Ancient Lakebed: Spirit Has Landed
Ancient Lakebed: Spirit Landing Site
Six Minutes of Terror
|Mars Exploration Rover (MER-A) Spirit Landing Site MGS MOC Release No. MOC2-594, 3 January 2004. In areas where no MOC coverage exists, gaps were filled using images from the Mars Odyssey Thermal Emission Imaging System (THEMIS) visible imager, a lower-resolution camera built by Malin Space Science Systems and operated by Arizona State University. The Gusev Crater landing ellipse is centered near 14.8 degrees S, 184.8 degrees W. Sunlight illuminates each image in the mosaic from the left (in some cases, upper left, in others, lower left).|
Image Credit: Mars Global Surveyor, Malin Space Systems
Excitement built as the first Mars Exploration Rover (MER-A), Spirit, landed on Mars just after 8:35 p.m. Pacific Standard Time today, 3 January 2004 (04:35, 4 January 2004 UTC). From entry into the top of the atmosphere at twenty-seven times the speed of sound (Mach 27) to zero at the surface, up to one kilometer of bounces stood between the golf-cart sized rover and its destination in an ancient lakebed. As shown in the banner image, flight controllers at NASA’s Jet Propulsion Laboratory, in Pasadena, California, gave a few ‘high-five’ congratulatory gestures, as nearly three and half years of engineering and planning reached its next stages.
The period between entering the atmosphere and coming to rest is referred to by the engineering team as ‘six minutes of terror’. From Mach 27 to rest involves a large number of moving parts, including heat shield protection from 1600 C external temperatures, supersonic parachute deployment, heat shield detachment, rocket firing and airbag deployments. The EDL, or entry, descent and landing sequence, is considered one of the most challenging. While flight planners must trust their testing and computer controlled descent steps, the margin for correction is hindered by telemetry delays that make landing an automated sequence.
|A view of Gusev Crater.|
The Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) picture is a mosaic of MOC images of the Spirit landing site. The rover expected to land somewhere within the approximately 83 km (~52 mi) long by ~10 km (~6 mi) wide ellipse on the floor of Gusev Crater. The landing site is shown at 25 meters (82 feet) per pixel.
Gusev Crater, is intriguing because it appears to be the site of an ancient lakebed, where layers of sediment were deposited by a long-term flow of water into the basin formed by the crater. From orbit, the crater looks like a big lake bed with a winding riverbed feeding into it, and represents a candidate for investigating martian water history as an example of what are called paleolakes.
MOC has acquired 71 pictures of the landing site over a period spanning 3 Mars years (from July 1999 through December 2003), and more than 85 pictures were acquired within Gusev Crater specifically to support the Mars Exploration Rover landing site selection process.
These recent pictures were acquired not only in different years, but in different seasons, so the illumination angle, overall brightness, and patterns of emphemeral, dark dust devil streaks and wind streaks are different from image to image within the mosaic.
Gusev is a large crater basin, some 170 kilometers (105 miles) across. Most scientists believe it once was fed by water flowing through an enormous valley channel, Ma’adim Vallis.Snaking its way northward along the Martian landscape for more than 900 kilometers (560 miles), Ma’adim Vallis is 1.5 times as long as the Grand Canyon.
In images of Gusev taken by the Mars Orbital Camera(MOC) aboard the orbiting Mars Global Surveyor (MGS) spacecraft,some exposed outcrops appear to show faint layering. The prevailing scientific theory is that Gusev Crater contains sediment washed down Ma’adim Vallis from the highlands to the south nearly 4 billion years ago.
Some researchers also believe that landforms visible in MOC images of the mouth of Ma’adim Vallis, where it enters Gusev Crater, resemble landforms seen in some terrestrial river deltas.
"Deltas of this nature take tens of thousands of years, hundreds of thousands of years on Earth to be formed," says Nathalie Cabrol of the SETI Institute and NASA Ames Research Center. "So here you have the place where water has been acting for a long time. And depositing and eroding sediments and shaping the landscape for – possibly that long."
|Viking image of Gusev Crater, an ancient proposed lakebed that will be targeted in forthcoming Mars Exploration Rover mission.|
New Mexico State University planetary scientist Jim Murphy noted: "When the first spacecraft, Mariner 4, flew by Mars 38 years ago and took 21 pictures, it saw only 1 percent of the surface of the planet. It was heavily cratered like the moon, suggesting the planet was biologically dead."
"The main concern [for the landers] is cold temperatures that can affect the instruments," Murphy said. The rovers will touch down just south of Mars’ equator during late southern winter and their expected 90-day mission lifespans will keep them operating until early autumn. Surface temperatures will likely range from zero to minus 100 Celsius, or roughly from freezing to 150 below zero on the Fahrenheit scale, he said.
But according to astrobiologist, Dr. Chris McKay of NASA Ames, "the key environmental factor for making Mars a better place for life, a kinder, gentler planet, is not making it warmer. The key factor is raising the pressure up from 6 to maybe 100 millibar. [One hundred millibar is one-tenth of the pressure on Earth at sea level.] Not much higher than that would be needed".
|The Mars Global Suveyor launched on November 7, 1996.|
"At that pressure", McKay continued, "liquid water could exist on a very cold Mars. Lake Vanda in Antarctica could be an analog, for example, for Gusev Crater, which Nathalie Cabrol and many others have shown is likely once to have been full of water. If you look around at the terrain around Gusev, you can see that it would have been very cold at the time. So the remnant of an ice-covered lake could be what the MER-A lander ‘Spirit’ is going to land in. And what might it find? Probably the best thing it might find in a place like this is a fossil".
The robotic rovers are carrying cameras, spectrometers and geology instruments to analyze their surroundings. "We should get some fabulous pictures," Murphy said.
About the Missions
By launching the Mars Global Surveyor (MGS) spacecraft in November 1996, NASA and the Jet Propulsion Laboratory began America’s return to Mars after a 20-year absence. Images and measurements from two NASA spacecraft orbiting Mars, Global Surveyor and Odyssey, have provided scientists and engineers evaluating potential landing sites with details of topography and geology.
|A simulated image of the Mars rover protected by descent-bracing airbag pyramid.|
The Surveyor spacecraft is a rectangular-shaped box with wing-like projections extending from opposite sides. When fully loaded with propellant at the time of launch, the spacecraft weighed only 1,060-kilograms (2,342 pounds). The spacecraft travelled nearly 750 million kilometers (466 million miles) over the course of a 300-day cruise to reach Mars on September 11, 1997. During mapping operations, the spacecraft circled Mars once every 118 minutes at an average altitude of 378 kilometers (235 miles). After mapping finishes, the spacecraft will function as a communications satellite to relay data back to Earth from surface landers launched as part of future Mars missions.
JPL, a division of the California Institute of Technology, manages the Mars Exploration Rover project for NASA’s Office of Space Science, Washington, D.C.