The ALH84001 findings are timely in light of next July’s scheduled landing of the Mars Pathfinder spacecraft. The Pathfinder mission will investigate the structure of the martian atmosphere, surface meteorology and geology, and it will assess the elemental composition of the planet’s rocks and soil. It is first and foremost an engineering demonstration, however, in which key technologies and concepts for future Mars missions will be tried and tested.
A second Mars mission, scheduled for launch in January 1999, may open the door to a wider range of exploration. It may expand upon the findings of the Alan Hills meteorite. This mission, called the Mars Surveyor Lander, will focus on obtaining soil samples and measurements from below Mars’ sterilized surface, as well as detecting subsurface water.
The plan is for two “microprobes” to ride piggyback aboard the Mars Surveyor Lander during its 11-month journey. Just prior to its entry into the martian atmosphere, the microprobes will separate and fall to the surface at a high velocity, each encased in a protective “aeroshell.” The aeroshell is designed to do two things: first, to help it survive the fiery entry into the atmosphere and, second, to absorb the forces of the impact with the surface. Upon impact, the microprobes will split into a forebody and aftbody system. The forebody, which should penetrate between one to six feet underground, will contain the primary electronics and instruments. The aftbody, which will be connected to the forebody by an electrical cable, will remain near the surface to collect meteorological data and deploy an antenna for relaying data to Earth. The probes will make direct measurements of the martian surface, including water and soil samples, using a meteorological pressure sensor and temperature sensors for measuring thermal properties of the martian soil.
Still, the target region for the microprobes and the Lander is in the polar region, far from the ancient highlands where ALH84001 is thought to have originated.
As our knowledge of Mars grows, and as studies of ALH84001 and other martian meteorites continue, the priorities of future Mars missions will likely reflect these garnered insights. Some priorities were discussed at the world’s first Astrobiology Workshop, held September 9 at NASA Ames Research Center in Mountain View California. The workshop participants were no doubt galvanized by the announcement two weeks earlier of the possible fossilized bacteria in the Alan Hills meteorite. Suddenly, papers, talks, and proposals – many planned before the discovery – took on a new urgency.
A case in point: Jack D. Farmer, a geologist at Ames’ Exobiology Branch, urged an aggressive, multilevel approach using robotics to explore Mars for both extinct and extant lifeforms. According to Farmer, and now a growing number of scientists, the best place to search for extinct lifeforms would be the ancient terrains where liquid water was once present in abundance on the surface. Site selection, he writes in the abstract of his paper, will be critical because “we cannot expect to land just anywhere on Mars and find the kinds of deposits that are likely to preserve evidence of past martian life or climatic history.” Perhaps the calling card from Mars in the form of ALH84001 may help focus site selection a bit?
The exploration for extant martian life, Farmer adds, will require a fundamentally different approach from those used in the past. “The Viking missions revealed the surface of Mars to be inhospitable for life as we know it,” he wrote. “However, it has also been suggested that life could exist in the subsurface of Mars (perhaps tens to hundreds of kilometers depth), where an extensive hydrosphere could be present. It is also possible that areas of rising ground water may provide shallow subsurface oases capable of sustaining life. During the upcoming decade of exploration, we could initiate systematic orbital searches for such ‘oases’.”
However and whenever it is done, the search for life on Mars and in the universe will continue to be very important to scientists and the general public alike, thanks to ALH84001. The search, however, is only just beginning. How the search will be conducted — which martian surfaces drilled, what rocks overturned, what craters and rivulets probed — will depend in no small way on further findings and studies carried out in labs right here on Earth with martian and other meteorites.
ALH84001 is only one out of a dozen confirmed meteorites from Mars. It is estimated, however, that nearly a million more meteorites lie beneath the ice sheets in the Antarctic. One wonders how many of those embedded stones are from Mars and what secrets lie buried within them.