Word: asteroidal
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Dates: during 1990-1999
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Paleontologists know plenty about the demise of the dinosaurs, not just how it happened--most likely in the aftermath of a cataclysmic comet or an asteroid impact 65 million years ago--but also the variety of species that were around at the time. But there is very little evidence about the other end of the age of dinosaurs. No one knows precisely when the "terrible lizards" arose or what the earliest dinosaurs were like...
...pivot point at the center of galaxies, planets in turn orbit stars, and moons in turn orbit planets. Last week astronomers writing in the journal Nature announced that this cosmic reductionism goes even further. For the first time, ground-based telescopes spotted a tiny moonlet orbiting a mere asteroid in Earth's own solar system...
...most respects the asteroid that's causing the celestial stir is nothing remarkable. Known to astronomers as Eugenia, it measures about 133 miles across and is one of thousands of bits of cosmic flotsam in the great rubble stream between Mars and Jupiter. When an international team of astronomers working at the Canada-France-Hawaii Telescope (CFHT) on Mauna Kea in Hawaii turned their attention toward Eugenia one evening last fall, however, they spotted something curious. Off on the upper-left corner of the fuzzy-looking image was another smear of light they couldn't identify. "These blobs are often...
...Hawaii discovery did not mark the first time a moonlet had been found around an asteroid. In 1993 the Galileo spacecraft sped past the 20-mile-wide asteroid Ida and spotted a scrap of moon just under a mile wide circling it. But the only way Galileo could detect the tiny target was to fly there across many millions of miles of space and do its exploring up close. Now, thanks to new optics in the CFHT, it's possible to search for moonlets from the comfortable perch of a faraway Earth...
Already the discovery of the moonlet is paying scientific dividends. By analyzing the orbit of the satellite, astronomers are drawing surprising inferences about the composition of Eugenia itself. Most asteroids are thought to be about three times as dense as water, but Eugenia is barely 20% denser, suggesting it either is made of loosely packed rubble or is rich in ordinary ice. Further analysis could help settle the question, and more discoveries of more moonlets could shed similar light on Eugenia's asteroid-belt sisters...