Mars Asteroid Impact More Likely Than Before

sheldie writes "The probability of asteroid 2007 WD5 impacting Mars has been revised following further observations. The chance of impact has increased from 1.3% to 3.9%" This is a follow-up to earlier coverage of this asteroid from last week.

Re:Versus Jupiter

[plover]

Measurement inaccuracies in the observations of its current trajectory. It's not like we can hold a tape measure up to it and figure out its precise position, or put it on a scale to check its mass.

The more it moves, however, the higher the precision of the measurements can be. So as time progresses, the astronomers will be able to reduce the circle of uncertainty.

Re:Versus Jupiter

[Anonymous Coward]

Accuracy of measurements, mainly.

Also, regarding Jupiter and Shoemaker-Levy 9: Jupiter is a much larger target with a much larger gravitational field. In fact, Comet Shoemaker-Levy 9 was actually orbiting Jupiter (not the Sun), and it was easy enough to see that its orbit was decaying. That fact alone means a collision was near certain.

Increasing probability

[Will_Malverson]

Remember how these things work - they made a few observations, from which they made a cone through which they're 95% (or whatever) sure that the asteroid will pass. Mars filled up about 1.3% of that cone, and so they can say that there's a 1.3% chance that Mars will be hit by the asteroid.

A few days later, with better observations, the cone shrinks, and now Mars takes up 3.9% of the cone. As the cone shrinks, Mars will continue to consume a larger and larger portion of it, right up until the time (maybe) that the cone shrinks outside of Mars and they determine that there will be no impact.

So remember, this is not unusual, and *every* non-impact event follows this pattern: Scientists find potential impact. Impact probability increases. Impact probability increases. (maybe a few more repetitions, too) Suddenly, they decide that it's not going to hit, and impact probability goes to zero.

Impact results

[lpangelrob]

No one's brought up the consequences of a collision yet, so here it is, from the first press release [nasa.gov]:

If the asteroid is indeed on a collision course, it would hit Mars with a velocity of about 13.5 km/s (8.4 miles per second), and would produce an explosion equivalent to about 3 MT of TNT. We can only speculate as to the effects of such an impact, but it would be reasonable to expect a crater nearly a kilometer across and a significant amount of dust lifted into the atmosphere.

It also notes the asteroid is 160 ft / 50 m across, and any impact probably will not be observed (by human eyes, anyways) because it will impact Mars where there are no instruments.

Large Object Also Heading For Earth

[Ed Almos]

2007 TU24 - approaching
Approximate diameter: 319 meters (H=20.131)
Closest Earth approach: 1.44 LD at 0826 UTC on 29 Jan. -----
Inside ten LD of Earth: 24 Jan. until 3 Feb.
Inside Earth's Hill sphere: 27 to 31 Jan.
Closest Moon approach: 2.20 LD at 1533 UTC 29 Jan.
Data based on: JPL SSD orbit solution #13 downloaded 6 Dec.
based on 87 observations spanning 54 days
Optical observation: observed from 13 locations during 53.8661 days
discovered at 0626 UTC on 11 Oct. by the Catalina Sky Survey
last observed at 0313 UTC on 4 Dec. by the Spacewatch 1.8m telescope

This shows that a rock 319m in diameter will pass by the Earth on January 29th 2008, it's closest point will be about 1.4 times the moons orbit or about 357,000 miles. This is VERY VERY close.

Regards

Ed Almos

Re:Preview of news media coverage

[Smidge204]

What "science" do you have in mind? Mars has already a bazillion craters to look at

But no FRESH ones. All the craters are millions of years old and have been weathered and contaminated. A fresh divot would expose deeper soils and rocks that have not previously been exposed to the atmosphere.

Also, there are things to learn about the mechanics of larger impacts on Earth-like planets. Since comparisons have been drawn between this and the Tunguska explosion, perhaps studying this will help prove or disprove that theory.
=Smidge=

Re:Versus Jupiter

[Markrian]

Actually, since the asteroid's mass is negligible to that of the planets, its mass is irrelevant to its trajectory as it can be considered a test particle. We only need to know six pieces of information - three spatial coordinates, and three velocity components. It's easy to measure four of these very accurately, but the radial distance and velocity of the asteroid with respect to us are harder. These are where the majority of the uncertainty comes from.

Re:Versus Jupiter

[Jeff DeMaagd]

From the tone in the question, I would guess that you've never taken a proper science class.

The basic point with scientific measurement is that you can take measurements, but you need to have realistic expectations as to the accuracy of those measurements and retain the error bounds throughout the calculations. For example, 1cm read from an ordinary ruler shouldn't be taken as 1.00000000000000 cm. It should be taken as something like 1cm plus or minus 0.05 cm. That's a possible error bound of plus or minus 5%.

Re:scared for earth

[Deadstick]

The same object missed us by 5 million miles -- about 1/8 the separation between Earth and Mars orbits -- two months ago and we didn't see it until two weeks later.

rj

Re:Versus Jupiter

[sm62704]

Yeah, blame OUR government! Like there aren't any other governments, or like Europe doesn't have a space agency, or China, or Russia. Or like ours is the ONLY inefficient government.

I mean, my government (with the best legislators money can buy) really sucks, but it's not like any of the others do such a great job, either. Maybe ours sucks worst but they all suck.

Re:Taking All Bets

[sm62704]

If a comment is modded down far enough, it won't be seen. If a funny or interesting comment is modded "troll" or "offtopic" there's a chance I'll miss a chuckle or worse, Ill miss being enlightened about something.

Then there's the karma thing. I'm not worried about mine, as it seems (so far knock on wood) to be impervious to anything; I get modded troll and offtopic all the time (sometimes they mod me offtopic and they're right, like this one should be) but someone whose karma is merely "good" could miss a chance to have that talk he wants with his fellow slashdotters.

But what rankles me is the ones who mod you down for seemingly no reason. They especially do it to ACs, thinking (I guess) that a negative mod won't hurt someone not logged in, but forgetting that you can check a little box to post AC.

I especially hate being called a troll. Mod me offtopic but damn it, I do NOT troll.

Re:Wait...

[gilboad]

... In case someone doesn't know what the OP meant [1].

- Gilboa
[1] http://www.nss.org/resources/books/fiction/SF_018_lucifershammer.html [nss.org]