Mars Encounter, Christmas
Compared to the twin NASA rovers, a European lander expected to reach Mars around Christmas Day is smaller, less mobile, and more biologically-oriented in its testing protocols. Called Mars Express, the lander is so called because it will be built more quickly than any other comparable planetary mission. Its soft-lander is called Beagle 2 –so named since it will conduct biological experiments and share an investigative rapport with the ship in which Charles Darwin sailed when formulating his ideas about evolution. In contrast to the twin NASA rovers also on their way now to Mars, Beagle 2 is more of a mining station and furnace than a wheeled car.
|Mars Express launches from Russian Cosmodrome Credit: ESA|
"This is the first time Europe has gone to Mars," said Ed Weiler, associate administrator for NASA’s Office of Space Science, while noting that the European Space Agency, ESA, launched its own probe June 2nd. "I sent an email after the successful Mars Express, wishing ESA luck," said NASA’s Weiler. "After the [first Mars Exploration Rover] MER-A launch, ESA sent me a congratulatory email."
|Mars Express spacecraft.
"Beagle is a softlander," said Weiler. "It would be great to have multiple landers on Mars. The last time we had multiple landers on Mars was 1976." Commencing on December 19th, it will take approximately five days from when the orbiter reaches Mars, before the lander encounters the martian red soil on Christmas. The overall mission’s operational duration is one martian year (687 Earth days), but the spacecraft is designed for a further martian year’s operation. Because of power constraints, the lander is hoped to function for 180 martian days (about six Earth months).
To begin its atmospheric entry, the mission profile is geared for a final soft landing using a sophisticated system of parachutes and airbags. With a landed mass of less than 30 kg, Beagle 2 represents the most ambitious science payload-to-systems mass ratio ever attempted. Almost a third of the payload will carry out various types of analysis or be used to manipulate and collect samples for study on the surface of Mars. One of its main tasks will be the step-wise heating of martian soil in a kind of oven, to determine the elemental composition of any volatiles including organic compounds.
Because of complex communications links need to relay high-resolution photos back to Earth, the first images from the cameras of Beagle 2 and Mars Express are expected to be available between the end of the year and the beginning of January 2004. As soon as it comes to a halt on the martian surface, Beagle 2’s outer casing will open to reveal the inner workings. In addition to this delicate camera work, the payload carries seven scientific instruments that will perform a series of remote-sensing experiments.
"We are addressing a series of noble objectives," says Agustin Chicarro, Mars Express Project Scientist. "As well as helping to answer the big questions about water and life, our investigations will provide clues as to why the north of the planet is so smooth and the south so rugged, how the Tharsis and Elysium mounds were lifted up and whether active volcanoes exist on Mars today. We should also find out about the minerals in the rocks and the composition of the atmosphere in greater detail than ever before". If all goes well, the lander will settle near the equator in a region known as Isidis Planitia.
|Landing ellipses centered on Mars’ third largest impact basis Credit: NASA JPL/MSSS/MOC|
First, solar panels will unfold: they will catch sunlight to charge the batteries which will power the lander and its experiments throughout the mission. Next, a robotic arm will spring to life. Attached to the end of the arm will be Beagle’s PAW (Payload Adjustable Workbench) where most of the experiments are situated. These include a pair of stereo cameras, a microscope, two types of spectrometer (Mössbauer and X-ray), and a torch to illuminate surfaces. The PAW also houses the corer/grinder and the mole, two instruments for collecting rock and soil samples for analysis.
The robotic arm will stretch and rotate to give the two stereo cameras a good panoramic view of the landing site. After taking some shots, the cameras will take close up images of near-by soil and rocks as potential candidates for further analysis. These cameras will provide digital pictures from which a 3D model of the area within reach of the robotic arm may be constructed. As the PAW cannot be operated in real time from Earth, this 3D model will be used to guide the instruments into position alongside target rocks and soil and to provide information on the geological setting of the landing site. When a suitable rock has been chosen, the PAW will be rotated until the grinder is in position to grind away the weathered surface. The PAW can then be repositioned for the microscope or spectrometers to analyse the freshly exposed material. The microscope will pick out features a few thousandths of a millimeter across on rock surfaces exposed by the grinder. It will reveal the texture of the rock, which will help determine whether it is of sedimentary or volcanic origin.
When a rock looks particularly interesting, a sample will be drilled out with the corer and taken to the gas analysis package (GAP) inside the shell of the lander by means of the robotic arm. This is a drill bit that can either be moved over a surface to remove weathered material or be positioned in one spot to drill a core of a hopefully pristine sample. The mole will be able to crawl up to several meters across the surface at the rate of 1 cm every six seconds. Once it has reached a boulder, it will burrow underground to collect samples in a cavity in its tip. Alternatively, the PAW can be positioned so that the mole can burrow vertically underground to collect samples possibly 1m below the surface.
The mole carried on the back of the PAW will also collect soil samples and return them to the GAP. This is where investigations most relevant to detecting past or present life will be conducted. The instrument has twelve ovens in which rock or soil samples can be heated gradually in the presence of oxygen. The carbon dioxide generated at each temperature will be delivered to a mass spectrometer which will measure its abundance and the ratio of carbon-12 to carbon-13. The mass spectrometer will also study other elements and look for methane in samples of atmosphere. The temperature at which the carbon dioxide is generated will reveal its nature, as different carbon bearing materials combust at different temperatures.
According to mission status reports, "The Mars Express spacecraft is in good health and is operating normally. Some payload activities were executed on September 30, 2003, involving the Ultraviolet and Infrared Atmospheric Spectrometer (SPICAM) and Visible and Infra Red Mineralogical Mapping Spectrometer (OMEGA) spectrometers. SPICAM and OMEGA were turned on in order to check the mechanisms of these instruments. The Planetary Fourier Spectrometer (PFS) and High Resolution Stereo Camera (HRSC) Interplanetary Cruise checkouts were conducted successfully on 6 October 2003. The remaining orbiter instruments checkouts to be done during the Interplanetary Cruise phase were completed by the end of October. The first Interplanetary Cruise checkout of the Beagle-2 lander was conducted on 7 October 2003. The second and final Beagle-2 checkout for this phase was completed on the 3rd of November. On the spacecraft side, preparations and simulations for Beagle-2 ejection and Mars Orbit Insertion are proceeding well."
The only previous landers to look directly for evidence of life on Mars were NASA’s Vikings in 1976. However, Mars’s harsh, oxidising atmosphere would almost certainly have destroyed any such evidence on the surface. Beagle 2 hopes to surmount this problem by using a ‘mole’ to retrieve samples of soil from as much as 1m below ground. It will also use a corer and grinder to expose the interior of rocks for study.
The Beagle 2 lander will look for signatures of life on Mars, whether long-dead or still-living, by measuring the ratio of two different types of carbon in the rock. Biological processes on Earth favour the lighter isotope of carbon, carbon-12, over the heavier carbon-13. Hence, a high carbon-12 to carbon-13 ratio is taken as evidence of life and has been found in rocks up to 4 billion years old, even where geological processing has occurred. The hope is that the same occurred on Mars.
The summary of expected events involve the following scientific objectives:
The Mars Express Orbiter will:
The Beagle 2 lander will:
Mars Express forms part of an international Mars exploration program, featuring also the US probes Mars Surveyor and Mars Odyssey, the two Mars Exploration Rovers and the Japanese probe Nozomi. Using some of the same mission elements, future European explorers will head towards Venus in 2005, Mercury in 2009, and next year towards landing on a comet with the recently rescheduled Rosetta mission ‘s launch.