Light emitted from farther away, and thus older, quasars lacked this wavelength, because the light was getting absorbed by neutral helium as well as helium with a single ion-or charged particle.
Ion engines are incredibly efficient, which makes them well suited to deep space travel.
离子引擎是令人难以置信的高效率，所以非常合适深入的太空旅行。
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Helium ion microscopy (HIM) offers the highest spatial resolution surface imaging of any scanning beam method, as well as extremely high surface sensitivity.