Space oddity

杏吧论坛 College鈥檚 Darby Dyar explains the enduring mystery of Earth鈥檚 unusual moon.

The moon is full of mystery. 

One of the biggest mysteries? Why it鈥檚 there at all.

鈥淲e have no idea why the moon is here,鈥 Darby Dyar recently told Meredith Hoddinott of Vox鈥檚 鈥溾 podcast.

Even among the many moons in our own solar system, ours stands out. Other planets鈥 moons are small and oddly shaped. Our moon, in contrast, is huge, smooth and round. Most of our moon is composed of anorthosite 鈥 a glittery, reflective mineral that creates that lunar glow when it is bathed in the light of the sun. 

One theory of the moon鈥檚 origin postulates that in the early days of our solar system, a too-close-for-comfort planet called Thea crashed into Earth, and the resulting debris came back together to form the moon. 

But as scientists like Dyar analyze the moon rock samples that Apollo brought back to Earth more than 50 years ago, they have found that the chemical signatures of moon minerals are identical to those on Earth 鈥 and there鈥檚 not a trace of theoretical Thea鈥檚 fingerprints to be found.

Some theorize that Thea was completely subsumed by Earth and now exists deep within its magma core. Though we still don鈥檛 know the whole story, scientists like Dyar know one thing: The answer is there.

鈥淚 feel like rocks鈥ell such involved stories, and you just have to ask them the right questions,鈥 said Dyar, for whom the Moon鈥檚 beauty and mystery has never faded in all her years of study. After teaching class at night, she gazes out her office window at it.

鈥淢y favorite thing is鈥very now and then I go get the [moon rocks] out of the safe, and I stand here, hold the sample in my hand and look at the moon.鈥

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