Far-out science.When scientists announced last year that they had discovered the most-remote object known in the solar system solar system, the sun and the surrounding planets, natural satellites, dwarf planets, asteroids, meteoroids, and comets that are bound by its gravity. The sun is by far the most massive part of the solar system, containing almost 99.9% of the system's total mass. The principal members of the sun's retinue are the eight major planets; other parts of the solar system are discussed in separate articles: see comet, asteroid, and meteor., they reported that the icy body probably had a moon. That's because the object, named Sedna, seemed to spin unusually slowly, just once every 20 days. Only the tug of a small companion body could slow the rotation to such a leisurely rate, the astronomers reasoned. The Hubble Space Telescope, however, failed to find a moon (SN: 4/24/04, p. 262). Now, new measurements show that Sedna rotates some 50 times as fast as earlier observations indicated. Scott Gaudi of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and his colleagues studied Sedna's spin using the MMT Telescope on Mount Hopkins in Arizona. With that telescope's sensitivity, the researchers could discern tiny periodic variations in Sedna's brightness, providing a better estimate of the body's rotation than was possible before. The researchers describe their findings online (http://arwiv.org/abs/astro-ph/0503673). In a separate study, scientists using the Gemini North Telescope atop Hawaii's Mauna Kea Mauna Kea (mou`nə kā`ə), dormant volcano, 13,796 ft (4,205 m) high, in the south central part of the island of Hawaii. It is the loftiest peak in the Hawaiian Islands and the highest island mountain in the world, rising c.32,000 ft (9,750 m) from the Pacific Ocean floor. found no evidence of ice or frozen methane on Sedna. That's unlike conditions on two other remote solar system bodies, Pluto Pluto, in astronomyPluto, in astronomy, a dwarf planet and the first Kuiper belt, or transneptunian, object (see comet) to be discovered (1930) by astronomers. Pluto has an elliptical orbit usually lying beyond that of Neptune. Although Pluto was long regarded as a planet, since the discovery (beginning in 1992) of other Kuiper belt objects, including one with a diameter larger than that of Pluto, astronomers have recognized the need to reclassify Pluto, and its moon CharonCharon, in astronomyCharon, in astronomy, the natural satellite, or moon, of Pluto.Charon, in mythologyCharon, in Greek mythology: see Hades..Astronomers propose that Sedna initially had an icy surface but that bombardment by cosmic rays cosmic rays - Notionally, the cause of bit rot. However, this is a semi-independent usage that may be invoked as a humorous way to handwave away any minor randomness that doesn't seem worth the bother of investigating. "Hey, Eric - I just got a burst of garbage on my tube, where did that come from?" "Cosmic rays, I guess." Compare sunspots, phase of the moon. and the sun's ultraviolet light produced a dark, hydrocarbon veneer. Because Pluto and Charon lie closer to the sun than Sedna does, they're subject to more collisions with solar system debris. Those collisions either prevent the formation of a dark coating or deliver fresh supplies of bright ice on top of the coating. Chad Trujillo of the California Institute of Technology in Pasadena and his colleagues report their findings in an upcoming Astrophysical Journal.--R.C. |
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