In the family history of all the stars in the Universe, our own is a toddler. Most stars were born billions of years before the Sun. Many are so old they have already consumed their nuclear fuel and cooled off to a compact Earth-sized remnant known as a white dwarf. And of the billions of stars in our own Milky Way galaxy, roughly half host an Earth-sized planet in the zone that would allow for liquid water and the chemistry of life.
