like in Chelyabinsk only happens once every 5000 years, provided their wording "heavy window damage" is closer to "widespread window damage" than to "light window damage". Time will show if that holds up.

Some years ago, I tried to collect videos of fireballs from the CNEOS list: See post #94 and post #95 from Nov 30, 2019. Based on the available videos, including the more recent ones, and the calculated total impact energy of the fireballs they show, ordinary people can get an impression of what the visual differences are between smaller and larger fireballs, as they can appear in the sky, by day and by night. Though a fireball can be spectacular, experience also shows there can be instances where it is better to get away from the windows, perhaps even to duck and cover.
 
Oh S#$t.
https://twitter.com/x/status/1837152501524525308

https://twitter.com/x/status/1837546929321824696

gephardtdaily.com

Sound of explosions rattle windows, nerves across the Salt Lake Valley, beyond | Gephardt Daily

SALT LAKE COUNTY, Utah, Sept. 19, 2024 (Gephardt Daily) - Residents across the Salt Lake Valley were shaken and stirred early Thursday afternoon when a series of loud explosions rattled windows and nerves from one end of the Valley to the other. The source of the blasts was the Tooele Army Depot...
gephardtdaily.com gephardtdaily.com
By Patrick Benedict -September 19, 2024 🤔
SALT LAKE COUNTY, Utah, Sept. 19, 2024 (Gephardt Daily) – Residents across the Salt Lake Valley were shaken and stirred early Thursday afternoon when a series of loud explosions rattled windows and nerves from one end of the Valley to the other.

The source of the blasts was the Tooele Army Depot conducting routine detonations of old and obsolete military munitions, something they’ve been doing at the Tooele County installation since World War II.

When atmospheric conditions are right, the explosions sound like a dull thud; if not, they can sound and feel like something from a modern day battlefield. Such was the case Thursday, when thousands reported hearing and feeling detonations dozens of miles from the blast sites, prompting hundreds of calls to local law enforcement.

The Salt Lake Valley Emergency Communications Center reported 1,300-plus calls in the course of an hour, more than 400 of them made to 911.

“We understand that the sounds and vibrations that were experienced today surprised people and were scary,” the Tooele Army Depot said in a message on social media. “We know that these types of things can be concerning to some people. It’s not something that they experience every day.

“Tooele Army Depot is tasked with destroying the Nation’s old, obsolete, and unsafe munitions. We do that to ensure our Warfighters have the best tools to use when needed.

“The operations we conducted today are something that we do every year and have done since WWII. We are permitted to conduct open detonations from April through October. We only conduct these operations when weather conditions are right to mitigate the sounds and shaking from the detonations. There was no danger to the public from these operations.

“Today’s detonations were propagated further than normal because of the increased moisture in the ground and lack of cloud cover, which amplifies the effects of the detonations.

“We do our best to be good neighbors while also accomplishing our mission,” the TAD statement said.
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https://twitter.com/x/status/1837096264586121587
This is an image of the lunar impact flash that appeared at 20:43:22.97 on September 12, 2024, and the change in brightness, as well as the starry sky from the site of the lunar impact flash at the same time. It fell to the west of Von Braun Crater (LAT41, LON280). Assuming an entry speed of 17 km/s and an entry angle of 45 degrees, the mass of the meteoroid was about 1.2 kg, and the crater diameter was about 5 m (corrected).

藤井大地 @dfuji1
This lunar impact flash was probably the 51st observation since my graduate school days, finally exceeding 50! However, unlike Otani's one season, it took 13 years from the first observation to reach this number (laughs). It is said that astronomical observation begins and ends with the moon. I am still a novice, but I will do my best.
 
For those of you who don't have an X account, here's what the first X post above says:
In the video below clips from
@psicoactivopod
and
@VettedPodcast
about a James Webb telescope discovery:- James Webb has discovered an object about 10 light years out that seems to be approaching - Congress members are allegedly being briefed about the object- The object is allegedly massive and changing trajectory - Breakthrough Listen is aiming telescopes at it to get more data
@psicoactivopod

@VettedPodcast

@ClintWeldon
and
@skwirrellmate
discussing the discovery. Links to each podcast in the comments.#ufox #uapX #ufotwitter #uaptwitter
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Don't know how true this is, of course.
 
Wandering Star said:
Ten light years is a little more than twice the distance to the nearest star, Proxima Centauri.

A bit far to detect anything, much less to report to Congress.

If true, very strange.
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First thing we would need to know is if there is anything to that story in the first place. From the little I have heard and read on it, the story basically originates with one guy (or several guys?) claiming that they got that information from an undisclosed source? Can we find any substantial evidence that supports those claims?
 
tschai said:
Yes, and even if traveling at light speed still takes 10 years to get here. If they are ET they are late to the party, the neighborhood is already spoken for.
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Cosmos said:
First thing we would need to know is if there is anything to that story in the first place. From the little I have heard and read on it, the story basically originates with one guy (or several guys?) claiming that they got that information from an undisclosed source? Can we find any substantial evidence that supports those claims?
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What I find interesting is that this rough timing of 10 years (if it travels at light speed, which shouldn’t officially be possible for any such object, be it natural or Alien?) of when that object theoretically comes close to earth seems relatively close to the timing of several huge asteroid/comet junks that are supposed to come very close to earth around 2028-2029:

Cosmos said:
[…]With the one of a kind table here, which you can arrange however you like yourself, the following becomes visible:

Close Approach, closer than moon.jpg


Take a close look at the table above. Could it be that what is coming is revealing itself for all to see (for quite some time) there? Notice the huge chunks coming very close to earth in 2028 and 2029, one of which is quite well know by now, called Apophis. But the other one, curiously enough, is not well known at all, and is called "2001 WN5", while it is three times the size of Apophis! Then notice that quite a number of other big chunks will come near earth till 2100, or so. Could it be that Apophis and/or "2001 WN5" might not be alone and have "companions"? AND now think about the facts in the first two charts within this post above...
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https://twitter.com/x/status/1840055631652209040
https://twitter.com/x/status/1838326714637967562

When did scientists discover this phenomenon?
NASA scientists first laid eyes on the rocky remnant with the help of the Asteroid Terrestrial-Impact Last Alert System, or ATLAS. This went down on August 7 and prompted further study. The asteroid’s predicted trajectory was then published in the Research Notes of the American Astronomical Society. Thankfully, this isn’t the beginning of an apocalyptic movie as it won’t hit the Earth

theskylive.com

Asteroid (NEO) 2024 PT5 | TheSkyLive

Complete observing guide and realtime information about Asteroid (NEO) 2024 PT5 for astronomy and science enthusiasts at all levels.
theskylive.com theskylive.com

https://twitter.com/x/status/1839749429106225551

https://twitter.com/x/status/1839293272285466965
 
The Dart Mission
https://twitter.com/x/status/1841178196898709577


A recently discovered comet, A11bP7I, is reclassified as C/2024 S1 ATLAS as it makes a close approach past the sun on "October 28 at a distance of 50,000 kilometers [31,068 miles] from the surface lower regions of the solar atmosphere (of the corona)."

https://twitter.com/x/status/1841260127162417615

https://twitter.com/x/status/1840415318038200495

https://twitter.com/x/status/1841230106251145530
https://twitter.com/x/status/1841324864113885305

Chris Hadfield @Cmdr_Hadfield
This huge, peanut-shaped asteroid whizzed past the Earth 2 weeks ago. It's over 1100'/350m long. Glad it missed us!details: https://tinyurl.com/uah4n9h6radar image: @NASA DSN Goldstone

x.com

x.com x.com
 
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