
A huge fireball exploded in Earth's atmosphere in December, according to Nasa - okket
https://www.bbc.com/news/science-environment-47607696
======
JoeDaDude
This one was detected by satellite, but scientists have been using acoustic
detection of meteorite explosions for some time. Fittingly, they used
detectors made for nuclear explosions, the Comprehensive Test Ban Treaty
Organization's infrasound network [1].

I learned this from reading this highly recommended book on the subject:
Asteroids: Relics of Ancient Time by Michael K. Shepard [2] (amazon link)

[1] [https://www.norsar.no/r-d/safe-society/nuclear-test-ban-
moni...](https://www.norsar.no/r-d/safe-society/nuclear-test-ban-
monitoring/infrasound-monitoring/)

[2]
[https://www.amazon.com/reader/110706144X?_encoding=UTF8&quer...](https://www.amazon.com/reader/110706144X?_encoding=UTF8&query=kiloton#reader_110706144X)

~~~
XzetaU8
Vela Incident
[https://en.wikipedia.org/wiki/Vela_Incident](https://en.wikipedia.org/wiki/Vela_Incident)

------
okket
Also: "Imagine what might have happened if this meteor had exploded not over
the Bering Sea but over nuclear-armed North Korea, India, or Pakistan during a
time of increased tensions or actual conflict."

[https://twitter.com/AtomicAnalyst/status/1107660418967916545](https://twitter.com/AtomicAnalyst/status/1107660418967916545)

~~~
r721
Chelyabinsk meteor exploded almost over a city:

"The first explosion was the most powerful, and was preceded by a bright
flash, which lasted about five seconds. Initial newspaper altitude estimates
ranged from 30–70 km, with an explosive equivalent, according to NASA, of
roughly 500 kilotonnes of TNT (2,100 TJ), although there is some debate on
this yield (500 kt is exactly the same energy released by the Ivy King nuclear
explosion in 1952). According to a paper in 2013, all these ~500 kiloton yield
estimates for the meteor airburst are "uncertain by a factor of two because of
a lack of calibration data at those high energies and altitudes."

The hypocentre of the explosion was to the south of Chelyabinsk, in
Yemanzhelinsk and Yuzhnouralsk. Due to the height of the air burst, the
atmosphere absorbed most of the explosion's energy."

[https://en.wikipedia.org/wiki/Chelyabinsk_meteor](https://en.wikipedia.org/wiki/Chelyabinsk_meteor)

------
cubano
I mean, with all the money the US currently spends on military budgets, I
can't for the life of me figure out why it is so hard to find the 50-100mil or
so (estimated) it would cost for a few orbital IR telescopes and just deal
with this problem once and for all.

A Pegasus XL rocket can lift 976 pounds (443 kilograms) into low-Earth orbit
for about $13.5 million...put two "budget" telescopes on one launch and get to
work.

~~~
viach
It is expected to happen only about 3 times in a century (from article).

In other words, building this system of telescopes won't affect the next
elections in any positive way.

~~~
balt_s
Everyone else likely missed it, but I want you to know I appreciate this joke.

~~~
dpark
> _Everyone else likely missed it_

I’m sure you’re the only one to notice the obvious joke.

------
Wildgoose
It's possible that in 1178 an asteroid hit the Moon with a 120,000 megaton
blast - an Extinction Event if it had hit the Earth.

(By way of comparison, the Hiroshima Bomb was 15 kilotons).

Recorded by monks at Canterbury at the time, and only a possibility - but
something to consider.

[https://en.wikipedia.org/wiki/Giordano_Bruno_(crater)](https://en.wikipedia.org/wiki/Giordano_Bruno_\(crater\))

~~~
nkrisc
According to the same page, more recent developments don't support the theory:

> High-resolution images obtained by the Japanese satellite SELENE in 2008
> were used to date the crater by counting the smaller craters within it and
> its ejecta deposits. This gave an age of 4(+6, −3) million years, much too
> old for the hypothesis.[2]

> This raises the question of what the monks saw. An alternative theory holds
> that the monks just happened to be in the right place at the right time to
> see an exploding meteor coming at them and aligned with the Moon. This would
> explain why the monks were the only people known to have witnessed the
> event; such an alignment would only be observable from a specific spot on
> the Earth's surface.[8]

~~~
hinkley
What the monks reported sounds like it might be consistent with the optical
disturbances caused by superheated air:

> From the midpoint of the division a flaming torch sprang up, spewing out,
> over a considerable distance, fire, hot coals and sparks. Meanwhile the body
> of the Moon which was below writhed, as it were in anxiety, and to put it in
> the words of those who reported it to me and saw it with their own eyes, the
> Moon throbbed like a wounded snake. Afterwards it resumed its proper state.
> This phenomenon was repeated a dozen times or more, the flame assuming
> various twisting shapes at random and then returning to normal. Then, after
> these transformations, the Moon from horn to horn, that is along its whole
> length, took on a blackish appearance.

An air burst between observer and observed would move around on the wind,
causing ripples to come and go.

~~~
nkrisc
> An air burst between observer and observed would move around on the wind,
> causing ripples to come and go.

Agreed. Far more likely that an impact causing the moon to wobble or visibly
move, which would have to be an obscenely destructive impact.

------
mttyng
Assuming we (Earth) get some reasonable warning time for a problematic impact,
the logistics of alerting -and then moving- a large metropolitan area like
NYC, for example, are interesting. Where do we place these people? What about
the city's infrastructure? Do we just stand by, brace for impact and hope for
the best? Or is there something more we could do to mitigate the disaster? I
know a lot of that depends on the amount of time beforehand, but I find the
problem intriguing.

~~~
jwm20
You may be interested in a recent episode of the 99 Percent Invisible podcast
([https://99percentinvisible.org/episode/atomic-
tattoos/](https://99percentinvisible.org/episode/atomic-tattoos/)). The title
of the podcast comes from a Cold War program carried out in 1952 in which
students could opt to receive a small tattoo of their blood type, with the
goal of creating a "walking blood bank" in the event of a disaster requiring
mass transfusions.

Related to your question, the episode also explores the history of "duck and
cover." It turns out it's there is some credibility to the technique. In
September 1945, the US sent a team called the Atomic Bomb Casualty Commission
to Japan to research and interview survivors of nuclear blasts. They located
survivors just a few blocks from the explosion epicenter, who had been
sheltered by concrete basements. They also heard stories of people who were
killed just by shattering windows and falling debris. With just some ability
to shelter, survivability might be higher than you suspect.

~~~
Stratoscope
We had a recent example of the value of "duck and cover" \- and more
specifically what happens if you _don 't_ do it - the Chelyabinsk meteor.

"Its explosion created panic among local residents, and about 1,500 people
were injured seriously enough to seek medical treatment. All of the injuries
were due to indirect effects rather than the meteor itself, mainly from broken
glass from windows that were blown in when the shock wave arrived, minutes
after the superbolide's flash."

Many of the injured went to a window to see the spectacle in the sky, not
realizing that the shock wave was about to shatter the window in their face.

[https://en.wikipedia.org/wiki/Chelyabinsk_meteor](https://en.wikipedia.org/wiki/Chelyabinsk_meteor)

~~~
dsfyu404ed
>Many of the injured went to a window to see the spectacle in the sky, not
realizing that the shock wave was about to shatter the window in their face.

Same thing happened in the Halifax explosion.

~~~
rtkwe
That explosion was close enough that there would be basically no chance to
react between the actual explosion and the shock wave.

------
golemotron
> Measuring several metres in size, the space rock exploded 25.6km above the
> Earth's surface, with an impact energy of 173 kilotons.

What causes a meteor to explode 25km above the earth? Thermal expansion of
internal gas?

~~~
bufferoverflow
It's called an explosion, but it's more of a conversion of kinetic energy to
heat due to friction against the air. As the rock heats up, it starts to fall
apart, and then smaller pieces go through that as well.

Here's a neat simulation of the process:

[https://www.youtube.com/watch?v=tbh6GjRChnQ](https://www.youtube.com/watch?v=tbh6GjRChnQ)

~~~
iamgopal
Isn't it more about air compression instead of friction ?

~~~
EForEndeavour
Correct. Further reading: [https://www.quora.com/Why-does-a-spacecraft-heat-
up-during-r...](https://www.quora.com/Why-does-a-spacecraft-heat-up-during-
reentry)

------
ppeetteerr
Well this is terrifying. Time to call in the Space Force!

~~~
stunt
To justify the costs of Space Force, First, we need to find space terrorists.
Or, find aliens and sell weapons to them.

~~~
TeMPOraL
There's oil on Titan!

(No, really, there is!)

------
christophilus
> The space rock exploded with 10 times the energy released by the Hiroshima
> atomic bomb

Well, that's fun.

~~~
mrguyorama
Kinetic energy is a hell of a thing. That squared term really adds up quick

~~~
folex
Can you elaborate plz?

~~~
rtkwe
The energy of an object is (1/2)mv^2. Doubling velocity quadruples the kinetic
energy.

------
donretag
Why does the BBC not use the NASA acronym?

~~~
airstrike
Certain languages (British English and Portuguese, to name the two I know)
dictate that if you pronounce the acronym as if it were a word, you only
capitalize the first letter.

Nasa and Nato, but NSA and WTO.

~~~
dyoo1979
Example reference: see the "abbreviations and acronyms" section in:
[https://www.theguardian.com/guardian-observer-style-
guide-a](https://www.theguardian.com/guardian-observer-style-guide-a)

Hilariously enough, "Nasa" is specifically called out as an negative example
from the English Wikipedia style guidelines:
[https://en.wikipedia.org/wiki/Wikipedia:Manual_of_Style/Capi...](https://en.wikipedia.org/wiki/Wikipedia:Manual_of_Style/Capital_letters#Acronyms)

------
Datenstrom
While I was working at NASA I was told by a colleague that Trump canceled the
asteroid deflection program that was being ran at the LaRC facility. Now
looking for a reference all I can find is news about him starting an asteroid
deflection program because of this incident.

I'm not sure of the details since I was working in an AI research department.

~~~
jtuente
I mean, that's not how the US budget works. But yes, his budget proposal
included nixing an Obama-era project to redirect an asteroid to lunar space
for a manned mission. I wouldn't call that a deflection program.

~~~
Rebelgecko
I'd say deflecting an asteroid so that it goes closer to Earth still counts as
deflecting :) That said, the cancellation was a shame since it gave the Lunar
Gateway a concrete and useful purpose.

------
kahirsch
Lindley Johnson, _planetary defence officer_ at Nasa, told BBC News a fireball
this big is only expected about two or three times every 100 years.

Best title ever.

~~~
tudelo
Can't compete with that guys job title at the class reunion.

~~~
Tepix
Well, there's also a "planetary protection officer", Lisa Pratt (and deputy
planetary protection officer Elaine Seasly) :-)

~~~
cyberfart
There was also this 9 years old kid who applied for planetary protection
officer position :)

[https://www.businessinsider.de/child-applies-nasa-
planetary-...](https://www.businessinsider.de/child-applies-nasa-planetary-
protection-officer-job-opening-2017-8)

------
kempbellt
The gods are angry

------
vectorEQ
"That's another thing we have in our defence, there's plenty of water on the
planet."

so that's what planetary defence people do :D since it's unrealistic to
prepare to defend the planet actually, let's just point at things :D and call
them out for being in our defence! :D we have mountains too! they are also in
our defence!

------
kosei
Womp womp, article didn't get picked up when I posted it last night. Guess I
should have retitled / waited until morning!

[https://news.ycombinator.com/item?id=19418939](https://news.ycombinator.com/item?id=19418939)

