Near-Earth objects and close calls

thorbiorn

The Living Force
FOTCM Member
Sometimes trying another language gives a new slant to one's understanding. On the French Wiki about bolides, they have a table which when translated says:
Names, mass and duration

Name MassAltitudeDuration[My comments]
Shooting star 1 gram110-80 km1-2 secWould it reach up to 0.5 kg, could it be less than a gram?
Bolide order of kilogram80-50 km2-5 sDuration would also depend on incoming speed and angle.
-"-From 0.5 to 10 tonnes80-13 km5-40 s10 tons sounds harmless, but the Chelyabinsk superbolide weighed an estimated 11,000 tons!
If one has access to the trajectory data of a fireball, they will often tell at which altitude it was extinguished, and the duration of the event.
There are some comments in the Wiki about the process the meteor is subject to when entering into the atmosphere of the Earth:
Fragmentation process
A meteoroid that survives its re-entry into the atmosphere can either come out and is called a low-speed bolide, or reach the ground and the pieces that remain are then called meteorites. During the crossing, the object undergoes a more or less important ablation depending on the density and the nature of the material constituting it. The forces in action, when slowing down, tend to shatter the rock. The larger a body, the more likely it is to break: generally, this occurs between 70 and 90 kilometers above sea level, with the most massive bolides capable of fragmenting at 10 km above sea level. At the time of fragmentation, the speed drops rapidly and the meteor reaches Earth or, more often, disperses into dust in the atmosphere. The fragments reaching the ground become as many meteorites. Fewer than 500 tennis ball-sized stones reach the earth's surface each year4.
One way of understanding why the speed drops upon fragmentation is that the total surface area increases compared to what it was before. At the same time, the density of the surrounding air keeps increasing too leading to even more resistance. Both these effects lead to a slower speed.
The light
The light emitted by a bolide is produced by two different mechanisms: the molten rock and especially the flow of the gas which surrounds it, brought to a temperature of several tens of thousands of degrees because of the compression. Above 80 km altitude, the Earth's atmosphere is not dense enough to oppose the entry of bodies of significant mass. Below, the thermal energy due to friction can heat the bolide up to 4000 K3; the material constituting the object or those formed by reaction, generally liquid, flow over the surface. A gaseous part is entrained by the flow.

A bolide can emit a light of different colors, the witnesses speak of light ranging from blue to red. The color of the meteor depends on the composition of its matter and the air. Meteoroids are made up of metals such as silicon, nickel, iron, magnesium, and possibly carbon, which produce different colors.
This has probably been mentioned before, but here is a nice picture that shows the colour different metals can give when heated:

maxresdefault (1).jpg

The sounds
There appear to be two sources of sound if they are present, those resulting from sonic booms and those caused by electric effects
Meteors also produce sounds. Usually, the noise is heard after several seconds or even several minutes after visual observation. These sounds correspond to the arrival of a supersonic "bang" similar to that of a jet plane passing the sound barrier. If the meteoroid splits up (usually between 70 and 90 kilometers above sea level), each piece emits its own shock wave that can interfere with the others. Many observers say they have also heard hissing noises, called electrophonic sounds, produced by unidentified phenomena.
 

thorbiorn

The Living Force
FOTCM Member
Meteorite falls and meteorite finds
Usually, we estimate the changes in the rate of fireballs based on optical observations done by people or cameras. Another way of estimating the amount of incoming object might be to study new meteorite falls. In order to find meteorites based on previous visual observation, one often needs enough data to generate a plausible trajectory using mathematical models, as described in the following article:
ACCURATE 3D FIREBALL TRAJECTORY AND ORBIT CALCULATION USING THE 3D-FIRETOC AUTOMATIC PYTHON CODE
This article has been published in the Monthly Notices of the Royal Astronomical Society by Eloy Peña-Asensio, Josep Maria Trigo-Rodríguez, Maria Gritsevich, Albert Rimola.
On Google Scholar one can try "meteorite fall statistics". There are a few papers like:
Their research indicates variations in the meteorite fall rate.
Abstract— The discovery of 154 meteorite fragments within an 11 km2 area of wind‐excavated basins in Roosevelt County, New Mexico, permits a new calculation of the accumulation rate of meteorite falls at the Earth's surface.

Thermoluminescence dating of the coversand unit comprising the prime recovery surface suggests the maximum terrestrial age of the meteorites to be about 16.0 ka. The 68 meteorite fragments subjected to petrological analyses represent a minimum of 49 individual falls. Collection bias has largely excluded carbonaceous chondrites and achondrites, requiring the accumulation rate derived from the recovered samples to be increased by a factor of 1.25. Terrestrial weathering destroying ordinary chondrites can be modelled as a first‐order decay process with an estimated half‐life of 3.5 ± 1.9 ka on the semiarid American High Plains. Having accounted for the age of the recovery surface, area of field searches, pairing of finds, collection bias and weathering half‐life, we calculate an accumulation rate of 9.4 × 102 falls/a per 106 km2 for falls > 10 g total mass. This figure exceeds the best‐constrained previous estimate by more than an order of magnitude. One possible reason for this disparity may be the extraordinary length of the fall record preserved in the surficial geology of Roosevelt County. The high accumulation rate determined for the past 16 ka may point to the existence of periods when the meteorite fall rate was significantly greater than at present.
Following some of the 30 citations of this paper might lead to other papers that treat this question.

In the process of writing and I found a Chinese video that shows a few finds of quite substantial specimens weighing several kg. 罕见的陨石 I can't tell if these are new or old finds. Btw. They also have videos in Chinese about impacts: https://haokan.baidu.com/web/search/page?query=地外行星撞击 or meteors: https://www.baidu.com/sf/vsearch?pd=video&tn=vsearch&ie=utf-8&wrsv_spt=10&wd=流星
 

thorbiorn

The Living Force
FOTCM Member
From a couple of month ago:
The results of Zamora, Ocaña, Sánchez de Miguel and Mole were based on newspaper reports, and some of these reports may have been about event that also appears in the NASA list. If one instead of the newspaper reports used the same statistical tools as Zamora et al. and applied them to the more than 850 observations registered in this NASA list, of which many have been added since the above paper was published in 2015, would one be able to find patterns that are statistically significant and would they confirm the dates Zamora et al suggested?
@seek10 is a professional and helped me to represent the data in the NASA list in different ways. Here are a few diagrams.
First a year by year presentation that @seek10 made:
Screenshot 2021-05-01 182757.png
By month
Then I tried to represent the observations according to the months of the year. The variation is limited though one could try to see if there are any meteor showers that are particularly active in certain months.
Screenshot 2021-05-01 185612.png
By day of the week
Below is the number of hits according to the day of the week. Days are counted from Sunday and the value of Sunday is 0, therefore the value of Saturday is 6. In the diagram below Tuesday and Friday are taking a harder hit than Sunday and Monday or is it simply that observers are off duty on Sunday? I found this rather interesting.
Screenshot 2021-05-01 185859.png
By the ordinal date of the year

Finally, there is also the number of events for any given ordinal date of the year. Here the diagram was not helpful. Instead, you will find the list of data. To look up the day of the year that each of these "dayOfTheYear" numbers corresponds to, try the ordinal date where one finds this system:
Screenshot 2021-05-01 194109.png
In the list below, day 343 would typically, that is in a normal year correspond to December 9. I have not done any analysis of these numbers. Feel free to play.

dayOfTheYear​
Record Count​
343​
6​
49​
6​
204​
6​
281​
6​
136​
6​
127​
6​
15​
6​
325​
6​
18​
6​
245​
5​
311​
5​
43​
5​
218​
5​
48​
5​
22​
5​
2​
5​
285​
5​
335​
5​
77​
5​
295​
5​
32​
5​
277​
5​
332​
5​
330​
5​
109​
5​
229​
5​
282​
5​
37​
5​
238​
4​
96​
4​
284​
4​
46​
4​
365​
4​
154​
4​
177​
4​
207​
4​
345​
4​
124​
4​
8​
4​
267​
4​
179​
4​
97​
4​
63​
4​
293​
4​
55​
4​
317​
4​
300​
4​
86​
4​
297​
4​
185​
4​
251​
4​
268​
4​
230​
4​
329​
4​
106​
4​
120​
4​
270​
4​
348​
4​
212​
4​
112​
4​
134​
4​
68​
4​
313​
4​
117​
4​
299​
4​
248​
4​
314​
4​
333​
4​
67​
4​
35​
4​
12​
4​
139​
4​
92​
4​
103​
4​
350​
4​
93​
4​
10​
3​
228​
3​
322​
3​
73​
3​
47​
3​
196​
3​
145​
3​
194​
3​
257​
3​
188​
3​
357​
3​
33​
3​
283​
3​
346​
3​
274​
3​
363​
3​
226​
3​
265​
3​
141​
3​
364​
3​
211​
3​
40​
3​
153​
3​
172​
3​
6​
3​
235​
3​
208​
3​
279​
3​
287​
3​
232​
3​
315​
3​
57​
3​
164​
3​
17​
3​
256​
3​
263​
3​
111​
3​
337​
3​
28​
3​
247​
3​
9​
3​
21​
3​
27​
3​
318​
3​
104​
3​
90​
3​
156​
3​
280​
3​
52​
3​
227​
3​
113​
3​
155​
3​
166​
3​
78​
3​
82​
3​
74​
3​
304​
3​
306​
3​
83​
3​
352​
3​
50​
3​
138​
3​
342​
3​
255​
3​
150​
3​
157​
3​
142​
3​
59​
3​
240​
3​
143​
3​
323​
3​
319​
3​
56​
3​
38​
3​
130​
3​
171​
3​
181​
3​
220​
3​
344​
2​
358​
2​
160​
2​
169​
2​
202​
2​
236​
2​
70​
2​
148​
2​
174​
2​
261​
2​
288​
2​
359​
2​
60​
2​
107​
2​
167​
2​
186​
2​
223​
2​
11​
2​
362​
2​
110​
2​
262​
2​
215​
2​
209​
2​
276​
2​
272​
2​
51​
2​
71​
2​
355​
2​
1​
2​
199​
2​
128​
2​
88​
2​
4​
2​
187​
2​
62​
2​
243​
2​
149​
2​
210​
2​
198​
2​
241​
2​
252​
2​
206​
2​
24​
2​
239​
2​
16​
2​
347​
2​
260​
2​
25​
2​
353​
2​
89​
2​
100​
2​
85​
2​
296​
2​
356​
2​
114​
2​
286​
2​
3​
2​
61​
2​
87​
2​
222​
2​
191​
2​
91​
2​
213​
2​
29​
2​
116​
2​
305​
2​
94​
2​
76​
2​
19​
2​
101​
2​
95​
2​
122​
2​
147​
2​
115​
2​
105​
2​
273​
2​
132​
2​
193​
2​
126​
2​
221​
2​
203​
2​
26​
2​
66​
2​
163​
2​
158​
2​
64​
2​
224​
2​
324​
2​
146​
2​
266​
2​
133​
2​
275​
2​
278​
2​
170​
2​
190​
2​
308​
2​
65​
2​
327​
2​
161​
2​
98​
2​
334​
2​
173​
2​
326​
1​
151​
1​
178​
1​
184​
1​
197​
1​
168​
1​
53​
1​
246​
1​
216​
1​
144​
1​
234​
1​
72​
1​
349​
1​
125​
1​
254​
1​
39​
1​
271​
1​
152​
1​
44​
1​
123​
1​
309​
1​
340​
1​
290​
1​
294​
1​
331​
1​
7​
1​
233​
1​
307​
1​
192​
1​
217​
1​
361​
1​
129​
1​
302​
1​
336​
1​
339​
1​
23​
1​
81​
1​
140​
1​
242​
1​
244​
1​
14​
1​
176​
1​
79​
1​
165​
1​
321​
1​
41​
1​
292​
1​
189​
1​
201​
1​
214​
1​
20​
1​
200​
1​
180​
1​
316​
1​
30​
1​
36​
1​
250​
1​
175​
1​
118​
1​
135​
1​
264​
1​
289​
1​
58​
1​
54​
1​
137​
1​
182​
1​
341​
1​
108​
1​
159​
1​
162​
1​
219​
1​
298​
1​
354​
1​
360​
1​
75​
1​
121​
1​
183​
1​
205​
1​
225​
1​
253​
1​
258​
1​
119​
1​
312​
1​
31​
1​
 

sToRmR1dR

The Living Force
FOTCM Member
A newly-discovered asteroid will flyby Earth on May 4, 2021.

Posted by Teo Blašković on May 4, 2021

 

sToRmR1dR

The Living Force
FOTCM Member
A newly-discovered asteroid made a close approach to Earth on May 6, 2021.

Posted by Teo Blašković on May 6, 2021

 

Laura

Administrator
Administrator
Moderator
FOTCM Member
Russian complex "Okno-M" recorded an increase in activity in space


09:44 08.05.2021(updated: 17:02 08.05.2021)

MOSCOW, May 8 - RIA Novosti. The Russian optical-electronic complex for monitoring space objects "Okno-M" recorded an increase in activity, the Defense Ministry said.

According to the ministry, in the first four months of 2021, the system provided control over about 30 thousand space objects, while in the whole of 2020 more than 25 thousand of them were monitored.

The detection complex is located inTajikistan , in the Pamir Mountains, at an altitude of 2200 meters above sea level.

"Okno-M" makes it possible to control space objects in orbits in the altitude range from 120 to 50 thousand kilometers. Moreover, at the maximum range, the complex is capable of detecting objects the size of a tennis ball.

The Okno complex was put on experimental combat duty in 1999. After modernization in 2014, the complex received the designation "Okno-M", its detection range increased from 40 thousand to 50 thousand kilometers. In general, since 1999, the complex has carried out more than 12.5 million measurements of space objects, discovered more than 7,500 new high-orbit space objects, and monitored the launch of about 800 spacecraft into working orbits.

The complex includes modern optical-electronic stations for detecting and collecting information, television detection equipment and new generation computing facilities, created on the basis of domestic element base. The complex uses signals received as a result of reflection of solar radiation from space objects as information carriers. The work of "Okna-M" is fully automated.
 

Pashalis

Ambassador
Ambassador
FOTCM Member
Out of curiosity I just looked up how many objects came closer to earth than the moon in 2021. Already 54 such objects slipped by this year! And we still have more than 7,5 months to go until the end of this year. In the whole of last year 107 such objects slipped by earth. If that trend continues (see below) it very much looks like the all-time record number of last year (107 objects) could be overtrumped again quite significantly this year:

128 days (in 2021) ≙ 54 Objects recorded
365 days ≙ approx. 154 Objects (theoretical extrapolation for the whole year of 2021)

Compared to 107 such objects recorded in 2020.
 

sToRmR1dR

The Living Force
FOTCM Member
A newly-discovered asteroid made a close approach to Earth on May 8, 2021.

Posted by Teo Blašković on May 10, 2021

 
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