Sky & Telescope Noticias de Ultima Hora Diciembre del 2000

® La revista esencial de la Astronomía

Traducción por Kosmos Instrumentación Especializada

Friday, December 29
Saturn's Satellites: 30 and Counting

Satellite sleuths extraordinaire: (left to right) Brett Gladman, Jean-Marc Petit, Matthew Holman, and and J. J. Kavelaars pose on the catwalk of the Canada-France-Hawaii telescope in Hawaii. Not shown are team members Hans Scholl, Philip Nicholson, Joseph Burns, and Brian Marsden. Courtesy J.-M. Petit. Click on image for larger view.

Brett Gladman (Nice Observatory) and his international observing partners have announced their discovery of two more moons around Saturn. One of the new finds, designated S/2000 S 11, was spotted on November 9th by team member Matthew Holman with the 1.2-meter reflector at Whipple Observatory in Arizona. Gladman and J. J. Kavelaars (McMaster University) spotted S/2000 S 12 on September 23rd using the 3.6-meter Canada-France-Hawaii telescope on Mauna Kea. It is probably only 5 kilometers across, whereas S 11 has a diameter of perhaps 35 km. Counting these additions, Saturn now has 30 known moons — 19 of which were found in the past 20 years. The dozen discovered by Gladman's team appear to fall into three orbital groupings: most travel in the same direction that Saturn rotates and have orbital inclinations that cluster near 35° and 48°; the third group travels in the reverse (retrograde) direction with inclinations near 170°. "The situation of Saturn thus seems to resemble that of Jupiter," Gladman notes, "which also has one prograde and one retrograde cluster." He provides more details about his team's satellite sleuthing here.

— J. Kelly Beatty

Tuesday, December 26
A Warmer Early Universe

El Very Large Telescope del El Observatorio Europeo del Sur consiste de cuatro reflectores de 8.2 m en la cima del Cerro Paranal en Chile. Cortesia de ESO. Pulse en la imagen para ver una de mayor tamano.

El Big Bang es una de las teorias mas conocidas y debatidas en la cosmologia. La mayoria de los pensadores asumen que la explosion fue caliente, y que el universo se ha enfriado desde entonces dramaticamente. Aunque conocemos la temperatura actual de la radiacion remamente del Big Bang, llamada la radiacion cosmica de microondas de fondo (CMBR), hasta ahora, nadie ha hecho una medicion directa de la temperatura del antigua radiacion del Big Bang. Hoy en dia, la radiacion de fondo es de solo 2.7° Kelvin, pero mientras mas atras buscamos al antecesor, la radiacion CMBR deberia ser mas caliente.

Usando el telescopio reflector Kueyen de 8.2 metros del Very Large Telescope en Chile, Raghunathan Srianand (Inter University Center for Astronomy and Astrophysics), Patrick Petitjean (Institut d'Astrophysique de Paris) y Cedric Ledoux (European Southern Observatory) pudieron medir la temperatura del CMBR cuando el universo solo tenia 2,500 millones de anos de edad. Ellos encontraron que entonces el cosmos estaba entre 6° y 14° Kelvin.

Los resultados del equipo — anounciados en el numero del dia 21 de Nature — emergieron de observaciones del distante cuasar PKS 1235+0815. Examinando el espectro del objeto, los astronomos enconcontraron senales de carbon e hidrogeno que solo podria ocurrir a esas temperaturas especificas. Sus resultados estan en linea con otros formuladores de teorias que predicen que la temperatura de la CMBR deberia ser 9.7° K en esa era cosmica. Para mas detalles, vean el publicado de prensa en linea.

— David Tytell

Friday, December 22
George E. D. Alcock, 1912–2000

Renowned British comet and nova discoverer George Alcock reading Sky & Telescope at his home near London in 1998. Photograph by Roy Williams.

The world lost one of its foremost amateur astronomers with the death of George Eric Deacon Alcock on December 15th. He was 88. A schoolteacher from Peterborough, England, Alcock blazed into the annals of British astronomy in 1959 by discovering Comet 1959e on August 25th of that year using a pair of Zeiss 25x105 binoculars. It was the first comet discovered in the country in 65 years. Five days later, on August 30th, he swept up his second one, Comet 1959f.

Despite Britain's frequently cloudy skies and increasing light pollution, Alcock went on to visually discover three more comets and five novae. His last comet discovery in 1983 was his most famous — Comet IRAS-Araki-Alcock. He found it with 15x80 binoculars while observing indoors, through the closed, double-glazed window of his upstairs bedroom! On May 11th the naked-eye comet skimmed past the Earth at only 12 times the Moon's distance (about 4.5 million kilometers), closer than any other cometary visitor since Comet Lexell in 1770.

Alcock's discoveries put him in a class with another renowned English amateur, Caroline Herschel, who had a lifetime total of eight comet finds from 1786 to 1797. An avid weather observer and bird watcher, Alcock received major awards from astronomical organizations, including the naming of asteroid 3174 Alcock in his honor by the International Astronomical Union. A profile of him can be found in the May 1999 Sky & Telescope, page 84.

— Edwin L. Aguirre

Friday, December 22
Pluto Mission Back in Play

Left: "Not yet explored" remains as true about Pluto today as it was when the U.S. Postal Service issued this stamp in 1991. Click on image for a larger view.

NASA officials announced on Wednesday that the space agency will again consider sending a spacecraft to Pluto. The space agency will seek proposals for mission designs in three weeks, with an eye toward selecting a winning proposal later next year. The mission plan must be developed soon in order to launch the probe by 2004 (2006 at the latest) and thus take advantage of a speed-boosting flyby of Jupiter. That could get the spacecraft to its distant destination by 2012. In making the announcement, NASA associate administrator Edward J. Weiler said he'll consider proposals for craft that would reach Pluto by 2015, whether or not a Jupiter flyby was involved, but the total cost must be well below $500 million.

"This is probably our last chance to go to Pluto for a generation," Weiler noted. However, he cautioned repeatedly that there is no guarantee that a spacecraft will actually be built and launched. Still, his announcement was a dramatic change from his precipitous order last September to stop all work related to the proposed Pluto-Kuiper Express mission. The space agency had combined missions to Europa and Pluto in 1997 under a single program that shared development funds and technical expertise. But when steeply escalating costs threatened both efforts in mid-2000, Weiler opted to defer the Pluto mission indefinitely so that work could continue on the Europa orbiter.

The back-to-the-drawing-board announcement came after months of lobbying by outer-planet specialists. Key to the turnaround was a late-November report by NASA's Solar System Exploration Subcommittee that recommended going to Pluto before Europa. The latter mission has higher scientific priority overall, but Pluto's atmosphere may soon freeze out as the icy world drifts farther from the Sun. Weiler said the Europa orbiter will be developed regardless of the Pluto mission's outcome, and that it will be launched no later than 2011.

Meanwhile, the results of a nationwide survey, also released on Wednesday, show that the U.S. public supports the exploration of two fascinating bodies in the outer solar system. Sponsored by Sky & Telescope, the poll found that 64 percent of Americans want NASA to send a spacecraft to Europa, while 58 percent approve sending a probe to Pluto. The exploration of Mars also continues to receive strong support, as 70 percent of people would like to see samples of the red planet returned to Earth for analysis. (Details of the nationwide poll can be found here.) "We all learn in school that our solar system has nine planets," says Richard Tresch Fienberg, Sky & Telescope's editor in chief. "It's downright dissatisfying that one of them remains unvisited after 40 years of interplanetary exploration." Fienberg encourages NASA to mount a Pluto mission in an editorial appearing in the magazine's February 2000 issue.

— J. Kelly Beatty

Tuesday, December 19
Roger W. Tuthill, 1919 – 2000

Roger W. Tuthill with one of his Solar Skreen filters. Photo by Nancy Tuthill.

Long-time amateur astronomer and entrepreneur Roger W. Tuthill of Mountainside, New Jersey, died of heart failure on December 15th following a brief illness. He was 81. Known to myriad friends and acquaintances as Tut, it was a midlife look at the Moon through a telescope in 1960 that ignited his lasting passion for astronomy. During the ensuing decade he became an increasingly well-known amateur astronomer, publishing several important articles on telescope making in Sky & Telescope.

With one of the century's longest total solar eclipses pending and organized eclipse travel almost nonexistent, Tut led a large group of amateurs to Africa's western Sahara Desert in the summer of 1973. During a preliminary scouting trip he planned to thwart the desert's intense daytime heat with a tent he made of aluminized Mylar. The experiment failed because of the tent's "maddeningly annoying" noise as it rippled in the ever-present wind. But sitting inside and looking up, Tut discovered that aluminized Mylar was a safe and effective solar filter. Sliced into small strips, pieces of the tent were handed out as free eclipse viewers to hundreds of locals in a practice he continued during 17 future eclipse expeditions.

Tut patented aluminized Mylar as a solar filter and founded a small company to sell his Solar Skreen to amateurs. Eventually he added other products and quit his day job as an engineer at a welding company to run the business full time. Tut presaged the future when he introduced the first computer-pointed amateur telescope in the early 1980s, though the unit was never a commercial success. Tuthill's business was scaled back in recent years as he entered semiretirement. According to his wife, Nancy, the business will continue selling Solar Skreen and other small products.

Tut was proactive in his support of several amateur organizations, including the Springfield Telescope Makers in Vermont, where he was a fixture at the club's annual Stellafane convention for three decades. For the thousands of amateurs who met Tut there and at other gatherings in North America or during his globetrotting eclipse expeditions, he will be best remembered for his strong handshake and warm, smiling greeting whether he was meeting someone for the first or 500th time. He truly was, as his company's slogan proclaimed, everyone's astronomical friend.

— Dennis di Cicco

Monday, December 4
Martian Sediments:
Ancient Lakebeds or Blow-ins?

Two examples of Martian layered sediments, as recorded by Mars Global Surveyor. Far left: Stair-stepped hills found within an impact crater in west Arabia Terra. Left: Eroded benches within Candor Chasma, one of the central canyons of Valles Marineris. Courtesy Malin Space Science Systems and Science. Click on image for larger view.

Dramatic new images show that Mars once had an environment that created sediment-like layers within craters and canyons across much of the planet's midsection. In some locales hundreds of individual beds can be counted, occasionally creating stacks of alternating light and dark layers 2 to 4 kilometers tall. In the region known as Terra Meridiani, the sediments extend continuously for hundreds of kilometers.

As detailed by Michael C. Malin and Kenneth S. Edgett in the December 8th issue of Science, the layers could be explained by two very different climatic scenarios. "The first, and perhaps favored, model draws heavily on comparison to Earth to invoke a planet and environment capable of sustaining liquid water on its surface," they state. Thus the sediments occur preferentially in confined areas where water would tend to collect.

The other scenario, which Malin and Edgett consider "a plausible but uniquely Martian explanation," envisions times when the Martian atmosphere was denser, enough so to mobilize and deposit huge amounts of dust. For example, the red planet's polar tilt is known to oscillate between 15° and 35° every 100,000 years, a cycle that probably induces drastic changes in atmospheric pressure and climate as the thick polar ice caps vaporize and become redistributed. At such times the planet might have experienced ferocious dust storms, or the atmosphere may have aided in the transport of volcanic ash or impact debris.

"We think both models have some validity," Malin told Sky & Telescope, "or we wouldn't have included both."

Although surface ages are notoriously difficult to estimate on Mars, the two researchers believe most of the sediments date from the earliest span of Martian history, between 3.5 and 4.3 billion years ago. But the evidence for such ancient ages is weak, Malin admits. In fact, Nathalie Cabrol (NASA/Ames Research Center) and her colleagues have used Viking images to identify roughly 200 Martian craters with lakebed sediments that she believes were laid down much more recently -- some only few hundred million years ago. "To say they are all ancient, I would be cautious," Cabrol warns. "What would the agent be to expose all these ancient layers in recent times? How do you do that? Maybe they are more recent than Malin and Edgett think, or something happened recently on Mars to exhume them."

The crater sediments only add to the new and much more confusing picture of Mars that is emerging from Mars Global Surveyor data. When one observation indicates that the red planet had a warmer, wetter past, another (like widespread outcrops of the mineral olivine) argues for eons of cold, dry conditions. "We caution that the Mars images tell us that the story is actually quite complicated," Edgett notes, "and yet the implications are tremendous."

Viernes, Diciembre 1º
¿Un Gigante del Cinturón de Kuiper?

Izq.: Uno de los decubrimientos de las imágenes del 28 de noviembre de un nuevo y potencialmente gran objeto en el distante cinturón de Kuiper Belt. Pulse la imagen para ver una de mayor tamaño. Cortesía de Project Spacewatch.

Ordinarily the discovery of a 20th-magnitude blip wouldn't be much cause for excitement, but the one found early on November 28th is a special case. If preliminary calculations are borne out by further observations, the object now designated 2000 WR₁₀₆ may prove to equal the size of Ceres, the largest asteroid. Located about 1½° south of the star Epsilon Geminorum, the new find was spotted first by Robert S. McMillan and later by Jeffrey A. Larsen (University of Arizona) with the 0.9-meter Spacewatch telescope on Kitt Peak. They noticed its shifting position by eye in a computer display of successive frames -- the motion was too slow to be picked up by Spacewatch's automatic-detection software.

The object's actual size remains very uncertain in part because astronomers aren't yet sure of its distance from the Sun. Right now the best estimate is 43 astronomical units (6.4 billion kilometers), which means it is a Kuiper Belt object (KBO) beyond the orbit of Pluto. An object this far away takes nearly three centuries to circle the Sun, so astronomers will need to observe it over many weeks or months for its motion to betray the orbit's true character. However, according to Brian G. Marsden (IAU Minor Planet Center), the assumed distance is unlikely to change very much.

Another unknown is the albedo, or reflectivity, of the body's surface. If 2000 WR₁₀₆ is bright, like Pluto or Charon, then its diameter might not exceed 500 km, something akin to Vesta in size. But just the opposite might be true. "Many people think KBOs have albedos closer to comet nuclei -- very dark," William J. Romanishin (University of Oklahoma) told members of the Minor Planet Mailing List. In that case, the Spacewatch discovery could exceed 1,200 km in diameter. Ceres, first seen almost exactly 200 years ago, is roughly 950 km across.

Apparently the object has escaped detection until now because it spent many years lurking among the stars of the northern Milky Way. With modern electronic detectors, it is actually within the detection range of many backyard telescopes. Anyone interested in trying to spot it should check out the ephemeris provided here by the Minor Planet Center.

J. Kelly Beatty

Copyright © 1996 Sky Publishing Corporation, Todos los derechos reservados. Este material no debe ser reproducido de cualquier forma sin permiso. Para más información contacte a Sky Publishing Corp., P.O. Box 9111, Belmont, MA 02178-9111, En E.E.U.U.: 1-617-864-7360. Fax: 1-617-576-0336 (Sólo editorial), 1-617-864-6117 (todo lo demás). O por e-mail a webmaster@skypub.com.

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