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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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