By Dr. Emily Baldwin                                                          ASTRONOMY NOW

   NASA’s Spirit and Opportunity rovers celebrate their fifth year exploring the Red Planet this month, in a mission that was only expected to last three months.

   Spirit landed in Gusev Crater on 3 January 2004, with Opportunity following to the opposite side of Mars at Meridiani Terra 21 days later. Five years later and they are still exceeding all expectations, and have a full schedule ahead of them. "The American taxpayer was told three months for each rover was the prime mission plan," says Ed Weiler, associate administrator for NASA's Science Mission Directorate at NASA Headquarters. "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 incredible discoveries about the history of water on Mars and in their five years have taken around a quarter-million images, driven more than 20 kilometres, climbed a mountain, descended into craters, struggled with sand traps and aging hardware, survived dust storms, and relayed more than 36 gigabytes of data through NASA's Mars Odyssey orbiter.

   "These rovers are incredibly resilient considering the extreme environment the hardware experiences every day," says John Callas, JPL project manager for Spirit and Opportunity. "We realize that a major rover component on either vehicle could fail at any time and end a mission with no advance notice, but on the other hand, we could accomplish the equivalent duration of four more prime missions on each rover in the year ahead."

   In the past the rovers have experienced a few lucky encounters with strong Martian winds and even a dust devil that cleaned off dust accumulating on the rovers’ solar panels, but it’s been a good 18 months since Spirit received such attention and as a result, the rover barely had enough power to survive its third southern hemisphere winter. But with the rover's energy slowly rising as spring takes hold, the team plans to navigate the rover to a pair of destinations about 200 metres south of the site where Spirit spent most of 2008. One location is a mound that might yield support for an interpretation that a plateau Spirit has studied since 2006, called Home Plate, is a remnant of a once more extensive sheet of explosive volcanic material. The other destination is a house-size pit called Goddard, the origin of which is much speculated.

   "Goddard doesn't look like an impact crater," says Steve Squyres of Cornell University and principal investigator for the rover science instruments. "We suspect it might be a volcanic explosion crater, and that's something we haven't seen before."

   One of Spirit’s most important discoveries so far has been a patch of bright, silica-rich soil that the rover churned up with its broken wheel in mid 2007. The silica was likely produced in an environment of hot springs or steam vents and a light-toned ring of material around the inside of ‘Goddard’ might add information to the silica soil.

   For Opportunity, the next major destination is the 22 kilometre wide Endeavour Crater, more than 20 times larger than Victoria crater where Opportunity spent most of the last two years. Endeavour is 11 kilometres from Victoria, but the rover will travel considerably farther as it takes a route avoiding major obstacles like rocks and boulders. Since climbing out of Victoria Crater four months ago, Opportunity has driven nearly two kilometres of its route, stopping only to inspect loose rocks the team plans to examine along the way. High-resolution images from NASA's Mars Reconnaissance Orbiter, which reached Mars in 2006, are helping the team plot routes around potential sand traps that were not previously discernable from orbit.

   "The journeys have been motivated by science, but have led to something else important," says Squyres. "This has turned into humanity's first overland expedition on another planet. When people look back on this period of Mars exploration decades from now, Spirit and Opportunity may be considered most significant not for the science they accomplished, but for the first time we truly went exploring across the surface of Mars."

Submitted by Mitch Menschel  (1/09)

Report From The Voyager

   NASA's "Voyager 2" spacecraft (launched in 1977) is nearing what is described as the outer edge of our solar system.  In approx. one additional decade, the unmanned, nuclear-powered probe is expected to reach what is called the "heliopause."  This is the point that defines the outer limit of our solar system and the geginning of interstellar space.

   The craft continues to transmit important measurements and other data back to Earth, and it is far enough out at this time to be able to detect a warp in the shape of our solar system.  Previous observations and theories have suggested such an asymmetrical condition.  It has now been confirmed.

   Scientists suggest that this condition is most likely due to disturbances in the interstellar magnetic field,  Such disturbances may be part of the normal environment in the galactic arms of our galaxy, including the one in which our solar system resides.

   More details are available from the full report, through Voyager scientist Edward Stone of the California Institute of Technology.

--- A report by Dr. Andrew Jonas

April / 2009