NASA 小惑星衝突から地球を守る専門部署を設立

具体的な役割は、地球に接近する小惑星や彗星をいち早く発見し、分析すること。そして危機が迫る場合は政府や関係各機関の間の調整役もこなします。
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NASAが、小惑星が地球に衝突するような事態に備える専門部署、Planetary Defense Coordination Office (PDCO)の設立を発表しました。要するに隕石衝突から地球を守る防衛隊といったところです。

PDCOの具体的な役割は、地球に接近する小惑星や彗星をいち早く発見し、分析すること。そして危機が迫る場合は政府や関係各機関の間の調整役もこなします。 NASAはこれまでも地球に接近する天体があれば世界の宇宙機関と連携して対応してきました。PDCOはこれまで単発でこなしてきたこれらの緊急対応を受け持ち、連邦緊急管理庁(FEMA)ほかとも連携して"潜在的な危機・影響"の発見、警告、科学的分析を行います。

NASAが小惑星や彗星などの管理をし始めた1998年以来、地球近傍の宇宙空間には1万3500個の小天体が発見されてきました。現在でも、年間1500個ペースで新しい小惑星や彗星が発見されています。

ただ、すでに地球近傍の直径3000フィート(約915m)規模の小天体は、その9割ほどが発見されたと目されます。今後はPDCOが直径40フィート(約140m)級の天体の発見にシフトしていく計画です。このため、米国政府は2016年予算のうち5000万ドルをPDCOに割り当てました。これは5年前に比べると10倍以上の金額です。

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2013年にロシア・チェリャビンスクに落下した隕石の例を思い出せば、いつ何時我々に危機が訪れるかはわかりません。NASAは2020年の実行を目標として、地球に衝突する恐れのある小惑星の軌道を意図的に変えさせる「小惑星再配置ミッション(Asteroid Redirect Mission)を計画しています。

またNASAと欧州宇宙機関(ESA)は共同で、小惑星に人工物(宇宙船など)を衝突させてその軌道を変えさせようとするAsteroid Impact and Deflection Assessment(AIDA)計画の研究も進めています。こうした研究の成果を、いざ現実に実行に移す事態となったとき活躍するのがPDCO、ということになりそうです。

映画『アルマゲドン』の、小惑星に核爆弾を埋め込んで爆発させ、その軌道を変えるというストーリーは、我々一般市民が見ても「まあまあ、映画だから」と思わせるものでした。ところが実際はこのように、大真面目に検討されていることだというのは(別に石油採掘企業の中年オヤジを宇宙へ送り込むわけではないものの)なんとも面白いところです。

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