NASA’s Big, Big Vision
Its name--HR 4796--lacks poetry and at 220 light-years, or 1,300 trillion miles, away from Earth, it’s not exactly in the neighborhood. But the images unveiled last week of debris swirling around the distant white star provide the most vivid snapshot yet of planets in the process of formation.
The images are also an early triumph for NASA’s newly launched 20-year mission to seek evidence of life-bearing planets with high-tech ground- and space-based equipment. That mission, predicts NASA chief Daniel Goldin, could identify 480 Earth-size planets and develop observation technologies sophisticated enough to photograph “oceans, clouds, continents and mountain ranges” on planets orbiting stars up to 100 light-years away from our own sun.
There is as much boosterism as science in Goldin’s predictions. Yet there’s no doubt that his ambitious plan has helped restore sure footing to an agency that has often stumbled since Neil Armstrong’s “small step for a man” onto the moon’s surface nearly three decades ago. The agency’s next intended step, a manned mission to Mars, was dismissed as too expensive by Congress in the 1980s. The end of the Cold War slowed NASA’s progress further, and now the agency is being chided by Congress for mammoth cost overruns on the international space station, under construction.
Goldin’s planet-finding project is likely to get a warmer reception than the space station because the human urge to know whether man is alone in the universe is irrepressible.
The first sophisticated theories about planetary formation grew out of another human urge: the desire to find evidence of orderly evolution in the natural world. Philosopher Immanuel Kant and mathematician Pierre-Simon de Laplace theorized that our solar system’s planets formed from a disk of gas and dust that coagulated into nicely smooth balls circling our young sun. Their “nebular hypothesis” saw the solar system as striving, in Kant’s words, “to evolve itself out of the crude state of chaos.”
The modern version of the nebular hypothesis portrays a far less noble and kempt affair in which planets form into balls but then are battered by lightning and solar winds that strip them of life-giving chemicals. According to this theory, life may develop only when these barren rocks collide by chance with chemical-bearing comets.
NASA’s search for extraterrestrial life is focused on finding Earth-like planets. Some of the agency’s critics say that in so doing, NASA is making the same mistake that Kant and Laplace did in the 19th century: assuming that the cosmos will be shaped in ways that are familiar to us.
But there are good scientific reasons for NASA to be looking for planets like Earth. Water, for example, is the ideal solvent for the complex chemical reactions that lead to life, and water’s two chemical constituents, hydrogen and oxygen, are common throughout the galaxy. Moreover, planets smaller than Earth lack the mass to hold on to water and atmosphere.
However starry-eyed, NASA’s vision is sharper than it might seem.
