推荐回答（1个）
每当说起外星人，我们总是充满想象，脑海中会浮现各种各样的奇异镜头：有触须的猛兽，皮肤苍白、瘦骨嶙峋的类人怪物，以及释放纯净能量、微微发光的生物。由于科学家仍未找到有关外星人体貌特征的证据，所以，没人知道人类在与外星人面对面时会是怎样的一番情景。尽管缺乏确凿证据，不过天文学和生物学仍会为这种接触提供一些线索。一些科学家甚至对可能存在于遥远世界的外星人特征做出大胆猜测。 这些外星生命的模样取决于人类遇到它们的地点和方式。除了飞碟外星，还有两个可能性：一是通过造访地球附近的行星和卫星，与我们的邻居亲密接触；二是给居住在绕外星人恒星运转的、更为遥远行星上的生物打“星际电话”。上述两个不同选择也让我们在那里发现的外星人相貌上存在差异。如果人类与外星人的首次接触发生在太阳系内，至少我们还对外星人的居住地有所了解。 太阳系中有多个星球可能适于类地生命的存在，这种生命基于碳生物化学特性，将水作为生存要素。例如，火星地下土可能很温暖，足以支持像地球细菌一样的微生物，而在太阳系的一些外层卫星的海洋中，可能还有更大的猛兽存在，特别是木星的卫星木卫二。木卫二冰层下面甚至有可能存在深海，并延伸至这颗卫星的岩质核心，在那里，火山口不断往外喷射富含营养物的热水。 据美国华盛顿州立大学天体生物学家德克-舒尔策-马库奇(Dirk Schulze-Makuch)估计，火山口提供的能量可以养活大批微生物，而这些微生物反过来又能支持无数的食肉动物。木卫二上最高级的食肉动物(相当于地球上的大白鲨)可能是体重只有1克的可怕生物。他说：“木卫二可能支持虾一般大小的生物体。”当然，虾一般大小的生物体并不意味着它们具有虾一般的外形。 舒尔策-马库奇说：“很难对它们的外形特征做出估计。”即便在地球上，动物也能进化为各种各样的惊人外形，尽管如此，舒尔策-马库奇仍对外星生物做出大胆猜测。他说：“我猜测它们应该像蠕虫一样，这是地球上一种非常成功的生物体。”虽然有科学家认为，木卫二上可能有冰虫在冰冷海水中游动，但一些天体生物学家甚至发挥更大的想象空间，提出不以水为生的生命的可能性。
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