Science Digest

Science Digest

Monday, April 27, 2009

Hunt for Other 'Earths'

Recent discoveries by planet-hunters have made astronomers more optimistic that the universe has plenty of rocky, Earth-like planets that occupy the "habitable zone" around stars.

Since the discovery in 1995 of the first "exoplanet," astronomers have found more than 300 such worlds, almost all of them Jupiter-size "gas giants," the easiest to detect with today's technology. There has been speculation that such giant planets may migrate closer to their parent stars and, en route, obliterate any smaller, Earth-like bodies.

But that seems a bit less likely with the announcement last week by Swiss astronomer Michel Mayor and colleagues of the discovery of two planets orbiting the red dwarf Gliese 581, a relatively small, cool star about 20 light years from Earth. One of the planets, orbiting extremely close to the star, is 1.9 times the mass of Earth, the smallest "exoplanet" found to date. The other, about seven times the mass of Earth, is even more intriguing, for it is much farther from the star, at a distance that appears to place it in the theoretical habitable zone, where water might be able to remain liquid on the surface, as is the case with Earth.

That's wonderful news, said William Borucki, lead scientist on NASA's Kepler space telescope, which will begin observations in mid-May designed to find Earth-like planets and estimate their abundance in our galaxy.

"It really gives us confidence that we're going to be finding planets rather than a null result," he said. "The giant planets do not wipe out all the small planets. That's a great discovery."

MIT astronomer Sara Seager said of the Mayor discoveries, "It's not a huge surprise, but it's taking us down the inevitable path to finding planets like Earth. . . . It's just a matter of time."

The new planets were not seen directly but were detected through a wobble in the starlight coming from Gliese 581 that revealed the gravitational influence of the orbiting bodies. The Mayor team made the find using a spectrograph attached to a European Southern Observatory telescope in Chile.

Team member Stephane Udry said the planet found in the habitable zone is the "first serious 'water world' candidate." He told The Washington Post by e-mail that the possibility of life on such a planet remains purely a matter of speculation: "At this point we can just say that a small-mass planet is there at a good distance for water to exist on the surface and thus for life potentially to develop. Only observations will tell us if there is life there."

-- Joel Achenbach

Decoding an Old Script

Scientists studying tablets, seals and ceramics left behind by a 4,000-year-old civilization that existed in what is now eastern Pakistan and northwestern India have concluded that inscriptions on the artifacts appear to be an as-yet undeciphered human language.

Until now, scientists had been divided over whether the inscriptions -- which sometimes depicted a human or animal figure set beneath a row of symbols -- were merely pictograms or a language, with grammar and syntax.

A computational analysis has found that the inscriptions probably represent a language spoken by the people of the Harappan civilization, although no one knows how to decipher it. The research was published in the journal Science last week.

Computer scientist Rajesh Rao at the University of Washington and an international group of colleagues studied recurring patterns in the symbols on the artifacts and estimated the regularity with which the symbols appeared. The researchers analyzed the inscriptions in comparison with several human languages, including English and languages with ancient pedigrees -- Sumerian, Sanskrit and Old Tamil. They also studied the pattern of symbols in the DNA code and the computer language Fortran. The randomness with which symbols appeared predicted whether they were likely to be part of a human language.

Non-linguistic systems, such as the DNA code or religious hieroglyphs that show pictures of gods, tend to have symbols that recur at random or with mind-numbing regularity. All the languages, however -- including the symbols on the Harappan artifacts -- showed intermediate levels of randomness, in that symbols recurred in regular patterns as well as at random.

The Harappan civilization, which flourished from 2600 B.C. to 1900 B.C., coexisted with human societies in Egypt and Mesopotamia.

-- Shankar Vedantam

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