Chapter 4 of 5

The clue under my wheel

A failed wheel exposed silica-rich soil near Home Plate

Told in Spirit’s imagined voice · the events are real · source

Spirit Says Goodbye to Home Plate
SpiritA wheel that stopped turning changed how I travelled.
NASA/JPL-Caltech/Cornell
01My right-front wheel drive failed in 2006. My team kept exploring by driving me backward and dragging that wheel. It was a real limitation, not a special digging tool we had planned to use.
The dragged wheel uncovered something bright.
02On March 29, 2007, it exposed a patch of soil near Home Plate that the team named Gertrude Weise. A pale track stood out against the darker surface. Looking closely at an accidental disturbance opened a new investigation.
Wheel slippage during attempts to extricate NASA's Mars Rover Spirit from a patch of soft ground during the preceding two weeks had partially buried the wheels by the 1,899th Martian day, or sol, of the Spirit's mission
SpiritTwo instruments helped turn a color into a discovery.
NASA/JPL-Caltech
03Mini-TES first detected a silica signature from a distance. The team then brought my arm’s APXS close to the soil. Measurements on May 8 and 9 found approximately 90 percent silica. The mineral evidence mattered more than the patch’s bright appearance.
The soil pointed toward a wetter, warmer past.
04Scientists proposed hot springs or acidic volcanic steam as ways to concentrate the silica. Such environments on Earth can support microbes. My finding was evidence of potentially habitable conditions—not proof that life had lived on Mars.

The big idea

An unexpected exposure can reveal a hidden clue. Cameras locate a target; different instruments test its chemistry and mineral composition.

Think about it

Does bright soil alone tell us what it is made of?

Fact file

Right-front wheel failure
Sol 779 / 2006
The end-of-mission report documents the failed drive actuator; no invented sparks or exact motor-brush diagnosis.
Source ↗
Soil exposed
Sol 1150 / 29 March 2007
The exposure predates the instrument measurements and public announcement.
Source ↗
APXS measurements
Sols 1189–1190 / 8–9 May 2007
Mini-TES had flagged the target remotely on April 20. APXS found approximately 90% silica at close range.
Source ↗

In this chapter: Right-front wheel, Mini-TES and Alpha Particle X-ray Spectrometer

Sources: Main record · Mars Rover Spirit Unearths Surprise Evidence of Wetter Past · Mars Exploration Rover Spirit End of Mission Report · JPL D-92756

Machine illustration: AI-made. Photos: NASA Image and Video Library, credited on each picture.

Chapter 4 of 5

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