Astronomy Picture of the Day
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2004 February 23 
Posted on 02/23/2004 4:09:45 AM PST by petuniasevan
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2004 February 23
Explanation: If sometimes it appears that the entire Milky Way Galaxy is raining down on your head, do not despair. It happens twice a day. As the Sun rises in the East, wonders of the night sky become less bright than the sunlight scattered by our own Earth's atmosphere, and so fade from view. They will only rotate back into view when the Earth again eclipses our bright Sun at dusk. This battle between heaven and Earth was captured dramatically in a digitally enhanced double-exposure over the Kofa Mountains in Arizona, USA in 2003 May. Dark dust, millions of stars, and bright glowing red gas highlight the plane of our Milky Way Galaxy, which lies on average thousands of light years behind Earth's mountains.
 Martian polar ice cap viewed in 'normal' visible light. Credit: ESA |
The first trio of images from the OMEGA instrument on ESA's Mars Express, released on January 23, showed some colorful views of Mars' south polar ice cap. That is mainly because two of the images were taken at infrared wavelengths that defy easy translation into color. So, they were displayed in 'false' color.
William Smith, the British 'father' of geology, introduced false color to science in the 1800s. He wanted to draw a map of Great Britain to show the different types of rock that could be found across its surface and decided to color code the rocks.
The colors were not intended to represent the true colors of the rocks, but simply to act as a key to identifying them. Political maps of the world also use of false color, clearly showing the boundaries between countries because of the sudden change of color.
 OMEGA observed the southern polar cap of Mars on January 18, as seen on all three bands. The right one represents the visible image, the middle one the CO2 (carbon dioxide) ice and the left one the H2O (water) ice. Credits: ESA - OMEGA |
The other two images, the middle one showing the distribution of carbon dioxide ice and the left-hand image showing the distribution of water ice are falsely colored.
Both ice images are made from infrared radiation reflected by the surface of Mars. Because carbon dioxide and water absorb and reflect characteristically different wavelengths of infrared, OMEGA can identify each chemical compound by looking at the missing parts of the spectra received back from the surface.
The astronomers then used false color to show how much ice had been detected at the polar cap. The color scale is blue to red. The bluer the area, the more carbon dioxide ice in the middle image and, in the left-hand image, the more water ice. Red areas are deficient and yellow areas are intermediate zones.
Comparing the pictures, the wide yellow expanse on the left-hand image shows that the water ice is more widespread than the carbon dioxide ice. The carbon dioxide ice collects mostly in the blue peak of the middle image.
With this early success, OMEGA's Principal Investigator Dr Jean-Pierre Bibring, Institut d'Astrophysique Spatiale, France, is looking forward to the rest of mission. He says, "Our goal now is to map the whole planet."
So, as William Smith's 1815 map of Great Britain helped show the mineral wealth of England, Wales and Scotland, so OMEGA will eventually show the distribution of minerals and rock types across the surface of Mars. Like its predecessor, it too will be presented in glorious 'false' color.
MARS ROVERS UPDATE
SUNDAY, FEBRUARY 22, 2004 
The twin Mars Exploration Rovers spent the weekend hard at work on opposite sides of the planet as Opportunity examined exposed bedrock and Spirit studied the trench it dug in the soil.
Opportunity is using its arm to make close-up inspections of the "El Capitan" part of the street-curb-sized outcrop in the crater where the rover is working. Opportunity took 46 pictures with its microscope, examining several locations on "El Capitan" at a range of focal distances, NASA reported.
The Mossbauer Spectrometer and Alpha Particle X-ray Spectrometer studied the rock to assess what minerals and elements are present.
On Monday, Opportunity is scheduled to use the Rock Abrasion Tool to grind into part of El Capitan, giving the science devices a port hole to determine if the rock's interior is the same as the exterior.
Meanwhile, Spirit has spent a couple of days probing the wheel-dug trench nicknamed "Road Cut." Using the science instruments on its arm, the rover is collecting data about the subsurface soil exposed by the hole. A series of microscopic images of the trench floor and walls have also been obtained.
Spirit is preparing to resume driving to Bonneville Crater.
The next news conference on NASA Television is Thursday.
FRIDAY, FEBRUARY 20, 2004
1812 GMT (1:12 p.m. EST)
Spirit successfully dug its first hole in the soil this morning, carving a trench 6 centimeters deep with its left front wheel so the science instruments can study the subsurface soil characteristics, mission manager Jim Erickson told reporters in a teleconference today.
The science observations will be performed over the next couple of days, studying the trench floor and wall. Spirit resumes its drive on the road to Bonneville Crater Monday.
Meanwhile, Opportunity finished studying its trench and drove 15 meters (50 feet) on the last workday, the longest drive that rover has made to date. Dodging the trench and lander, Opportunity cruised to nearly the opposite side of the crater to the bedrock outcrop, Erickson said.
The rover is doing soil studies today, then moving three-tenths of a meter forward to get its arm within reach of the El Capitan area of the outcrop to begin a detailed study.
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Also, the photographer has on his site other beautiful photos he's taken.
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