Earth escapes obliteration by comet

Fight fire with fire

NASA have to speak to these people on their terms:

"Stupid Internet rumour is stupid"

Then it might sink in.

It became a sensation because somebody started the ball rolling and NASA issued a denial. As far as conspiracy theorists are concerned, if somebody connected with the government denies something then that means it must be a cover up. Had NASA simply ignored the idiot rumours they would have fizzled out after a couple of days.

Standard units please

I believe the correct unit for things of that size is the Wales rather than the bus. Could somone please correct this figure?

correct

but many smaller objects have mugh greater surface area and thus experience much greater drag. More of the energy will be dissapated in the atmosphere. Which if I had to choose I would rather it be. that or a large sparcly populated desert area. or Las Vegas.. that would be fine too.

Thinking...

What is your bullet-proof vest (atmosphere) is more likely to stop - a big bullet or a bunch of shotgun pellets?

"Remember, kiddies, F=MA ... It doesn't matter how many chunks you cut it into, the mass and vector remains the same. If it hits the Earth, the total energy transfer will also be the same. Think about it."

While true, the increased surface area means much more will burn up in the atmosphere.

Except you forgot the relationship between surface area, mass and how things burn up in the atmosphere.

yeah, but....

if it were lots of smaller pieces, they would stand a better chance of burning up on entry. Also, the 'total energy transfer' would be spread out over a much larger area (unless it was cut into chunks that didn't drift apart, at all) instead of all of it hitting in exactly the same place.

I did think about it. The atmosphere means that a single large chunk with a mass of, for example, 100 tonnes, stands a much greater chance of reaching the ground with some intact mass than any one of 100 chunks each weighing 1 tonne do.

re:One big bullet, or a shotgun blast?

Indeed, the total energy transfer will be approximately the same. However because the chunks have a much larger total surface area, they will experience far more drag in the upper atmosphere and because they have a much smaller volume each compared to their surface area, will experience more severe and deeper heating.

So while the planet will receive the same amount of energy total, most of that energy will be wasted into the upper atmosphere as the chunks burn up instead of falling to the ground and killing people.

1 big rock == 1 big crater, lots of dust, dead people, etc.

hundreds of small rocks == Most burn up on entry, those that don't burn up completely leave a few small craters scattered across the landscape. Some people might get unlucky and get hurt in the process.

Errr....

It missed already!

RE: One big bullet, or a shotgun blast

OTOH the surface area increases, and with it friction, which means that there is a high chance that if it enters the atmosphere it will burn up easier.

Thought about it.

The total surface area of the mass will vastly increase after a breakup which will affect any heat transfer and melt the ice ball far more quickly.

Bits bouncing off each other due to outgassing may deflect some of them off their normal path.

Of the bits that don't melt, the variously sized/massed bits will be affected differently by air resistance in the outer atmosphere, slowing each at a different rate. This will spread the total mass out over a longer trail which will impact the lower atmosphere over a longer period of time resulting in a lower total rate of energy transfer.

> It doesn't matter how many chunks you cut it into, the mass and vector remains the same.

But the surface area increases dramatically.

> If it hits the Earth, the total energy transfer will also be the same.

Only if it all hits the Earth.

Because of the increased surface area, far more of an inbound object would burn up in the atmosphere. The energy will be dissipated as light and heat, rather than transferred into the planet.

So although you are right in that the total amount of energy entering the atmosphere will be the same, you are wrong in thinking that the same amount of energy will transfer to the Earth.

Vic.

Unless, of course...

...only PART of the cloud of bits hits the earth while the other part skims on by, instead of the whole mass hitting in central impact...

...or the moon happens to be in position to block part of the debris cloud (Sure, it's unllkely -- but so is a comet colliding with the Earth!)...

...or if the smaller bits have time to vaporize in atmosphere before impact...

...or... or... or...

Take a handful of rocks...

...and pack them into a snowball. This is your average comet.

The tail of a comet is mainly snow and water vapor that is boiled off as your dirty snowball passes near the sun. When the comet leaves the inner solar system and heads back into the up-and-out, it re-freezes.

Eventually two things can happen -- either there is not enough snow and ice left to hold everything together as it passes the sun and things start scattering due to light pressure and gravitational perturbations, or a particularly large and juicy pocket of ice in the center of the mass boils off more quickly than the resulting vapor can escape and blows the thing apart.

NB: IANAA, but the above is my understanding of the processes.