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Forum » SpaceEngine » Science and Astronomy Discussions » Comets thread (Anything and everything to do with comets)
Comets thread
anonymousgamerDate: Monday, 25.02.2013, 01:48 | Message # 31
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Strange, I live in an area with a decent amount of light pollution and can see hundreds of stars...




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HarbingerDawnDate: Monday, 25.02.2013, 02:42 | Message # 32
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Quote (anonymousgamer)
Strange, I live in an area with a decent amount of light pollution and can see hundreds of stars...

You must never have lived anywhere with a large amount of light pollution. In or very near a large city, you'll be lucky if you can see even 10 stars.





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WatsisnameDate: Saturday, 02.03.2013, 05:12 | Message # 33
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I did not think this was real at first, until i saw Phil Plait's post about it:

A comet will come very close to Mars next year, possibly even impacting it

The orbit of the comet is predicted to bring it within 50,000 kilometers of Mars in October 2014. Considering the small uncertainty in the orbit, as well as outgassing which can slightly shift a comet's orbit over time, there is a (very) small chance it could actually impact Mars. That would be an event the likes of which we can scarcely even imagine!

Far more likely and just as interesting, Mars may pass through the much larger coma of the comet. It's not entirely clear what the results of this would be -- perhaps the moons will be pelted by small debris, and the Martian skies may erupt in an absolutely epic meteor shower. Hopefully our craft on and around Mars will get quite a show.





 
HarbingerDawnDate: Saturday, 02.03.2013, 05:54 | Message # 34
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I did not think this was real at first

That was my first reaction as well when it was posted on the Russian forum smile

Should be a spectacular sight, hopefully Curiosity/MRO get nice images!





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midtskogenDate: Saturday, 02.03.2013, 07:13 | Message # 35
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The Vatican gets hit a lightning, Russia hit by an asteroid, another one barely misses and a big comet is bound for Mars - is someone trying to express his opinion on the pope's resignation? tongue

Let's check again in a year or so for where this comet is heading. There could be a nice meteor shower if the nucleus passes close, but I think the satellites in orbit will be safe. The stuff surrounding comets is very sparse.

In 1910 the Earth passed through the tail of Halley's comet. There was a lot of public attention. People bought gas mask to protect themselves from the poisonous gases, etc. I don't think there was any meteor shower due to it. The distance then to the nucelus was more than 0.1 AU, though.

I remember Halley's comet in 1986. It was an absolutely non-impressive sight. You needed a telescope to see it well, and a fuzzy dot was all there was to see.





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WatsisnameDate: Saturday, 02.03.2013, 09:03 | Message # 36
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Quote (midtskogen)
There could be a nice meteor shower if the nucleus passes close, but I think the satellites in orbit will be safe. The stuff surrounding comets is very sparse.


I imagine you're right. It warrants some study and I'm curious to see if anyone does research on the subject, but I doubt the density of material in the coma would be great enough to be of concern to the spacecraft. On the other hand, at 55km/s it would only take a single mm to cm sized piece to cause catastrophic failure.

Jeez, and now I just remembered the potential debris hazard that plagues the New Horizons mission. What is it with random space debris as of late?! wacko







Edited by Watsisname - Saturday, 02.03.2013, 09:03
 
midtskogenDate: Saturday, 02.03.2013, 09:59 | Message # 37
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Quote (Watsisname)
I imagine you're right. It warrants some study and I'm curious to see if anyone does research on the subject, but I doubt the density of material in the coma would be great enough to be of concern to the spacecraft. On the other hand, at 55km/s it would only take a single mm to cm sized piece to cause catastrophic failure.

Yes, it's a risk. How realistic it is will depend on the distance, behaviour of the comet and the angle of the tail.

If it impacts, it would be really interesting to get seismic recordings from the surface, but there are no such instruments there that I know of.





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HarbingerDawnDate: Saturday, 02.03.2013, 10:40 | Message # 38
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If it impacts, it would be really interesting to get seismic recordings from the surface, but there are no such instruments there that I know of.

Not presently, though I think that one of the next missions to Mars will have a seismometer, but I don't think that will be there by 2014. However, an impact of an object that size could cause enough of a shock that Curiosity's accelerometers could measure it.

On the subject of the coma/tail, spacecraft have flown though the tails and comas of comets before without ill effect, so it can be done. Most of the meteoroids deposited by comets exist in a very narrow path along the comet's orbit.





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MartekDate: Saturday, 02.03.2013, 11:18 | Message # 39
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http://www.slate.com/blogs....14.html

Basically, if this happens, its going to be huge. Did they say 30 Miles in diameter? That would tear the Red Planet up, might even knock it off its orbit causing Earth to go off orbit too!

Thoughts?





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HarbingerDawnDate: Saturday, 02.03.2013, 12:16 | Message # 40
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Martek, this has already been posted about here. Additionally, this topic would have better been posted in this thread, a thread that you created. Making a new thread was unnecessary. Remember the forum rules when posting.

Quote (Martek)
That would tear the Red Planet up

Not really.

Quote (Martek)
might even knock it off its orbit

No.

Quote (Martek)
causing Earth to go off orbit too!

...wut?

Quote (Martek)
Thoughts?

Pull out a pencil and paper and apply a little high school physics to the problem. You'll find that the orbit of Mars would not be affected by the impact. Additional research would reveal that Mars has been hit my many such objects in the past, and it is still quite intact.

Protip: critically examine claims before you make them and/or absorb them from others.





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midtskogenDate: Saturday, 02.03.2013, 13:14 | Message # 41
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Not presently, though I think that one of the next missions to Mars will have a seismometer, but I don't think that will be there by 2014. However, an impact of an object that size could cause enough of a shock that Curiosity's accelerometers could measure it.

A big seismic event could tell a lot about Mars' interior, but I wonder if this event would be too big to make sense of it, since we would have nothing to compare it with. It would measure about 13 on the Richter scale, more that the "dinosaur" asteroid. No matter where you would be on the planet, the ground would begin to move a few meters no later than about 20 minutes after the impact. Perhaps the movement would be too slow for accelerometers to detect it, but the blast wave should travel a few times around the planet during the first day and give a decent punch at least the first time. But the shockwave wouldn't say anything about the interior.





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Edited by midtskogen - Saturday, 02.03.2013, 13:24
 
HarbingerDawnDate: Saturday, 02.03.2013, 13:23 | Message # 42
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Quote (midtskogen)
the blast wave should travel a few times around the planet during the first day and give a decent punch at least the first time.

Keep in mind that the air on Mars is so thin that it probably could not effectively carry a blast wave with much force over a large distance, so the main global effects would be limited to seismic activity and ejecta. And if the ground really did move a few meters it would probably be measurable by the vehicles on the ground.





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midtskogenDate: Saturday, 02.03.2013, 13:25 | Message # 43
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Keep in mind that the air on Mars is so thin that it probably could not effectively carry a blast wave with much force over a large distance

The Chelyabinsk meteor exploded 20 km above the ground or higher. There's not much pressure there. Yet the shockwave was clearly detected as far away as Antarctica.





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HarbingerDawnDate: Saturday, 02.03.2013, 13:42 | Message # 44
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The Chelyabinsk meteor exploded 20 km above the ground or higher. There's not much pressure there.

But there was thicker air below that through which the shockwave propagated. The propagation might have been different had that not been the case. It's also possible that it could have exploded as low as 15 km above the ground.





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midtskogenDate: Saturday, 02.03.2013, 14:24 | Message # 45
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And if the ground really did move a few meters it would probably be measurable by the vehicles on the ground.

A few meters is a rough estimate. But the movement would be very slow. It wouldn't be like in an elevator. You would need a pretty accurate accelerometer to detect it.

I have a Lehman type seismometer, a setup emulating a pendulum almost 100 meters long. I usually check the readings of my seismometer in the morning when I eat breakfast, and this was the case when the M9 quake struck Japan. It was 7000 km away, so the waves first rolled in here about 15 minutes after. When I saw the readings I checked the USGS site which then reported 7.8 or something like that. "No way", I thought, because my readings were totally off the scale. I had to watch this through. Then, as the surface wave rolled in, I began wondering if I physically could see the shaking 7000 km away. So I went to the seismometer in the basement, approached it on the floor as slowly as I could in order not to disturb it, and watched the pendulum for several minutes. It was indeed moving. Slowly moving in one direction for some time, 10-20 seconds, perhaps, stopped, continued to move, reversed, etc, moving somewhat irregularly, a couple of movements per minute. It was just a few millimeters. But it was quite interesting to see first hand that the ground was moving even 7000 km away. The amplitude was less than a centimeter, at a speed of perhaps a centimeter per minute, but the ground was indeed moving.

Back to Mars before I digress to much. So if a M9 event causes the ground to move a few millimeters 7000 km away, how much movement to expect from a M13 event? One magnitude higher means that the amplitude of the shaking increases by a factor of 10. 10^(13-9) = 10,000. So at a distance of 7000 km, should we expect ground movement up to 50 meters or so? Perhaps the math breaks down a bit on this scale, but measuring the movement in meters sounds right. If this was Earth, I don't think the movement would knock down people, the waves could be a few 100 km from peak to peak, perhaps people wouldn't even see it directly. Within less than one hour of the impact (within half an hour on Mars), no place would escape. It would surely trigger worldwide tsunamis, even in lakes, avalanches, earthquakes, groundwater to surface everywhere, perhaps violently. On Mars, if liquid water exists beneath the surface, it might start pushing its way to the surface. Then the shockwave, then debris, then dust. All on a global scale.

Olympus Mons is 22 km high. This comet might well be even larger...

Quote (HarbingerDawn)
But there was thicker air below that through which the shockwave propagated. The propagation might have been different had that not been the case. It's also possible that it could have exploded as low as 15 km above the ground.

It should be added that it was a pretty stretched explosion. Anyway, I think what exactly would happen on Mars will be subject to much guessing until it really happens.





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Edited by midtskogen - Saturday, 02.03.2013, 14:27
 
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