To understand Mars, scientists measure many aspects of the surface, atmosphere, and interior. They can make some of these measurements from Earth, but most require spacecraft on or orbiting the planet. Spacecraft instruments measure specific physical properties and are calibrated to match the results of other devices that observe the same conditions.
The actual measurements are made by a computer, which turns the signals from the instrument into binary numbers — "bits" of data consisting of only 0 or 1 — which the spacecraft transmits back to Earth for scientific analysis.
Viking Wind Experiment
The Viking Landers used a heated wire and a thermometer to measure wind speed.
A voltage was applied to keep the wire at a fixed temperature, so as wind cooled the wire, the voltage increased to keep it hot. The voltage readings were measured by computer and sent back to Earth. Scientists compared them with measurements made with the same instrument under controlled conditions to determine the true wind speed.
Lent by J. E. Tillman
Visible light — the range of colors our eyes can see — is only a tiny part of the electromagnetic spectrum, which includes energy at very long (radio waves) to very short (gamma rays) wavelengths. Planetary exploration requires measurements across the entire electromagnetic spectrum, using different instruments to measure the energy of specific wavelengths.