科学家们已经发射了很多宇宙飞船去探索太阳系的其他行星。
Scientists have launched many spaceships to explore other planets in the solar system.
以色列警方说，在过去的11天的战斗中，总共有520发火箭已经发射。
Israeli police said a total of 520 rockets had been fired in the past 11 days of fighting.
他认为，人类运用雷达天文学探测小行星和金星等天体，早已经发射出可以被外星智慧生物接收到的信号。
He argues that radar astronomy, which is used to probe things like asteroids and the surface of Venus, already gives off signals that could be picked up by aliens.
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