Terra
Terra has been imaging the whole planet every day since 2000. If you have seen a satellite view of wildfire smoke, a dust storm crossing an ocean, or plant life spreading through a year, you have very likely been looking at its data.
What makes Terra different
The entire Earth, every day
Its MODIS instrument sweeps a swath wide enough to image the whole planet in one to two days at moderate resolution. That is a different job from Landsat, which sees far more finely but takes sixteen days to come back.
A morning crossing
It crosses the equator around 10:30 local time on the descending part of each orbit. Its sibling Aqua crosses in the early afternoon, so the pair brackets the day and captures how cloud builds between morning and afternoon.
Five instruments on one platform
MODIS is the famous one, but Terra also carries instruments for aerosols, radiation balance, land-surface temperature and stereo terrain imaging — built to measure a system rather than take pictures.
Badly outliving its plan
Designed for six years, it is still returning data more than two decades later, which is why its record is long enough to show change rather than merely weather.
Terra was the flagship of NASA’s Earth Observing System, launched in December 1999 to treat the planet as one connected system — land, ocean, atmosphere and radiation measured together rather than by separate missions. Its most visible legacy is MODIS, whose daily global mosaics underpin much of what the public sees of Earth from space, from fire maps to phytoplankton blooms. Like Landsat 9 and NOAA-20 it flies sun-synchronous, near 700 km at about 98°, crossing every latitude at the same local time so images separated by decades stay comparable. Its orbit has been allowed to drift in later years as propellant ran low, which shifts that crossing time and is one sign of a long mission nearing its end.
Frequently asked questions
What is MODIS?
The Moderate Resolution Imaging Spectroradiometer — Terra’s main imager, observing in 36 spectral bands and covering the whole Earth every one to two days.
How is Terra different from Landsat 9?
Terra sees the whole planet daily at moderate resolution; Landsat sees a narrow strip in fine detail and repeats every 16 days. One is for global change, the other for local detail.
What is the difference between Terra and Aqua?
They carry similar instruments but cross the equator at different local times — Terra in the morning, Aqua in the afternoon — so together they show how conditions change through the day.
Is Terra still working?
Yes, well beyond its six-year design life, though it is in a late phase of its mission with a drifting orbit as propellant runs out.