Jubilant cheers resounded through the hallways at the Jet Propulsion Laboratory in Pasadena, California, as NASA's Phoenix spacecraft set down on the flat plains surrounding Mars's north pole today at 4:53:44 p.m. Pacific Daylight Time (23:53:44 Universal Time).
The triumphant landing caps a 9½-month, 422-million-mile voyage that began August 4, 2007.
The craft's arrival marked the first time since the Viking mission in 1976 that a Martian lander has used retrorockets in the final moments of its descent to the surface. NASA's three subsequent successful landers — Mars Pathfinder in 1996 and the twin rovers Spirit and Opportunity in 2003 — thumped roughly onto the surface inside cocoons of airbags.
Planetary landers are all-or-nothing propositions. When Mars Polar Lander attempted to set down on the south-polar terrain in December 1999, the outcome was, unfortunately, nothing. After the spacecraft began its descent to the surface, it was never heard from again.
The nerve-wracking wait was repeated today at the Jet Propulsion Laboratory in Pasadena, California. It was an especially tense time for the 22 people seated at the Entry Descent and Landing consoles in mission control, yet the spacecraft's fate was out of their hands. The craft was operating on its own, too far from Earth to be controlled directly.
Fortunately, in the years since MPL's demise, NASA's engineers had made fixes to the automated landing sequence and other critical systems to prevent another landing catastrophe. And this time around, the spacecraft radioed its activity throughout the descent and all the way to its successful touchdown. Phoenix landed within ¼° of being perfectly horizontal (meaning it didn't end up atop a large rock) and aligned roughly east-west as planned.
Within two hours, during an overflight of the Mars Odyssey orbiter that served as a radio relay to Earth, Phoenix sent a series of pictures confirming that its two circular solar-cell arrays had deployed correctly. But even more amazing were the late-afternoon views of the surrounding landscape, showing flat, rock-free terrain with subtle polygonl-shape patterns embedded in it.
In the coming days and weeks the seven experiments aboard Phoenix will study what's on — and under — the surface. A robotic arm is expected to dig down, in the hope of finding ice samples for onboard analysis.
The mission's name recounts a mythical bird that rose anew from the ashes of its funeral pyre. This spacecraft was built for a 2002 mission. But it was canceled in the wake of Mars Polar Lander's loss. But later, Peter Smith (University of Arizona) led a team that proposed bringing the unused spacecraft out of mothballs for another try at exploring Martian polar terrain.
You can follow progress of Phoenix — including images as they arrive at Earth — at the mission's website.