Sometimes we forget how recently we Earthlings thought our planet was the center of the universe, which up until the 17th century ended at Saturn and used the “fixed” stars as a mere decorative backdrop. It was only in 1610 — barely 400 years ago — that Galileo looked at the heavens through a telescope, glimpsed their teeming infinity and figured that Copernicus might be right about Earth’s place in the scheme of things.
Since then, our knowledge of the universe has expanded exponentially. At first, the discovery of additional planets beyond the seven that had been known since antiquity caused terrific excitement. When Keats famously compared his feelings about Chapman’s translation of Homer with the thrill felt by “some watcher of the skies/ When a new planet swims into his ken,” he would have had in mind William Herschel’s discovery of Uranus in 1781, 14 years before Keats was born. In those days, such a find evidently resonated for decades.
But the pace soon picked up. By the end of the 20th century, the number of known major bodies in the solar system alone had jumped to more than 70 — and astronomers were at the same time peering far beyond their own backyard, to what they like to call the very edges of the universe. So big was the window opened by the Hubble Space Telescope, in particular, that the momentous quickly became the routine. When scientists announced last year that they could now see so far into space they were actually looking back in time, in fact almost as far back as the Big Bang, the public yawned.
Yet astronomers were not, until very recently, discovering any more planets. Our own Sun’s little flock was set at nine with the 1930 discovery of Pluto — though that last puny fellow was nearly downgraded last year — but the first “extrasolar” planet was not convincingly detected until just six years ago. Although the existence of such bodies had long been suspected, evidence was hard to pin down. Distant planets cannot be seen in the dazzling light of their host stars, so scientists have to infer their presence by measuring a star’s wobble in response to some invisible planet’s gravitational pull.
The process is arcane enough to have kept the developments of the last six years out of the headlines, unlike the more obviously glamorous stories of water hunts on the moon or signs of life on Mars. But a meeting in England last week of the International Astronomical Union did finally attract a smidgen of attention. Astronomers have been quietly adding to the list of extrasolar planets since 1994, but recently, it turns out, their measurement techniques have improved to the point of triggering a sudden quantum leap in discoveries. Last Monday, four different groups of researchers announced the reliable detection of maybe a dozen new “off-Sun” planets, bringing the tally to over 50.
From Earthlings’ solipsistic point of view, one question naturally overrides all others: Are any of these planets like ours? That is, might they harbor life? Disappointingly, the answer so far is no. Not one of the solar systems hosting the newfound planets resembles the Sun’s, and all the planets are Jupiter-size gas balls following orbits inimical to the presence of smaller, Earth-like planets in the same system. If there is a trend, it is in the direction of confirming Earth’s rarity, if not yet its uniqueness.
So, once again, the ultimate headline is postponed. But that in no way undermines the genuine significance of the latest announcements, which is what they reveal about the rate of discovery, extraordinary by anyone’s reckoning. “We’re now at a stage where we are finding planets faster than we can investigate them and write up the results,” said U.S. astronomer Geoffrey Marcy last week.
What this means is that the big picture could change within a few years, even months. Already scientists say they have detected the “signatures” of many smaller, hidden planets likely to be more analogous to Earth. And they are seeing more and more hints of multi-planet systems, even around stars where only one planet has been firmly detected. Ahead of the deployment of more sophisticated space-based instruments in the next decade, scientists are not closing the door on any possibilities.
“Planet hunting,” as Mr. Marcy concluded last week, “has morphed from the marvelous to the mundane.” The media and other sensation seekers might think that a bad thing. Mr. Marcy thinks it’s wonderful. He’s right, of course, if only because the mundane is the historic seedbed of marvelous discoveries. In the meantime, it’s worth reflecting on another marvel brought into focus by last week’s conference: how unbelievably far we have come in 400 years.
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