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Another hint at an asteroid with a moon.

One of the major controversies of solar system astronomy in recent years has been the question of whether some asteroids have their own moons. There have been many intriguing observations that could support the idea--such as an asteroid briefly blocking the light of a star and the starlight then blinking a second time, as though a second object got in the way -- but all have lacked sufficient confirmation. Often such a "secondary event" would be noted by only one of several observers at different locations, a perfectly reasonable result but worthless at adding reliability to the one case in which something showed up.

Part of the problem has been that a few astronomers have taken the growing number of these unresolved examples to be evidence that the case for asteroids with moons is getting stronger. Such views have been rendered in scientific journals, but more conservative researchers have noted that two or three--or 10 -- 1nproven cases do not equal even a single firmly established one. The result has been that the question has to an extent become "tainted" with skepticism, with some scientists electing to avoid studying the matter rather than be subjected to possible ridicule.

Now four French astronomers have reported evidence for a possible moon around yet another asteroid, 146 Lucina. This case, too, is inconclusive, however, and the researchers -- J.E. Arlot of the Bureau des Longitudes in Paris and colleagues from the Meudon and Toulouse Observatories -- wrap their journal presentation in an extensive reminder of past nonconservatisms. "Clearly," they write in ICARUS (Vol. 61, p. 224), "since 1980, many observers have been more and more on guard against enthusiastic overinterpretation of transient brightness changes actually caused by the atmosphere." In fact, they point out, one result may even have been that possible evidence of real secondary events was "suppressed."

Fortified with that caveat, the authors describe a "secondary" of their own. On April 18, 1982, they aimed Meudon Observatory's 102-centimeter refractor at a star (AGK3 + 17[deg.]1309) whose location was close to where 146 Lucina was due to pass in its orbit. Later analysis indicated that the line through the asteroid and the star actually followed a track on earth's surface that was about 60 kilometers south of Meudon, and other observers, based much closer to the track, even reported a blink in the starlight that apparently represented Lucina itself. Arlot's colleagues at Meudon, however, also recorded a blink, though they were out of position to see Lucina's own. "A possible interpretation," they suggest, "is the existence of a faint satellite in the neighborhood of 146 Lucina." Projecting the lines of sight back to the asteroid's distance, the researchers calculate that the possible moon would be at least 5.7 km in diameter and about 1,600 km from Lucina.

The researchers used a video camera equipped with an image-intensifier tube to record the image digitally, and note that the system eliminated the need for an aperture-restricting diaphragm to narrow down the amount of sky in view. Such diaphragms can sometimes produce false signals or noise that can mislead interpretation of an uncertain result. The french team, though spared that difficulty, had another: the lack of a second, "reference" star in their field of view. Such a star, by maintaining its usual brightness while the other star was being briefly blocked by some intervening object like a moon of Lucina, would have served to indicate that the brief blink of the primary star was not due merely to some irregularity like an electrical surge in the image intensifier's power supply.

That lack leaves some U.S. researchers unpresuaded, but the French group readily acknowledges that "we must now wait for observations." The Space Telescope, for example, due for launch in 1986, may be able to help in at least some cases.
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Title Annotation:146 Lucina
Author:Eberart, Jonathan
Publication:Science News
Date:May 18, 1985
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