“Mysterious Object Hurtles Towards Earth”
“Weird Object Zooming by Earth Wednesday is Likely an Asteroid”
“Mysterious Space Object Rocks the Web”
The small asteroid 2010 AL30 has made quite a splash in the news today. The titles above are just some examples of news stories floating around the internet. Unfortunately the large number of news stories and blogs calling this object a “mystery” sheds a lot of light on how bad modern reporting can be. As the 3rd headline story above put it: “Something is hurtling toward the planet. And we say ‘something’ because neither we, nor anybody in the scientific field, seems to know exactly what it is.”
Well not quite…
We know exactly what it is. It’s a small asteroid. Sure we don’t know what kind of asteroid it is (is it stoney, basaltic, carbonaceous, iron-nickel?) but those observations will be made soon if they haven’t already. We know the asteroid’s orbit, where it’s been and will be in the future.
The “mystery” part seems to be based on early speculation that AL30 was a returning piece of long-lost space hardware. Such speculation is not crazy and there have been examples of this in the past. An object discovered in 2002 turned out to be the Saturn IVB upper stage from Apollo 12 (I had a small part in confirming its man-made origin). Every time a small asteroid is found on a Earth-like orbit, there is always speculation that it is man-made. Such speculation is usually quickly refuted.
Much of the early speculation of AL30 was posted on the Minor Planet Mailing List (MPML), a Yahoo Groups forum used by amateurs and professionals interested in the observations of asteroids. It is a great forum for sharing ideas and calling attention to interesting observations though the level of expertise ranges from expert to novice. The possibility of AL30 being artificial was quickly brought up on the MPML and then just as quickly refuted. Unfortunately that short exchange was enough to get the asteroid labeled as “mysterious”. Once one trusted news source calls it a “mystery” it isn’t long before the average “copy and paste” stories spread like wild fire.
Even if AL30 was man-made, it really wouldn’t be much of a mystery. We’d quickly figure out what launch it was a part of. It’s orbit is now well determined allowing the NEO Project Office at JPL to find no instances of a previous close approach to Earth in the past 50 years. This rules out a man-made origin. Then again calling it a “mystery” in the press may get more people to read the story. Science can be boring if we have all the answers. Maybe by making it seem that we are uncertain of something, it makes it appear that we can’t rule out anything (maybe its an asteroid, a comet, a man-made spacecraft, maybe even something secret, or an UFO) and that makes for a better story.
Enough ranting, what do we actually know about 2010 AL30…
Not much has changed from my previous posting on the object. It is still predicted to pass within 129,000 km of Earth tomorrow morning (Jan 13) at ~12:46 UT. The figure below by JPL shows its path through cislunar space.
Path of 2010 AL30 on Jan 13. Credit: NASA/JPL.
What if AL30 were to hit the Earth? How much of an impact (no pun intended) would it make?
A group at the University of Arizona/Lunar and Planetary Lab has created a web GUI (called the Earth Impact Effects Program) that estimates the effect of an impacting asteroid on Earth. Entering in the following parameters for AL30 (these are just estimates but are realistic based on our current knowledge of the object):
- Projectile Diameter: 15.00 m = 49.20 ft = 0.01 miles
- Projectile Density: 3000 kg/m3
- Impact Velocity: 9.50 km/s = 5.90 miles/s
- Impact Angle: 45 degrees
- Target Density: 2500 kg/m3
- gives us the following results …
- Energy before atmospheric entry: 2.39 x 1014 Joules = 0.57 x 10-1 MegaTons TNT
- The average interval between impacts of this size somewhere on Earth is 12.1 years
- Atmospheric Entry:
- The projectile begins to breakup at an altitude of 44700 meters = 147000 ft
- The projectile bursts into a cloud of fragments at an altitude of 22900 meters = 75100 ft
- The residual velocity of the projectile fragments after the burst is 6.12 km/s = 3.8 miles/s
- The energy of the airburst is 1.40 x 1014 Joules = 0.33 x 10-1 MegaTons.
- No crater is formed, although large fragments may strike the surface.
This would be one nice fireball and look very similar to many of the bright ones reported on this blog. Small pieces of the asteroid would probably survive to reach the ground as meteorites. Note, this group states that a 15-meter asteroid should hit the Earth once every 12 years while in yesterday’s posting I said once every 50 years. The once every 50 years number comes from global infrasound data and the every 12 year interval from asteroid survey data. It is probably safe to say that a 15-meter impact happens once every 10-50 years.
One other caveat, the above calculation assumes the asteroid is a fractured rock. If it were a solid piece of nickel-iron, the impact would be much greater as seen below.
- Atmospheric Entry:
- The projectile begins to breakup at an altitude of 3470 meters = 11400 ft
- The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 5.65 km/s = 3.51 miles/s
- The impact energy is 2.26 x 1014 Joules = 0.54 x 10-1MegaTons.
- The broken projectile fragments strike the ground in an ellipse of dimension 0.101 km by 0.0714 km
- Crater Dimensions:
- Crater shape is normal in spite of atmospheric crushing; fragments are not significantly dispersed.
- Final Crater Diameter: 427 m = 1400 ft
- Final Crater Depth: 91 m = 299 ft
- Richter Scale Magnitude: 3.7
Luckily nickel-iron meteorite falls are very rare and a very minor fraction of all impactors.