That's because below its triple point, a substance can't actually take a liquid form.

气相和固相...那是因为它下降了 三相点，一种不以液体形式存在的物质。

That's the triple point. And that's what Mariner 9 used to map out Mars!

这三点。 这就是 Mariner 9) 用来画火星的东西！

The triple point of water is 6.105 millibars and exactly 273.16 Kelvin.

水的三相点是 6。105 毫巴 和 0。01 x 正好。

We also talked about phase changes, including the critical point, the triple point, and how that all applies on Mars.

我们还谈到了形状变化，临界点 三相点，以及这如何适用于火星。

The triple point of carbon dioxide is about 5 times atmospheric pressure, so liquid carbon dioxide can't naturally exist on Earth.

二氧化碳的三相点高出5倍 大气压，所以没有二氧化碳。

A triple point is the temperature and pressure at which a substance coexists as a solid, a liquid, and a gas.

三相点是它所在的温度和压力 物质有固体、液体和气体。

Now, you'll notice on the diagram that at pressures and temperatures below the triple point, there's only the gas phase and the solid phase.

我们在图表上注意到，在压力 温度低于三相点，就在那里。

It also made a lot of sense for the Mariner 9 mission to use the pressure of the triple point of water as the reference point for its Martian maps.

因为它对水手九号有意义。 使用水的三相点压力作​​为参考。