(From west to east)

• Astraea is in the constellation of Leo.
• Iris is at opposition on the 4th in the constellation of Libra.
• Juno is at opposition on the 19th in the constellation of Serpens Cauda.

• Information about the Minor Planets can be found at the Minor Planet Observer website.

"PASADENA, Calif. -- Data from NASA's Cassini mission reveal Saturn's moon Phoebe has more planet-like qualities than previously thought.

Scientists had their first close-up look at Phoebe when Cassini began exploring the Saturn system in 2004. Using data from multiple spacecraft instruments and a computer model of the moon's chemistry, geophysics and geology, scientists found Phoebe was a so-called planetesimal, or remnant planetary building block. The findings appear in the April issue of the Journal Icarus.

"Unlike primitive bodies such as comets, Phoebe appears to have actively evolved for a time before it stalled out," said Julie Castillo-Rogez, a planetary scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Objects like Phoebe are thought to have condensed very quickly. Hence, they represent building blocks of planets. They give scientists clues about what conditions were like around the time of the birth of planets and their moons."

Cassini images suggest Phoebe originated in the far-off Kuiper Belt, the region of ancient, icy, rocky bodies beyond Neptune's orbit. Data show Phoebe was spherical and hot early in its history, and has denser rock-rich material concentrated near its center. Its average density is about the same as Pluto, another object in the Kuiper Belt. Phoebe likely was captured by Saturn's gravity when it somehow got close to the giant planet."

Cassini Imaging Team

"As fast as NASA's New Horizons spacecraft is heading toward Pluto, the drive to honor this historic exploration of the ninth planet is speeding toward its finish. Less than a week remains to put your name on the petition supporting an effort for the U.S. Postal Service to commemorate Pluto and New Horizons on a postage stamp.

In just over a month since the drive was announced, more than 10,000 people have signed the online petition. But mission leads would like to have many more signatures before they close out the list on March 13 - the 82nd anniversary of the announcement of Pluto's discovery by American astronomer Clyde Tombaugh."

LORRI Looks Back

New Horizons gallery

Find New Horizons in the iTunes App Store here.

  "PASADENA, Calif. - Findings from NASA's Dawn spacecraft reveal new details about the giant asteroid Vesta, including its varied surface composition, sharp temperature changes and clues to its internal structure. The findings were presented today at the European Geosciences Union meeting in Vienna, Austria, and will help scientists better understand the early solar system and processes that dominated its formation.

Images from Dawn's framing camera and visible and infrared mapping spectrometer, taken 420 miles (680 kilometers) and 130 miles (210 kilometers) above the surface of the asteroid, show a variety of surface mineral and rock patterns. Coded false-color images help scientists better understand Vesta's composition and enable them to identify material that was once molten below the asteroid's surface.

Researchers also see breccias, which are rocks fused during impacts from space debris. Many of the materials seen by Dawn are composed of iron- and magnesium-rich minerals, which often are found in Earth's volcanic rocks. Images also reveal smooth pond-like deposits, which might have formed as fine dust created during impacts settled into low regions."

"The International Astronomical Union (IAU) recently approved a proposal from the MESSENGER Science Team to assign 23 new names to impact craters on Mercury. The IAU has been the arbiter of planetary and satellite nomenclature since its inception in 1919. In keeping with the established naming theme for craters on Mercury, all of the newly designated features are named after famous deceased artists, musicians, or authors."

The MESSENGER app is available for download.

"At 10:31 p.m. PDT today, April 27, (1:31 p.m. EDT), NASA's Mars Science Laboratory, carrying the one-ton Curiosity rover, will be within 100 days from its appointment with the Martian surface. At that moment, the mission has about 119 million miles (191 million kilometers) to go and is closing at a speed of 13,000 mph (21,000 kilometers per hour).

"Every day is one day closer to the most challenging part of this mission," said Pete Theisinger, Mars Science Laboratory project manager at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "Landing an SUV-sized vehicle next to the side of a mountain 85 million miles from home is always stimulating. Our engineering and science teams continue their preparations for that big day and the surface operations to follow."

On Sunday, April 22, a week-long operational readiness test concluded at JPL. The test simulated aspects of the mission's early surface operations. Mission planners and engineers sent some of the same commands they will send to the real Curiosity rover on the surface of Mars to a test rover used at JPL."

SPIRIT UPDATE: Spirit Remains Silent at Troy - sols 2621-2627, May 18-24, 2011:

"No communication has been received from Spirit since Sol 2210 (March 22, 2010).

More than 1,300 commands were radiated to Spirit as part of the recovery effort in an attempt to elicit a response from the rover. No communication has been received from Spirit since Sol 2210 (March 22, 2010). The project concluded the Spirit recovery efforts on May 25, 2011. The remaining, pre-sequenced ultra-high frequency (UHF) relay passes scheduled for Spirit on board the Odyssey orbiter will complete on June 8, 2011.

Total odometry is unchanged at 7,730.50 meters (4.80 miles)."

OPPORTUNITY UPDATE: Studies of 'Amboy' Rock Continue as Solar Energy Improves - sols 2927-2934, April 18-25, 2012 :

"Opportunity is positioned on the north end of Cape York on the rim of Endeavour Crater with an approximate 15-degree northerly tilt for favorable solar energy production.

The solar insolation is improving and the rover has benefitted from some small, dust cleaning events. Radio Doppler tracking passes for the geo-dynamic investigation were performed on Sols 2927, 2931 and 2933 (April 18, 22 and 24, 2012).

The project is also continuing the regular campaign of Microscopic Imager mosaics of the extended region of the rock target "Amboy," followed by Alpha Particle X-ray Spectrometer measurements of the imaged area. These measurements were performed on Sols 2929, 2931 and 2933 (April 20, 22 and 24, 2012). More dust cleaning events have occurred, improving the solar array dust factor by small amounts.

As of Sol 2934 (April 25, 2012), solar array energy production was 366 watt-hours with an atmospheric opacity (Tau) of 0.521 and an improved solar array dust factor of 0.546.

Total odometry is unchanged at 21.35 miles (34,361.37 meters)."

Landing sites

"A Martian dust devil roughly 12 miles high (20 kilometers) was captured whirling its way along the Amazonis Planitia region of Northern Mars on March 14. It was imaged by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. Despite its height, the plume is little more than three-quarters of a football field wide (70 yards, or 70 meters).

Mars' Whirling Dust Devil Video

Dust devils occur on Earth as well as on Mars. They are spinning columns of air, made visible by the dust they pull off the ground. Unlike a tornado, a dust devil typically forms on a clear day when the ground is heated by the sun, warming the air just above the ground. As heated air near the surface rises quickly through a small pocket of cooler air above it, the air may begin to rotate, if conditions are just right.

The image was taken during late northern spring, two weeks short of the northern summer solstice, a time when the ground in the northern mid-latitudes is being heated most strongly by the sun."

MARS RECONNAISSANCE ORBITER HIRISE IMAGES
All of the HiRISE images are archived here.

"Ten years ago, on Feb. 19, 2002, the Thermal Emission Imaging System (THEMIS), a multi-band camera on NASA's Mars Odyssey orbiter, began scientific operations at the Red Planet. Since then the camera has circled Mars nearly 45,000 times and taken more than half a million images at infrared and visible wavelengths. "THEMIS has proven itself a workhorse," said Philip Christensen of Arizona State University, Tempe, the camera's principal investigator and designer. "It's especially gratifying to me to see the range of discoveries that have been made using this instrument."

Highlights of science results by THEMIS over the past 10 years include:

• Confirming a mineral exposure selected as the landing site for NASA's Mars Exploration Rover Opportunity
• Discovering carbon-dioxide gas jets at the south polar ice cap in spring
• Discovering chloride salt deposits across the planet
• Making the best global image map of Mars ever done
• Identifying safe landing sites landing sites for NASA's Mars Phoenix lander by finding the locations with the fewest hazardous boulders
• Monitoring dust activity in the Martian atmosphere
• Discovering that a large crater, Aram Chaos, once contained a lake
• Discovering that Mars has more water-carved channels than previously thought
• Discovering dacite on Mars, a more evolved form of volcanic lava not previously known on the Red Planet

THEMIS combines a five-wavelength visual imaging system with a nine-wavelength infrared imaging system. By comparing daytime and nighttime infrared images of an area, scientists can determine many of the physical properties of the rocks and soils on the ground.

Mars Odyssey has a two-hour orbit that is nearly "sun-synchronous," meaning that Odyssey passes over the same part of Mars at roughly the same local time each day. In September 2008 its orbit was shifted toward an earlier time of day, which enhanced THEMIS' mineralogical detection capability.

Says Christensen, "Both Odyssey and THEMIS are in excellent health and we look forward to years more science with them."

NASA launched the Mars Odyssey spacecraft April 7, 2001. Odyssey arrived at Mars Oct. 24, 2001. After arrival the spacecraft spent several months in a technique called aerobraking, which involved dipping into the Martian atmosphere to adjust its orbit. In February 2002, science operations began."

Global Martian Map

"A simulated fly-through using the newly assembled imagery is available online.

The fly-through plus tools for wandering across and zooming into the large image are at THEMIS."

Daily Mars Odyssey THEMIS Images
Can be found at the Thermal Emission Imaging System (THEMIS) website.

The Odyssey data are available through a new online access system established by the Planetary Data System.