Posting out of order here. I have a ton of notes on this morning’s Moon sessions, but before piecing together pages of lunar science, I want to share something neat: Science results on Crater Carancas. This newest, smallest crater on the planet Earth was formed September 15, 2007 in Peru. The impact site is fairly near Lake Titicaca and the Bolivia border. The path of the meteor through the atmosphere was observed by numerous people, including a group sitting out on a hotel roof a few kilometers from the impact site. The folks presenting, T Kenkmann and P Schultz (links go to their papers), visited the site a few weeks and a few months after the impact to see what could scientifically be learned through interviews and measurements.
As you may have read at the time, there were several reports of toxic fumes associated with this impact, and some fear that it was actually a missile or falling piece of space debris. All these reports and fears appear to be nothing more than over-active imaginations at work. This was a rock. More accurately this was a Rocky Asteroid called a Chondrite (sub type H). This is good news, but a bit troubling. This type of asteroid turned meteor turned meteorite isn’t supposed to be able to make landfall when small. It was thought (using what are called Pancake Models) that these objects burn up in the atmosphere and spread into a cloud of small, unlikely to survive to the ground, pieces.
Clearly, the models were missing something.
This Carancas crater is/was (it’s quickly eroding) about 14 meters in diameter and the ejecta from the impact spread over 300 meters, with one chunk going through the roof of a shed a couple hundred meters from the impact site. While many of the meteor bits were taken by locals, tourists, etc before the scientists got there (you can actually buy some here), the total mass of the meteor bits and dust still at the site when the scientists got there was surprisingly large. It is estimated that the impacting “object” (I’ll explain below) was roughly 1m in size and 1780 kg.
The parent body was likely much larger. Using modeling, it is estimated that a roughly 2ton object hit the atmosphere at 75 degrees. As it passed through the atmosphere braking and breaking took place, with the object fragmenting in such a way that the pieces didn’t have the energy necessary to pass through the bow shock (a special type of shockwave that comes off the nose of an object passing through a medium). With all the fragments trapped inside the bowshock they were effectively collimated and in many ways acted like a single object, hitting the ground in a stream. The impact contained roughly 62 million joules of kinetic energy, and flung the soil up into a really cool crater. Unfortunately, this object landed on the bank of what was a dry riverbed. As it dug into the earth, it hit the water table (only about 1.5 meters down, and within 15-30 minutes the crater floor was filled with water.
Over the months since the impact the sides of the crater have slumped, objects in the crater rim have slid down, and erosion has taken place. Soon this crater will look like just another watering hole for the local llamas – It will just be a local watering hole surrounded by fascinating dust and rocks. (Samples collected contained glassy particles and lapillus fragments.)
This impact raises some intriguing questions. Objects like this could have hit us often, but because the craters really aren’t all that dramatic, they may have eroded into oblivion before anyone figured out their significance. Have we been getting casually drizzeled on by Chondrites on the scale of decades (or longer) and just not known it? The newly realized threat these rocky bodies pose to life on Earth needs to be assessed. While this object didn’t cause any significant economic or bodily harm (and in fact appears to be lining a few pockets with green), it could have. This object did force one farmer to repair a roof, and it could conceivable have destroyed a building if it had hit a support structure (or just hit a weak building). Now, as we map the skies with LINEAR and the upcoming LSST telesocpes, we need to consider broadening our idea of dangerous, and look a bit harder for the rocks that just might decide to impact.
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