Cassini Flyby of Enceladus

The spacecraft Cassini did a flyby of Saturn's moon Enceladus five days ago, on March 12th. This flyby was unique in that Cassini flew by Enceladus at the height of a mere 50 kilometers (31 miles) above the surface of the moon. This particular video was made by Brent Buffington, who's a Cassini navigation team member. The animation shows Cassini preparing for the flyby and then shooting past the moon. As Cassini swings past Enceladus, the spacecraft rotates into various positions, allowing each instrument on board to take measurements. The left-hand window shows the field-of-view for the prime instrument, while the right-hand windows show the view from the different instrument boresights. The instruments include:

UVIS (Ultraviolet Imaging Spectrograph) - a long narrow magenta field of view

VIMS (Visible-Infrared Mapping Spectrometer) - a big red square

ISS (Imaging Subsystem; i.e., the visible light camera) - a white square; a small white square is the narrow angle camera, a large white square is the wide angle camera

CIRS (Composite Infrared Spectrometer) - a red circular field-of-view and two small red parallel narrow fields-of-views

HGA (High Gain Antenna; used for communicating with Earth)

Radar - a green circle, centered on the high gain antenna

The video can also be viewed at Youtube.

Credit: NASA

WMAP Reveals Neutrinos, End of Dark Ages, First Second of Universe

Credit (all illustrations): NASA/WMAP Science Team

NASA released this week five years of data collected by the Wilkinson Microwave Anisotropy Probe (WMAP) that refines our understanding of the universe and its development. It is a treasure trove of information, including at least three major findings:

New evidence that a sea of cosmic neutrinos permeates the universe

Clear evidence the first stars took more than a half-billion years to create a cosmic fog

Tight new constraints on the burst of expansion in the universe's first trillionth of a second

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WMAP measures a remnant of the early universe - its oldest light. The conditions of the early times are imprinted on this light. It is the result of what happened earlier, and a backlight for the later development of the universe. This light lost energy as the universe expanded over 13.7 billion years, so WMAP now sees the light as microwaves. By making accurate measurements of microwave patterns, WMAP has answered many longstanding questions about the universe's age, composition and development.

The universe is awash in a sea of cosmic neutrinos. These almost weightless sub-atomic particles zip around at nearly the speed of light. Millions of cosmic neutrinos pass through you every second.

"A block of lead the size of our entire solar system wouldn’t even come close to stopping a cosmic neutrino,” said science team member Eiichiro Komatsu of the University of Texas at Austin.

WMAP has found evidence for this so-called "cosmic neutrino background" from the early universe. Neutrinos made up a much larger part of the early universe than they do today.

Microwave light seen by WMAP from when the universe was only 380,000 years old, shows that, at the time, neutrinos made up 10% of the universe, atoms 12%, dark matter 63%, photons 15%, and dark energy was negligible. In contrast, estimates from WMAP data show the current universe consists of 4.6% percent atoms, 23% dark matter, 72% dark energy and less than 1 percent neutrinos.

Cosmic neutrinos existed in such huge numbers they affected the universe’s early development. That, in turn, influenced the microwaves that WMAP observes. WMAP data suggest, with greater than 99.5% confidence, the existence of the cosmic neutrino background - the first time this evidence has been gleaned from the cosmic microwaves.

Much of what WMAP reveals about the universe is because of the patterns in its sky maps. The patterns arise from sound waves in the early universe. As with the sound from a plucked guitar string, there is a primary note and a series of harmonics, or overtones. The third overtone, now clearly captured by WMAP, helps to provide the evidence for the neutrinos.

The hot and dense young universe was a nuclear reactor that produced helium. Theories based on the amount of helium seen today predict a sea of neutrinos should have been present when helium was made. The new WMAP data agree with that prediction, along with precise measurements of neutrino properties made by Earth-bound particle colliders.

Another breakthrough derived from WMAP data is clear evidence the first stars took more than a half-billion years to create a cosmic fog. The data provide crucial new insights into the end of the "dark ages," when the first generation of stars began to shine. The glow from these stars created a thin fog of electrons in the surrounding gas that scatters microwaves, in much the same way fog scatters the beams from a car’s headlights.

"We now have evidence that the creation of this fog was a drawn-out process, starting when the universe was about 400 million years old and lasting for half a billion years," said WMAP team member Joanna Dunkley of the University of Oxford in the U.K. and Princeton University in Princeton, N.J. "These measurements are currently possible only with WMAP."

A third major finding arising from the new WMAP data places tight constraints on the astonishing burst of growth in the first trillionth of a second of the universe, called “inflation,” when ripples in the very fabric of space may have been created. Some versions of the inflation theory now are eliminated. Others have picked up new support.

"The new WMAP data rule out many mainstream ideas that seek to describe the growth burst in the early universe," said WMAP principal investigator, Charles Bennett, of The Johns Hopkins University in Baltimore, Md. "It is astonishing that bold predictions of events in the first moments of the universe now can be confronted with solid measurements."

The five-year WMAP data were released this week, and results were issued in a set of seven scientific papers submitted to the Astrophysical Journal.

Prior to the release of the new five-year data, WMAP already had made a pair of landmark finds. In 2003, the probe's determination that there is a large percentage of dark energy in the universe erased remaining doubts about dark energy's very existence. That same year, WMAP also pinpointed the 13.7 billion year age of the universe.

The Earth and Moon from Mars

Credit: NASA/JPL-Caltech/University of Arizona

This is an image of Earth and the moon, acquired on October 3, 2007, by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter.

At the time the image was taken, Earth was 142 million kilometers (88 million miles) from Mars, giving the HiRISE image a scale of 142 kilometers (88 miles) per pixel, an Earth diameter of about 90 pixels and a moon diameter of 24 pixels. The phase angle is 98 degrees, which means that less than half of the disk of the Earth and the disk of the moon have direct illumination.

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On the day this image was taken, the Japanese Kayuga (Selene) spacecraft was en route from the Earth to the moon, and has since returned spectacular images and movies.

On the Earth image we can make out the west coast outline of South America at lower right, although the clouds are the dominant features. These clouds are so bright, compared with the moon, that they are saturated in the HiRISE images. In fact the red-filter image was almost completely saturated, the blue-green image had significant saturation, and the brightest clouds were saturated in the infrared image. This color image required a fair amount of processing to make a nice-looking release. The moon image is unsaturated but brightened relative to Earth for this composite. The lunar images are useful for calibration of the camera.

NASA: New Radar Maps of the Moon's South Pole

Above: This movie is a simulation of the amount of solar illumination in the south polar region of moon over a solar day generated using high resolution topography. (Credit: NASA)

NASA has obtained new high-resolution radar maps of the Moon's south pole--a region the space agency is considering as a landing site when astronauts return to the Moon in the years ahead.

"We now know the south pole has peaks as high as Mt. McKinley and crater floors four times deeper than the Grand Canyon," says Doug Cooke, deputy associate administrator for the Exploration Systems Mission Directorate at NASA Headquarters. "These data will be an invaluable tool for advance planning of lunar missions."

Scientists at NASA's Jet Propulsion Laboratory collected the data using the Goldstone Solar System Radar located in California's Mojave Desert. Three times in 2006, JPL scientists targeted the moon's south polar region using Goldstone's 70-meter radar dish. The antenna, three-quarters the size of a football field, sent a 500-kilowatt strong, 90-minute long radar stream 231,800 miles to the Moon. The radar illuminated the rough-hewn lunar surface over an area measuring about 400 by 250 miles. Signals were reflected back to two of Goldstone's 34-meter antennas on Earth. Scientists have been analyzing the echoes ever since, and the data were released by NASA for the first time this week.

NASA is eying the Moon's south polar region as a possible site for future outposts. The location has many advantages; for one thing, there is evidence of water frozen in deep dark south polar craters. Water can be split into oxygen to breathe and hydrogen to burn as rocket fuel--or astronauts could simply drink it. Planners are also looking for "peaks of eternal light." Tall polar mountains where the sun never sets might be a good place for a solar power station.

These are the highest-resolution maps to date. The best images, previously, were generated by the Clementine spacecraft, which could resolve lunar terrain features near the south pole at 1 kilometer per pixel. The JPL radar maps are 50 times more detailed.

As wonderful as they are, however, these images will pale in comparison to next-generation photos from NASA's Lunar Reconnaissance Orbiter. The spacecraft is scheduled to launch in late 2008 and its camera will beam back photos of the moon with details as small as 1 meter.