Two wayward space rocks,
which separately crashed to Earth in 1998 after circulating in our solar
system's asteroid belt for billions of years, share something else in common:
the ingredients for life. They are the first meteorites found to contain both
liquid water and a mix of complex organic compounds such as hydrocarbons and
amino acids.
A detailed study of the
chemical makeup within tiny blue and purple salt crystals sampled from these
meteorites, which included results from X-ray experiments at the Department of
Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), also found
evidence for the pair's past intermingling and likely parents.
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| Blue halite and tweezer tips for scale. Credit: Dr. Queenie Hoi Shan Chan |
These include Ceres, a brown
dwarf planet that is the largest object in the asteroid belt, and the asteroid
Hebe, a major source of meteorites that fall on Earth.
The study, published Jan. 10
in the journal Science Advances, provides the first comprehensive chemical
exploration of organic matter and liquid water in salt crystals found in
Earth-impacting meteorites. The study treads new ground in the narrative of our
solar system's early history and asteroid geology while surfacing exciting
possibilities for the existence of life elsewhere in Earth's neighborhood.
"It's like a fly in
amber," said David Kilcoyne, a scientist at Berkeley Lab's Advanced Light
Source (ALS), which provided X-rays that were used to scan the samples' organic
chemical components, including carbon, oxygen, and nitrogen. Kilcoyne was part
of the international research team that prepared the study.
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| A blue crystal recovered from a meteorite that fell near Morocco in 1998. The scale bar represents 200 microns (millionths of a meter). Credit: Queenie Chan/The Open University, UK |
While the rich deposits of
organic remnants recovered from the meteorites don't provide any proof of life
outside of Earth, Kilcoyne said the meteorites' encapsulation of rich chemistry
is analogous to the preservation of prehistoric insects in solidified sap
droplets.
Queenie Chan, a planetary
scientist and postdoctoral research associate at The Open University in the
U.K. who was the study's lead author, said, "This is really the first time
we have found abundant organic matter also associated with liquid water that is
really crucial to the origin of life and the origin of complex organic
compounds in space."
She added, "We're
looking at the organic ingredients that can lead to the origin of life,"
including the amino acids needed to form proteins.
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| Artist's rendering of asteroids and space dust. Credit: NASA/JPL-Caltech |
If life did exist in some
form in the early solar system, the study notes that these salt
crystal-containing meteorites raise the "possibility of trapping life and/or
biomolecules" within their salt crystals. The crystals carried microscopic
traces of water that is believed to date back to the infancy of our solar
system - about 4.5 billion years ago.
Chan said the similarity of
the crystals found in the meteorites - one of which smashed into the ground
near a children's basketball game in Texas in March 1998 and the other which
hit near Morocco in August 1998 - suggest that their asteroid hosts may have
crossed paths and mixed materials.
There are also structural clues
of an impact - perhaps by a small asteroid fragment impacting a larger asteroid,
Chan said. This opens up many possibilities for how organic matter may be
passed from one host to another in space, and scientists may need to rethink
the processes that led to the complex suite of organic compounds on these
meteorites.
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| Ceres, a dwarf planet in the asteroid belt pictured here in this NASA-produced false-color image, may be the source of organic matter found on two meteorites that crashed to Earth in 1998. Credit: NASA |
There are also clues, based
on the organic chemistry and space observations, that the crystals may have
originally been seeded by ice- or water-spewing volcanic activity on Ceres, she
said.
"Everything leads to
the conclusion that the origin of life is really possible elsewhere," Chan
said. "There is a great range of organic compounds within these
meteorites, including a very primitive type of organics that likely represent
the early solar system's organic composition."
Chan said the two meteorites
that yielded the 2-millimeter-sized salt crystals were carefully preserved at
NASA's Johnson Space Center in Texas, and the tiny crystals containing organic
solids and water traces measure just a fraction of the width of a human hair.
Chan meticulously collected these crystals in a dust-controlled room, splitting
off tiny sample fragments with metal instruments resembling dental picks.
"What makes our
analysis so special is that we combined a lot of different state-of-the-art
techniques to comprehensively study the organic components of these tiny salt
crystals," Chan said.
Yoko Kebukawa, an associate
professor of engineering at Yokohama National University in Japan, carried out
experiments for the study at Berkeley Lab's ALS in May 2016 with Aiko Nakato, a
postdoctoral researcher at Kyoto University in Japan. Kilcoyne helped to train
the researchers to use the ALS X-ray beamline and microscope.
The beamline equipped with
this X-ray microscope (a scanning transmission X-ray microscope, or STXM) is
used in combination with a technique known as XANES (X-ray absorption near edge
structure spectroscopy) to measure the presence of specific elements with a
precision of tens of nanometers (tens of billionths of a meter).
"We revealed that the
organic matter was somewhat similar to that found in primitive meteorites, but
contained more oxygen-bearing chemistry," Kebukawa said. "Combined
with other evidence, the results support the idea that the organic matter
originated from a water-rich, or previously water-rich parent body - an ocean
world in the early solar system, possibly Ceres."
Kebukawa also used the same
STXM technique to study samples at the Photon Factory, a research site in
Japan. And the research team enlisted a variety of other chemical experimental
techniques to explore the samples' makeup in different ways and at different
scales.
Chan noted that there are
some other well-preserved crystals from the meteorites that haven't yet been
studied, and there are plans for follow-up studies to identify if any of those
crystals may also contain water and complex organic molecules.
Kebukawa said she looks
forward to continuing studies of these samples at the ALS and other sites:
"We may find more variations in organic chemistry."
This article was initially published on Phys.org. You can
read the article here.