Mars Astronauts Likely to Witness 1 Megaton Asteroid Impacts | Hacker News Reader

Mars Astronauts Likely to Witness 1 Megaton Asteroid Impacts

technologyreview.com

30 pointsLibertatea22 comments

Their model suggests that Tunguska-type events of around 10 megatons should occur roughly once a century and smaller 1 megaton events once every 15 years.

If the rate is 1/15 years on Earth, why haven't I witnessed any yet? I suspect the answer is that Earth is rather large. Mars may not be quite as big, but it's still quite implausible that our Mars visitors should happen to be at just the wrong place at the wrong time, even with a 5-times increase in risk.

It seems like if a 1 megaton impact were occurring on Earth every 15 years people would have noticed more than seems to be the case. You would expect more than one such event per century to occur on land and I think the vast majority of the Earth's land is populated, at least sparsely.

Also for the past 50 years or so governments have been very interested in tracking large explosions so even such events occurring over water should have been detected and, I would think, mentioned in the media.

Yes. This doesn't pass the smell test. I first suspected the article produces a garbled version of the research, but the abstract says the same too:

http://arxiv.org/abs/1212.3273

" In particular, for energies of one megaton or larger we find near one impact every three years for Mars, an interesting and concerning result for future Mars explorations. The corresponding calculations for our planet give a probability of one impact per 15 years"

Doesn't pass my smell test either. I suspect perhaps there are some jiggered parameters in the model.

Perhaps the "1 megaton" nomer is for what encounters our atmosphere, not necessarily what impacts our surface.

That might be the case, but then it's not really something to be worried about, is it? I mean, then they're basically saying that astronauts on Mars will see shooting stars a bit more often than on Earth.

It is, because on Mars there isn't an atmosphere there to burn up that 1 megaton asteroid into something more innocuous.

Just to be clear, Mars does have an atmosphere. It's pretty thin, but it's real enough to provide protection against micrometeorites and some of the radiation.

It ain't gonna stop a school-bus sized meteorite, though.

It is now, and communication travels quickly now, but what about in the past?

Hell, we've had one in the past century (almost) - the aforementioned Tunguska event. And nobody got around to investigating it for two decades.

Today it would be big news. Last century, it was a mystery. If one had landed in the middle of Africa in 1700, would the Western world even hear about it?

If they're taking an average over the Earth's entire history, and the actual distribution of impacts over time is not uniform (as seems likely), that might explain the discrepancy. Though in that case it seems odd that they would use that average to predict a probability going forward.

When they say one megaton, do they mean total energy released during entry or something? There's no way we're having the equivalent of a one megaton nuke (minus the fallout) on the surface every fifteen years ...

Or are we just in a dry patch?

Edit: The actual paper says 'impact' so I don't know what to think here.

>Here’s the interesting part: these guys calcaulte that Mars experiences a 1 megaton event every three years.

We've had orbiting satellites around Mars for over a decade. Wouldn't they be capable of seeing such an impact?

We've had launch and nuclear explosion detection satellites around the Earth for decades and we haven't detected anything like 1 megaton impact event every 15 years.

What does this actually mean? Obviously it is pretty obvious if it lands on top of you, but if there is a 1 megaton impact of a meteorite landing 10 miles away what are the consequences? Given the lower gravity and atmospheric pressure would you be basically sand blasted with remnants?

Using some online calculators for the effects of nuclear weapons, I suspect the answer would be that you'd be reasonably safe at 16km:

http://www.alternatewars.com/BBOW/ABC_Weapons/Nuke_Effects_C...

http://meyerweb.com/eric/tools/gmap/hydesim.html

I don't know if a meteor impact would produce the same prompt radiation as a H-bomb, but the much less dense Martian atmosphere might negate that.

Most of the ionizing radiation from an H bomb is produced by nuclear fusion or from fission from the trigger and decay products. An asteroid impact wouldn't produce any of that. The only ionizing radiation it might produce are some x-rays from the fireball plasma (but I'm not sure the plasma would even be hot enough for that).

The blast and thermal effects would presumably be comparable, however, so at 16 km you'd definitely notice (and might be in a very uncomfortable situation).

Nevertheless, these kind of predictions require further study.

There's the money quote. Quite literally.

There are all sorts of people who see the path to Mars littered with bags of money and are quite happy to insert themselves into the path.

First sentence: "Asteroid impacts are among the most feared of natural catastrophes."

Maybe I'm being picky, but I don't think that this is actually true.

The word "among" makes it a pretty subjective thing.

Ok so what is that in Hiroshimas?

According to 10 seconds googling, little boy and fat man were both somewhere around 20 KILOtons.

About 50X.

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