Ancient Supernova Explosions Left Their Scars on Earth & Moon
It?s a popular science fiction idea?the earth being threatened by the blast
of a nearby supernova (anywhere within a few dozen light years). And one that
would draw down the curtain on life as we know it.
But with a planetary history of over four billion years, the Earth has likely
suffered the slings and arrows of exploding stars more than once in past
eons.
This week?s New Scientist features a nice overview of research to find clues:
Evidence for past supernovae is thin on the ground, although in 1999 German
researchers found traces of iron-60 in south Pacific sediments (
Physical Review Letters, vol 83, p 18). This
isotope, with a half-life of 2.6 million years, is not made in significant
quantities by any process on Earth, but is expelled by supernovae. The
interpretation is disputed, but if iron-60 is a supernova?s dirty footprint, it
suggests
a
star exploded only a few million years ago within about 100 light years of
us.
is a giant sponge soaking up everything thrown at it as we go around the
galaxy,? he told reporter Stephen Battersby.
Cosmic rays from a supernova would have scorched the moon, leaving signs of
damage in surface minerals that could be visible to microscopes. Moreover, the
radiation would also have generated isotopes (for example, krypton-83 and
xenon-126).
Exploring the moon poses many challenges. While it doesn?t suffer the
movement of tectonic plates or have an atmosphere with the kind of weather that
would erode craters and other signs of cosmic impacts, constant exposure to
background cosmic rays would erode the ?signature? of any one supernova?s single
blast wave of radiation at the surface.
But Crawford and his colleagues believe the answer is to search for clues in
relatively recent lava flows, because once cooled and covered over, they could
preserve the mark of cosmic rays from the time they were exposed.
What kind of digs would this involve? A robot probe with a drill to sink into
an area with lava flows; the robot could collect scoops of the soil and
(presumably) perform tests for isotopes on the spot.
Needless to say, setting up a drilling rig on the moon is unlikely to be at
the top of NASA?s list. But at the international level, Crawford believes there?s reason to be
optimistic an expedition could be done in the near future.
Ancient Supernova Explosions Left Their Scars on EarthAncient Supernova Explosions Left Their Scars on Earth
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Originally Posted by MoonDancer
