[X] My Assistant

[scalbers]

Seriously tho, when will we have a better idea of what's actually going to happen? Will it literally be on the day? If so, that'll be a "don't stray too far from the computer" day, won't it?

It might become easier to observe as the bright moon gets out of the way...

[dburt]

...The two artistic views could be regarded as the same scenario - mine would be the initial impact (I was actually aiming at that) throwing ejecta up and Stu's would be the aftermath several minutes later when ejecta has settled down and the dusty "fireball" rose up and cooled down...

Agreed, and agree that, in principle, the mushroom cloud might be reduced by the relative thinness of the atmosphere and weakness of the fireball. Of course, what interests me is the ground-hugging, ground-scouring, dust storm-like impact surge cloud and the distance of its effects would be felt from the impact site - probably at least 10 crater diameters (judging from recent imagery), implying that Oppy wouldn't want to be there.

-- HDP Don

[karolp]

I guess even if it missed, that would still be a great opportunity for the orbiters - they will be within thousands of kilometers from the asteroid - any guesses on imaging it from orbit just like other asteroid-imaging spacecraft did?

[JRehling]

Well, if the time of the asteroid breaking the plane is fairly well known, then the possible impact points could be narrowed down to one hemisphere (probably longitudinally constrained, if the asteroid is near the ecliptic). And if the expected trajectory is to one side of Mars, then an impact would be more likely on that half of Mars than the other half. (Eg, if it is expected to pass north of Mars's north pole, then an impact in the northern hemisphere of Mars would be more likely than an impact in the southern hemisphere.) But I would expect the latter constraint to be very loose until it is determined if the asteroid hits at all. So maybe there would be a 55% probability for the one hemisphere vs. the other. But as the time draws closer, that would presumably collapse to 100%-0% (assuming there is a hit at all).

[PDP8E]

The Near Earth Object Program at

http://neo.jpl.nasa.gov/news/

has/will have the latest news....

here is an animated gif I lifted off their website:



The animation shows the motion of the uncertainty region of 2007 WD5 as it approaches Mars.
The thin white line is the orbit of Mars.
The vertical fuzzy line is the current uncertainty region of the asteroid
The blue line traces the motion of the center of the uncertainty region, which is the most likely position of the asteroid.

cheers

[ugordan]

here is an animated gif I lifted off their website:

That's apparently an old animation, already posted in post #32 of this thread and does not take into account the 3 "precovery" observations which reduced the projected miss distance to the current 21 000 km. I'm most interested in seeing how that translates to the uncertainty ellipse.

[Stu]

If I'm reading Emily's latest blog entry correctly, the odds of an impact have now possibly shrunk to 1 in 25...?

[nprev]

"Possibly" is the keyword here, Stu; they may have also increased to 1 in 300 based on 'precovery' observations. Looks like we're still awhile from dialing in on a good range of odds, although personally I doubt they'll ever drop below 1 in 50 (if we're lucky.)

Since I have a spectacular record of guessing wrong...please please please let me be wrong here!!!

[SteveM]

If I'm reading Emily's latest blog entry correctly, the odds of an impact have now possibly shrunk to 1 in 25...?

Emily quotes the Minor Planet Mailing List which is here.

The latest post there from Aldo Vitagliano explains the discrepancy between the two results Emily reported:

The reason for the discrepancy between these results and those I gave in my previous post is that (perhaps arbitrarily) I discarded the following two observations having residuals substantially larger than the average, while JPL did not.
2007 12 04.22377
2007 12 05.2261
If I include the above observations in my MonteCarlo runs, I get nearly the same results as JPL.

I am not expert in probability and statistics, but I would say that a probability estimate which is so crucially dependent on two
observations lying among others in the middle of the observational arc is in itself very uncertain. In other words, it seems to me that even the error estimate is affected by a large error ... :-)

Regards
Aldo Vitagliano

It sounds like it's still very much a gamble, with the current odds 1/25, and we won't know more until the astronomers get some more observations.

Steve M

[SteveM]

JPL has now published the new odds on Mars impact.

The impact probability for a collision of asteroid 2007 WD5 with Mars on January 30 has increased from 1.3% to 3.9%.

Pre-discovery observations of asteroid 2007 WD5, taken on November 8, 2007 have allowed its orbit to be refined and the uncertainties for the late January Mars encounter have been improved. The impact probability resulting from the recent orbit refinement has increased to a surprising 3.9% (about 1 in 25 odds). The uncertainty region during the Mars encounter now extends over 400,000 km along a very narrow ellipsoid that is only 600 km wide. Since the uncertainty region intersects Mars itself, a Mars impact is still possible. However, the most likely scenario is that additional observations of the asteroid will allow the uncertainty region to shrink so that a Mars impact is ruled out. In the unlikely event of an impact, the time would be 2008 January 30 at 10:56 UT (2:56 a.m. PST) with an uncertainty of a few minutes.

The new image shows that the most probable path passes on the other side of Mars (compared to the earlier prediction).



Steve M

This post has been edited by SteveM: Dec 28 2007, 09:18 PM

[Shaka]

I hope the MER are old enough to remember how to "duck and cover".

[ugordan]

I don't think you have to worry about that just yet.

I have a feeling we're all lining up for a big disappointment here. Suppose the impact odds come up to 1/10 and then be completely ruled out. Talk about an anticlimax...

Still, Shaka's observation raises an interesting question: how many (if any) of you would be willing to sacrifice (or, rather, consciously put at risk of destruction) one of the rovers in exchange for being able to witness an event this rare (and not necessarily witness it by the rover itself)?

[Stu]

how many (if any) of you would be willing to sacrifice (or, rather, consciously put at risk of destruction) one of the rovers in exchange for being able to witness an event this rare (and not necessarily witness it by the rover itself)?

Not me, no way. Even if an impact was absolutely guaranteed there's no guarantee that the asteroid would make a "useful" crater; it might not show us anything dramatically new. The rovers could die tomorrow, yes, but there might still be another good couple of years left in these most amazing of resources yet, so it would be foolish to put one at them of risk of destruction for anything less than a potentially paradigm-shifting discovery - trying to reach a "green patch" half-way down a dangerously steep slope, or attempting to investigate a strange flickering glint of what might just possibly be ice on the underside of a big boulder that could only be reached by crossing a veritable minefield of jagged, dangerous rocks...

An impact would be cool, definitely, and I'm hoping we all get to see one, but if we don't then I won't lose any sleep over it; the best we could hope for from one of the rovers far enough outside the impact zone to have a good chance of surviving the event would be a shuddery image or two of a dust cloud above the horizon. WHatever happens, happens.

[ugordan]

Even if an impact was absolutely guaranteed there's no guarantee that the asteroid would make a "useful" crater; it might not show us anything dramatically new.

I was thinking the same thing, actually. To me the most exciting prospects would be actually recording the moment of impact (chances of which are second to none - both from Mars/Earth ground or orbital assets; this would not be SL9 by far) and maybe detecting various volatiles (MEX PFS?) released to the atmosphere by the excavation event. The crater itself would end up being at a remote location and all we'd get would be CRISM mineralogy and HiRISE imagery. How different than Victoria can a crater without dust and erosion look anyway?
The question is if a known (big) impact would add significant knowledge to what we already know about Mars. It might actually do more to raise the awareness about NEOs here on Earth and the importance of detecting them on time.

[Juramike]

Even if an impact was absolutely guaranteed there's no guarantee that the asteroid would make a "useful" crater; it might not show us anything dramatically new.

I totally beg to differ.

We'd learn volumes about how dust clouds disperse and affect the atmospheric layers during impact events. Sure, we've got theoretical models, but backing them up with observations would be really useful. Heck, even watching the dust cloud drift around would give us even more information about meteorology and local wind fields on Mars.

(I agree strongly with ugordan. Showing (eventually) a new crater on Mars would drive home the "This could be you" message.)