人工衛星の急増による光害リスク深刻化

【パリＡＦＰ＝時事】地球を周回する人工衛星の急増による光害が「自然に地球規模で前例のない脅威をもたらしている」と警鐘を鳴らす論文が２０日、英科学誌ネイチャー・アストロノミーに掲載された。（写真はスペースＸの人工衛星の軌跡を示す長時間露出画像。資料写真。）
　米宇宙開発企業スペースＸがインターネット通信衛星「スターリンク」の衛星群を初めて打ち上げた２０１９年以降、地球低軌道を回る衛星の数は倍増している。
　低軌道に衛星が新たに投入されると、地球を周回している物体に衝突し、宇宙ごみ（スペースデブリ）が発生する危険が高まる。衝突の連鎖反応でさらに細かい宇宙ごみが生まれ、地球に光を反射する宇宙ごみの雲はさらに拡大する。
　研究チームは、夜空が明るくなることで天文台の活動が被る影響を科学・財政面から調査した。このような調査は初めてだという。
　その結果、現在チリに建設中の「ベラ・ルービン天文台」の場合、今後１０年で夜空が７．５％明るくなり、観測可能な星の数も約７．５％減少することが分かった。論文共著者のジョン・バレンティン氏によれば、年間損失額は約２１８０万ドル（約２９億円）に相当する。
　バレンティン氏は、天体現象を観測できなくなる事態も発生し得るとしている。
　光害の増加は予想以上に深刻とみられる。
　今回発表された別の論文は、広範なシミュレーションモデルに基づき、現在の光害の測定値は実際よりはるかに低く示されていると指摘している。【翻訳編集ＡＦＰＢＢＮｅｗｓ】
〔ＡＦＰ＝時事〕（2023/03/22-18:12）

Astronomers on Monday warned that the light pollution created by the soaring number of satellites orbiting Earth poses an unprecedented global threat to nature.
The number of satellites in low Earth orbit have more than doubled since 2019, when US company SpaceX launched the first mega-constellation, which comprise thousands of satellites.
An armada of new internet constellations are planned to launch soon, adding thousands more satellites to the already congested area fewer than 2,000 kilometres (1,250 miles) above Earth.
Each new satellite increases the risk that it will smash into another object orbiting Earth, creating yet more debris.
This can create a chain reaction in which cascading collisions create ever smaller fragments of debris, further adding to the cloud of space junk reflecting light back to Earth.
In a series of papers published in the journal Nature Astronomy, astronomers warned that this increasing light pollution threatens the future of their profession.
In one paper, researchers said that for the first time they had measured how much a brighter night sky would financially and scientifically affect the work of a major observatory.
Modelling suggested that for the Vera Rubin Observatory, a giant telescope currently under construction in Chile, the darkest part of the night sky will become 7.5 percent brighter over the next decade.
That would reduce the number of stars the observatory is able to see by around 7.5 percent, study co-author John Barentine told AFP.
That would add nearly a year to the observatory's survey, costing around $21.8 million, said Barentine of Dark Sky Consulting, a firm based in the US state of Arizona.
He added that there is another cost of a brighter sky that impossible to calculate: the celestial events that humanity will never get to observe.
And the increase in light pollution could be even worse than thought.
Another Nature study used extensive modelling to suggest that current measurements of light pollution are significantly underestimating the phenomenon.
- 'Stop this attack' -
The brightening of the night sky will not just affect professional astronomers and major observatories, the researchers warned.
Aparna Venkatesan, an astronomer at the University of San Francisco, said it also threatened our ancient relationship with the night sky.
Space is our shared heritage and ancestor -- connecting us through science, storytelling, art, origin stories and cultural traditions -- and it is now at risk, she said in a Nature comment piece.
A group of astronomers from Spain, Portugal and Italy called for scientists to stop this attack on the natural night.
The loss of the natural aspect of a pristine night sky for all the world, even on the summit of K2 or on the shore of Lake Titicaca or on Easter Island is an unprecedented global threat to nature and cultural heritage, the astronomers said in a Nature comment piece.
If not stopped, this craziness will become worse and worse.
The astronomers called for drastically limiting mega-constellations, adding that we must not reject the possibility of banning them.
They said that it was naive to hope that the skyrocketing space economy will limit itself, if not forced to do so, given the economic interests at stake.