Reference · Glossary
17 words you’ll meet on Mars pages, each explained in one sentence, from sol, a Mars day of 24 h 39 min 35 s, to launch window, the few weeks every 26 months when trips to Mars take the least fuel. Each entry shows the word at work with a live example.
Updated Sources (6)
An astronomical unit (AU) is the average distance between Earth and the Sun: about 149.6 million km (93 million mi).
A lander touches down on Mars and works from one spot, unlike a rover, which drives.
A launch window is the stretch of time, about every 26 months, when Earth and Mars line up so a spacecraft can reach Mars using the least fuel.
Local mean solar time is the clock a rover team works by: the average time of day at the rover’s spot, ignoring the Sun’s seasonal drift.
Magnitude is how bright something looks from Earth, on a scale where a lower number means brighter: a magnitude 1 star looks 100 times brighter than one of magnitude 6.
Coordinated Mars Time (MTC) is a proposed name for Mars’s version of UTC: the average solar time at the prime meridian, through the crater Airy-0, which NASA’s Mars24 calls Airy Mean Time.
A Mars year lasts 687 Earth days (about 669 sols), and scientists number them from Mars Year 1, which began on April 11, 1955.
Opposition is when Earth passes between the Sun and Mars, so Mars rises at sunset, stays up all night and looks its brightest — about every 26 months.
An orbiter circles Mars without landing, studying the planet from above — and many also relay rover data back to Earth.
Here, the phase angle is how far ahead of Earth Mars sits in its orbit, seen from the Sun; trips to Mars work best when it is about 44°.
A raw image is a picture as a rover sent it to Earth, compressed and not yet calibrated, posted by NASA soon after it arrives and long before the calibrated, archived version.
A rover is a robot vehicle that drives across Mars, following plans its team on Earth sends ahead of each drive.
A sample return mission collects rock, soil or dust from another world and brings it back to Earth to study in labs.
Ls is Mars’s position around the Sun in degrees — 0° starts northern spring, 90° summer, 180° autumn and 270° winter — so it tells you the season.
Signal delay is how long a radio message takes to travel between Earth and Mars at the speed of light: from about 3 to 22 minutes each way, depending on where the planets are.
A sol is a day on Mars — 24 h 39 min 35 s, about 40 minutes longer than ours — and rovers count them from the day they land.
A transfer orbit is the path a spacecraft coasts along around the Sun from Earth’s orbit to Mars’s, timed so that it and Mars arrive at the same place at the same time.
A sol is one day on Mars: 24 h 39 min 35 s. Rovers number their sols from landing day, so Perseverance is on sol 2,004.
Ls is where Mars is in its orbit, in degrees from 0 to 360. It works as a season clock: 0° starts northern spring. Right now it’s 4.5°.
Not officially. Coordinated Mars Time (MTC) works like UTC, and each rover team keeps the local time where its rover sits.
So nobody has to know the jargon first. A word with a dotted underline opens a one-line definition, and the full entry lives here.