“How shall we praise the magnificence of the dead, / The great man humbled, the haughty brought to dust?” There you have the first two lines of Conrad Aiken’s great poem “Tetélestai”—its title a Greek word meaning, “It is finished.” “Tetélestai” is a requiem for the nobody, the little person who failed to make waves, the one who might be me, who might be you: “Say that I have no name, no gifts, no power, / Am only one of millions, mostly silent; / One who came with lips and hands and a heart, / Looked on beauty, and loved it, and then left it.”
It is finished. This moment will arrive for each of us, and we know it, even as we deny it. At least I deny it.
But what we deny even more is Earth’s forthcoming demise, including all of our kind and every other thing, living and dead. And that day will come. And this is not a religious tract.
Stars have lifespans, and our star is half over. Five billion of our sun’s allotted 10 billion years have passed. We have five billion to go. But long before that, we’ll be toast. In a debated one-to-four-billion years the sun will expand and lap the shores of Earth. Tetélestai.
The sun burns, but it is not a fire. It’s a nuclear furnace composed largely of hydrogen (70 percent) and helium (28 percent).
Now, a hydrogen atom has only one proton. A helium atom has two protons and two neutrons. Protons strongly repel each other, which is why atoms refuse to fuse on the stovetop. But at the sun’s core, heat and pressure overcome proton repulsion, and hydrogen protons smash together. So four hydrogen atoms, with their four protons, fuse (in a series of steps) to become one helium atom, with its two protons and two neutrons. Nuclear fusion. The new helium atom is lighter than the four hydrogen atoms that made it, and since energy changes form but never goes away, the excess energy is released as heat and light. That would be our sunshine.
In the sun, nuclear fusion converts 600 million tons of hydrogen into 596 million tons of helium plus four million tons of energy every second.
Flash forward. The sun’s core runs out of hydrogen fuel. The core is now all helium (which begins fusing into carbon), while the surrounding rings are hydrogen. Gravity crunches the core. Helium atoms take up less space; the core shrinks, gets hotter. The hotter core cooks the hydrogen rings hotter, and the hydrogen atoms fuse into helium faster. Faster fusion produces more heat, which expands outward. As the core shrinks, the sun gets bigger. And redder. Our sun will become a red giant. It will swallow its nearest planet, Mercury. As for us? Hot times. Oceans boiling away. Our goose, cooked.
But wait—there’s hope: new earths. Maybe lots of new earths. Planets that orbit their suns at the optimum distance for water to run, for life to live. NASA’s Kepler Mission hauled into our hopes some 2,300 planet-candidates just in our own little galaxy. The Kepler spacebased telescope, launched in March 2009, keeps its wide eye fixed on the same 100,000 sun-like stars (in a region in the Cygnus and Lyra constellations), continuously and simultaneously measuring the brightness of each star. When, from Kepler’s perspective, a planet crosses in front of its star (called a transit), the star dims and the telescope records the hours of dimming. If it’s really a planet orbiting, the dimming is periodic and as regular as my granddaddy’s trips to the post office. NASA tells us we have evidence for gas giants, hot super-Earths, and ice giants. It’s only matter of time before another habitable earth is found. And we have time.
