Planets continue to make the news in new ways all the time. And with almost every finding that some observatory or institution announces to the public, there comes the obligatory comment on what this might mean for life in the universe. Most of these comments are brief and simplistic. But we shouldn’t become jaded; this is a real and important topic, and it becomes more overwhelmingly important to the human future the farther into the future you care to look.
Two exoplanet findings that were announced in the last two weeks are either good or bad news for mankind, depending on how you think. On the one hand they are genuinely positive for how abundant living worlds may be throughout the universe.
On the other hand, one of them in particular is profoundly unsettling in what it hints about our own future.
The first finding was theoretical, worked out by modeling the interactions of suns with their planets in extreme circumstances. The suns in question are red-dwarf stars, the dimmest and most abundant stars in the cosmos.
They’re dim enough that planets would have to huddle close to them to receive comfortable, liquid-water warmth. Fortunately, this is what the planets of such small, low-mass stars tend to do.
The catch: a world orbiting so close to a red-dwarf star should have its atmosphere stripped away by the outbursts and flares that happen early in such a star’s life.
But nature leaves a way to get through this fix, Rodrigo Luger and Rory Barnes of the University of Washington reported on Jan. 28.
A planet that starts off more like Neptune than Earth — that is, a massive body that’s mostly atmosphere — can have most but not all of its gas stripped away by the young red dwarf, leaving a world parked in the right place that’s more or less a good Earth.
The idea may sound simple, but the details were a bear. Such a lucky outcome might be unusual, but there are so many red dwarfs swarming among the brighter stars, and so many of them are proving to have exo-Neptunes, that the sheer numbers make the scenario look good.
If we ever get a radio wake-up call from another civilization, this is the kind of world it may come from.
The wings of the owl of Minerva
The Path of the Upward Spiral
The other news, released on Jan. 27, is more sobering. It too deals with the worlds of a dwarf star. Yale planet hunters Sarbani Basu and Debra Fischer untangled the signs of five planets, all roughly Earth-size, periodically crossing the face of the star Kepler-444. We observe this happening by a stroke of luck: their orbits appear exactly edge-on from Earth’s point of view.
Other exo-solar systems like this were already known. The remarkable thing about this one is the age of the star: 11.2 billion years. That’s much older than our 4.6-billion-year-old sun and solar system. Kepler-444 and its planets formed when the universe was less than 20 percent of its present age.
Astronomers had not known that rocky, Earth-like planets could form so early in cosmic history. The heavy elements that make up the bulk of a good world — iron, silicon, oxygen, magnesium, and other rock-forming elements — accumulated in the universe only gradually.
They emerge only from the smoke and ashes of dead stars that cooked them up from hydrogen in their nuclearreactor interiors. Material from the early universe is quite deficient in such elements. But clearly now, there was enough to make rocky planets anyway.
In fact, astronomers estimate that a majority of the Earths in the Milky Way have a billion or two years’ head start on us.
Why is this so sobering for our future? Because it removes what used to be a tidy explanation for a troubling mystery. If the universe is full of life-friendly planets, and if life often evolves to intelligence and space travel as it has done here, the mystery is why aren’t we already overrun with waves of aliens? Since ages and ages ago? One theory was that we’re among the first; others haven’t had time yet to evolve and spread very far. But now that explanation is shot to pieces.
The fact that Earth hasn’t been a constant busy alien spaceport since the Precambrian Era is an aspect of the Fermi Paradox, named for the nuclear physicist Enrico Fermi, who in 1950 pointedly asked, “Where are they?”
Clearly, something prevents the development of abundant advanced life that builds interstellar spacecraft. And we don’t know what it is.
