15 Apr 15
Originally posted by googlefudgeYou're quite right. Sorry for my undeliberate desinformation. I pulled it out of my memory and got it wrong somewhere in the process.
Yes. we will survive.
Because there are currently no stars likely or able to go supernova close enough
to us to do us harm.
Betelgeuse is much to far away to be a threat.
It's likely peak brightness would be comparable to the full moon, and the gas/dust
produced would be so tenuous by the time it reached us that it would pose no threat.
T ...[text shortened]... a needs to be within ~50 light years of us [with
some caveats].
Betelgeuse is ~600 ly away.
Did I mistake Betelgeuze from another red giant in the neighborhood? On which is a radiative threat to us? Or have I read too many ScFi novels? I think Hoyle once wrote a story with this scenario, but I cannot remember which.
Again, sorry...
16 Apr 15
Originally posted by FabianFnasWe are in fact safe from any supernova, the nearest one that could possibly blow is Spika, about 260 light years from Earth and that is too far to effect Earth even if it did blow.
You're quite right. Sorry for my undeliberate desinformation. I pulled it out of my memory and got it wrong somewhere in the process.
Did I mistake Betelgeuze from another red giant in the neighborhood? On which is a radiative threat to us? Or have I read too many ScFi novels? I think Hoyle once wrote a story with this scenario, but I cannot remember which.
Again, sorry...
16 Apr 15
3 edits
Originally posted by FabianFnas"undeliberate disinformation" is a contradiction. I think the word you were looking for is "misinformation".
... undeliberate desinformation...
I pulled it out of my memory and got it wrong somewhere in the process.
Personally I would have said that as just;
“I misremembered”
It is a phrase I used before. I have also used the phrase;
"I misimaginated"
when I imagined something somehow incorrectly or erroneously. But, for some reason, the word "misimaginated" isn't officially recognized; but I use it anyway.
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16 Apr 15
Originally posted by sonhouseNot strictly true.
We are in fact safe from any supernova, the nearest one that could possibly blow is Spika, about 260 light years from Earth and that is too far to effect Earth even if it did blow.
First the closest possible known object that might go nova is
[according to wiki 😉 ]
http://en.wikipedia.org/wiki/IK_Pegasi
At ~150 ly... although it's forecast to be [much] farther way if/when it actually blows.
However while a supernova closer than 50ly [possibly needing to be less than 10 ly] is highly unlikely
and we have no current candidates for such an object, a gamma ray burster that has one of it's beams
pointed at us could wipe us out from WAY farther out.
Such objects emit silly huge amounts of energy, even in supernova terms, and concentrate the
energy in a narrow beam, massively increasing the range at which it can cause significant harm.
However the odds of such an event occurring in the lifetime of any civilisation on Earth are even smaller.
It's certainly not something I lose sleep over 🙂
Odds are now fairly good that any actually civilisation-threatening sized asteroid [as opposed to merely
city destroying] would be detected in time for us to divert it, and we can improve on that, and pick up
smaller but still dangerous ones as well.
What we cannot currently do anything about [but is really unlikely] is a "first time into the solar system,
never seen before, civilisation/biosphere-killer sized, comet" on a "strait-into-the-Earth" trajectory.
6~18 months warning is not enough to either evacuate or deflect/destroy such an object.
16 Apr 15
Originally posted by googlefudgeEven at 150 ly it won't pose a problem for the Solar System, like they say, it has to be within 50 ly to cause damage. But the idea of a jet aimed our way, we have statistics in our favor since the jet would cover, say 10 square degrees and there are 360^2 degrees, the jet, even if it happened would have less than one percent chance of being aimed right at Earth.
Not strictly true.
First the closest possible known object that might go nova is [hidden] [according to wiki 😉 ] [/hidden]
http://en.wikipedia.org/wiki/IK_Pegasi
At ~150 ly... although it's forecast to be [much] farther way if/when it actually blows.
However while a supernova closer than 50ly [possibly needing to be less than 10 ly] is highly ...[text shortened]... tory.
6~18 months warning is not enough to either evacuate or deflect/destroy such an object.
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17 Apr 15
Originally posted by sonhouseNot all supernova produce them... [jets that is] Gamma Ray Burster's are special.
Even at 150 ly it won't pose a problem for the Solar System, like they say, it has to be within 50 ly to cause damage. But the idea of a jet aimed our way, we have statistics in our favor since the jet would cover, say 10 square degrees and there are 360^2 degrees, the jet, even if it happened would have less than one percent chance of being aimed right at Earth.
On the subject of supernovae... I love this xkcd "what if" post...
https://what-if.xkcd.com/73/
Lethal Neutrinos
How close would you have to be to a supernova to get a lethal dose of neutrino radiation?
........ SNIP ......
The physicist who mentioned this problem to me told me his rule of thumb for estimating supernova-related numbers:
However big you think supernovae are, they're bigger than that.
Here's a question to give you a sense of scale:
Which of the following would be brighter, in terms of the amount of energy delivered to your retina:
A supernova, seen from as far away as the Sun is from the Earth,
or
The detonation of a hydrogen bomb pressed against your eyeball?
Applying the physicist rule of thumb suggests that the supernova is brighter. And indeed, it is ...
by nine [freaking] orders of magnitude. .....
Emphasis [and freaking] added by me.
And gamma ray burster's make supernovae look small scale....
17 Apr 15
Originally posted by googlefudgeDo you have any actual stats on that? As I stated earlier, one source puts city destroying sized asteroids at 99% undetected. Is there an estimate for civilization destroying asteroids?
Odds are now fairly good that any actually civilisation-threatening sized asteroid [as opposed to merely city destroying] would be detected in time for us to divert it, and we can improve on that, and pick up smaller but still dangerous ones as well.
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17 Apr 15
Originally posted by twhiteheadWell it's a function of scale.
Do you have any actual stats on that? As I stated earlier, one source puts city destroying sized asteroids at 99% undetected. Is there an estimate for civilization destroying asteroids?
A merely city destroying asteroid need only be ~100 meters across.
A civilisation destroying asteroid needs to be kilometres [plural] across.
There are vastly fewer kilometre+ wide asteroids, and they are much easier to see.
Brightness going up with the square of size.
We therefore know where most of the Earth crossing asteroids of that size are.
The link is broken, but wiki lists the detection of 1km+ sized near Earth asteroids
at >90% as of 2008.
The danger lies with asteroids in the 140m~1km size range, which could could cause
major damage, even if they are not civilisation or life ending.
20 Apr 15
Originally posted by googlefudgeThe worse case scenario is a few hundred years from now, a terrorist Jihad group gets into space and covers one up with RF absorbing rubber and sends the thing deliberately to off NYC or London....
Well it's a function of scale.
A merely city destroying asteroid need only be ~100 meters across.
A civilisation destroying asteroid needs to be kilometres [plural] across.
There are vastly fewer kilometre+ wide asteroids, and they are much easier to see.
Brightness going up with the square of size.
We therefore know where most of the Earth ...[text shortened]... range, which could could cause
major damage, even if they are not civilisation or life ending.
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21 Apr 15
Originally posted by wolfgang59Because we generally find and track asteroids with visible or IR telescopes,
Why isn't the government doing something about this? 😠
and black RF absorbing runner isn't going to do anything but make it brighter
in IR.
Also, if the propulsion used to deflect this asteroid has any great power to deflect it
quickly it will stand out like a sore thumb. If it's low power and moves it slowly then
it will be a long time before it hits.
Couple this with several hundred years of technological progress into a future in which
a bunch of terrorists [a typically highly incompetent breed] manage to SECRETLY get
hold of interplanetary space travel capability and this will be spotted by the asteroid
space guard system and it will be re-deflected back.
This is assuming of course that the terrorist spacecraft isn't just tracked to the asteroid
in the first place, which would be fairly trivially easy with even today's technology and
someone sent to find out who was doing unauthorised asteroid mining.
No if 'terrorists' want to achieve global devastation their best bet is a relativity bomb.
Send a probe out to a star several solar systems over.
Built a huge and very powerful rocket to accelerate 40,000 tons of matter up to ~35% C
Accelerate said rocket up to 35% C on a course to hit the Earth.
Do so slowly enough that the rocket exhaust signature is lost in the glare of the star.
Relativity bomb arrives in solar system travelling 35% C and isn't detected with enough time
to respond.
R-Bomb hits the Earth with ~58,007 GT TNT
Or roughly the energy of a 6 mile wide rocky asteroid impacting at 17km/s [roughly speaking the
same size as the asteroid thought to have wiped out the non-avian dinosaurs]
http://impact.ese.ic.ac.uk/cgi-bin/crater.[WORD TOO LONG]
Of course we are imagining here a bunch of terrorists with the resources and technical knowledge
of a large and very advanced national space program, which they somehow operate in complete
secret.