Figure.
Photocatalytic Reaction of Titanium Oxide
Abiotic oxygen can
be produced from water in the presence of titanium oxide and an
electron acceptor
under UV light. Our report suggests that this photocatalytic reaction
can supply
significant amount of abiotic oxygen on habitable extrasolar planets.
(September 10, 2015) The
Earth’s atmosphere contains oxygen because plants continuously produce it
through photosynthesis. This abundant supply of oxygen allows life forms like
animals to flourish. Therefore, oxygen had been thought to be an essential
biomarker for life on extrasolar planets. But now, a research assistant
professor Norio Narita of the Astrobiology Center of NINS, which was founded in
April 2015, and an associate professor Shigeyuki Masaoka, of the Institute of
Molecular Science of NINS, have presented a novel hypothesis that it could be
possible for planets to have large quantities of abiotic (non-biologically
produced) oxygen. This study is a good example of interdisciplinary studies
that combine knowledge from different fields of science to promote astrobiology
in the search for life on extrasolar planets. The study is published in
Scientific Reports on Sep 10, 2015.
Until now, it had been thought that if a planet has oxygen,
that must mean that some form of plants are producing it through
photosynthesis. Therefore, it had been assumed that when searching for signs of
life on habitable extrasolar planets, the presence of oxygen in the atmosphere
could be considered a definitive biomarker. However, non-biological chemical
reactions can also affect atmospheric compositions of extrasolar planets. Now,
the research team led by Dr. Narita has shown that, abiotic oxygen produced by
the photocatalytic reaction of titanium oxide, which is known to be abundant on
the surfaces of terrestrial planets, meteorolites, and the Moon in the Solar
System, cannot be discounted.