m or km?
"Don't be fooled by those big egg-shaped pics: the real comet is the little eight-bit smudge at the top and what you're seeing is probably about 450kms across."
Er, I think you mean 450m across?
The first images of Comet Siding Spring, a celestial body deemed so menacing that humanity cocooned its very best robots, has turned out to be rather smaller than imagined. The first images of the comet, captured by the High Resolution Imaging Science Experiment (HiRISE) camera aboard NASA's Mars Reconnaissance Orbiter, …
A 450m diameter comet nucleus is not even close to being large enough to be an extinction level event.
It could cause local devastation and some global cooling (due to dust) but it is too small to cause major global damage. If (for example) such an object hit in the middle of the UK there would be little damage (if any) to more distant parts of the EU (e.g. Italy and Spain) let alone to the rest of the world.
This comet masses less than 1/1000 of the dinosaur killer asteroid and therefore has less than 1/1000 of the energy release on impact.
Assuming it is an aerated slush puppy, as the theory goes, how much would actually make it through the atmosphere to land fall or the more likely sea splash? A more tangential approach would likely not have too much effect 100km or more from the descent path and impact point.
"It could cause local devastation and some global cooling (due to dust) but it is too small to cause major global damage. If (for example) such an object hit in the middle of the UK there would be little damage (if any) to more distant parts of the EU (e.g. Italy and Spain) let alone to the rest of the world."
What if it hits in the sea? That wet stuff that covers 3/4 of the earths surface. That'd be some pretty big waves. I'd not like to be too close to beach on that day although I'm sure some daft bugger would try to surf it.
The point is that even compared with actual earthly mountain, that is at best a hill. It is not even a Munro. Everest for e.g. is roughly 7km above sea level and very, very much denser than a dirty snowball. In Mars terms Everest is a tiddler. Olympus Mons is so tall it nudges the edge of space. If it were on Earth you would not just need some oxygen bottles, but a pressure suit to climb it.
So, molehill is thus entirely appropriate especially in the context of the aphorism it very obviously references. Do you need it spelling out?
In the same way that shooting down your neighbour's quadcopter toy with a rifle is a bad bet compared to a shotgun, even one loaded with buckshot. Only one of the low velocity pellets needs to hit a rotor or a wire or a piece of electronics.
It's also how the missile that took down the Malaysian Airlines jet over Ukraine works. Instead of directly hitting the aircraft it has a proximity fuse and explodes nearby peppering it with shrapnel. A more advances form of old style flak that used best guess altitude fuses.
"Was it the NASA spokesman or the observers who thought that one kilometer was about half a mile? It seems a rather inaccurate approximation."
The estimate of the comet's nuclear diameter is also rather inaccurate. A kilometer by one guess, a half-mile by another, both are within the error bar and convey some idea of the comet's size to Euro-metric types and metric-challenged 'Muricans alike.
If you still work in miles then you should know half a mile is 880 yards. Using the rule of thumb estimate of 100m being 110 yds, half a mile is 800m*. Shirley even 'Merkins can grock that one but probably not if they find decimal point confusing.
* 804.672m for the pedants