Astro News Briefs: September 8–14

Halley's Comet Spotted

September 12, 2003 | Most skywatchers lost interest in Halley’s Comet soon after it swung through the inner solar system in 1986, and professionals last sighted its bare nucleus outside Saturn's orbit in 1994. But a team of European astronomers recently tracked down Halley at a distance of 28.06 astronomical units from the Sun, nearly at the distance of Neptune. Last March Olivier Hainaut (European Southern Observatory) and several colleagues simultaneously used three of the four 8.2-meter Very Large Telescope reflectors in Chile to image the comet’s predicted field near the head of Hydra. No trace of the nucleus was visible on any single exposure. But when the astronomers stacked all 81 exposures (totaling 9 hours) with offsets to keep Halley’s predicted position fixed, the comet barely emerged into definite view at magnitudfe 28.2. Hainaut believes these exposures would have been good enough to record Halley even at its aphelion distance of 35.3 a.u., its turnaround point farthest from the Sun, which it will reach in 2023.

The European Southern Observatory issued a
press release about the comet's recovery on September 1st.


Mirror Chosen for Webb Telescope

September 11, 2003 | It's been one year since NASA selected California-based TRW to build the James Webb Space Telescope (JWST). And this week Northrop Grumman, which acquired TRW in late 2002, announced that it will fabricate the JSWT's 6.5-meter primary mirror out of beryllium, a strong but lightweight metal. A panel of industry specialists opted for beryllium over the other candidate material, ultralow-expansion glass, because it offered the better combination of low mass, high stiffness, and the ability to withstand the extremes of outer space. Production of the mirror's 18 hexagon-shaped segments will begin next year. With its launch planned for 2011, JWST will ultimately replace the aging Hubble Space Telescope. However, whether the two missions will overlap awaits a decision by NASA officials. The Webb telescope will operate from the L2 Lagrangian point, a gravitationally stable location about 1.5 million kilometers away on the anti-sunward side of Earth.

For more information on the James Webb Space Telescope, go to
http://www.jwst.nasa.gov/


A New Moon for Neptune

September 11, 2003 | The outer solar system just got a little more crowded, as astronomers have discovered another small moon circling Neptune. The new find, designated S/2003 N1, travels in a distant and highly irregular orbit that averages nearly 50 million miles from the planet and takes 26.3 years to complete one revolution. Observers David C. Jewitt, Jan Kleyna, and Scott S. Sheppard identified the tiny object, about 40 kilometers across, as a 26th-magnitude blip in images acquired on August 29th with the giant Subaru telescope atop Mauna Kea, Hawaii. Based on orbital calculations by Brian G. Marsden (Minor Planet Center), its motion was matched to that of an object first seen in August 2001 and two times thereafter. S/2003 N1 is Neptune's 12th satellite.

Sheppard provides details about the new moonlet, including the Subaru images at http://www.ifa.hawaii.edu/~sheppard/satellites/iaucneptune.html.


Uranus's Lost-and-Found Moonlet

September 10, 2003 | In 1999, while inspecting 13-year-old images taken of Uranus by Voyager 2, planetary specialist Erich Karkoschka (University of Arizona) spotted a tiny moonlet circling about 50,000 kilometers above the blue-hued planet. But because it was so faint and small, no more than 40 km across, his find could not be confirmed by telescopes back on Earth. Consequently, two years ago the International Astronomical Union decided to remove S/1986 U10 from its official list of Uranian satellites. But thanks to observations made August 25th using the Hubble Space Telescope's new Advanced Camera for Surveys, Karkoschka's claim has been verified. Mark R. Showwalter (Stanford University) and Jack J. Lissauer (NASA/Ames Research Center) found the 24th-magnitude object about 48° ahead of its predicted position. S/1986 U10 circles Uranus every 15.3 hours and is the planet's 22nd known moon.

For a tabulation of all 130 known moons see SkyandTelescope.com's Guide to Planetary Satellites.


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