Scientists believe that oxygen first showed up in the atmosphere about 2.7 billion years ago. They think it was put there by a one-celled organism called "cyanobacteria," which had recently become the first living thing on Earth to make oxygen from water and sunlight.

Like the little engine that could, geologic activity on the surface of Saturn's moon Titan-maybe outgassing cracks and perhaps icy cryovolcanoes-is belching puffs of methane gas into the atmosphere of the moon, creating clouds.

The newly discovered 10th planet, 2003 UB313, is looking more and more like one of the solar system's major players. It has the heft of a real planet (latest estimates put it at about 20 percent larger than Pluto), a catchy code name (Xena, after the TV warrior princess), and a Guinness Book-ish record of its own (at about 97 astronomical units-or 9 billion miles from the sun-it is the solar system's farthest detected object). And, astronomers from the California Institute of Technology and their colleagues have now discovered, it has a moon.

For several years geologists have been gathering evidence indicating that Earth has gone into a deep freeze on several occasions, with ice covering even the equator and with potentially devastating consequences for life. The theory, known as "Snowball Earth," has been lacking a good explanation for what triggered the global glaciations.

A planet larger than Pluto has been discovered in the outlying regions of the solar system with the Samuel Oschin Telescope at Palomar Observatory, California Institute of Technology planetary scientist Mike Brown announced today.

Much of the heat within our planet is caused by the radioactive decay of the elements uranium and thorium. Now, an international team of particle physicists using a special detector in Japan has demonstrated a novel method of measuring that radioactive heat.

The current mean temperature on the equator of Mars is a blustery 69 degrees below zero Fahrenheit. Scientists have long thought that the Red Planet was once temperate enough for water to have existed on the surface, and for life to possibly have evolved. But a new study by Caltech and MIT scientists gives this idea the cold shoulder.

An extrasolar planet under three suns has been discovered in the constellation Cygnus by a planetary scientist at the California Institute of Technology using the 10-meter Keck I telescope in Hawaii. The planet is slightly larger than Jupiter and, given that it has to contend with the gravitational pull of three bodies, promises to seriously challenge our current understanding of how planets are formed.

The Sumatra-Andaman earthquake of December 26 was an unmitigated human disaster. But three new papers by an international group of experts show that the huge data return could help scientists better understand extremely large earthquakes and the disastrous tsunamis that can be associated with them.