March 27 2009: Asteroid 2009 FD to fly by the Earth

We have another fairly interesting asteroid flying by the Earth tomorrow called 2009 FD. Spaceweather.com gives the following information:

Asteroid	Date(UT)	Miss Distance	Mag.	Size
2009 DD45	Mar. 2	0.2 LD	11	35 m
2009 FK	Mar. 19	1.0 LD	17	9 m
2009 DO111	Mar. 20	1.2 LD	13	117 m
2009 FX4	Mar. 23	6.1 LD	19	37 m
2009 FD	Mar. 27	1.6 LD	13	160 m

among a lot of others. 2009 DO111 and 2009 FD are the two brightest after 2009 DD45, which had a fair amount of media attention when it flew by considering the close distance despite the fact that it wasn't all that large so it wouldn't have caused any damage anyway.

Oh, and this one was pretty interesting as well simply for its size (note that it was discovered a full 11 years ago):

1998 OR2

Mar. 12

69.8 LD

14

3.3 km

Back to 2009 FD: this is what it looks like at closest approach:

And here's what its orbit looks like compared to the other planets nearby:

(moved it back a few months so that the names wouldn't blur together)


And now for the obligatory "what if it hit"? Let's go with porous rock, and assume it landed 1000 km away in the Pacific (4000 m depth).

The projectile begins to breakup at an altitude of 72500 meters = 238000 ft

The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 6.34 km/s = 3.94 miles/s

The impact energy is 6.46 x 10¹⁶ Joules = 1.54 x 10¹MegaTons.

The broken projectile fragments strike the ground in an ellipse of dimension 1.18 km by 0.833 km

The crater opened in the water has a diameter of 2.08 km = 1.29 miles

For the crater formed in the seafloor:

The result of the impact is a crater field, not a single crater. The following dimensions are for the crater produced by the largest fragment.

Transient Crater Diameter: 0.000754 m = 0.00247 ft

Transient Crater Depth: 0.000267 m = 0.000875 ft

Final Crater Diameter: 0.000943 m = 0.00309 ft

Final Crater Depth: 0.000201 m = 0.00066 ft

The crater formed is a simple crater

The floor of the crater is underlain by a lens of broken rock debris (breccia) with a maximum thickness of 0 m = 0.000306 ft.

At this impact velocity ( <>

The air blast will arrive at approximately 3030 seconds.

Peak Overpressure: 136 Pa = 0.00136 bars = 0.0193 psi

Max wind velocity: 0.321 m/s = 0.717 mph

Sound Intensity: 43 dB (Easily Heard)

So...very exciting, but no big deal. If it fell in the ocean we'd be hearing about mission after mission to check out the crater field and recover fragments. If it fell on land nearby then evacuations would have to take place, but the chance of that happening is almost nonexistent. Actually, considering all that I think an impact from an asteroid just about this size (in the ocean) would be just right in order to shake people out of their false sense of security and make them realize that the Earth really is just a tiny globe with an extremely thin layer of protection...and our only home. In the meantime I'll just have to blog about the possibility.