European Space Agecny (ESA) / Johns Hopkins University Advanced Physics Laboratory (APL) Asteroid Impact and Deflection mission (AIDA)

The proposed Asteroid Impact and Deflection Assessment mission, currently under study by the European Space Agency and the Advanced Physics Laboratory at Johns Hopkins University, now has a target: Didymos, a binary asteroid scheduled to pass within 11 million km of Earth in 2022.

Didymos consists of two bodies. The larger body is about 800 meters in diameter; the smaller is about 150 meters.

The AIDA mission plan calls for a Double Asteroid Redirection Test (DART) built by Johns Hopkins to strike the smaller of the two bodies at about 6.25 kilometers per second. An Asteroid Impact Monitor (AIM) built by ESA would study the twin asteroids before, after, and during the impact. One topic of interest is how the impact affects the orbital mechanics of the two bodies around one another.

An ESA website says, “the recent Russian meteor and, on the same day, our planet’s close encounter with an even larger chunk of celestial debris underline the need for us to learn more about these high-speed space rocks.”

The choice of a binary asteroid is also interesting in light of recent studies of past impacts.

The asteroid which hit the Earth 65 million years ago and wiped out the dinosaurs may have been a binary asteroid. Recent gravity surveys around the Chicxulub crater in Mexico suggest the crater might have been formed by a binary impact, according to Petr Pravic at the Academy of Sciences of the Czech Republic. Additional evidence comes from a paper on crater formation which was published last month in Earth and Planetary Science Letters.

Morphology and Population of Binary Asteroid Impact Craters was published by Katarina Miljković of the Institute of Earth Physics in Paris, France; Gareth S. Collins and Sahil Mannick of the Department of Earth Sciences and Engineering at Imperial College London; and Philip A. Bland of the Department of Applied Geology at Curtin University.

The authors sought to answer the question of why binary-asteroid impacts appear to be under-represented in the geological record. Astronomical observations show that 15% of all Near Earth Asteroids are binaries, but only 2-4% of all craters on Earth and 2-3% of all craters on Mars are clearly distinguishable as doublet craters. One example of such a doublet is Lac à l’Eau Claire, also known as the Clearwater Lakes, near Hudson Bay, Canada as seen in this Space Shuttle photo:

Lac à l'Eau Claire, also called the Clearwater Lakes, near Hudson Bay, Canada as seen from the Space Shuttle

The authors simulated simulated crater formation and found that binary-asteroid impacts could result in three possible shapes: single (circular or elliptical) craters, overlapping (tear-drop or peanut-shaped) craters, and distinct doublet craters. According to their simulations, the most common result will be a single circular crater. About one in four will form an elongated or overlapping crater, and only one in six will form a doublet.

The Chicxulub crater in Mexico shows asymmetrical features which indicate a binary impact, according to Miljković in New Scientist.

This recognition may mean that planetary defense is even harder than we thought. Miljković told New Scientist she was “not sure if any of the proposed asteroid deflection techniques could deflect both binary components with a single weapon.”

Written by Astro1 on March 2nd, 2013 , Planetary Defense

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