Can Mars sustain life? A spacecraft on NASA's latest mission to the red planet will be trying to answer exactly that question, provided it has a successful touchdown as planned on Sunday.
After travelling 675 million kilometres over nine months since its launch on 4 August last year, NASA's Phoenix Mars Lander is aiming for a landing in the unexplored northern regions of Mars. But first, it must survive what its developers call the final ''seven minutes of terror'' to reach the surface.
''There are many, many risks and uncertainties,'' said Dr. Edward Weiler, associate administrator of the NASA science division. Since the start of planetary exploration, 55 per cent of spacecraft sent to land on Mars have failed, he said. Only five of 13 international attempts to land on Mars have been successful, although NASA has lost only one, the Mars Polar Lander in 1999.
Phoenix is a robotic spacecraft on a space exploration mission to Mars under the Mars Scout Program. The scientists conducting the mission will use instruments aboard the Phoenix lander to search for environments suitable for microbial life on Mars, and to research the history of water there.
The multi-agency $420-million programme is headed by the Lunar and Planetary Laboratory at the University of Arizona, under the direction of NASA. The programme is a partnership of universities in the United States, Canada, Switzerland, Denmark, Germany and the United Kingdom, NASA, the Canadian Space Agency, and the aerospace industry.
The Phoenix is named after the mythical bird that rose from its ashes, because the spacecraft is made up of remnants of parts from space crafts of two earlier attempts to explore Mars.
The spacecraft has the skeleton and some instruments from the 2001 Mars Surveyor lander, which remained grounded because of cost overruns, as well as instruments that are based on those aboard the unsuccessful Mars Polar Lander. That is why NASA managers like to compare it to a used car.
Although the Phoenix lander has been tested and rechecked to correct all known design flaws and potential errors, Dr. Weiler said, ''there are always the unknown unknowns.''
If all goes as planned, the lander is to set down on Vastitas Borealis, the arctic planes of Mars roughly equivalent to northern Canada on Earth, about 15 minutes before mission control receives confirmation at 7:53 p.m. Eastern time. The first picture from the spacecraft, expected to be an image of its deployed solar power panels, should arrive about two hours later, mission managers said.
The progress of the spacecraft in the Martian atmosphere will be as follows:
- 14 minutes before touchdown: Phoenix jettisons cruise stage and turns heat shield towards the surface.
- 7 minutes to touchdown: Phoenix, traveling at 20,400 kmph, experiences retardation due to friction. Heat shield temperature reaches 1400 degrees Celsius.
- 3 minutes 40 seconds to touchdown: Phoenix is traveling at 1,600 kmph and is 13 kilometres above the Martian surface. It jettisons its heat shield and deploys its parachute, while using its radar to gather readings on its speed and distance from the surface.
- 40 seconds to touchdown: Phoenix is traveling at 200 kmph and is 1 kilometre above the Martian surface. Parachute is abandoned and the first of twelve rocket thrusters start firing in sequence to slow down the craft.
- 0 seconds to touchdown: Phoenix lands on Mars at a speed of 8.3 kmph.
It has been 32 years since NASA, with the twin Viking landers in 1976, has put a craft on the Martian surface using rockets to slow the descent. The last previous attempt was the 1999 Mars Polar Lander, which crashed when its engines cut off prematurely.
The later Mars Pathfinder and the two robot rovers, the Opportunity and the Spirit, which have operated for three years in the equatorial region, landed using air bags to cushion the impact. Mr. Goldstein said air bags were not practical for heavier craft like the Phoenix because the added weight of bigger bags would severely cut into the scientific payload.
Unlike the wheeled rovers, the Mars Phoenix Lander is to stay in one spot and dig for evidence of water and other conditions that could have supported primitive life.
Phoenix carries improved versions of University of Arizona panoramic cameras and volatiles-analysis instrument from the ill-fated Mars Polar Lander, as well as experiments that had been built for the Mars Surveyor 2001 Lander, including a JPL trench-digging robot arm, a set of wet chemistry laboratories, and optical and atomic force microscopes. The science payload also includes a descent imager and a suite of meteorological instruments.
The instrument suite includes:
- Robotic Arm (RA) - designed to extend 2.35 metres from its base on the lander, and have the ability to dig down to half a metre below the surface. It will take samples of dirt and water ice that will be analyzed by other instruments on the lander.
- Robotic Arm Camera (RAC) - is attached to the Robotic Arm just above the scoop is able to take full-color pictures of the area, as well as verify the samples that the scoop will return, and examine the grains of the area where the Robotic Arm has just dug up.
- Surface Stereo Imager (SSI) - is a stereo camera expected to take many stereo images of the Martian Arctic. It will also be able, using the Sun as a reference, to measure the atmospheric distortion of the Martian atmosphere due to dust, air and other features.
- Thermal and Evolved Gas Analyzer (TEGA) - is a combination of a high-temperature furnace with a mass spectrometer. It will be used to bake samples of Martian dust, and determine the content of this dust. It has 8 different ovens, each about the size of a large ballpoint pen, which will be able to analyze one sample each, for a total of 8 different samples.
- Mars Descent Imager (MARDI) - was intended to take pictures of the Martian soil as the lander descended. However, due to potential data corruption problem with the hardware that handles multiple images, it won't be used.
- Microscopy, Electrochemistry, and Conductivity Analyzer (MECA) - is an instrument package consisting of a wet chemistry lab (WCL), optical and atomic force microscope, and a thermal and electrical conductivity probe. Using this instrument, researchers will examine soil particles as small as 16 micrometres across. They will measure electrical and thermal conductivity of soil particles using a probe on the RA scoop.
- Meteorological Station (MET) - will record the daily weather during the course of the Phoenix Mission. It is equipped with a variety of temperature and pressure sensors to do so. It is also equipped with LIDAR, or Laser Imaging Detection and Ranging, which will be used to find the amount and number of dust particles in the air.
Is there water on Mars?
Scientists have been keen to find evidence of water on Mars because it is essential to life as we know it, and having an "onsite" source of it would be crucial to any future manned missions to the planet.
"Liquid water is the holy grail on Mars. Where is it? Does it exist at all?" said Phoenix principal investigator Peter Smith of the University of Arizona.
For the first half of the 20th century, it was thought that liquid water sloshed around all over the surface of Mars, in dark patches assumed to be seas covering portions of the planet's surface. Mariner 4's 1965 flyby, which returned the first images of the planet's surface, dashed hopes of finding any Martian seas: The surface looked as inactive and pockmarked with craters as the moon.
Mariner 9, however, found signs that liquid water had once flowed across the Martian landscape through ancient riverbeds, as well as evidence of water erosion. Other missions, including two current rovers, Spirit and Opportunity, have found ample evidence that water once flowed through rivers, pooled in lakes and spewed from hydrothermal vents.
But this liquid water flowed mostly in very ancient times, when conditions on Mars were much different than they are today. Now, the planet's atmospheric pressure is too low (about 1/100th of Earth's) for liquid water to last on the surface. The only place on the surface where water exists is at the poles, and there it is found only in its frozen form.
In February 2002, NASA's Mars Odyssey orbiter extended the known regions of water on Mars when it detected the signature of water ice just under the surface of the Martian arctic regions, and lots of it.
"It's not just a little bit that you might expect to get frozen into the ground from the atmosphere, but it's like 70 to 80 per cent of the upper meter of the surface is ice," Smith said. "The amount of ice was a huge surprise."
Because the arctic regions of the planet haven't been explored from the surface and the underground ice has so far only been detected indirectly, this subsurface arena is "all of a sudden this mystery zone in my opinion," Smith said.
Exactly how these substantial subsurface layers of water ice formed is unknown. Some scientists say it could be a remnant of an ancient northern sea that has been theorized to exist when Mars was much warmer. It may also have formed as water vapour froze out of the atmosphere, which is partly how the polar caps on Mars form today. But this deposition typically only creates a small amount of soil-trapped ice.
"So you wonder how you can get 70 percent water in just the pore spaces [between soil grains], it doesn't make any sense!" Smith said. "So there must be some other way that you're getting this large amount of water in that area."
Phoenix will aim to shed some light on the origin of this ice, which is expected to be so cold that it will be as hard as concrete, and to characterize it by chipping away pieces for analysis. Smith and the other Phoenix investigators also hope the lander will help determine whether or not the ice periodically melted and wet the Martian soil to create a habitable zone that could have possibly supported some form of Martian life.