

Billion-Ton Comet May Have Missed Earth by a Few Hundred Kilometers in 1883 - gnosis
http://www.technologyreview.com/view/425780/billion-ton-comet-may-have-missed-earth-by-a-few-hundred-kilometers-in-1883/

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mchouza
A more skeptical analysis by Phil Plait:
[http://blogs.discovermagazine.com/badastronomy/2011/10/17/di...](http://blogs.discovermagazine.com/badastronomy/2011/10/17/did-
a-fragmenting-comet-nearly-hit-the-earth-in-1883-color-me-very-skeptical/)

~~~
ChuckMcM
Was going to add this one as well. A comet of that size, that close, would
have raised questions in other places. The point that we didn't have nearly
the observational capacity a couple of hundred years ago that we have today is
well made, we certainly might have dodged a bullet, we have seen two comments
hit the bigger planets (Jupiter and Saturn) but we only noticed because we
were looking.

So I share the skepticism that this was a Comet in 1883 but I don't doubt for
a moment comets have come that close to the planet.

~~~
jacquesm
They got a lot closer than that in recent times, but not quite as massive:

<http://en.wikipedia.org/wiki/Tunguska_event>

In the long run cometary impact is pretty much a certainty and close passes
are a lot more likely than impact.

So even if this particular observation is probably attributable to something
else there is a good chance that something like it did happen at another point
in time in the last 2,000 years or so.

<http://en.wikipedia.org/wiki/Chicxulub_crater> was 65M years ago,
<http://en.wikipedia.org/wiki/Sudbury_Basin> 1.9B years ago,
<http://en.wikipedia.org/wiki/Vredefort_crater> 2B years and so on. The
<http://www.passc.net/EarthImpactDatabase/index.html> Earth Impact Database
holds currently 183 recorded impacts over a period of about 2.4 billion years.

2400M / 183 gives a probability of 7.6x10-8, but that's for impacts, and near
misses don't leave any evidence other than people that happened to be looking
in that direction. The question then is how many near misses before you get a
'hit', probably a fairly large number depending on how you classify a near
miss. Anything closer than the earth moon orbit would be fine with me as a
'near miss' (according to George Carlin an _accident_ is a near miss, but
never mind that). The exposed target of the earth-moon bounded sphere is
substantially larger (~2000 times or so?) and would increase the chance of a
near miss from the impact figure to about 0.000167 for any given year, or
about once every 6,000 years. And the base figure here is craters that we
_know_ about, which means they're likely on the land, that misses 2/3rd of the
planet.

I'm sceptical about this but I would not rule it out entirely.

~~~
ChuckMcM
There is a really interesting question which I posed to the NASA near earth
team at one of their talks at Ames which was "what sort of evidence would an
intra-atmospheric near miss produce?" Which is to say a comet that missed by
50,000 to 125,000' rather than further out. The speculation is that it would
result in wide spread fires (the compressive heating of the air in front of it
would ignite things). Basically it could transfer a lot of energy to the
atmosphere. But most felt that a comet that close would be in pieces and at
least some of it would leave a crater trail.

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pgsandstrom
The paper in question: <http://arxiv.org/ftp/arxiv/papers/1110/1110.2798.pdf>

It is written in comic sans and one of the authors is using a yahoo mail.
Maybe I'm just being an elitist nerd, but really...

~~~
tolos
Hector Javier Durand-Manterola is the author with the yahoo address. It looks
like he did work at Universidad Nacional Autónoma de México (UNAM), where the
other two authors are from, at one point [1]. He's authored a few other
astronomy papers at arxiv [2] even though he doesn't seem to be in the
database. Perhaps he has retired from academic life.

[1] <http://www.researchgate.net/profile/Hector_Durand-Manterola/>

[2]
[https://www.google.com/#q=site:arxiv.org+hdurand_manterola%4...](https://www.google.com/#q=site:arxiv.org+hdurand_manterola%40yahoo.com)

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venus
> A sobering thought.

An even more sobering thought is that even in the present day, if we detected
something like that heading our way, there'd be absolutely nothing we could
but sit and wait for it to arrive.

~~~
rorrr
That's not true. If we knew for a fact that it would cause global extinction,
we would throw everything at it.

We could blow it up with nukes.

We could put a relatively heavy space probe next to it and deflect its course.

~~~
rizzom5000
When faced with impending doom, optimism and pessimism are both equally fine
sentiments. The caveat is that only one of them accurately reflects reality,
not that it matters at that point.

I also suppose that industriousness would be helpful for taking one's mind
away from the reality of that impending doom.

But hell, nukes to deflect a comet? Sure, we may as well try it -- but I only
suggest doing this if we are 100% certain that the comet will both hit us and
destroy us. We could conceivably cause our own extinction via a false positive
provided by some faulty monitoring device - wait, did that already happen?
Nevermind.

~~~
AlexMennen
If there is a significant chance that a comet will hit and destroy us, it
makes sense to do everything we can to prevent it from doing so. Given the
stakes, .1% chance should be more than enough for us to take it seriously. It
does not seem plausible that we could harm ourselves much by nuking a comet
that wasn't going to hit us anyway.

~~~
rizzom5000
It does seem plausible that we could in fact harm ourselves by attempting to
launch a nuclear device out of Earth's orbit. We do have a record of failed
launches, several of them recent. Once the nuclear device is out of orbit
however, I agree that the harm it can do to us is negligible.

Edit: Also, it just occurred to me the possibility of deflecting a comet
(which was never in our path) into our path, instead of away from it, which is
really great material for a Hollywood comedy.

~~~
rorrr
If a billion-ton comet is about to hit our planet, a failed attempt to launch
a nuke doesn't matter in the slightest.

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apaprocki
The link to the original L'Astronomie journal article, which contains a
diagram and photograph is here:

[http://books.google.com/books?id=Vt1NAAAAMAAJ&pg=PA347#v...](http://books.google.com/books?id=Vt1NAAAAMAAJ&pg=PA347#v=onepage&q&f=false)

"PASSAGE SUR LE DISQUE SOLAIRE" p. 347, L'Astronomie Vol. IV

Transcript (French) <https://gist.github.com/4136038>

Transcript (English, Google Translated) <https://gist.github.com/4136045>

Also, it appears there are letters to the journal regarding the original
article in the subsequent Vol. V, which can be viewed here:
[http://hdl.handle.net/2027/mdp.39015069401779?urlappend=%3Bs...](http://hdl.handle.net/2027/mdp.39015069401779?urlappend=%3Bseq=80)

------
lutusp
A quote: "They point out that nobody else on the planet seems to have seen
this comet passing in front of the Sun, even though the nearest observatories
in those days were just a few hundred kilometers away. That can be explained
using parallax."

It can also be explained by the simple fact that (a) not many observatories
specialize in observing the sun even now, and (b) the observation may only
have lasted a few hours (as with this year's Venus transit). Remember Occam's
razor -- the simplest explanation is to be preferred.

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temphn
No photographic evidence. No corresponding accounts. No raw data.

    
    
      Bonilla published his account of this event in a French 
      journal called L'Astronomie in 1886. Unable to account for 
      the phenomenon, the editor of the journal suggested, 
      rather incredulously, that it must have been caused by 
      birds, insects or dust passing front of the Bonilla's 
      telescope.
    

As the saying goes: when you hear hoof-steps, think horses, not zebras.

~~~
mistercow
Yeah the prior probability of "fragmenting comet within 8000 km of Earth"
seems kind of a lot lower than that of "dust in front of the telescope".

~~~
quarterto
<http://rationalwiki.org/wiki/Improbable_things_happen>

~~~
mistercow
That's a silly argument. Yes, improbable things happen, but our _beliefs_
should be informed by whatever hypothesis is assigned the highest probability.

The difficulty that a hypothesis with very low prior probability (like this
one) has is that in order for it to reach a level of probability necessary to
compete with the more mundane explanations like dust or birds, it is going to
have to be backed by very strong evidence. This is the Bayesian expression of
"extraordinary claims require extraordinary evidence". The hypothesis needs to
make some predictions that are exceptionally unlikely given those mundane
hypotheses.

Unfortunately, it's difficult to see what predictions those might be. The
authors of the paper don't give any, and their primary "evidence" for the
hypothesis - that nobody else saw the object - is actually _more_ likely given
the birds/dust hypothesis than the comet hypothesis.

So yes, there's a tiny possibility that this could have been a comet, but if
so, it's hard so imagine that it could ever be elevated to the point of a
hypothesis that we should even take seriously, much less one that we should
believe.

------
dmix
> They point out that nobody else on the planet seems to have seen this comet
> passing in front of the Sun, even though the nearest observatories in those
> days were just a few hundred kilometers away.

This is 1883 and noone else recorded seeing it? Even in all of mexico?

~~~
Gustomaximus
The do say in the article about no-one seeing it;

"That can be explained using parallax. If the fragments were close to Earth,
parallax would have ensured that they would not have been in line with the Sun
even for observers nearby. And since Mexico is at the same latitude as the
Sahara, northern India and south-east Asia, it's not hard to imagine that
nobody else was looking."

Is this realistic? Also would the time of day matter? If the sun was low to
the horizon etc.

~~~
lutusp
> The do say in the article about no-one seeing it; "That can be explained
> using parallax ..."

> Is this realistic?

No. Even today not many observatories specialize in sun observations. It's not
at all surprising that only one astronomer witnessed this, and it's a stretch
to suggest the explanation that the observed object was therefore very close
-- there are many more plausible explanations.

> Also would the time of day matter?

No, not for an object silhouetted against the sun. Consider this year's Venus
transit -- everyone who could see the sun at the appointed time, also could
see the transit.

------
SpikeDad
Is there a remedial school for headline writers? Naturally it missed the Earth
or we wouldn't be here. Perhaps the headline writer meant - "Billion-Ton
commet MISSED Earth by perhaps a few hundred kilometers in 1883".

To quote George Carlin - "It's not a near miss. A collision is a near miss.
It's a near HIT!"

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TimJRobinson
I'm confused as to why this is coming up now, did they find some new evidence
or residual rock from this comet? If not how do they now know that it was
actually a comet and not simply a mistake on the astronomers part as they
previously thought it was?

~~~
lutusp
> ... how do they now know that it was actually a comet and not simply a
> mistake on the astronomers part as they previously thought it was?

They don't. The linked article assumes the veracity of the original account,
it doesn't introduce anything new.

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polarcuke
Well if this is true I guess there is one more thing for us to be thankful for
today!

~~~
Geee
It doesn't matter because we wouldn't be here thinking about it. On the other
hand, the extinction event would have been a gold mine for the future
archaeologists that would have evolved on Earth in the next 100 million years.

~~~
monochromatic
You're right, let's NOT be thankful that we're still here.

~~~
Geee
What do you mean? You can't be subjectively thankful of something that you
wouldn't otherwise exist to be the subject of. However, I'm thankful that
everyone else is here, including you.

~~~
monochromatic
> You can't be subjectively thankful of something that you wouldn't otherwise
> exist to be the subject of.

Sure you can. You couldn't be disappointed if things had gone the other way,
but you can certainly be thankful to have dodged a bullet.

------
VMG
Anthropic principle? If it had hit we wouldn't be talking about it.

