Carolyn Porco: Could a Saturn moon harbor life?
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【話題】 土星の月に生命は存在するか？

【時間】３分２７秒

【要約】

Ⅰ．２年前（2007年）のTEDトーク

　　①エンセルディスの南極に見える縞模様の亀裂

　　②ジェット噴射の写真

　　　　間欠泉と前生物的な化合物が存在するのでは？

Ⅱ．その後２年間の研究

　　ジェット噴射の組成分析

　　　　・プロパン

　　　　・ベンゼン

　　　　・シアン化水素、

　　　　・ホルムアルデヒド

　　　　・塩分を含んだ氷

　　岩石と接触した状態で液体の水が存在する可能性

　　つまり生命を育む環境が存在する可能性

Ⅲ．生命存在の可能性について自信を深めた

　　将来、人類がエンセルディスへ旅することは可能だ

【語彙】

Cassini ：カッシーニ、探査衛星の名前

Saturn ：土星

anomalously ：異常に

Enceladus ：エンセルディス、土星の月

fracture ：亀裂

onset ：開始

towering jets ：ジェット噴射のような柱状のも

erupt ：噴出する

geysers ：間欠泉（定期的に噴き出す温泉）

prebiotic ：前生物的な、アミノ酸のことを指しているのでしょう

【transcripts】

Two years ago here at TED I reported that we had discovered at Saturn, with the Cassini Spacecraft, an anomalously warm and geologically active region at the southern tip of the small Saturnine moon Enceladus, seen here. This region seen here for the first time in the Cassini image taken in 2005. This is the south polar region, with the famous tiger-stripe fractures crossing the south pole. And seen just recently in late 2008, here is that region again, now half in darkness because the southern hemisphere is experiencing the onset of August and eventually winter.

And I also reported that we'd made this mind-blowing discovery -- this once-in-a-lifetime discovery of towering jets erupting from those fractures at the south pole, consisting of tiny water ice crystals accompanied by water vapor and simple organic compounds like carbon dioxide and methane. And at that time two years ago I mentioned that we were speculating that these jets might in fact be geysers, and erupting from pockets or chambers of liquid water underneath the surface, but we weren't really sure. However, the implications of those results -- of a possible environment within this moon that could support prebiotic chemistry, and perhaps life itself -- were so exciting that, in the intervening two years, we have focused more on Enceladus.

We've flown the Cassini Spacecraft by this moon now several times, flying closer and deeper into these jets, into the denser regions of these jets, so that now we have come away with some very precise compositional measurements. And we have found that the organic compounds coming from this moon are in fact more complex than we previously reported. While they're not amino acids, we're now finding things like propane and benzene, hydrogen cyanide, and formaldehyde. And the tiny water crystals here now look for all the world like they are frozen droplets of salty water, which is a discovery that suggests that not only do the jets come from pockets of liquid water, but that that liquid water is in contact with rock. And that is a circumstance that could supply the chemical energy and the chemical compounds needed to sustain life.

So we are very encouraged by these results. And we are much more confident now than we were two years ago that we might indeed have on this moon, under the south pole, an environment or a zone that is hospitable to living organisms. Whether or not there are living organisms there, of course, is an entirely different matter. And that will have to await the arrival, back at Enceladus, of the spacecrafts, hopefully some time in the near future, specifically equipped to address that particular question. But in the meantime I invite you to imagine the day when we might journey to the Saturnine system, and visit the Enceladus interplanetary geyser park, just because we can.

Thank you.

キャロライン・ポルコ「土星の月に生命は存在するか？」