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The Question

(Submitted November 10, 1997)

There are some scientists that proposed that a supernova occurred 65 million years ago at a distance of 130 light years from Earth that could be the engine of dinosaur extinction.

Is it possible to determine if an event of this nature occurred during this time frame? Or at another earlier time?

The Answer

Supernova have been suggested as possible culprits in mass extinctions many times. For example, there's a paper about how supernovae could cause mass extinctions on the Los Alamos National Labs e-print server by Juan Collar at http://xxx.lanl.gov/abs/astro-ph/9505028 (be sure to follow the 'cited-by' links to get differing viewpoints).

However, in the case of the Cretaceous-Tertiary (KT) extinction that killed the dinosaurs 65 million years ago, there is ample evidence of both an asteroid strike and catastrophic volcanic upheaval (the Deccan Traps). Adding a supernova to these events is probably unnecessary. This is not to say that a supernova could not cause a mass extinction, just that it probably didn't cause that one.

As for evidence, supernova remnants only remain detectable for a few tens of thousands of years. When supernovae form pulsars, their typical velocities are a few thousandths of lightspeed, so in 65 million years, a pulsar could have traveled from near Earth to any point in the Galaxy and had numerous encounters with other stars, randomizing its velocity, so we could not find a particular pulsar and discover that it was in the right place at the right time.

Cosmic rays from a nearby supernova could cause a detectable change in isotopes on Earth. That was one of the first explanations Luis Alvarez thought of when he found the iridium at the KT boundary. However, other elements and isotopes which would be expected from such an event were not found, leading to the meteor theory.

David Palmer
for Ask an Astrophysicist

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