original article:
http://www.nytimes.com/2011/06/24/opinion/global/24iht-june24-ihtmag-das-32.html?src=recg
An international team of astronomers recently presented compelling evidence that our galaxy is teeming with lonely Jupiter-sized planets adrift between stars. Alone in the void, unattached to any parent sun, these cosmic orphans appear to fill the heavens in vast numbers. Extrapolating from what they observed, Takahiro Sumi, an astrophysicist at Osaka University, and his colleagues reported in the journal Nature that there could be as many as 400 billion of these lonely wanderers in our Milky Way galaxy alone....
As if on cue, NASA then announced that its Kepler spacecraft, two years into a three-and-a-half year mission to find Earth-size planets around nearby stars, had found a totally unexpected profusion of candidates. Of the 1,235 suspected planets spotted so far, moreover, about a third were in multiplanet solar systems like ours. Judging from these discoveries, it would appear that planets out there are as numerous as grains of sand. Twenty-five years ago, when I was a student in high school, only nine planets were known, all in our solar system. We learned their names and sequence from the sun, from the fleet-footed Mercury to icy Pluto. We learned of the runaway greenhouse effect that had stoked Venus to blistering temperatures and read about the giant storm that is Jupiter’s red spot, and we gazed at pictures of the rings of Saturn that the Voyager spacecraft had sent back....
It may come as a surprise that it was only in 1995 that a planet beyond our solar system was first sighted. The discovery by the Swiss astronomers Michel Mayor and Didier Queloz was confirmed soon after by an independent team in the United States. I was a graduate student then and remember the great excitement this stirred among astronomers. Like Kant, many had believed that the processes that gave rise to our solar system were not unique, and that there were other planets in the universe. Now, observations had finally caught up with belief.
Finding “exoplanets” (for extrasolar planet, as planets outside our solar system are now referred to) is no easy matter. Planets emit no light of their own, and only reflect the light of their stars. Given the interstellar distances involved, even the stars nearest to us appear only as pinpoints, so it’s a technological challenge to identify a planet thousands of times dimmer.
Mayor and Queloz met the challenge by using a spectrograph at the Haute-Provence Observatory in southeastern France to observe the rhythmic wobble of a sun-like star known as 51 Pegasi, a wobble created by the gravitational tug of an orbiting planet. This “radial velocity” technique has been used since to find many planets, but its reliance on spotting the wobble of a star tends to pick out larger planets close to their parent star — like the Jupiter-sized one Mayor and Queloz reported — which most scientists think could not be capable of supporting life.
There are ways to detect smaller planets, and the Kepler spacecraft launched on March 7, 2009, was specifically designed, according to NASA, “to survey a portion of our region of the Milky Way galaxy to discover dozens of Earth-size planets in or near the habitable zone and determine how many of the billions of stars in our galaxy have such planets.” Kepler continuously monitors 145,000 stars in the Milky Way for the brief dimming of light that would indicate a “planetary transit” — a planet crossing the face of the star....
The team that discovered the wandering orphan planets, led by Takahiro Sumi and including David Bennett from the University of Notre Dame, used an even more arcane technique — gravitational microlensing — to spot these otherwise totally invisible bodies. Based on Einstein’s premise that gravity bends light, the technique can see dark objects in the sky by measuring the light they bend from stars behind them. The astrophysicists thus saw 10 drifters, and estimated that there may be one or two of them for each of the approximately 200 billion stars in the Milky Way.
That’s a quantum leap from the nine I knew in high school (reduced to eight after Pluto was demoted to a “dwarf planet” in 2006 by the International Astronomical Union), and even from the 500 or so exoplanets confirmed as of early this year. And if Jupiter-size planets, which are easier to spot, are numbered in the billions, surely there must be many Earth-size planets out there, spinning around their stars at just the right distance to support life? It is time to rewrite the texts.
You may wonder at this point why something so Earth shattering as the discovery of innumerable planets has not caused more excitement in the broad public....
The confirmation that planets are a dime a dozen is really the culmination of the scientific revolution first started by Copernicus and Galileo and Kepler more than four centuries ago, a revolution in which our home planet lost its special place at the center of the universe. The prevailing cosmology before Copernicus — codified by the astronomer Claudius Ptolemy in the first century A.D. and, though dead wrong, accepted for the next 1,500 years — held that the Sun, Moon and planets (the six known ones) all revolved around Mother Earth, under a canopy of stars. It was a rational and well organized universe, in which the Roman Catholic Church could point with authority to heaven above and hell below.
Then Nicolaus Copernicus, a timid Polish canon, put forward an alternate, heliocentric system in which the Sun replaced Earth at the center. In 1543, just before he died, Copernicus finally summoned the courage to publish his treatise, De Revolutionibus Orbium Coelestium (“On the Revolutions of Heavenly Spheres”), which would inspire Galileo Galilei and Johannes Kepler to pursue the studies that became modern astronomy. In an age when science was inextricably linked to religion, the Catholic Church did not surrender lightly its geocentric universe. To challenge it was “false and contrary to Scripture,” Galileo was told by the Inquisition, and even though he disowned his ideas, he spent his last years under house arrest. (In 2000, Pope John Paul II formally apologized for Galileo’s trial).
But there was no turning back. Within a few decades, Isaac Newton confirmed Kepler’s ideas on planetary motion and described the natural laws that have shaped our view of the cosmos ever since. Once the Earth had been displaced from the center of the universe, it was only a matter of time before the Sun was reduced to a garden variety star in a remote spiral arm of the Milky Way galaxy; the Milky Way itself to one of a hundred billion galaxies; and our planet to a speck of cosmic dust.
