The mass of a helium atom is less than the combined mass of two hydrogen atoms.

一个氦原子的质量会小于两个氢原子的总质量。

A helium nucleus is a tiny bit lighter than the combined mass of the 4 protons it is made from.

氦原子核虽然由四个质子形成但重量却比四个质子轻一点。

If their combined mass is more than 2.8 times that of the Sun they'll collapse to form a black hole.

如果它们的总质量超过太阳的2.8倍，它们就会坍缩形成黑洞。

Durante and his colleagues found that Saturn's bling has a combined mass of about one-and-a-half to two times 10 to the 19th kilograms… that's less than half the mass of its smallest moon.

这些使我们能够将环的总质量与它们的年龄联系起来。 ” 杜兰特和他的同事发现， 土星的金光闪闪的总质量约为 10 到 19 千克的 1. 5 到 2 倍… … 这还不到其最小卫星质量的一半。