Killer Asteroid - 450 to 1 odds of collision in 2036

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Killer Asteroid - 450 to 1 odds of collision in 2036

Postby John E. » Wed Apr 16, 2008 1:56 pm UTC

http://news.yahoo.com/s/afp/20080415/sc ... 0415214429

Seems to odds of a killer asteroid hitting the earth in 2036 are 450 to one.

Maybe something ought to be done about this?

The asteroid is supposed to be chock full of iridium which is priced at $450/ounce. According to wikipedia, that metal is used in supercolliders in the production of antiprotons.

And also an iridium - bearing asteroid impact is associated with the extinction of the dinosaurs.

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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby TomBot » Wed Apr 16, 2008 2:11 pm UTC

I must say I'm skeptical. Apparently the risk was 1/45000, now down to 1/450 because of the chance that it could hit an artificial satellite. Suppose we assume that if it hit a satellite, that would perturb it just right so that we would be very certain it would hit Earth later. That means the chance of the asteroid hitting a satellite is just shy of 1/450. Which seems pretty incredible, since we're 100 times less sure it will hit Earth, a much bigger target.

My guess is that between NASA and this kid, someone mentioned 1/450 in some other context, and the media picked it up and ran. Maybe as the chance of the asteroid hitting Earth given that it hits a satellite - I'd believe that. Anyway, we need more info - surely NASA has some official thing to say?

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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby demon » Wed Apr 16, 2008 2:41 pm UTC

http://www.theregister.co.uk/2008/04/16 ... is_denial/
yeah, apparently they do. and did. still, more details would be welcome.

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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby segmentation fault » Wed Apr 16, 2008 4:05 pm UTC

its like having your own C3PO.

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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby Adalwolf » Wed Apr 16, 2008 6:55 pm UTC

Even if it hit, it won't kill anyone, as we'll all be dead from the Large Hadron Collider or from whatever happens in 2012.
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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby 22/7 » Wed Apr 16, 2008 7:06 pm UTC

Does anyone actually know why there are odds of it hitting Earth? Isn't this a simple "here's our orbit, here's the orbit of this asteroid, they do or do not coincide"?
Totally not a hypothetical...

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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby Belial » Wed Apr 16, 2008 7:15 pm UTC

Margin of error on our calculations?
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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby Gunfingers » Wed Apr 16, 2008 7:17 pm UTC

Well it's more "Here's our orbit as we understand it, and here's our orbit as we expect it to be in 2036. Based on what we've observed of this asteroid we're pretty sure this is it's orbit, so this will probably be it's orbit in 2036. Based on our observations we have this range of error, and some numbers within that range indicate bad things."

I think. So not an astronomer.

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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby Token » Wed Apr 16, 2008 7:21 pm UTC

Yeah, I imagine that numerically extrapolating a multiple-body gravitational system 28 years into the future isn't helped by the fact that the Earth's diameter is quite a bit smaller than that of it's orbit.
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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby John E. » Wed Apr 16, 2008 8:21 pm UTC

demon wrote:http://www.theregister.co.uk/2008/04/16/esa_german_schoolboy_apophis_denial/
yeah, apparently they do. and did. still, more details would be welcome.


Well that a relief - still, someone ought to go up and get that iridium.

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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby oxoiron » Thu Apr 17, 2008 8:01 pm UTC

John E. wrote:Well that a relief - still, someone ought to go up and get that iridium.
After it hits the Moon, then we will have an excuse to go there one more time for the first time ever.

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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby Robin S » Thu Apr 17, 2008 9:47 pm UTC

TomBot wrote:That means the chance of the asteroid hitting a satellite is just shy of 1/450. Which seems pretty incredible, since we're 100 times less sure it will hit Earth, a much bigger target.
Maybe the volume of space within the asteroid's radius of a satellite actually is 100 times greater than the volume surrounding the Earth.
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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby Arancaytar » Fri Apr 18, 2008 7:54 am UTC

oxoiron wrote:
John E. wrote:Well that a relief - still, someone ought to go up and get that iridium.
After it hits the Moon, then we will have an excuse to go there one more time for the first time ever.

Apologies to Buzz. I don't want him kicking my ass.

You think we didn't go to the moon, why don't you tell Louis Armstrong to his face? ( :P )
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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby Weaver » Fri Apr 18, 2008 12:07 pm UTC

http://www.physorg.com/news127666265.html

The Near-Earth Object Program Office at NASA's Jet Propulsion Laboratory in Pasadena, Calif., has not changed its current estimates for the very low probability (1 in 45,000) of an Earth impact by the asteroid Apophis in 2036.

Contrary to recent press reports, NASA offices involved in near-Earth object research were not contacted and have had no correspondence with a young German student, who claims the Apophis impact probability is far higher than the current estimate.

This student's conclusion reportedly is based on the possibility of a collision with an artificial satellite during the asteroid's close approach in April 2029. However, the asteroid will not pass near the main belt of geosynchronous satellites in 2029, and the chance of a collision with a satellite is exceedingly remote.

Therefore, consideration of this satellite collision scenario does not affect the current impact probability estimate for Apophis, which remains at 1 in 45,000.

NASA detects and tracks asteroids and comets passing close to Earth. The Near Earth Object Observation Program, commonly called "Spaceguard," discovers, characterizes and computes trajectories for these objects to determine if any could be potentially hazardous to our planet.

Source: NASA

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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby 22/7 » Fri Apr 18, 2008 7:52 pm UTC

oxoiron wrote:
John E. wrote:Well that a relief - still, someone ought to go up and get that iridium.
After it hits the Moon, then we will have an excuse to go there one more time for the first time ever.

Apologies to Buzz. I don't want him kicking my ass.

Oh gawd. Please tell me you're kidding.
Totally not a hypothetical...

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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby oxoiron » Fri Apr 18, 2008 10:17 pm UTC

CLARIFICATION: I don't think the Moon landings were faked. The joke was that on one occasion Aldrin lost his cool with one of the nutjobs who does think so. I always forget that dry humor on the internet is often indistinguishable from plain, old stupidity.

@Arancaytar: Nice job with the Louis Armstrong comment. I enjoyed that.
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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby 22/7 » Fri Apr 18, 2008 10:31 pm UTC

Ok, I figured you were, but... gawd I hate it when people argue that. Continue.
Totally not a hypothetical...

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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby Rysto » Fri Apr 18, 2008 10:44 pm UTC

I was going to make a crack about how everyone knows that the moon landings were filmed on a sound stage on Mars, but then I remembered where I'd originally heard that line.

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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby Swordfish » Sat Apr 19, 2008 1:26 am UTC

Anyone stop to think about how insignificant an impact with a several ton satellite would be for a rock that masses 210,000,000 metric tonnes?
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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby Robin S » Sat Apr 19, 2008 3:04 pm UTC

Well, the satellite itself could still be knocked into the Earth, or small fragments could be broken off the asteroid.
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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby Weaver » Sat Apr 19, 2008 3:55 pm UTC

I think the concern here isn't that it would divert the asteroid into a direct-impact trajectory, but that it would impart enough angular momentum or velocity shift to cause a collission on the next near pass in 20+ years. Smacking a geo-synch commo platform might well do it - if it were even going to get close to those satelites.

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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby Swordfish » Sun Apr 20, 2008 5:10 am UTC

Maybe hitting a satellite could divert it enough so that it'll hit the Earth sometime before the Sun expands and engulfs the inner solar system, and that may still be a gross overestimate. A communication satellite in geostationary orbit has about 47 Gigajoules (47 billion joules) of kinetic energy, while the asteroid has nearly 10 Exejoules (10 quintillion joules). So the asteroid has 210 million times the kinetic energy that the satellite does. Even if the satellite imparted its full 47 Gigajoules of kinetic energy onto Apophis, it would divert its orbit by an unmeasurable amount.
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Re: Killer Asteroid - 450 to 1 odds of collision in 2036

Postby Weaver » Sun Apr 20, 2008 9:27 am UTC

OK, dug into the source info more.

Satelite collision, while not insignificant in orbital effect, is insignificant when compared to the range of uncertainty of other effects.

100s of km diversion vs. ~30million km uncertainty (due to Sun, Moon, and planetary mass uncertainty, variable solar effects, albedo effects, etc.)

Here's NASA's info on the subject:

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

Spoiler:
Predicting Apophis' Earth Encounters in 2029 and 2036
SUMMARY

Researchers at NASA/JPL, Caltech, and Arecibo Observatory have released the results of radar observations of the potentially hazardous asteroid 99942 Apophis, along with an in-depth analysis of its motion. The research will affect how and when scientists measure, predict, or consider modifying the asteroid's motion. The paper has been accepted for publication in the science journal "Icarus" and was presented at the AAS/DPS conference in Orlando, Florida in October of 2007. The Apophis study was led by Jon Giorgini, a senior analyst in JPL's Solar System Dynamics group and member of the radar team that observed Apophis.

The analysis of Apophis previews situations likely to be encountered with NEAs yet to be discovered: a close approach that is not dangerous (like Apophis in 2029) nonetheless close enough to obscure the proximity and the danger of a later approach (like Apophis in 2036) by amplifying trajectory prediction uncertainties caused by difficult-to-observe physical characteristics interacting with solar radiation as well as other factors.

BACKGROUND

Upon its discovery in 2004, Apophis was briefly estimated to have a 2.7% chance of impacting the Earth in 2029. Additional measurements later showed there was no impact risk at that time from the 210-330 meter (690-1080 foot) diameter object, identified spectroscopically as an Sq type similar to LL chondritic meteorites. However, there will be a historically close approach to the Earth, estimated to be a 1 in 800 year event.


Arecibo Radar Image of Apophis

Apophis Position Uncertainty
The Arecibo planetary radar telescope subsequently detected the asteroid at distances of 27-40 million km (17-25 million miles; 0.192-0.268 AU) in 2005 and 2006. Polarization ratios indicate Apophis appears to be smoother than most NEAs at 13-cm scales. Including the high precision radar measurements in a new orbit solution reduced the uncertainty in Apophis' predicted location in 2029 by 98%.

While trajectory knowledge was substantially corrected by the Arecibo data, a small estimated chance of impact (less than 1 in 45,000 using standard dynamical models) remained for April 13, 2036. With Apophis probably too close to the Sun to be measured by optical telescopes until 2011, and too distant for useful radar measurement until 2013, the underlying physics of Apophis' motion were considered to better understand the hazard.


RESULTS OF THE STUDY

(1) Extending the "Standard Dynamical Model"
Trajectory predictions for asteroids are normally based on a standard model of the solar system that includes the gravity of the Sun, Moon, other planets, and the three largest asteroids.

However, additional factors can influence the predicted motion in ways that depend on rarely known details, such as the spin of the asteroid, its mass, the way it reflects and absorbs sun-light, radiates heat, and the gravitational pull of other asteroids passing nearby. These were examined, along with the effect of Earth's non-uniform gravity field during encounters, and limitations of the computer hardware performing the calculations.

One would normally look for the influence of such factors as they gradually alter the trajectory over years. But, for Apophis, the changes remain small until amplified by passage through Earth's gravity field during the historically close approach in 2029.

For example, the team found solar energy can cause between 20 and 740 km (12 and 460 miles) of position change over the next 22 years leading into the 2029 Earth encounter. But, only 7 years later, the effect on Apophis' predicted position can grow to between 520,000 and 30 million km (323,000 and 18.6 million miles; 0.0035-0.2 AU). This range makes it difficult to predict if Apophis will even have a close encounter with Earth in 2036 when the orbital paths intersect.


Present era through 2029

Small factors 2029-2036
It was found that small uncertainties in the masses and positions of the planets and Sun can cause up to 23 Earth radii of prediction error for Apophis by 2036.

The standard model of the Earth as a point mass can introduce up to 2.9 Earth radii of prediction error by 2036; at least the Earth's oblateness must be considered to predict an impact.

The gravity of other asteroids can cause up to 2.3 Earth radii of prediction uncertainty for Apophis.

By considering the range of Apophis' physical characteristics and these error sources, it was determined what observations prior to 2029 will most effectively reduce prediction uncertainties. Observing criteria were developed that, if satisfied, could permit eliminating the 2036 impact possibility without further physical characterization of Apophis.

Such observations could reduce the need for a visit by an expensive spacecraft and reduce the risk of Apophis being prematurely eliminated as a hazard under the standard model, only to drift back into the hazard classification system years later as the smaller, unmodeled forces act upon it.

(2) Mitigation
Mitigation was not specifically studied, but the team found small variations in the energy absorption and reflection properties of Apophis' surface are sufficient to cause enough trajectory change to obscure the difference between an impact and a miss in 2036. Changing the amount of energy Apophis absorbs by half a percent as late as 2018 - for example by covering a 40 x 40 meter (130 x 130 foot) patch with lightweight reflective materials (an 8 kg payload) - can change its position in 2036 by a minimum of one Earth radius.


Apophis Trajectory Change
A change somewhat greater than this minimum would be required to allow for prediction uncertainties. For Apophis, scaling up to distribute 250 kg (550 pounds) of a reflective or absorptive material (similar to the carbon fiber mesh being considered for solar sails) across the surface could use the existing radiation forces to produce a 6-sigma trajectory change, moving at least "99.9999998" percent of the statistically possible trajectories away from the Earth in just 18 years.

While no deflection is expected to be necessary, the team's research demonstrates that any deflection method must produce a change known in advance to be greater than all the error sources in the prediction, including some greater than those considered with the standard model.

(3) Impact probability

The study did NOT compute new impact probabilities. This is because key physical parameters (such as mass and spin pole) that affect its trajectory have not yet been measured and hence there are no associated probability distributions.

The situation is similar to having 6 apples (the measured Apophis parameters) and 6 boxes whose contents are unknown (the unmeasured Apophis parameters), then trying to compute the probability one has a total of 12 apples (impact probability). The result reflects back what is assumed about the unknown contents of the boxes, but doesn't reveal new information. The contents of the boxes must be observed (measured) to learn something new.

For similar reasons, the Apophis study instead uses the minimum and maximum range-of-effect in place of computing impact probabilities to provide reasonable criteria for excluding impact in the absence of detailed physical knowledge, once new position measurements are obtained at six key times.

(4) Non-Apophis Conclusions

Aspects of the study relevant to asteroids other than Apophis:

The Standard Dynamical Model can misestimate impact risk for the more numerous sub-km objects preceded by close planetary encounter(s). This problem might be addressed by reassessing impact potential after planetary encounters, given new measurements.
The minimum-maximum effect of unmeasured parameters can provide enough information to exclude threats in certain cases.
Amplification of small trajectory offsets makes valid prediction across a close-encounter difficult without physical knowledge, but offers the potential to redirect the entire uncertainty region and has significant implications for costly spacecraft missions.
A deflection effort must be known in advance to produce change greater than predicted uncertainties due to ALL parameters, not only the Standard Dynamical Model. For example, if a method produces 10 Earth-radii of change, but prediction uncertainties from all sources are 20 Earth-radii, the deflection would move the asteroid around within the noise, producing an unpredicted result or even a new hazard.
FUTURE

The future for Apophis on Friday, April 13 of 2029 includes an approach to Earth no closer than 29,470 km (18,300 miles, or 5.6 Earth radii from the center, or 4.6 Earth-radii from the surface) over the mid-Atlantic, appearing to the naked eye as a moderately bright point of light moving rapidly across the sky. Depending on its mechanical nature, it could experience shape or spin-state alteration due to tidal forces caused by Earth's gravity field.

This is within the distance of Earth's geosynchronous satellites. However, because Apophis will pass interior to the positions of these satellites at closest approach, in a plane inclined at 40 degrees to the Earth's equator and passing outside the equatorial geosynchronous zone when crossing the equatorial plane, it does not threaten the satellites in that heavily populated region.

Using criteria developed in this research, new measurements possible in 2013 (if not 2011) will likely confirm that in 2036 Apophis will quietly pass more than 49 million km (30.5 million miles; 0.32 AU) from Earth on Easter Sunday of that year (April 13).

CREDITS

In addition to Giorgini, co-authors of the report include Dr. Lance A. M. Benner and Dr. Steven J. Ostro of JPL; Dr. Michael C. Nolan, Arecibo Observatory, Puerto Rico, and Michael W. Busch of the California Institute of Technology.

Arecibo Observatory is operated by Cornell University under a cooperative agreement with the National Science Foundation. JPL is managed for NASA by the California Institute of Technology in Pasadena.

UPDATE NOTES

2008-Apr-16:
In response to inquiries, accidental impact with an artifical satellite in 2029 is vanishingly unlikely. As mentioned above, (1) Apophis does not pass near the zones where most satellites are located and (2) man-made satellites and Apophis both have small cross-sectional areas. Even if a high-velocity impact occurred, a large satellite could change Apophis' position 7 years later (in 2036) by only 100's of km at most. This is less than 1/10th the size of the smallest issues considered in the paper, very much in the noise of the calculations, and can have no meaningful effect on Earth impact probability estimation (which already incorporates more than 30 million km of uncertainty). At such a late date, impact with an artificial satellite would be like a bug on the windshield of Apophis. Deflection efforts are dependent on being early enough to leverage the dynamics of the 2029 encounter. Events during the encounter lack such leverage.

2008-Feb-22:
Paper received JPL's 2008 Edward Stone Award for Outstanding Research Publication.

2007-Dec-13:
The paper will be published in the January 2008 issue of Icarus. Reference: Giorgini JD, Benner LAM, Ostro SJ, Nolan MC, Busch MW, Predicting the Earth encounters of (99942) Apophis, Icarus 193 (2008), pp. 1-19.


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