Re “Life Among the Stars” (cover story, March 18): There may be trillions of planets in the universe. The important question to consider is what conditions should exist to make a planet habitable for animal life. Peter Ward and Donald Brownlee in their book Rare Earth: Why Complex Life Is Uncommon in the Universe show that more than 100 narrowly tuned constraints have to be satisfied for an Earth-like planet to exist. If so, this could bring the probability to one, i.e., us! Astrophysicist Frank Drake arrived at the same conclusion 40 years ago.
Re “Life Among the Stars” (cover story, March 18): There may be trillions of planets in the universe. The important question to consider is what conditions should exist to make a planet habitable for animal life. Peter Ward and Donald Brownlee in their book Rare Earth: Why Complex Life Is Uncommon in the Universe show that more than 100 narrowly tuned constraints have to be satisfied for an Earth-like planet to exist. If so, this could bring the probability to one, i.e., us! Astrophysicist Frank Drake arrived at the same conclusion 40 years ago.