Once Upon a Time on Mars
Dennies Overbye 丹尼斯·奥弗比
hree and a half billion years ago， waves splashed and streams surged across this dusty expanse on Mars now known as Jezero Crater. On a nascent Earth， chemistry was coagulating toward the exalted state we call life.
Astronomers， philosophers and science fiction writers have long wondered whether nature ran the same experiment there as on Earth. Was Mars another test tube for Darwinian evolution？
So humans have sent their progeny across time and 300 million miles of space in search of long-lost relatives， ancient roots of a family tree that might be traced in the Red Planet's soil.
The Perseverance rover and its little sibling， the Ingenuity helicopter， landed in a cloud of grit on Feb. 18， bristling with antennas and cameras. Perseverance will spend the next Martian year — the equivalent of two Earth years — prowling， poking and collecting rocks from Jezero Crater and the river delta that enters it. The rover will scrutinize the debris chemically and geologically， and take photographs， so that scientists on Earth can search for any signs of ancient fossilization or other patterns that living organisms might have produced.
Perseverance and Ingenuity operate on very long leashes: 12 minutes of light-travel time — and signal delay — across the ether from Pasadena， where their creators and tenders wait to see what they have accomplished lately. Like the teenagers you let out the door with the car keys， Perseverance and Ingenuity are no more intelligent and responsible than humans have trained them to be.
Those rocks will be picked up and returned to Earth in a five-year series of maneuvers involving relay rockets， rovers and orbital transfers starting in 2026 that will make the retrieval of the moon rocks look as easy as shipping holiday cookies to your relatives. The rocks that return starting in 2031 will be scrutinized for years， like the Dead Sea Scrolls， for what they might say about the hidden history of our lost twin and，perhaps， the earliest days of life in the Solar System.
The generation that followed World War II carried out the first great reconnaissance of the solar system. It could be the destiny of this generation to carry out the next great reconnaissance， to discover if we have or ever had any neighbors on these worlds. In Jezero Crater，the dream lives on. We may not ever live on Mars， but our machines already do.