The Tanpopo mission is an orbital
astrobiology experiment investigating the potential interplanetary transfer of
life,
organic compounds, and possible terrestrial particles in the low Earth orbit. The purpose is to assess the
panspermia hypothesis and the possibility of natural interplanetary transport of microbial life as well as prebiotic organic compounds.
The collection and exposure phase took place from May 2015 through February 2018 utilizing the Exposed Facility located on the exterior of Kibo, the
Japanese Experimental Module of the
International Space Station.[1] The mission, designed and performed by Japan, used ultra-low density silica gel (
aerogel) to collect
cosmic dust by,[2] which is being analyzed for amino acid-related compounds and microorganisms following their return to Earth.[3] The last samples were retrieved in February 2018 and analyses are ongoing.[4] The principal investigator is Akihiko Yamagishi, who heads a team of researchers from 26 universities and institutions in Japan, including
JAXA.
Mission
The capture and exposure experiments in the Tanpopo mission were designed to confirm the hypothesis that extraterrestrial
organic compounds played important roles in the generation of the first terrestrial life, as well as examination of the hypothesis of panspermia. If the Tanpopo mission can detect microbes at the higher altitude of
low Earth orbit (400 km), it will support the possible interplanetary migration of terrestrial life.[5][6] The mission was named after the plant
dandelion (Tanpopo) because the plant's seeds evoke the image of seeds of lifeforms spreading out through space.
The Tanpopo mission exposures took place at the Exposed Facility located on the exterior of the Kibo module of the ISS from May 2015 through February 2018.[4] It collected
cosmic dust and exposed dehydrated
microorganisms outside the International Space Station while orbiting 400 km (250 mi) above the Earth. These experiments will test some aspects of panspermia, a
hypothesis for an
exogenesis origin of life distributed by
meteoroids,
asteroids,
comets and
cosmic dust.[7] This mission will also test if terrestrial microbes (e.g., aerosols embedding microbial colonies) may be present, even temporarily and in
freeze-dried form in the low Earth orbit altitudes.[7]
Three key microorganisms include Deinococcus species: D. radiodurans, D. aerius and D. aetherius.[8] Containers holding
yeast and other microbes were also placed outside the Kibo module to examine whether microbes can survive being exposed to the harsh cold environment of
outer space. Also, by evaluating retrieved samples of exposed terrestrial microbes and astronomical organic analogs on the exposure panels, they can investigate their survival and any alterations in the duration of interplanetary transport.
Researchers also aim to capture
organic compounds and prebiotic organic compounds — such as
aminoacids — drifting in space.[9] The mission collected
cosmic dust and other particles for three years by using a two-layer
aerogel ultra-low density silica gel collector with a density of 0.01 g/cc (0.0058 oz/cu in) for the upper layer and ~0.03 g/cc (0.017 oz/cu in) for the base layer.[7] Some of the aerogel collectors were replaced every one to two years through February 2018.[9][4]
The official ISS experiment code name is "Astrobiology Japan" representing "Astrobiology exposure and micrometeoroid capture experiments".[10]
Objectives
The objectives of Tanpopo lie in following 6 topics:[11]
Sources of organic compounds to the surface of Earth[12]
Organic compounds on micrometeorites are being exposed to the space environment before return to Earth for analyses
Possibility for terrestrial microbe detection at the ISS orbital altitude due to the processes of volcanic eruptions, thunderstorms, meteorite impacts, and electromagnetic fields around the Earth
Survival of some species of microbes in the space environment
Capture of artificial micro-particles (space debris) by aerogel
Two aerogel densities to capture particles moving at high velocity
Analyses
The aerogels were placed and retrieved by using the robotic arm outside Kibo. The first year samples were returned to Earth in mid-2016,[12] panels from the second year were brought back in late 2017, and the last set ended exposure in February 2018.[4] The last aerogels were placed inside the 'landing & return capsule' in early 2018 and ejected toward Earth for retrieval.[7] After retrieving the aerogels, scientists are investigating the captured microparticles and tracks formed, followed by microbiological, organochemical and mineralogical analyses. Particles potentially containing microbes will be used for
PCR amplification of
rRNA genes followed by
DNA sequencing.[13]
Early mission results from the first sample show evidence that some clumps of microorganism can survive for at least one year in space.[14] This may support the idea that clumps greater than 0.5 millimeters of microorganisms could be one way for life to spread from planet to planet.[14] It was also noted that
glycine's decomposition was less than expected, while
hydantoin's recovery was much lower than glycine.[3]
^Tabata, M; Imai, E; Yano, H; Hashimoto, H; Kawai, H; et al. (2014). "Design of a Silica-aerogel-based Cosmic Dust Collector for the Tanpopo Mission Aboard the International Space Station". Transactions of the Japan Society for Aeronautical and Space Sciences, Aerospace Technology Japan. 12 (ISTS 29): Pk_29–Pk_34.
arXiv:1406.3160.
Bibcode:
2014JSAST..12.Pk29T.
doi:
10.2322/tastj.12.Pk_29.
S2CID118448985.
^Kawaguchi, Y.; Yang, Y.; Kawashiri, N.; Shiraishi, K.; Takasu, M.; Narumi, I.; Satoh, K.; Hashimoto, H.; Nakagawa, K.; Tanigawa, Y.; Momoki, Y.H.; Tanabe, M.; Sugino, T.; Takahashi, Y.; Shimizu, Y.; Yoshida, S.; Kobayashi, K.; Yokobori, S.; Yamagishi, A. (2013). "The possible interplanetary transfer of microbes: assessing the viability of Deinococcus spp. under the ISS Environmental conditions for performing exposure experiments of microbes in the Tanpopo mission". Orig Life Evol Biosph. 43 (4–5): 411–28.
Bibcode:
2013OLEB...43..411K.
doi:
10.1007/s11084-013-9346-1.
PMID24132659.
S2CID15967438.
^
abKawaguchi, Yuko; et al. (13 May 2016). "Investigation of the Interplanetary Transfer of Microbes in the Tanpopo Mission at the Exposed Facility of the International Space Station". Astrobiology. 16 (5): 363–376.
Bibcode:
2016AsBio..16..363K.
doi:
10.1089/ast.2015.1415.
PMID27176813.