Astronomy Picture of the Day 05-15-04

Explanation: In this stunning vista recorded with the Hubble Space Telescope's Advanced Camera for Surveys, distant galaxies form a dramatic backdrop for disrupted spiral galaxy Arp 188, the Tadpole Galaxy. The cosmic tadpole is a mere 420 million light-years distant toward the northern constellation Draco. Its eye-catching tail is about 280 thousand light-years long and features massive, bright blue star clusters. One story goes that a more compact intruder galaxy crossed in front of Arp 188 - from left to right in this view - and was slung around behind the Tadpole by their gravitational attraction. During the close encounter, tidal forces drew out the spiral galaxy's stars, gas, and dust forming the spectacular tail. The intruder galaxy itself, estimated to lie about 300 thousand light-years behind the Tadpole, can be seen through foreground spiral arms at the upper left. Following its terrestrial namesake, the Tadpole Galaxy will likely lose its tail as it grows older, the tail's star clusters forming smaller satellites of the large spiral galaxy.

Instrument en route to one comet observes a second one
SOUTHWEST RESEARCH INSTITUTE NEWS RELEASE
Posted: May 14, 2004

The Alice ultraviolet imaging spectrometer, one of three NASA instruments aboard the European Space Agency (ESA) Rosetta comet orbiter, successfully passed its space checkout last month. The checkout occurred approximately 20 million kilometers from Earth under radio command and control, leading to textbook "first light" observations of the interplanetary hydrogen and a nearby, bright comet called C/2002 T7 (LINEAR).

"Rosetta's launch was bang on the mark, and the spacecraft is well on its way to its target comet. During this journey, Rosetta will also explore the atmosphere of Mars during a flyby in 2007 and two asteroids in later years," says Dr. Alan Stern, Alice principal investigator and director of the Space Studies Department at Southwest Research Institute. "When Rosetta encounters Churyumov-Gerasimenko, the ancient comet it is targeted to orbit in 2014, the NASA-SwRI Alice instrument will become the first ultraviolet spectrometer to ever reach a comet."

"Alice will spend hundreds of days in cometary orbit, analyzing the composition of Churyumov-Gerasimenko's atmosphere, mapping its surface and studying the properties of fine dust particles coming off the comet," Stern says. "This investigation will provide an unprecedented window into both the origin of comets and the way comets work."

"Alice is a highly miniaturized spectrometer with more than 1,000 times the data-gathering capability of instruments flown a generation ago, and a sensitivity for atmospheric measurements comparable to the Hubble Space Telescope -- yet it weighs less than 4 kg and draws just 3 watts of power," explains Alice Project Manager John Scherrer, also of SwRI. "The successful turn on and checkout of Alice in space represents a major milestone in the U.S. Rosetta program."

Alice Operations Scientist and SwRI Manager Dr. Joel Parker continues, "We really couldn't have expected a healthier instrument than we have. All subsystems are performing nominally, and every indication we have is that the instrument's scientific performance is on spec."

Alice was built and is operated by SwRI for NASA. The instrument is designed to probe the atmosphere and surface of Churyumov-Gerasimenko. A sister Alice instrument is also set to launch aboard the New Horizons mission to Pluto in January 2006 for studies of that distant world's atmosphere.

SwRI also built and will operate the Ion and Electron Spectrometer (IES) flying aboard Rosetta. Principal Investigator Dr. James Burch, vice president of the SwRI Space Science and Engineering Division, leads IES operations. Despite its mass of just 1.04 kilograms, laboratory tests showed the spectrometer achieves sensitivity comparable to other instruments weighing five times more. IES will simultaneously measure the flux of electrons and ions surrounding the comet over an energy range extending from the lower limits of detectability, near 1 electron volt, up to 22,000 electron volts. It uses a novel, electrostatic scanning technique to view particles from directions encompassing 70 percent of the celestial sphere. Although not yet fully operational, preliminary tests of IES show it too is operating nominally.

The Jet Propulsion Laboratory (JPL) manages the U.S. Rosetta project for NASA.

SwRI is an independent, nonprofit, applied research and development organization based in San Antonio, Texas, with more than 2,800 employees and an annual research volume of more than $355 million.

THURSDAY, MAY 13, 2004
The Mars rover Opportunity has spent the past several days exploring around the rim of Endurance Crater, giving scientists different views of the landscape.

The latest Mission Control report:

On Sol 103, Opportunity traversed approximately 13 meters (about 43 feet) farther south along the eastern rim of "Endurance Crater," reaching the beginning of the "Karatepe" area. On sol 104, the rover approached "Lion Stone," a rock at the crater's edge that stands about 10 centimeters tall (about 4 inches) and is about 30 centimeters long (12 inches). This brought Opportunity's total mission odometry to 1,054meters (3,458 feet)!

On Sol 105, Opportunity acquired a series of microscopic images of Lion Stone and the surrounding soil.

The rover then went on to collect a short Moessbauer integration on the rock during the day, performed a tool change to the alpha particle X-ray spectrometer in late afternoon, and acquired that integration in the early morning of Sol 106. That sol also included additional microscopic images and a successful "bump" maneuver to reposition the rover so the top of Lion Stone was in position for the rock abrasion tool on Sol 107. Remote sensing was also acquired during the two sols, including panoramic camera images of the heatshield that protected Opportunity during its toasty trip through the martian atmosphere. The heatshield impacted approximately 250 meters (about 820 feet) south of Endurance Crater.

Plans for Sol 107 are to perform a rock abrasion tool grind on Lion Stone with subsequent microscopic images and alpha particle X-ray spectrometer overnight integration. The tentative plan for Sol 108 is to leave Lion Stone and begin traverse to observation position 2 on the southeastern rim of Endurance Crater.

WEDNESDAY, MAY 12, 2004
Spirit drove 80 meters (262.5 feet) on sol 124, bringing its total odometry to 1,909.52 meters (1.2 miles). Spirit has less than 1.2 kilometers (.75 mile) to go before reaching the base of the"Columbia Hills," and will reach them by sol 160. Later in the martian day, after completing the sol 124 drive, Spirit took a 360-degree afternoon panorama of its surroundings with the navigation camera.

On sol 125, Spirit continued driving and set a new one-sol driving record of 123.7 meters (405.8 feet). Science on Sol 125 included morning atmospheric sky and ground remote sensing, mini thermal emission spectrometer observation of the sol 126 instrument deployment device work volume, imaging with the panoramic camera, and cloud observations.

After the long sol 125 drive, Spirit was in perfect position to work with the instrument deployment device on sol 126. This included alpha particle X-ray spectrometer, Moessbauer and microscopic imager work on a target called "Lead Foot" (in honor of the big drive on sol 125). The Moessbauer was used as the feeler for all these activities but touched down on rocks rather than soil at the "Lead Foot" location, compromising the Moessbauer and microscopic imager data (images out of focus). Spirit also did some driving on this sol, and added 55.6 meters (182.4 feet) to the odometer, bringing Spirit's new drive total to 2,089 meters (1.3 miles). At the end of the sol, Spirit successfully executed a sequence that used the panoramic camera to find the Sun and correct for accumulated rover attitude errors.

Spirit rover image from 5/12/2004 (Sol 127):

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