It's thought to have formed when a small planet impacted Earth at a grazing angle billions of years ago.

人们普遍认为它是在数十亿年前一颗小行星以掠角撞击地球时所形成的。

It's big compared to Earth, and is thought to have formed when a small planet impacted Earth at a grazing angle.

它相对地球来说很大，被认为是由一颗小行星切线撞击地球时产生的。