This is one of the Tagish Lake meteorite fragments. Credit: Michael Holly, Creative Services, University of Alberta.
asteroids may have been like “molecular factories” cranking out life’s
ingredients and shipping them to Earth via meteorite impacts, according
to scientists who’ve made discoveries of molecules essential for life in
material from certain kinds of asteroids and comets. Now it appears
that at least one may have been less like a rigid assembly line and more
like a flexible diner that doesn’t mind making changes to the menu.
January, 2000, a large meteoroid exploded in the atmosphere over
northern British Columbia, Canada, and rained fragments across the
frozen surface of Tagish Lake. Because many people witnessed the
fireball, pieces were collected within days and kept preserved in their
frozen state. This ensured that there was very little contamination from
Tagish Lake meteorite fell on a frozen lake in the middle of winter and
was collected in a way to make it the best preserved meteorite in the
world,” said Dr. Christopher Herd of the University of Alberta,
Edmonton, Canada, lead author of a paper about the analysis of the
meteorite fragments published June 10 in the journal Science.
first Tagish Lake samples — the ones we used in our study that were
collected within days of the fall — are the closest we have to an
asteroid sample return mission in terms of cleanliness,” adds Dr.
Michael Callahan of NASA’s Goddard Space Flight Center in Greenbelt,
Md., a co-author on the paper.
Tagish Lake meteorites are rich in carbon and, like other meteorites of
this type, the team discovered the fragments contained an assortment of
organic matter including amino acids, which are the building blocks of
proteins. Proteins are used by life to build structures like hair and
nails, and to speed up or regulate chemical reactions. What’s new is
that the team found different pieces had greatly differing amounts of
see that some pieces have 10 to 100 times the amount of specific amino
acids than other pieces,” said Dr. Daniel Glavin of NASA Goddard, also a
co-author on the Science paper. “We’ve never seen this kind of
variability from a single parent asteroid before. Only one other
meteorite fall, called Almahata Sitta, matches Tagish Lake in terms of
diversity, but it came from an asteroid that appears to be a mash-up of
many different asteroids.”
identifying the different minerals present in each fragment, the team
was able to see how much each had been altered by water. They found that
various fragments had been exposed to different amounts of water, and
suggest that water alteration may account for the diversity in amino
research provides new insights into the role that water plays in the
modification of pre-biotic molecules on asteroids,” said Herd. “Our
results provide perhaps the first clear evidence that water percolating
through the asteroid parent body caused some molecules to be formed and
others destroyed. The Tagish Lake meteorite provides a unique window
into what was happening to organic molecules on asteroids
four-and-a-half billion years ago, and the pre-biotic chemistry
the variability in Tagish Lake turns out to be common, it shows
researchers have to be careful in deciding whether meteorites delivered
enough bio-molecules to help jump-start life, according to the team.
reactions are concentration dependent,” says Callahan. “If you’re below
the limit, you’re toast, but if you’re above it, you’re OK. One
meteorite might have levels below the limit, but the diversity in Tagish
Lake shows that collecting just one fragment might not be enough to get
the whole story.”
the meteorites were the most pristine ever recovered, there is still
some chance of contamination though contact with the air and surface.
However, in one fragment, the amino acid abundances were high enough to
show they were made in space by analyzing their isotopes.
are versions of an element with different masses; for example, carbon
13 is a heavier, and less common, variety of carbon. Since the chemistry
of life prefers lighter isotopes, amino acids enriched in the heavier
carbon 13 were likely created in space.
found that the amino acids in a fragment of Tagish Lake were enriched
in carbon 13, indicating they were probably created by non-biological
processes in the parent asteroid,” said Dr. Jamie Elsila of NASA
Goddard, a co-author on the paper who performed the isotopic analysis.
The team consulted researchers at the Goddard Astrobiology Analytical Lab
for their expertise with the difficult analysis. “We specialize in
extraterrestrial amino acid and organic matter analysis,” said Dr. Jason
Dworkin, a co-author on the paper who leads the Goddard laboratory. “We
have top-flight, extremely sensitive equipment and the meticulous
techniques necessary to make such precise measurements. We plan to
refine our techniques with additional challenging assignments so we can
apply them to the OSIRIS-REx asteroid sample return mission.”
OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, Security — Regolith Explorer)
is a Goddard-managed mission, led by the University of Arizona, that
will be launched toward asteroid “1999 RQ36” in 2016 and return a sample
to Earth in 2023. The OSIRIS-REx team is led by Dr. Michael Drake,
Director of the University of Arizona’s Lunar and Planetary Laboratory.
Tagish Lake research was funded by the Natural Sciences and Engineering
Research Council of Canada, the Alberta Ingenuity Fund, and NASA.