Introduction Launched into the night sky nearly 26 years ago, on December 19, 1999, from Vandenberg Air Force Base (now Space Force Base), Terra was NASA’s first Earth Observing System (EOS) Flagship mission to study Earth’s land surface from space via a coordinated series of polar-orbiting and low-inclination satellites that produce long-term global observations useful […]
Introduction
Launched into the night sky nearly 26 years ago, on December 19, 1999, from Vandenberg Air Force Base (now Space Force Base), Terra was NASA’s first Earth Observing System (EOS) Flagship mission to study Earth’s land surface from space via a coordinated series of polar-orbiting and low-inclination satellites that produce long-term global observations useful for understanding the interactions between Earth’s atmosphere, land, snow and ice, oceans, and radiant energy balance. Scheduled for a six-year tour, Terra outlasted its life expectancy by nearly two decades. Despite its longevity, Terra’s mission scientists stopped making inclination adjustments in 2020, allowing the satellite to slowly drift out of its contained orbit. The mission team has also begun the painful process of shutting down the five key instruments as the satellite is prepped for retirement.
“Terra’s impressive human legacy stems from the fact that the mission’s history is grounded in NASA icons,” said Nyssa Rayne [NASA Goddard Space Flight Center (GSFC)—TerraOutreach & Communications Coordinator]. “Even today, Terra continues to benefit from legendary figures, including the current project scientist and instrument calibration/validation experts, who have shaped this mission in monumental ways.”
An Auspicious Beginning to More Than Two Decades of Science
Terra’s mission of discovery was designed to provide a better understanding of the total Earth system. Up to this point, the research community knew very little about how the land interacted with the atmosphere on a regional and continental scale. The community also lacked a way to quantify surface properties, such as albedo, roughness, evaporation rate, and photosynthesis, from satellite data.
Terra was designed, engineered, and programmed to address these knowledge gaps. Often described as a small bus, Terra measures almost 7 m (23 ft) long and 3.5 m (11 ft) across. In the vast expanse of space, however, Terra travels in an orbit around Earth, like a gnat circling the Sphere in Las Vegas. Carried into space aboard an Atlas-Centaur IIAS expendable launch vehicle from Vandenberg Air Force Base, CA, Terra was placed in orbit 705 km (438 mi) above the planet’s surface, capturing a viewing swatch from each overpass that could be stitched together to produce whole global images. Its flight path was designed to cross the equator to coincide with the time of day when cloud cover along the equator was at a minimum (10:30 AM local time).
Five Instruments Wrapped in a Silver Package
First named EOS-AM, the concept of the Terra mission was envisioned in the 1980s and implemented in the 1990s. Terra builds on the lessons learned from past pioneering programs, including the Upper Atmosphere Research Satellite (UARS), Landsat, the Ocean Topography Experiment (TOPEX)/Poseidon, and the series of Total Ozone Mapping Spectrometer (TOMS) instruments. After many scientific conversations and arguments, it was finally decided that Terra would carry five instruments capable of gathering data that would benefit a variety of Earth scientific disciplines – see . An international effort, Terra carries instruments from the United States, Japan, and Canada that allow scientists to document relationships between Earth’s systems and examine their connections. The five instruments include:
Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), which obtains high-resolution images of the Earth at 14 different wavelengths of the electromagnetic spectrum that can be used to create detailed maps of land surface, temperature, emissivity, reflectance, and elevation;
Clouds and the Earth’s Radiant Energy System (CERES), which measures Earth’s total radiation budget as well as cloud property estimates that enable scientists to clarify the role that clouds play in the planet’s radiative flux;
Multi-angle Imaging SpectroRadiometer (MISR), which improves the field’s understanding of the fate of sunlight in the Earth’s environment, distinguishing between different types of clouds, aerosol particles, and surfaces; and
Moderate Resolution Imaging Spectroradiometer (MODIS), which combines data gathered from CERES and MISR to determine the impact of clouds and aerosols on the Earth’s energy budget.
Focusing a Zoom Lens on Earth
“ASTER's accurate topographic data will be used for engineering, energy exploration, conserving natural resources, environmental management, public works design, firefighting, recreation, geology and city planning, to name just a few areas,” Michael Abrams [NASA Jet Propulsion Laboratory—US Principal Investigator] told Universe Today in a June 30, 2009 article.
ASTER was designed to capture high-resolution images of Earth. The data cover a range of land scales – anything from the size of 14 bath towels (15 m2 per pixel) to one-fifth of a basketball court (90 m2 per pixel). The instrument was developed as a partnership between NASA, Japan’s Ministry of Economy, Trade and Industry (METI), the National Institute of Advanced Industrial Science and Technology (AIST) in Japan, and the Japan Space Systems (J-spacesystems).
ASTER consists of three telescopes – Visible Near-Infrared (VNIR), Short-Wave Infrared (SWIR), and Thermal Infrared (TIR). (The SWIR is no longer operational.) All three instruments point perpendicular to the direction of motion to change the viewing angle and produce stereoscopic images of our planet. The three telescopes also gather high-resolution images at 14 different bands of the electromagnetic spectrum, ranging from visible to infrared light.
The instrument’s data are used to create detailed maps of land surface temperature, reflectance, and emissivity, how effectively a surface emits thermal radiation. ASTER also produces detailed views of the effects of Earth’s landforms and topography – see Figure 2. These data are used to understand factors that control climate conditions, e.g., evaporation, water flow, and mass movement. It can also be used to explore how fire can change Earth’s surface.
Earth’s Reflection Affects Climate
“Earth’s climate is really driven by a delicate balance between how much of the Sun’s energy is absorbed by the Earth as visible light, and how much the Earth emits to space in the form of infrared radiation,” Norman Loeb [Langley Research Center—PI] told EarthSky in a November 30, 2009 article. “The objective is to observe the Earth’s radiation budget, together with the clouds...over several years, and preferably over several decades, [that] enables us to improve our understanding of how the climate system is changing and really provides an invaluable resource for testing climate models that are used to simulate future climate change.”
Terra maintains two CERES instruments that measure albedo, or solar radiation reflected from Earth’s surface, and emitted thermal infrared radiation. It also explores the role that clouds play in modulating radiative fluxes by examining solar-reflected and Earth-emitted radiation from the land surface to the top of the atmosphere.
CERES was developed at NASA’s Langley Research Center. The satellite has two instruments onboard. One instrument gathers information using cross-track scan mode, where a mirror sweeps back and forth, perpendicular to the sensor's path. This mode builds two-dimensional images of Earth. This data contributes to the Earth Radiation Budget Experiment and the Tropical Rainfall Measuring Mission. [PLEASE REVISIT THIS EXPLANATION. ] The second CERES instrument gathers information in biaxial scan mode, where scanning occurs along two different axes simultaneously. The data provide angular flux information to derive Earth’s radiation balance.
Researchers pair CERES data with other instruments on Terra to create a fully resolved global diurnal cycle of Earth’s radiation budget at the surface and at different layers of the atmosphere, including the top of the atmosphere. The CERES data products capture variations in Earth’s radiation budget at hourly, daily, and monthly timescales. Climate, weather, and applied science research communities use this data to address a range of research topics that involve the exchange of energy between Earth and space and between the major components of the Earth system – see Figure 3.
Checking in on the Lower Atmosphere from Space
MOPITT was designed to obtain information about the lower atmosphere, especially as it interacts with the land and ocean biospheres. It was developed as a joint project between the Canadian Space Agency, the University of Toronto, and the National Center for Atmospheric Research (NCAR) in Boulder, CO. The instrument has a spatial resolution of 22 km (14 mi) and covers a swath of Earth’s surface about half the size of Los Angeles [640 km (398 mi)].
MOPITT uses gas correlation spectroscopy to measure the concentration, fate, and distribution of CO, a product of car exhaust, forest fires, and factory exhaust. MOPITT offers near-global coverage every three days of the region being scanned – see Figure 4. These data help scientists identify sources of regional pollution, monitor regional pollution patterns, and track the long-range transport of pollutants.
MOPITT was the longest running record of CO concentration collected from space. The dataset is often combined with MISR data to map aerosols and CO to track sources of air pollution. On April 9, 2025, MOPITT was the first casualty of Terra’s slow demise. It was turned off to conserve energy for the remaining four instruments.
Focusing on the Tiniest Particles from Multiple Perspectives
“The MISR team has pioneered novel methods for tracking aerosol abundances and particle properties, cloud and aerosol plume heights, height-resolved wind vectors, ice and vegetation structures, and other physical attributes of our planet,” said David Diner [NASA/Jet Propulsion Laboratory—MISR Principal Investigator]. “These efforts and those of the broader scientific community have led to key insights about how the Earth’s climate and environment are changing.”
MISR was developed at NASA’s Jet Propulsion Laboratory to measure variations of surface and cloud properties as well as aerosols – see Figure 5. These data are used to evaluate the long-term interactions between sunlight and aerosols in the atmosphere and on Earth. Researchers can use MISR data to monitor the monthly, seasonal, and long-term trends in the amount and type of atmospheric aerosol particles.
MISR trains its nine cameras on Earth to capture images from multiple angles that gather reflected sunlight scattered by Earth’s surface, clouds, and suspended airborne particles within a 360 km (224 mi) swath of land. One camera points to the lowest point, while others provide forward and aft-ward view angles at 26.1°, 45.6°, 60.0°, and 70.5°. As MODIS flies overhead, each region of the Earth’s surface is successively imaged by all nine cameras in each of four wavelengths that span the visible and infrared spectrum. Its capabilities allow measurements of natural and human-caused particulate matter in the atmosphere, particulate abundance and type, heights of aerosol plumes and cloud tops, along with their speed and direction of motion and the types and extent of land surface cover.
According to Diner, outdoor airborne fine particulate matter constitutes the largest environmental health risk worldwide. This fine particulate matter are responsible for millions of premature deaths per year as well as a wide range of adverse human health outcomes. Terra revolutionized the study of these particles, making it possible for researchers to distinguish aerosols resulting from natural and anthropogenic sources and to investigate how different types of aerosols impact human health. Diner points to how MISR data has been used to examine particulate matter in regions of rapid urbanization, such as Asia and North Africa, as well as track aerosol transport after wildfires.
“MISR’s greatest achievement is the diversity of scientific investigations and research papers that have resulted from its unique observational approach,” he said. Diner also points to the associated retrieval algorithms, which have produced an unprecedented data record spanning more than two and a half decades.
The Swiss Army Knife in Terra’s Toolkit
MODIS was designed to monitor atmospheric, land, and oceanic processes, including surface temperature, ocean color, global vegetation, cloud characteristics, temperature and moisture profiles, and snow cover. The instrument was developed at NASA’s Goddard Space Flight Center. It provides large-scale coverage, about 2300 km (~1429 mi) of land at a spatial resolution of 250 m (~820 ft). MODIS can visualize every point on Earth every one to two days. This approach is ideal for tracking a variety of Earth’s systems. It measures the distribution and properties of clouds, as well as aerosols, water vapor, and temperature. MODIS data are also used as input to a radiative transfer model that calculates radiative fluxes at the surface and within the atmosphere.
MODIS data helps scientists determine the amount of water vapor in a column of the atmosphere and the vertical distribution of temperature and water vapor, measurements that are crucial to understanding Earth’s climate system. MODIS also uses visible images and remotely sensed data to monitor changes in land cover by natural forces, such as fires, or anthropogenic changes, such as cropland burning and farming. MODIS data helps researchers understand photosynthetic activity of plants on land and in the ocean to improve estimates of the gaseous mixture in the atmosphere. MODIS data also improves weather models and forecasts that can prepare communities for major storm events – see Figure 6.
Researchers combine atmospheric models developed using MODIS data with aerosol products from MISR data to create a generation of maps of near-surface particulate matter concentrations that have been used in numerous health studies. One such study is the Global Burden of Disease, which estimates that more than four million premature deaths occur each year due to exposure to airborne particles.
Data, Data Everywhere, Managing Decades of Information
Terra instruments have been in operation since the satellite was launched more than a quarter of a century ago. The technology at the time was state-of-the-art, allowing Terra to complete more than 100,000 orbits, downloading and transmitting data twice during each orbit to ground stations in Alaska, Norway, and NASA’s Wallops Flight Facility. Terra has produced the longest record of environmental data providing the research community a way to evaluate the effects of natural and human-induced changes in the environment.
The five instruments gather near real-time data for use in monitoring and managing on-going events. The vast amount of data has generated 87 data products that are distributed through the Land Processes Distributed Active Archive Center (LPDAAC), the Atmospheric Science Data Center (ASDC), the Ocean Color Web, the Atmosphere Archive and Distribution System, and the National Snow and Ice Data Center (NSIDC). The datasets work in concert with other data products to expand the scientific community’s knowledge about Earth systems, resulting in more than 27,000 scientific publications.
Terra’s data in the EOSDIS archive constitute an invaluable two-decade-long record of a wide range of Earth processes. Higher level data processing is completed by Science Investigator-led Processing Systems. In addition, data is available in a variety of archives. Earthdata Search and Earth Explorer make all ASTER products available to all users at no cost. It contains Level-1 (L1A), L1B, L1T data, as well as data from the Global Digital Elevation Model and the North American ASTER Land Surface Emissivity Database. The U.S. Geological Survey Global Visualization Viewer (GLoVis) and ASTER/AIST data archives allow users to search the entire ASTER data archive using a browser interface. Application for Extracting and Exploring Analysis Ready Samples (AppEEARS) offers a simple and efficient way to access and transform geospatial data from a variety of federal data archives. It allows users to subset geospatial datasets using spatial, temporal, and band/layer parameters.
Over the past two decades, Terra’s data acquisition process has transitioned from scheduled downloads to data-driven acquisition. In a 2020 EarthData article, Greg Dell [Earth Science Mission Operations—Project Deputy Director-Operations] explained the priorities in managing data moving from a model of producing a long-term record for the research community to getting data that the scientific community can use as quickly as possible.
“This is a big paradigm shift over the course of the mission,” said Dell. “We’ve been able to accommodate this paradigm shift with ground automation and better, faster networks.”
Crunching the reams of data gathered by Terra’s five instruments requires a series of algorithms for processing so the scientific community can use it effectively. The acknowledgement of this need began at the launch of the mission, with the creation of the Algorithm Theoretical Basis Documents (ATBDs). ATBDs provided the theoretical basis – both the physical theory and the mathematical procedures and possible assumptions being applied – for the calculations that have to be made to convert the radiances received by the instruments to geophysical quantities. Even in Terra’s early days, developers invited panelists from around the world to evaluate algorithmic iterations to assess the strengths and weaknesses of the code. This perspective has continued with the review of newer algorithms by the user community to ensure they can use the data effectively.
In a continued momentum toward transformation, NASA funded the development of Terra Fusion, a new dataset and toolkit that merges all of the data gathered by the five instruments into a format and spatial context to be used by scientists. The one dataset approach allows the community to find synergy to address large, real-world problems. Data fusion continues to facilitate new research into air pollution, smoke from wildfires, clouds and aerosols, ocean biology, agriculture and land use, vegetation dynamics, hydrology, Earth’s radiation budget, and other Earth science fields that have traditionally used Terra data.
Terra Science Gives Back to Communities Around the World
According to Rayne, since it began in 1988, the idea behind EOS was that interdisciplinary science teams would collaborate with NASA groups to address real-world problems. This unique approach brought together teams that previously may have been siloed across the agency and academia to increase the momentum driving team science. These efforts have yielded impressive outcomes that have advanced various scientific fields but also benefited people around the world. The following subsections describe ways that Terra data have been applied to a variety of topics of societal interest and importance.
Chasing the Path of Totality During an Eclipse
While an eclipse is not highly unusual, it is an exciting event to witness. The shadow that forms when the Moon blocks the Sun’s radiation briefly changes the environment, dropping atmospheric temperature, quieting birds, and imparting an eerie sense of awe. Often these events do not cross heavily populated parts of the planet. During the past quarter century, Terra has had several opportunities to observe eclipses from its orbital vantage point – a prime location to follow the path of totality where the Sun’s rays are completely blocked from Earth’s surface.
Not long after Terra’s launch, the Moon cast a shadow that moved across southeast Asia and North America during an annular solar eclipse on June 20, 2002. Few regions were within the path of totality to witness this event, but MISR on Terra trained its nine cameras along the path to monitor the effect of the eclipse as it passed the central Pacific Ocean.
MODIS also captured true-color images of an exceptionally long total solar eclipse on July 2009 that reached 6 minutes and 39 seconds. The path of totality crossed Japan, Korea, and eastern China.
During the August 2017 eclipse, the path of totality cut across the United States, with a shadow passing over Oregon, Idaho, Wyoming, Nebraska, Kansas, Missouri, Illinois, Kentucky, Tennessee, North Carolina, Georgia, and South Carolina. MODIS captured false-color images of the shadow – see Figure 7. It was the first eclipse to cross the entire continent in almost 100 years and the first to travel coast-to-coast since the founding of the country in 1776. The Earth Observer reported on this remarkable event in NASA Provides Unique Views of the 2017 “Eclipse Across America” [Sept.–Oct. 2017, 29:5, 4–17].
Finally, Terra’s location was not ideal to capture the April 8, 2024 path of totality that crossed over the eastern United States and Canada. The satellite was able to capture most of the shadow with limited visible contrast. The Earth Observer staff participated in festivities and covered the event in the article, “Looking Back on Looking Up: The 2024 Total Solar Eclipse,” published on the outlets website on Aug. 22, 2024.
Monitoring Remote Regions for the Spark of a Flame
Terra provides the bird’s eye view of the planet’s surface that is perfect for monitoring remote regions. This vantage point is beneficial for land managers to inform decisions and prepare communities for threats, including wildfire and hurricanes. Data from Terra can also be used to map changes to an ecosystem after a fire event.
Terra’s MODIS produced false-color image of the area ravaged by the Camp Fire in 2018, which spanned an area roughly the size of Chicago. Researchers, fire management, and policy makers could interactively browse more than 700 global, full-resolution satellite image layers. The images were paired with underlying data to monitor and evaluate the scarred region – see Figure 8.
Terra has also captured images from fires in the state of New South Wales in southeastern Australia. In November 2019, the fire season began early with Terra capturing smoke on the edge of the continent. The resulting 70 fires that season destroyed 1.1 million hectares (2.7 million acres). In addition to monitoring the fire damage after containment, scientists use Terra data to monitor the movement of smoke across the continent and around the planet.
The following year, Terra captured images of California’s Mineral fire, which began in July 2020 and grew to more than 11,000 acres (17 mi2) amid favorable fire conditions of high winds and dry grass and timber in the region. Fire management used MODIS information to monitor sparks that had potential for starting new fires. This information helped determine evacuation orders and kept surrounding communities appraised of the fire’s movement.
Heavy Rain Inundates the Outback
Researchers use the instruments on Terra to provide a set of eyes to monitor for fires, but it is also beneficial for monitoring flood conditions. Channel Country in the Australian outback is a region that experiences cycles of drought and flood. During periods of heavy rainfall, the excess water drains to a nearby lake. The wet periods can promote growth in pasture lands and support wetlands and endemic species.
In March 2025, this region received unusually heavy rain. In one week, more than a year’s worth of rain fell, swelling multiple rivers and inundating roadways that isolated small towns and grazing lands for weeks. MODIS captured images of flooding across the region – see Figure 9. Officials used the images from Terra and Landsat to direct helicopter evacuations of citizens and livestock.
Experts monitored the region in real time throughout the event. They cited several factors for the unusually heavy rain, including streams of humid air from the north and east that converged over interior Queensland. They also pointed to a low-pressure trough that drove the moisture-laden air to higher and cooler levels of the atmosphere, triggering the formation and release of heavy rain.
Tracking Churning Ice from Space
Explorers have sought a shortcut from the Atlantic to the Pacific Ocean for centuries. The race for the Northwest Passage was supercharged in the 19th century to shore up trade routes. Many explorers accepted this challenge, and many lives were lost in the quest. It was not until 1905 that Roald Amundsen successfully navigated the Arctic Ocean, emerging into the Pacific Ocean from the Amundsen Gulf, named on his behalf.
The Arctic Ocean continues to be an area of interest today, not only for trade, but also because of the valuable mineral resources along the surrounding shallow continental shelf. Yet, this region still remains tricky to navigate due to chaotic growth and movement of sea ice around the confined northern ocean.
MODIS captured images of this remote region of the planet, offering a bird’s eye view of stationary ice clinging to the shallow shelf. Using this information, researchers studied the seasonal break-up of ice in 2024. They noted the churning, slow rotation of the ice before chocking the few outlet paths into the Atlantic and Pacific Oceans – see Figure 10. Monitoring the release of icebergs updates the status of navigating shipping lanes.
An Eye on an Eruption
MODIS is also beneficial in monitoring volcanic eruptions from space. On January 18, 2017, Terra passed over Alaska and captured an ash plume emanating from the Bogoslof Volcano on Bogoslof Island along the southern edge of the Bering Sea – see Figure 11. Researchers from the Alaska Volcano Observatory (AVO) in collaboration with the U.S. Geological Survey, the University of Alaska Fairbanks Geophysical Institute, and the Alaska Division of Geological and Geophysical Surveys produced updates as the eruption evolved. The group issues one of four levels of alert ranging from calm (green) to imminent eruption (red). AVO announced a red alert for Bogoslof on January 19, 2017. Beyond the ash plume, the cloud of debris produced cumulonimbus clouds that resulted in lightning strikes.
Tracking Lumbering Atmospheric Monsters
Terra instruments provide researchers information about the location and intensification of tropical storms in the Atlantic Ocean and cyclones in the Pacific Ocean. The National Hurricane Center uses information from Terra and other satellites to observe the storm and predict its potential path before issuing watches and warnings to communities in the line of danger.
On September 2, 2008, a tropical storm in the North Atlantic Ocean caught the scientific community’s attention. The storm received a name – Omar – and Terra offered one of the many lenses to monitor its movement across the Atlantic – see Figure 12. The following day, Omar was downgraded to a tropical depression but moved over a warm patch of ocean water, allowing it to rapidly intensify into a category 4 hurricane. Forecasters relied on the constant stream of information from Terra’s instruments to update their models and keep the community apprised of the storm’s movement to prepare and make plans for evacuation.
During the early months of the COVID-19 pandemic, Terra continued to monitor the planet from high above. On August 25, 2020, MODIS produced images of a collection of thunderstorms at the center of an intensifying hurricane, named Laura, forming in the Gulf of Mexico. MISR trained its nine cameras on the storm to gather information on changing windspeed and cloud-top height as the storm intensified – see Figure 13. Laura made landfall at Cameron, LA at 1:00 AM as a category 4 hurricane, with sustained winds of 150 mph (130 knots). The hurricane was the strongest storm to hit southwest Louisiana since 1851 when storm records were initiated.
Far Surpassing the Six-year Lifespan… but an Inevitable Decline
Since its launch, Terra has consistently orbited Earth from pole to pole, training all five instruments on the planet’s surface and gathering simultaneous data, with the Earth Science Mission Operations (ESMO) team vigilantly monitoring the satellite’s energy and performance day and (until quite recently) night. As the satellite aged, the team began performing periodic inclination adjustments to maintain the satellite’s orbit and preserve its fuel supply to ensure it could continue to collect data. Their oversight has been so effective that a mission designed with a six-year lifetime continues to operate in 2025. This unplanned longevity is true for all three of the EOS Flagships.
Inevitably, the decades in Earth’s orbit has taken a toll on the flight hardware. Eventually the fuel to keep the satellite stable in its orbit will run out – even if the instruments onboard are still functioning nominally. To conserve Terra’s remaining fuel to allow for controlled reentry into Earth’s atmosphere and to extend science operations aa long as possible, in late 2020 NASA Headquarters decided it was time to stop making adjustments to maintain Terra’s orbit. As a consequence, the satellite has begun to drift in its orbit, slowly sliding into an earlier equator crossing time. By Fall 2022, Terra’s orbit lowered to about 5 km (3 mi) and began crossing the equator at 10:15 AM. While these changes seem significant, they only created minor adjustments to orbital repeat time and swath width. The research community continued to gather data about atmospheric dynamics, water and energy cycles, atmospheric chemistry, physical and radiative properties of clouds, air-land exchanges of energy, carbon and water, and vertical profiles of CO vulcanology. The Earth Observer discussed the consequences – and opportunities – of these orbit shifts to Terra (and Aqua and Aura) in the article NASA Holds Discussions about the Future of the EOS Flagship Missions [Jan.–Feb. 2023, 35:1, 13–17].
Along with the adjustments in Terra’s orbit, the satellite has also experienced power limitations due to slow degradation of the battery that powers the spacecraft. While ESMO and the instrument Science Teams managed these reductions for as long as possible without impacts on science, early this year the first sacrifice to science had to be made. MOPITT was switched to safe mode on February 1, 2025 and then turned off on April 9, 2025. As of this writing, the remaining four instruments continue to function, with limitations to the ASTER telescopes.
“It really is a testament to great work by the entire team for being able to keep this spacecraft up in the air and healthy and to be able to produce like it has,” Terri Wood [EDOS—Project Manager] told EarthData in 2020. “It’s people, processes, and programs that make this happen. I just think it’s a real testament to what we can do around here.”
Since Terra’s launch, NASA has sent a series of satellites into orbit to explore the planet’s surface and ultimately learn more about our home. The Afternoon Constellation (A-Train) consisted of five NASA satellites – Aqua (launched in 2002), Aura (launched in 2004), the second Orbiting Carbon Observatory (launched in 2014), the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO), and CloudSat (both launched in 2006). More information on the A-train satellites are available in the highlight article, titled “The Earth Observer: Offering Perspectives from Space through Time.” These eyes in the sky continue to produce the data that scientists need to answer long-standing questions and tackle complex concerns with new, imaginative approaches.
A Bittersweet Conclusion
Terra began as a spark of imagination during collective conversations among the scientific community more than 40 years ago. This unique approach to team science has resulted in one of the first satellites to study Earth from a holistic perspective, gathering data about the land, water and the atmosphere at the same time, contributing to a diverse collection of scientific disciplines to tackle large questions through team science. Unlike many previous, smaller satellites, Terra was designed from scratch with state-of-the-art technology. The exquisite design ensured each instrument continued to collect data long past the six-year lifespan, offering scientists around the world a long-term record of the planet.
As Terra reaches its conclusion, it will be joined by two sister satellites – Aqua and Aura. The loss of these three EOS flagship satellites, launched more than 20 years earlier, will change the way scientists monitor Earth and affect our understanding of the radiative balance of the planet. May the final years of Terra ignite the imagination of the next generation of scientists to catapult the study of our planet for generations to come.
“Terra was the quintessential and most significant of all of the EOS satellites that made contributions to all aspects of Earth science,” said Michael King [Earth Observing System—former Senior Project Scientist and MODIS—Team Lead]. “All five of the Terra [instruments] made significant and, in many cases, first-of-a-kind global observations relevant to climate change.”