(From west to east)

• Vesta is in the constellation of Pisces.
• Metis is in the constellation of Cetus.
• Harmonia is at opposition on the 11th in the constellation of Gemini.
• Euterpe is in the constellation of Leo.
• Information about the Minor Planets can be found at the Minor Planet Observer website.

"Cassini streaked past Titan on Dec. 21 at an altitude of 971 kilometers (603 miles), obtaining radar images of Titan's south polar region and a topographic profile of the dark, possibly liquid-filled area known as Ontario Lacus."

Cassini Imaging Team

"After an intense annual checkout - more like a deep-space workout - New Horizons getting some well-deserved rest.

New Horizons operators at the Johns Hopkins University Applied Physics Laboratory (APL) eased the spacecraft into electronic hibernation on Dec. 16, wrapping up nearly four months of tests, data collection and software upgrades. The spacecraft's Earth-bound crew has now turned its attention to detailed Pluto-encounter sequencing.

"I'm in awe of all the team accomplished during this checkout - multiple software uploads, full spacecraft and payload checkouts, instrument calibrations and new capability tests, star-tracker imaging, trajectory tracking refinement, science measurements and more, and all of it went well," says New Horizons Principal Investigator Alan Stern. "What a great team and spacecraft we have!"

New Horizons is spending most of its 9 1/2 -year cruise to Pluto in hibernation, with its major systems and most instruments turned off, save for an annual period when the team wakes it up for system checks and other activities. Mission managers expect each annual checkout to last about 10 weeks, but they also have to be flexible. The first annual checkout (ACO) in 2007 took about three months as operators took extra time to update the spacecraft's autonomy software and finished commissioning the science instruments."

New Horizons gallery."

"NASA's Dawn spacecraft shut down its ion propulsion system today as scheduled. The spacecraft is now gliding toward a Mars flyby in February of next year.

"Dawn has completed the thrusting it needs to use Mars for a gravity assist to help get us to Vesta," said Marc Rayman, Dawn's chief engineer, of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Dawn will now coast in its orbit around the sun for the next half a year before we again fire up the ion propulsion system to continue our journey to the asteroid belt."

Dawn's ion engines may get a short workout next January to provide any final orbital adjustments prior to its encounter with the Red Planet. Ions are also scheduled to fly out of the propulsion system during some systems testing in spring. But mostly, Dawn's three ion engines will remain silent until June, when they will again speed Dawn toward its first appointment, with asteroid Vesta."

"On December 26, the MESSENGER spacecraft will have traveled three billion miles since its launch, marking somewhat more than 60 percent of the probe's journey toward its destination to be inserted into orbit about Mercury.

"That MESSENGER's odometer reading has reached another major milestone reminds us of the long and complex route that our spacecraft must follow," offers Principal Investigator Sean Solomon, of the Carnegie Institution of Washington. "The year now ending has seen the first two spacecraft flybys of the innermost planet in more than three decades, encounters that have yielded a rich lode of new observations. The journey is far from over, but MESSENGER has a skilled team to guide it the rest of the way."

Mercury orbits deep within the Sun's gravity well. So, even though the planet can be as close as 82 million kilometers (51 million miles) from Earth, getting the probe into orbit around Mercury depends on an innovative trajectory using the gravity of Earth, Venus, and Mercury itself to slow and shape the probe's descent into the inner solar system. On its 4.9 billion-mile journey to becoming the first spacecraft to orbit the planet Mercury, MESSENGER has flown by Earth once, Venus twice, and Mercury twice. Still to come is one more flyby of Mercury in late September 2009.

Today the spacecraft entered its fourth superior solar conjunction of the mission, placing it on the opposite side of the Sun from Earth. (To see where MESSENGER is now, visit http://messenger.jhuapl.edu/whereis/index.php.) The Sun-Earth-probe angle will be between 2° and 3° until January 6, 2009, so during the next two weeks there will be no communication with the spacecraft."

"An international team of scientists who analyzed data from the Gamma Ray Spectrometer onboard NASA's Mars Odyssey reports new evidence for the controversial idea that oceans once covered about a third of ancient Mars.

"We compared Gamma Ray Spectrometer data on potassium, thorium and iron above and below a shoreline believed to mark an ancient ocean that covered a third of Mars' surface, and an inner shoreline believed to mark a younger, smaller ocean," said University of Arizona planetary geologist James M. Dohm, who led the international investigation.

"Our investigation posed the question, Might we see a greater concentration of these elements within the ancient shorelines because water and rock containing the elements moved from the highlands to the lowlands, where they eventually ponded as large water bodies?" Dohm said."

"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."

Mars Odyssey THEMIS Images
Thermal Emission Imaging System (THEMIS) website: http://themis.asu.edu/

December 24-31, 2008

The following new images from the Mars Odyssey spacecraft are now available:

• Dunes (Released 24 December 2008)
  
• Dark Slope Streak (Released 25 December 2008)
  
• Ganges Chasma (Released 26 December 2008)
  
• Channel (Released 29 December 2008)
  
• Volcanic Vent (Released 30 December 2008)
  
• Candor Chasma (Released 31 December 2008)
  
• All of the THEMIS images are archived here.

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

Mars Rovers Near Five Years of Science and Discovery

"PASADENA, Calif. -- NASA rovers Spirit and Opportunity may still have big achievements ahead as they approach the fifth anniversaries of their memorable landings on Mars.

Of the hundreds of engineers and scientists who cheered at NASA's Jet Propulsion Laboratory in Pasadena, Calif., on Jan. 3, 2004, when Spirit landed safely, and 21 days later when Opportunity followed suit, none predicted the team would still be operating both rovers in 2009.

"The American taxpayer was told three months for each rover was the prime mission plan," said Ed Weiler, associate administrator for NASA's Science Mission Directorate at NASA Headquarters in Washington. "The twins have worked almost 20 times that long. That's an extraordinary return of investment in these challenging budgetary times."

The rovers have made important discoveries about wet and violent environments on ancient Mars. They also have returned a quarter-million images, driven more than 21 kilometers (13 miles), climbed a mountain, descended into craters, struggled with sand traps and aging hardware, survived dust storms, and relayed more than 36 gigabytes of data via NASA's Mars Odyssey orbiter. To date, the rovers remain operational for new campaigns the team has planned for them."

Landing sites