Although the primary purpose of Deep Space 2 is to test new technologies for use in future science missions,
the two probes are also miniature data-gathering laboratories. The probes will penetrate the south polar
layered deposits of Mars near the landing site of the Mars Polar Lander. These layered deposits are believed
to contain a record of changes in the climate of Mars, in the form of dust and water ice. Each probe will
use microinstruments in the forebody to 1) collect a sample of soil and analyze it for the presence of water,
2) measure how quickly the probe cools after penetration to give scientists information on the
physical properties of the soil, and 3) measure how fast each probe slows down in the atmosphere-to
determine the pressure and temperature of the atmosphere-and in the ground, to estimate the hardness
of the soil and to look for layers. Data from the forebody will be collected and relayed to Mars
Global Surveyor, which is currently orbiting Mars on a mission to map the planet. Deep Space 2's
scientific objectives complement those of the Mars Polar
Several spacecraft around a planet could give scientists valuable information about different
locations on a planet, as well as provide the kind of information that a single spacecraft
could not. Networks of seismic stations (like those used on the Earth for many purposes, including
detecting earthquakes), for instance, can tell scientists about the structure of a planet deep
below its surface. A network of meteorological stations on Mars could help scientists understand
the atmosphere of the planet. Penetrators deployed around a planet can give scientists information
about the rocks and soil in many locations, rather than in just one or two. So, why haven't networks
of spacecraft ever been sent to another planet? Standard spacecraft are too large, and therefore
too costly, to launch in large numbers. In contrast, dozens of miniaturized spacecraft could be
launched at an affordable cost. Thus the Deep Space 2 probes could pave the way to make networks
of scientific stations on other planets a reality.
The Mars Rock - Are we alone in the universe?
Science's and theology's most talked about rock is the 1.6 kgs (4.2 lb.), potato-shaped
meteorite ALH84001. It was discovered on the Allan Hills ice field in Antarctica in 1984.
The geochemical composition of the gas trapped within the rock is such a close match to
the unique composition of the Martian atmosphere that it provides solid evidence that the
rock comes from Mars. The rock formed beneath the Martian surface 4.5 billion years ago,
and thus dates back to a very early period in the formation of Mars. There is evidence
that water seeped into the rock 3.6 billion years ago, when the climate of Mars was much
warmer and wetter than it is now. This rock remained under the surface until 16 million
years ago, when it was blasted into space by an asteroid striking the Martian surface.
The rock drifted through space until it fell to Earth 13,000 years ago.
Mars Rock ALH84001
The evidence for life having once existed in ALH84001 is a bit circumstantial. There are
four separate observations that suggest the work of tiny bacteria:
- Tiny, spherical blobs of carbonate, about the same diameter as a human hair, have a
shape and geochemistry similar to those formed in muddy sediments by bacteria.
- Two minerals, magnetite (an iron oxide) and pyrolite (an iron sulfide), are found
on the rim of the carbonate. Their shape and chemistry also resemble minerals created
- Other carbon compounds (polycyclic aromatic hydrocarbons, or PAHS) that are typically
created by organic means are present.
- Extremely tiny (1/1000th of a human hair) tubular and ovoid-shaped structures were
discovered using a scanning electron microscope. Although smaller than microorganism seen to date
on Earth, they are distinctly bug-shaped!
Bug-shaped structures found
in the Mars Rock
Each of these four structures could have formed through geologic processes without
the help of microorganisms. Their coincidence in the meteorite can most easily be
explained by the presence of bacteria, but does not provide conclusive evidence of life.
There's more to learn about Life on Mars
in at the Johnson Space Center website, or see
the original paper published in Science in 1996 by McKay et al.
Front row: Suzanne Smrekar, Jet Propulsion Laboratory; Albert Yen, Jet
Propulsion Laboratory; Aaron Zent, NASA/Ames Research Center; Marsha Presley-Holloway, Northern
Arizona University; Paul Morgan, Macquarie University and Northern Arizona University.
Back row:Jeffrey Moersch, NASA/Ames Research Center; David Catling, NASA/Ames Research Center;
Ralph Lorenz, University of Arizona; Julio Magalhaes, NASA/Ames Research Center. Missing:
Bruce Murray, California Institute of Technology; James Murphy, New Mexico State University
DS2 will estimate the soil conductivity (how quickly heat is transferred) on Mars by measuring how fast the
forebody approaches the ambient ground temperature. To determine the thermal response of the forebody,
a series of experiments were run at JPL on an engineering model of the forebody. These experiments were
done in a vacuum chamber to achieve the same low conductivity environment created by the extremely low
atmospheric pressures found on Mars.
Inside the sealed chamber, the engineering model forebody was
suspended on a pulley system, heated, and plunged into a large bucket of glass beads to simulate the
thermal effects of the emplacing a relatively warm probe into the frigid Martian ground. Glass beads
are used because they have a well-known low thermal conductivity. Comparing the data obtained in these
experiments to the data returned from Mars will make it possible to use the temperature data to estimate
the soil conductivity. A very high conductivity will indicate large amounts of ice in the subsurface.
A very low conductivity is likely to indicate fine-grained wind-deposited dust.
This page last updated: October 29, 1999
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