Arizona State University
Robert Burnham, (480) 458-8207
February 1, 2006
‘THOR’ Mars mission to seek underground water
A proposed new robotic mission to Mars plans to make the first exploration
of subsurface water ice in a potentially habitable zone.
If approved, the Tracing Habitability, Organics and Resources (THOR)
project – a low-cost mission designed for NASA’s Mars Scout program –
aims to send a projectile at high speed into the Martian surface while
observing the impact and its aftermath. The mission would be led by ASU,
in partnership with the Jet Propulsion Laboratory (JPL).
The THOR mission, planned for launch in 2011, aims to use a direct
approach to excavating material from beneath the surface of Mars: blasting
“The mission’s goal is to expose snow and ice in a previously unexplored
part of Mars: the deep subsurface,” says THOR’s principal investigator,
Phil Christensen of ASU’s Mars Space Flight Facility. “We’ll do this by
blowing a crater at least 30 feet deep in the Martian ground.”
Besides finding underground water, he says, THOR also proposes to look for
organic compounds, including methane, which Earth-based telescopes and
other Mars spacecraft have detected in the Martian atmosphere.
The mission aims to use a two-part spacecraft, which consists of an
“impactor” probe and an observer craft. The impactor is a simple
projectile made of pure Arizona copper. The observer spacecraft will carry
it until shortly before reaching Mars. After being released from the
observer, the impactor will streak through the Martian atmosphere to an
impact site lying between 30 degrees and 60 degrees latitude, in either
the northern or southern hemisphere of the Red Planet.
“In many areas of Mars’ middle latitudes, we see tantalizing evidence of
dust-covered layers of snow or ice,” Christensen says. “THOR will aim for
The suspected ice-rich layers were deposited during the past 50,000 to 1
million years, as the Martian climate changed because of orbital
According to the mission plan, when the impactor slams into the ground, it
will dig a crater more than 30 feet (10 meters) deep. The observer
spacecraft will study the debris plume jetting from the impact site.
The observer’s instruments will include a visible-light camera and an
infrared spectrometer. In addition to studying the plume, the
spectrometer’s role is to search the Martian atmosphere for organic
materials and gases, such as methane.
In the past, Christensen notes, Mars has been studied using fly-by and
orbiter spacecraft, and with landers. While highly valuable, such missions
have only scratched the surface, he says.
“The time has come to take Martian studies a step further – and deeper,”
Christensen says. “This unexplored region of Mars may provide chemical and
mineral clues to tell us about habitable areas on the planet.”
“The THOR mission plans to use a straightforward, low-risk approach to
reach the Martian subsurface,” says JPL’s David Spencer, the study lead
engineer for THOR.
Spencer is the former mission manager for Deep Impact, the comet mission
that pioneered the impact technique.
In comparing the two missions, Spencer says, “With such a large target
region on Mars, delivering THOR’s impactor will be less challenging than
the Deep Impact comet encounter.”
Christensen sees THOR’s scientific value continuing far beyond the impact.
“THOR’s crater will remain a test-site for all current Mars spacecraft and
those in years to come,” he says. “The crater might also be visited on the
ground by a future Mars rover, sometime in the next decade.”
NASA’s Mars Scouts are competitively proposed missions designed to advance
the goals of NASA’s Mars exploration program. The Mars Scout Program is
managed by JPL for NASA’s Office of Space Science, based in Washington.