Earth has had oceans for nearly four billion years¹ and Mars had lakes and rivers 3.5–3.8 billion years ago². However, it is still unknown whether water has ever condensed on the surface of Venus^3,4 because the planet—now completely dry⁵—has undergone global resurfacing events that obscure most of its history^6,7. The conditions required for water to have initially condensed on the surface of Solar System terrestrial planets are highly uncertain, as they have so far only been studied with one-dimensional numerical climate models³ that cannot account for the effects of atmospheric circulation and clouds, which are key climate stabilizers. Here we show using three-dimensional global climate model simulations of early Venus and Earth that water clouds—which preferentially form on the nightside, owing to the strong subsolar water vapour absorption—have a strong net warming effect that inhibits surface water condensation even at modest insolations (down to 325 watts per square metre, that is, 0.95 times the Earth solar constant). This shows that water never condensed and that, consequently, oceans never formed on the surface of Venus. Furthermore, this shows that the formation of Earth’s oceans required much lower insolation than today, which was made possible by the faint young Sun. This also implies the existence of another stability state for present-day Earth: the ‘steam Earth’, with all the water from the oceans evaporated into the atmosphere.

地球拥有海洋已有将近 40 亿年¹，而火星在 3.5-38 亿年前²拥有湖泊和河流。然而，水是否曾经凝结在金星表面^3,4仍然是未知数，因为这颗行星 - 现在完全干燥⁵ - 经历了全球表面重修事件，掩盖了它的大部分历史^6,7。水最初在太阳系类地行星表面凝结所需的条件非常不确定，因为迄今为止只用一维数值气候模型对它们进行了研究³这无法解释大气环流和云层的影响，它们是关键的气候稳定剂。在这里，我们使用早期金星和地球的三维全球气候模型模拟表明，由于强烈的太阳下水蒸气吸收，水云优先在夜间形成，具有很强的净变暖效应，即使在适度的条件下也能抑制地表水凝结。日晒（低至每平方米 325 瓦，即地球太阳常数的 0.95 倍）。这表明水从未凝结，因此，海洋从未在金星表面形成。此外，这表明地球海洋的形成需要比今天低得多的日照，而这得益于微弱的年轻太阳。这也意味着当今地球存在另一种稳定状态：