Should we even be searching for another Earth?


This collage prepared by combining NASA images, shows Saturn and six of its satellites. Along with a few of Jupiter’s moons, they are the likeliest places for life in our solar system thanks to their subsurface water. (Original images from NASA)

The hunt for planets that resemble Earth is today’s main public astronomy obsession, the way “Canals on Mars’ were big a century ago. Yet most professional astronomers are bored by the whole thing.

The reason is simple. We already know there are millions of Earth-mass planets in our galaxy’s comfort zones. When we started finding planets in the 1990s, our technology could only detect massive bodies orbiting low-mass stars, because we could only discover something if it was sufficiently tugging on its parent star to make it reliably wiggle. We spotted lots of them.

Nature always creates more small things than big ones. More minnows than whales. More viruses than linebackers. So, finding 500 Jupiters meant that many Earths must be there too, and probably a fifth of them would lie at comfortable-temperature distances from their parent star.         

Newer technologies soon let us find smaller bodies and, sure enough, Earth-mass planets have abundantly popped up. In a few years we’ll have catalogued thousands.  There. Done. So why the continued headlines? Once you learn that the Hudson River is filled with eels, is it really exciting to identify each one?

If we can find a distant planet whose atmosphere shows signs of free oxygen — which the new James Webb telescope may accomplish — we’d know it probably has plant life and who-knows what else. That discovery would be exciting.

Yet even that thrill would be short lived. Astronomers would be unable to offer any additional knowledge. The best possible image would be a dot, a single pixel. And a NASA space probe would require thousands of years to go there to send us further information. So knowledge about this planet would remain speculative. Would this be fun? Or frustrating? What’s your hunch?

The information gap would probably invite fraud and the kind of Web idiocy for which the internet is already famous. Count on people claiming psychic communications with the “advanced civilization” on that other Earth. Bottom line: the most realistic endpoint of today’s planet-seeking juggernaut will be a few thousand years of inconclusiveness.

Moreover, most assume that life requires an Earth-mass planet because that’s where we live and we’re not very imaginative. But the likeliest known place for life in our solar system is Jupiter’s moon Europa, followed by two of Saturn’s moons, simply because they all have subsurface oceans. Yet Europa’s mass doesn’t even resemble ours nor is it anywhere near our solar system’s “comfort zone” (where liquid water could exist on its surface.)

The bottom line is an interesting disconnect, where many laypeople find the search riveting, while most astrophysicists say: “Just in our own galaxy, millions of planets share our mass and temperature. If someone wants to discover and list them, go right ahead.” It’s valid science. Just be aware it won’t decisively answer any deep questions, nor provide any surprises.

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