NASA Downgrades Asteroid-Earth Collision Risk 244
coondoggie writes "NASA scientists have recalculated the path of a large asteroid known as Apophis and now say it has only a very slim chance of banging into Earth.. The Apophis asteroid is approximately the size of two-and-a-half football fields, and updated computational techniques and newly available data indicate the probability of an Earth encounter on April 13, 2036 for Apophis has dropped from one-in-45,000 to about four-in-a million, NASA stated."
Re:Metric? (Score:3, Informative)
It's about 0.0000001 times the size of Wales.
Re:Four in a million, huh? (Score:3, Informative)
Apparently those are some pretty big football fields.
Remember the Mars Orbiter (Score:2, Informative)
Re:Four in a million, huh? (Score:3, Informative)
Who writes this stuff?
And what are they drinking/smoking?
The title and the picture don't match. From Wikipedia:
"Based upon the observed brightness, Apophis' length was estimated at 450 metres (1,500 ft); a more refined estimate based on spectroscopic observations at NASA's Infrared Telescope Facility in Hawaii by Binzel, Rivkin, Bus, and Tokunaga (2005) is 350 metres (1,100 ft)."
Re:four in a million? (Score:4, Informative)
According to NASA, it is 1 in 135,000 and diameter is 0.270 km
http://neo.jpl.nasa.gov/risk/a99942.html [nasa.gov]
The image on TFA gives the impression that it is way larger than 20km and the summary claims that is is 200 yard = 0.182 km. And the text claims that it is four-in-a million aka 1 in 250.000.
1 in 4 million is still better odds (Score:1, Informative)
first four entries on impact table (Score:2, Informative)
There are three objects with higher probability of impact on the list, two of them much larger than Apophis (270 m diameter). Their diameters are 560 m and 780 m.
http://neo.jpl.nasa.gov/risk/ [nasa.gov]
Scroll down to "Objects not recently observed"
Re:Four in a million, huh? (Score:5, Informative)
Posted too soon, I did. Should have checked the source of the picture first.
What we have accompanying the article on Apophis is a picture of Asteroid 253 Mathilde. Apparently pulled off the NASA website at random by the author's of TFA.
Re:is this too early to predict path ? (Score:5, Informative)
All the models are run according the 'standard dynamic model' at JPL which includes gravity from the Sun, planets, large moons and large asteroids. Perturbations caused by objects outside the solar system are negligible compared to non-gravitational effects such as direct solar pressure and the Yarkovsky effect. These effects are impossible to model without knowledge of material composition, mass and structure, which you can't really get without going there.
However, the uncertainty caused by these non-gravitational effects is very small compared with the uncertainty caused by the fact that we just plain don't know quite where it is and how fast its going. In order to know where the asteroid will be in 2036 to within an Earth radius requires us to know where it is now to within about a meter -- the 2029 close approach in particular magnifies uncertainties incredibly (100x).
These state estimate uncertainties overwhelm any small errors in the dynamic model, and these new and improved probabilities come from refining the current state estimate. So yes, it is still valid to make these kind of predictions. You have to start early (10-20 years) to be able to stop it as well, so its important to keep an early eye on it.
Re:Metric? (Score:1, Informative)
In Canada we use the metric system but we don't refer to soccer as football, instead we have our own football fields which in stead of being 100yards long, are ~100meters long. Except that we still label the field using yards, so its 110yards.
Re:How useful is this, really? (Score:3, Informative)
You'd probably have to apply a few km/s Delta-V (at least) to it in order to do that. All estimates show it entering the Earth's sphere of influence at about 5.87 km/s, which would be reasonable for putting it in orbit, if it were in the right place. Unfortunately, as it moves past the earth it gets sped up and moves on a hyperbolic orbit, it speeds up, so theres no real way to do it just by changing its position slightly (which could be done for ~$300M).
Basically, changing its position slightly in order to prevent an impact requires a very small amount of energy. For a 50 mN thrust for 1 year, 20 years ahead of time (which is enough to move it in 2036 by around 20 Earth radii), moves it about 500 meters and thus does about 25 Joules worth of work*. However, consider changing the velocity of something the size of Apophis (2.1e10 kg) from 5.8 km/s to say 3 km/s -- thats 2.5e17 Joules worth of work. Thats 800 MW over 10 years. I think there are probably better asteroids to capture in this case, and its certainly not an easy task by any definition.
*forgive me if the numbers are a bit off, but its the correct order of magnitude anyway