Cassini Captures a Rarely-Seen Moon

While many of us here on Earth were waiting for the Moon to take a bite out of the Sun this past Sunday, Cassini was doing some moon watching of its own, 828.5 million miles away!

The image above is a color-composite raw image of Methone (pronounced meh-tho-nee), a tiny, egg-shaped moon only 2 miles (3 km) across. Discovered by Cassini in 2004, Methone’s orbit lies between Mimas and Enceladus, at a distance of 120,546 miles (194,000 km) from Saturn — that’s about half the distance between Earth and the Moon.

At an altitude of 1,200 miles (1900 km) this was Cassini’s closest pass ever of Methone, a rare visit that occurred after the spacecraft departed the much larger Tethys.

Along with sister moons Pallene and Anthe, Methone is part of a group called the Alkyonides, named after daughters of the god Alkyoneus in Greek mythology. The three moons may be leftovers from a larger swarm of bodies that entered into orbit around Saturn — or they may be pieces that broke off from either Mimas or Enceladus.

Earlier on Sunday, May 20, Cassini paid a relatively close visit to Tethys (pronounced tee-this), a 662-mile (1065-km) -wide moon made almost entirely of ice. One of the most extensively cratered worlds in the Solar System, Tethys’ surface is dominated by craters of all sizes — from the tiniest to the giant 250-mile (400-km) -wide Odysseus crater — as well as gouged by the enormous Ithaca Chasma, a series of deep valleys running nearly form pole to pole.

Cassini passed within 34,000 miles (54,000 km) of Tethys on May 20, before heading to Methone and then moving on to its new path toward Titan, a trajectory that will eventually take it up out of Saturn’s equatorial plane into a more inclined orbit in order to better image details of the rings and  Saturn’s poles.

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NASA Spacecraft Reveals Recent Geological Activity on the Moon

New images from NASA's Lunar Reconnaissance Orbiter (LRO) spacecraft show the moon's crust is being stretched, forming minute valleys in a few small areas on the lunar surface. Scientists propose this geologic activity occurred less than 50 million years ago, which is considered recent compared to the moon's age of more than 4.5 billion years.

A team of researchers analyzing high-resolution images obtained by the Lunar Reconnaissance Orbiter Camera (LROC) show small, narrow trenches typically much longer than they are wide. This indicates the lunar crust is being pulled apart at these locations. These linear valleys, known as graben, form when the moon's crust stretches, breaks and drops down along two bounding faults. A handful of these graben systems have been found across the lunar surface.

"We think the moon is in a general state of global contraction because of cooling of a still hot interior," said Thomas Watters of the Center for Earth and Planetary Studies at the Smithsonian's National Air and Space Museum in Washington, and lead author of a paper on this research appearing in the March issue of the journal Nature Geoscience. "The graben tell us forces acting to shrink the moon were overcome in places by forces acting to pull it apart. This means the contractional forces shrinking the moon cannot be large, or the small graben might never form."

The weak contraction suggests that the moon, unlike the terrestrial planets, did not completely melt in the very early stages of its evolution. Rather, observations support an alternative view that only the moon's exterior initially melted forming an ocean of molten rock.

In August 2010, the team used LROC images to identify physical signs of contraction on the lunar surface, in the form of lobe-shaped cliffs known as lobate scarps. The scarps are evidence the moon shrank globally in the geologically recent past and might still be shrinking today. The team saw these scarps widely distributed across the moon and concluded it was shrinking as the interior slowly cooled.

Based on the size of the scarps, it is estimated that the distance between the moon's center and its surface shrank by approximately 300 feet. The graben were an unexpected discovery and the images provide contradictory evidence that the regions of the lunar crust are also being pulled apart.

"This pulling apart tells us the moon is still active," said Richard Vondrak, LRO Project Scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "LRO gives us a detailed look at that process."

As the LRO mission progresses and coverage increases, scientists will have a better picture of how common these young graben are and what other types of tectonic features are nearby. The graben systems the team finds may help scientists refine the state of stress in the lunar crust.

"It was a big surprise when I spotted graben in the far side highlands," said co-author Mark Robinson of the School of Earth and Space Exploration at Arizona State University, principal investigator of LROC. "I immediately targeted the area for high-resolution stereo images so we could create a three-dimensional view of the graben.

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NASA gives update on mission to moon

NASA announced Monday that it is entering a new stage of a mission intended to place a pair of probes around Earth’s nearest neighbor and only satellite.

NASA officials said Monday mission controllers are preparing for the twin spaceships, named Grail-A and Grail-B, to enter the moon’s orbit on New Year’s Eve. The pair of probes are tasked with measuring the uneven gravity field of the moon and determine what lies beneath — straight down to the core.

NASA’s twin lunar Gravity Recovery and Interior Laboratory (GRAIL) probes were launched from Cape Canaveral Air Force Station on September 10, 2011. GRAIL-A is scheduled to arrive in lunar orbit beginning on Saturday, December 31, and GRAIL-B on Sunday, January 1. On New Year’s Eve, the pair of probes will fire their engine to slow down so that it could be captured into orbit. This move will be repeated by the other the following day.

Once in orbit, the pair will spend two months following each other around the moon. Scientists back on Earth will measure the varying distance between the pair of spaceships to calculate the lunar gravity field.

Speaking Monday, the team expressed confidence that the mission will continue to perform flawlessly, adding that they expect to gather an unprecedented amount of data from the mission.

“Both spacecraft have performed essentially flawlessly since launch, but one can never take anything for granted in this business,” said mission chief scientist Maria Zuber of the Massachusetts Institute of Technology.

Engineers said the chances of the probes overshooting are slim since their trajectories have been precise. Getting struck by a cosmic ray may prevent the completion of the engine burn and they won’t get boosted into the right orbit.

The straight-line distance from Earth to the moon is about 250,000 miles. It took NASA’s Apollo moon crews about three days to cover that distance. Each of the GRAIL twins is taking about 30 times that long and covering more than 2.5 million miles to get there. This low-energy, high-cruise time trajectory is beneficial for mission planners and controllers, as it allows more time for spacecraft checkout. NASA said the path would allow the program to save money and increase the chances of a successful mission.

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Smallest Full Moon of 2011 Occurs Tuesday

In my more than 40 years as an amateur astronomer, I've given countless numbers of people views of a variety of celestial objects through telescopes. And most people usually will tell me that the first object in the sky that attracted their attention as youngsters was the ever-changing moon.

Many may recall the attention given to our nearest neighbor in space in March when that months' full moon very nearly coincided with the lunar perigee — the point in the moon's orbit in which it is nearest to Earth. At a distance of 221,565 miles (356,575 kilometers), some media outlets even christened it the "Supermoon" of 2011 because of its unusual closeness.

But on Tuesday night (Oct. 11) we will have the astronomical opposite of a supermoon. At 10:06 p.m. EDT (0206 GMT), the moon will officially turn full, but it will be the smallest full moon of 2011.

The sky map of the smallest full moon of the year shows where it will appear on Tuesday night when it reaches its full phase.

Less than 10 hours after the October full moon peaks, at 8 a.m. EDT (1200 GMT) on Wednesday, the moon will arrive at the apogee of its orbit (the farthest point from Earth each month), which in October is a distance of 252,546 miles (406,434 km). That's only 154 miles (248 km) shy of the moon's absolute farthest point from Earth it can reach.

A puny full moon
Looking at the moon during Tuesday night, perhaps you will be struck by the noticeably small size of the moon's disk, even when it's near the horizon (which is supposed to make it appear larger as a result of the familiar "moon illusion" effect).

Last March, when the full moon was at perigee, some reported it as looking absolutely enormous as it emerged from above the eastern horizon. Not so on Tuesday, however, because the moon will very close to apogee, making this the smallest full moon of 2011.

By coincidence, October's full moon comes just days after the second annual International Observe the Moon Night on Oct. 8, in which skywatchers participated in hundreds of lunar observing events at skywatching parties around the world.

In fact, it will appear 12.3 percent smaller than the so-called supermoon of March 2011.

And because it is near its maximum distance from the Earth when full, the moon will also be traveling relatively slowly in its orbit. So both effects will combine to make its motion against the background stars especially small from night to night.

As a result, to the casual skywatcher it will seem that the moon is full for not just one night, but for three nights in a row: Monday, Tuesday and Wednesday. The defect of illumination on the moon's disk — or put another way, the dark sliver near the edge — will be very slight on Monday and Wednesday night.

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Cassini Celebrates 10 Years Since Jupiter Encounter

Ten years ago, on Dec. 30, 2000, NASA's Cassini spacecraft made its closest approach to Jupiter on its way to orbiting Saturn. The main purpose was to use the gravity of the largest planet in our solar system to slingshot Cassini towards Saturn, its ultimate destination. But the encounter with Jupiter, Saturn's gas-giant big brother, also gave the Cassini project a perfect lab for testing its instruments and evaluating its operations plans for its tour of the ringed planet, which began in 2004.

"The Jupiter flyby allowed the Cassini spacecraft to stretch its wings, rehearsing for its prime time show, orbiting Saturn," said Linda Spilker, Cassini project scientist based at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Ten years later, findings from the Jupiter flyby still continue to shape our understanding of similar processes in the Saturn system."

Cassini spent about six months - from October 2000 to March 2001 - exploring the Jupiter system. The closest approach brought Cassini to within about 9.7 million kilometers (6 million miles) of Jupiter's cloud tops at 2:05 a.m. Pacific Time, or 10:05 a.m. UTC, on Dec. 30, 2000.

Cassini captured some 26,000 images of Jupiter and its moons over six months of continual viewing, creating the most detailed global portrait of Jupiter yet.

NRC's 2010 Astrophysics Decadal Survey

National Research Council's Astro2010 report, New Worlds, New Horizons in Astronomy and Astrophysics. We appreciate the science community's efforts in defining a set of compelling science objectives for space-based astrophysical research for the coming decade, and for carefully considering the cost of the initiatives the report recommends.

We look forward to assessing the report's findings and recommendations for strengthening the nation's world-class space astrophysics program. From new worlds to new physics, the coming decade of discovery leverages not only our current space observatories – such as the Hubble, Spitzer, Chandra and Fermi space telescopes – but also our planned facilities – especially those from previous decadal surveys, the James Webb Space Telescope and the Stratospheric Observatory for Infrared Astronomy (SOFIA). The survey calls for new facilities that expand our reach into the cosmos that will include opportunities for coordination and cooperation with other Federal agencies and international partners.

Second CME to Hit Earth's Magnetic Field

Another great image from the Solar Dynamics Observatory (SDO) of the news-making solar event on August 1, 2010 resulting in two Coronal Mass Ejections (CMEs) launched in Earth's direction.

Earth's magnetic field is still reverberating from the CME impact of August 3rd, which sparked auroras as far south as Wisconsin and Iowa in the United States. Analysts believe a second CME is right behind it, due to arrive today. This second impact could re-energize the fading geomagnetic storm and spark a new round of Northern Lights.

Cassini Sees Moon Building Giant Snowballs in Saturn Ring

While orbiting Saturn for the last six years, NASA's Cassini spacecraft has kept a close eye on the collisions and disturbances in the gas giant's rings. They provide the only nearby natural laboratory for scientists to see the processes that must have occurred in our early solar system, as planets and moons coalesced out of disks of debris.

New images from Cassini show icy particles in Saturn's F ring clumping into giant snowballs as the moon Prometheus makes multiple swings by the ring. The gravitational pull of the moon sloshes ring material around, creating wake channels that trigger the formation of objects as large as 20 kilometers in diameter.

"Scientists have never seen objects actually form before," said Carl Murray, a Cassini imaging team member based at Queen Mary, University of London. "We now have direct evidence of that process and the rowdy dance between the moons and bits of space debris."

Murray discussed the findings today at the Committee on Space Research meeting in Bremen, Germany, and they are published online by the journal Astrophysical Journal Letters on July 14, 2010. A new animation based on imaging data shows how one of the moons interacts with the F ring and creates dense, sticky areas of ring material.

Saturn's thin, kinky F ring was discovered by NASA's Pioneer 11 spacecraft in 1979. Prometheus and Pandora, the small "shepherding" moons on either side of the F ring, were discovered a year later by NASA's Voyager 1. In the years since, the F ring has rarely looked the same twice, and scientists have been watching the impish behavior of the two shepherding moons for clues.

The newly found F ring objects appear dense enough to have what scientists call "self-gravity." That means they can attract more particles to themselves and snowball in size as ring particles bounce around in Prometheus's wake, Murray said. The objects could be about as dense as Prometheus, though only about one-fourteenth as dense as Earth.

The new findings could also help explain the origin of a mysterious object about 5 to 10 kilometers in diameter that Cassini scientists spotted in 2004 and have provisionally dubbed S/2004 S 6. This object occasionally bumps into the F ring and produces jets of debris.

"The new analysis fills in some blanks in our solar system's history, giving us clues about how it transformed from floating bits of dust to dense bodies," said Linda Spilker, Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "The F ring peels back some of the mystery and continues to surprise us."