Keenan chased down the chompers to investigate what whitening strips do to a tooth's chemical composition.

基南追踪这些牙齿，以研究美白牙贴会对牙齿的化学成分产生何种影响。

We measure the chemical composition of the atmosphere using isotopes: they're like different flavors of atomic elements.

我们用同位素测量大气的化学成分：它们就像不同味道的原子元素。

And then you combine those to make NH3, which is the chemical composition for ammonia.

然后将它们结合起来生成 NH3，这是氨的化学成分。

Supposedly, this alters the chemical composition of the baking soda to make it perform more like lye.

据说，这会改变小苏打的化学成分，使其表现得更像碱液。

But now in his 40s, he continues to study the chemical compositions of the brightest galaxies.

但如今，40 多岁的他仍在继续研究最亮星系的化学成分。

Again, the ability of dust particles to absorb solar radiation depends on their size, shape and mineralogical and chemical composition.

同样，尘埃颗粒吸收太阳辐射的能力取决于它们的大小、形状以及矿物和化学成分。

It's going to measure the internal ocean with a radar that can penetrate the ice on top and use cameras and spectrometers to map the chemical composition and geology on the surface.

它将用可以穿透顶部冰层的雷达来测量内部海洋，并使用相机和光谱仪来了解木卫二表面的化学成分和地质情况。

However, humans have not discovered any concrete evidence  of extraterrestrial organisms.We don't know which planets they live on or what shape they take —  even their chemical composition remains a mystery.

然而，人类还没有发现任何外星生物的具体证据。我们不知道它们生活在哪些行星上，也不知道它们的形状——甚至它们的化学成分仍然是个谜。