CDEX Web Magazine 地球発見

CDEX
Discover the Earth:Mission to the Unknown World Dr. Kenneth H. Nealson

Dr. Kenneth H. Nealson of the J. Craig Venter Institute is a scientist of international standing who has long been a world-leading researcher in the field of environmental microbiology, including the global ocean genome project and the explanation of the metabolism of iron-reducing bacteria. He is also a pioneer in the field of astrobiology and was involved in the planning of the Mars Sample Return Mission at the NASA Jet Propulsion Laboratory. On this occasion, he sailed on the CHIKYU on the expedition off Hachinohe in Aomori Prefecture exploring the biosphere deep beneath the seafloor, and examined the collected samples. Dr. Nealson, who continues to take on the challenge of those places where people haven’t ventured, makes a special contribution to this issue.
(Published online March 2013)


Watching the sunset over the Pacific Ocean north and east of Honshu, it’s easy to forget that one is on board one of the most remarkable research vessels in the world. The D/V CHIKYU is a spectacular drilling ship, capable of retrieving clean oceanic sediment (core) samples for biological research from many kilometers below the ocean bottom, and equipped with state-of-the art laboratories for sample characterization and analysis.The highly skilled international CHIKYU crew does everything from keeping the ship precisely positioned above the drilling site, to retrieving multi-ton samples with mm-scale precision.

Mission to Deep Life

 So just what is going on here? It is the Integrated Ocean Drilling Program (IODP) Expedition 337, in search of knowledge of the deep Earth biosphere, one of the great unknowns of our planet. It is estimated that a significant fraction of the biomass on Earth is hiding in this subsurface niche. This biomass consists of microbes (Bacteria and Archaea, and possibly Eukaryotes), but the details of these subsurface microbial ecosystems are only now beginning to be described. The pathway to this knowledge is being charted scientists from the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), using the D/V CHIKYU, built in Japan and operated by JAMSTEC. In many ways, the drilling missions of the CHIKYU are equal in complexity to detailed space missions: it takes serious technological advances, coupled with scientific commitment and expertise to retrieve biologically useful (i.e., uncontaminated) core samples from deep in the oceanic sediments. The major difference, of course, is that missions to Mars involve robotic rovers, or circling observation satellites (i.e., no sample has ever been returned from Mars), while missions to the subsurface involve humans working with the CHIKYU, to retrieve samples for detailed analyses. Thus, bringing up the deepest sample ever retrieved for biological analysis is truly an exciting prospect, and having these samples to analyze is a great privilege.