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By NASA
4 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
The six SCALPSS cameras mounted around the base of Blue Ghost will collect imagery during and after descent and touchdown. Using a technique called stereo photogrammetry, researchers at Langley will use the overlapping images to produce a 3D view of the surface. Image courtesy of Firefly. Say cheese again, Moon. We’re coming in for another close-up.
For the second time in less than a year, a NASA technology designed to collect data on the interaction between a Moon lander’s rocket plume and the lunar surface is set to make the long journey to Earth’s nearest celestial neighbor for the benefit of humanity.
Developed at NASA’s Langley Research Center in Hampton, Virginia, Stereo Cameras for Lunar Plume-Surface Studies (SCALPSS) is an array of cameras placed around the base of a lunar lander to collect imagery during and after descent and touchdown. Using a technique called stereo photogrammetry, researchers at Langley will use the overlapping images from the version of SCALPSS on Firefly’s Blue Ghost — SCALPSS 1.1 — to produce a 3D view of the surface. An earlier version, SCALPSS 1.0, was on Intuitive Machines’ Odysseus spacecraft that landed on the Moon last February. Due to mission contingencies that arose during the landing, SCALPSS 1.0 was unable to collect imagery of the plume-surface interaction. The team was, however, able to operate the payload in transit and on the lunar surface following landing, which gives them confidence in the hardware for 1.1.
The SCALPSS 1.1 payload has two additional cameras — six total, compared to the four on SCALPSS 1.0 — and will begin taking images at a higher altitude, prior to the expected onset of plume-surface interaction, to provide a more accurate before-and-after comparison.
These images of the Moon’s surface won’t just be a technological novelty. As trips to the Moon increase and the number of payloads touching down in proximity to one another grows, scientists and engineers need to be able to accurately predict the effects of landings.
How much will the surface change? As a lander comes down, what happens to the lunar soil, or regolith, it ejects? With limited data collected during descent and landing to date, SCALPSS will be the first dedicated instrument to measure the effects of plume-surface interaction on the Moon in real time and help to answer these questions.
“If we’re placing things – landers, habitats, etc. – near each other, we could be sand blasting what’s next to us, so that’s going to drive requirements on protecting those other assets on the surface, which could add mass, and that mass ripples through the architecture,” said Michelle Munk, principal investigator for SCALPSS and acting chief architect for NASA’s Space Technology Mission Directorate at NASA Headquarters in Washington. “It’s all part of an integrated engineering problem.”
Under the Artemis campaign, the agency’s current lunar exploration approach, NASA is collaborating with commercial and international partners to establish the first long-term presence on the Moon. On this CLPS (Commercial Lunar Payload Services) initiative delivery carrying over 200 pounds of NASA science experiments and technology demonstrations, SCALPSS 1.1 will begin capturing imagery from before the time the lander’s plume begins interacting with the surface until after the landing is complete.
The final images will be gathered on a small onboard data storage unit before being sent to the lander for downlink back to Earth. The team will likely need at least a couple of months to
process the images, verify the data, and generate the 3D digital elevation maps of the surface. The expected lander-induced erosion they reveal probably won’t be very deep — not this time, anyway.
One of the SCALPSS cameras is visible here mounted to the Blue Ghost lander.Image courtesy of Firefly. “Even if you look at the old Apollo images — and the Apollo crewed landers were larger than these new robotic landers — you have to look really closely to see where the erosion took place,” said Rob Maddock, SCALPSS project manager at Langley. “We’re anticipating something on the order of centimeters deep — maybe an inch. It really depends on the landing site and how deep the regolith is and where the bedrock is.”
But this is a chance for researchers to see how well SCALPSS will work as the U.S. advances human landing systems as part of NASA’s plans to explore more of the lunar surface.
“Those are going to be much larger than even Apollo. Those are large engines, and they could conceivably dig some good-sized holes,” said Maddock. “So that’s what we’re doing. We’re collecting data we can use to validate the models that are predicting what will happen.”
The SCALPSS 1.1 project is funded by the Space Technology Mission Directorate’s Game Changing Development Program.
NASA is working with several American companies to deliver science and technology to the lunar surface under the CLPS initiative. Through this opportunity, various companies from a select group of vendors bid on delivering payloads for NASA including everything from payload integration and operations, to launching from Earth and landing on the surface of the Moon.
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Last Updated Dec 19, 2024 EditorAngelique HerringLocationNASA Langley Research Center Related Terms
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By NASA
X-rays are radiated by matter hotter than one million Kelvin, and high-resolution X-ray spectroscopy can tell us about the composition of the matter and how fast and in what direction it is moving. Quantum calorimeters are opening this new window on the Universe. First promised four decades ago, the quantum-calorimeter era of X-ray astronomy has finally dawned.
Photo of the XRISM/Resolve quantum-calorimeter array in its storage container prior to integration into the instrument. The 6×6 array, 5 mm on a side, consists of independent detectors – each one a thermally isolated silicon thermistor with a HgTe absorber. The spectrometer consisting of this detector and other essential technologies separates astrophysical X-ray spectra into about 2400 resolution elements, which can be thought of as X-ray colors.NASA GSFC A quantum calorimeter is a device that makes precise measurements of energy quanta by measuring the temperature change that occurs when a quantum of energy is deposited in an absorber with low heat capacity. The absorber is attached to a thermometer that is somewhat decoupled from a heat sink so that the sensor can heat up and then cool back down again. To reduce thermodynamic noise and the heat capacity of the sensor, operation at temperatures less than 0.1 K is required.
The idea for thermal measurement of small amounts of energy occurred in several places in the world independently when scientists observed pulses in the readout of low-temperature thermometers and infrared detectors. They attributed these spurious signals to passing cosmic-ray particles, and considered optimizing detectors for sensitive measurement of the energy of particles and photons.
The idea to develop such sensors for X-ray astronomy was conceived at Goddard Space Flight Center in 1982 when X-ray astronomers were considering instruments to propose for NASA’s planned Advanced X-ray Astrophysics Facility (AXAF). In a fateful conversation, infrared astronomer Harvey Moseley suggested thermal detection could offer substantial improvement over existing solid-state detectors. Using Goddard internal research and development funding, development advanced sufficiently to justify, just two years later, proposing a quantum-calorimeter X-ray Spectrometer (XRS) for inclusion on AXAF. Despite its technical immaturity at the time, the revolutionary potential of the XRS was acknowledged, and the proposal was accepted.
The AXAF design evolved over the subsequent years, however, and the XRS was eliminated from its complement of instruments. After discussions between NASA and the Japanese Institute of Space and Astronautical Science (ISAS), a new XRS was included in the instrument suite of the Japanese Astro-E X-ray observatory. Astro-E launched in 2000 but did not reach orbit due to an anomaly in the first stage of the rocket. Astro-E2, a rebuild of Astro-E, was successfully placed in orbit in 2005 and renamed Suzaku, but the XRS instrument ceased operation before observations started due to loss of the liquid helium, an essential part of the detector cooling system, caused by a faulty storage system.
A redesigned mission, Astro-H, that included a quantum-calorimeter instrument with a redundant cooling system was successfully launched in 2016 and renamed Hitomi. Hitomi’s Soft X-ray Spectrometer (SXS) obtained high resolution spectra of the Perseus cluster of galaxies and a few other sources before a problem with the attitude control system caused the mission to be lost roughly one month after launch. Even so, Hitomi was the first orbiting observatory to obtain a scientific result using X-ray quantum calorimeters. The spectacular Perseus spectrum generated by the SXS motivated yet another attempt to implement a spaceborne quantum-calorimeter spectrometer.
The X-ray Imaging and Spectroscopy Mission (XRISM) was launched in September 2023, with the spectrometer aboard renamed Resolve to represent not only its function but also the resolve of the U.S./Japan collaboration to study the Universe through the window of this new capability. XRISM has been operating well in orbit for over a year.
Development of the Sensor Technology
Development of the sensor technology employed in Resolve began four decades ago. Note that an X-ray quantum-calorimeter spectrometer requires more than the sensor technology. Other technologies, such as the coolers that provide a
The sensors used from XRS through Resolve were all based on silicon-thermistor thermometers and mercury telluride (HgTe) X-ray absorbers. They used arrays consisting of 32 to 36 pixels, each of which was an independent quantum calorimeter. Between Astro-E and Astro-E2, a new method of making the thermistor was developed that significantly reduced its low-frequency noise. Other fabrication advances made it possible to make reproducible connections between absorbers and thermistors and to fit each thermistor and its thermal isolation under its X-ray absorber, making square arrays feasible.
Through a Small Business Innovation Research (SBIR) contract executed after the Astro-E2 mission, EPIR Technologies Inc. reduced the specific heat of the HgTe absorbers. Additional improvements made to the cooler of the detector heat sink allowed operation at a lower temperature, which further reduced the specific heat. Together, these changes enabled the pixel width to be increased from 0.64 mm to 0.83 mm while still achieving a lower heat capacity, and thus improving the energy resolution. From Astro-E through Astro-H, the energy resolution for X-rays of energy around 6000 eV improved from 11 eV, to 5.5 eV, to 4 eV. No changes to the array design were made between Astro-H and XRISM.
Resolve detector scientist Caroline Kilbourne installing the flight Resolve quantum-calorimeter array into the assembly that provides its electrical, thermal, and mechanical interfaces.NASA GSFC Over the same period, other approaches to quantum-calorimeter arrays optimized for the needs of future missions were developed. The use of superconducting transition-edge sensors (TES) instead of silicon (Si) thermistors led to improved energy resolution, more pixels per array, and multiplexing (a technique that allows multiple signals to be carried on a single wire). Quantum-calorimeter arrays with thousands of pixels are now standard, such as in the NASA contribution to the future European New Advanced Telescope for High-ENergy Astrophysics (newAthena) mission. And quantum calorimeters using paramagnetic thermometers — which unlike TES and Si thermistors require no dissipation of heat in the thermometer for it to be read out — combined with high-density wiring are a promising route for realizing even larger arrays. (See Astrophysics Technology Highlight on these latest developments.)
The Resolve instrument aboard XRISM (X-ray Imaging and Spectroscopy Mission) captured data from the center of galaxy NGC 4151, where a supermassive black hole is slowly consuming material from the surrounding accretion disk. The resulting spectrum reveals the presence of iron in the peak around 6.5 keV and the dips around 7 keV, light thousands of times more energetic that what our eyes can see. Background: An image of NGC 4151 constructed from a combination of X-ray, optical, and radio light.Spectrum: JAXA/NASA/XRISM Resolve. Background: X-rays, NASA/CXC/CfA/J.Wang et al.; optical, Isaac Newton Group of Telescopes, La Palma/Jacobus Kapteyn Telescope; radio, NSF/NRAO/VLA Results from Resolve
So, what is Resolve revealing about the Universe? Through spectroscopy alone, Resolve allows us to construct images of complex environments where collections of gas and dust with various attributes exist, emitting and absorbing X-rays at energies characteristic of their various compositions, velocities, and temperatures. For example, in the middle of the galaxy known as NCG 4151 (see figure above), matter spiraling into the central massive black hole forms a circular structure that is flat near the black hole, more donut-shaped further out, and, according to the Resolve data, a bit lumpy. Matter near the black hole is heated up to X-ray-emitting temperatures and irradiates the matter in the circular structure. The Resolve spectrum has a bright narrow emission line (peak) from neutral iron atoms that must be coming from colder matter in the circular structure, because hotter material would be ionized, and would have a different emission signature. Nonetheless, the shape of the iron line needs three components to describe it, each coming from a different lump in the circular structure. The presence of absorption lines (dips) in the spectrum provides further detail about the structure of the infalling matter.
A second example is the detection of X-ray emission by Resolve from the debris of stars that have exploded, such as N132D (see figure below), that will improve our understanding of the explosion mechanism and how the elements produced in stars get distributed, and allow us to infer the type of star each was before ending in a supernova. Elements are identified by their characteristic emission lines, and shifts of those lines via the Doppler effect tell us how fast the material is moving.
XRISM’s Resolve instrument captured data from supernova remnant N132D in the Large Magellanic Cloud to create the most detailed X-ray spectrum of the object ever made. The spectrum reveals peaks associated with silicon, sulfur, argon, calcium, and iron. Inset at right is an image of N132D captured by XRISM’s Xtend instrument.JAXA/NASA/XRISM Resolve and Xtend These results are just the beginning. The rich Resolve data sets are identifying complex velocity structures, rare elements, and multiple temperature components in a diverse ensemble of cosmic objects. Welcome to the quantum calorimeter era! Stay tuned for more revelations!
Project Leads: Dr. Caroline Kilbourne, NASA Goddard Space Flight Center (GSFC), for silicon-thermistor quantum calorimeter development from Astro-E2 through XRISM and early TES development. Foundational and other essential leadership provided by Dr. Harvey Moseley, Dr. John Mather, Dr. Richard Kelley, Dr. Andrew Szymkowiak, Mr. Brent Mott, Dr. F. Scott Porter, Ms. Christine Jhabvala, Dr. James Chervenak (GSFC at the time of the work) and Dr. Dan McCammon (U. Wisconsin).
Sponsoring Organizations and Programs: The NASA Headquarters Astrophysics Division sponsored the projects, missions, and other efforts that culminated in the development of the Resolve instrument.
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By NASA
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Preparations for Next Moonwalk Simulations Underway (and Underwater)
NASA’s IXPE (Imaging X-ray Polarimetry Explorer) has helped astronomers better understand the shapes of structures essential to a black hole – specifically, the disk of material swirling around it, and the shifting plasma region called the corona.
The stellar-mass black hole, part of the binary system Swift J1727.8-1613, was discovered in the summer of 2023 during an unusual brightening event that briefly caused it to outshine nearly all other X-ray sources. It is the first of its kind to be observed by IXPE as it goes through the start, peak, and conclusion of an X-ray outburst like this.
This illustration shows NASA’s Imaging X-ray Polarimetry Explorer (IXPE) spacecraft, at lower left, observing the newly discovered binary system Swift J1727.8-1613 from a distance. At the center is a black hole surrounded by an accretion disk, shown in yellow and orange, and a hot, shifting corona, shown in blue. The black hole is siphoning off gas from its companion star, seen behind the black hole as an orange disk. Jets of fast-moving, superheated particles stream from both poles of the black hole. Author: Marie Novotná Swift J1727 is the subject of a series of new studies published in The Astrophysical Journal and Astronomy & Astrophysics. Scientists say the findings provide new insight into the behavior and evolution of black hole X-ray binary systems.
“This outburst evolved incredibly quickly,” said astrophysicist Alexandra Veledina, a permanent researcher at the University of Turku, Finland. “From our first detection of the outburst, it took Swift J1727 just days to peak. By then, IXPE and numerous other telescopes and instruments were already collecting data. It was exhilarating to observe the outburst all the way through its return to inactivity.”
Until late 2023, Swift J1727 briefly remained brighter than the Crab Nebula, the standard X-ray “candle” used to provide a baseline for units of X-ray brightness. Such outbursts are not unusual among binary star systems, but rarely do they occur so brightly and so close to home – just 8,800 light years from Earth. The binary system was named in honor of the Swift Gamma-ray Burst Mission which initially detected the outburst with its Burst Alert Telescope on Aug. 24, 2023, resulting in the discovery of the black hole.
X-ray binary systems typically include two close-proximity stars at different stages of their lifecycle. When the elder star runs out of fuel, it explodes in a supernova, leaving behind a neutron star, white dwarf, or black hole. In the case of Swift J1727, the powerful gravity of the resulting black hole stripped material from its companion star, heating the material to more than 1.8 million degrees Fahrenheit and producing a vast outpouring of X-rays. This matter formed an accretion disk and can include a superheated corona. At the poles of the black hole, matter also can escape from the binary system in the form of relativistic jets.
IXPE, which has helped NASA and researchers study all these phenomena, specializes in X-ray polarization, the characteristic of light that helps map the shape and structure of such ultra-powerful energy sources, illuminating their inner workings even when they’re too distant for us to see directly.
Because light itself can’t escape their gravity, we can’t see black holes. We can only observe what is happening around them and draw conclusions about the mechanisms and processes that occur there. IXPE is crucial to that work.
/wp-content/plugins/nasa-blocks/assets/images/article-templates/anne-mcclain.jpg Alexandra Veledina
NASA Astrophysicist
“Because light itself can’t escape their gravity, we can’t see black holes,” Veledina said. “We can only observe what is happening around them and draw conclusions about the mechanisms and processes that occur there. IXPE is crucial to that work.”
Two of the IXPE-based studies of Swift J1727, led by Veledina and Adam Ingram, a researcher at Newcastle University in Newcastle-upon-Tyne, England, focused on the first phases of the outburst. During the brief period of months when the source became exceptionally bright, the corona was the main source of observed X-ray radiation.
“IXPE documented polarization of X-ray radiation traveling along the estimated direction of the black hole jet, hence the hot plasma is extended in the accretion disk plane,” Veledina said. “Similar findings were reported in the persistent black hole binary Cygnus X-1, so this finding helps verify that the geometry is the same among short-lived eruptive systems.”
The team further monitored how polarization values changed during Swift J1727’s peak outburst. Those conclusions matched findings simultaneously obtained during studies of other energy bands of electromagnetic radiation.
A third and a fourth study, led by researchers Jiří Svoboda and Jakub Podgorný, both of the Czech Academy of Sciences in Prague, focused on X-ray polarization at the second part of the Swift J1727’s outburst and its return to a highly energetic state several months later. For Podgorný’s previous efforts using IXPE data and black hole simulations, he recently was awarded the Czech Republic’s top national prize for a Ph.D. thesis in the natural sciences.
The polarization data indicated that the geometry of the corona did not change significantly between the beginning and the end of the outburst, even though the system evolved in the meantime and the X-ray brightness dropped dramatically in the later energetic state.
The results represent a significant step forward in our understanding of the changing shapes and structures of accretion disk, corona, and related structures at black holes in general. The study also demonstrates IXPE’s value as a tool for determining how all these elements of the system are connected, as well as its potential to collaborate with other observatories to monitor sudden, dramatic changes in the cosmos.
“Further observations of matter near black holes in binary systems are needed, but the successful first observing campaign of Swift J1727.8–1613 in different states is the best start of a new chapter we could imagine,” said Michal Dovčiak, co-author of the series of papers and leader of the IXPE working group on stellar-mass black holes, who also conducts research at the Czech Academy of Sciences.
More about IXPE
IXPE, which continues to provide unprecedented data enabling groundbreaking discoveries about celestial objects across the universe, is a joint NASA and Italian Space Agency mission with partners and science collaborators in 12 countries. IXPE is led by NASA’s Marshall Space Flight Center in Huntsville, Alabama. Ball Aerospace, headquartered in Broomfield, Colorado, manages spacecraft operations together with the University of Colorado’s Laboratory for Atmospheric and Space Physics in Boulder.
Learn more about IXPE’s ongoing mission here:
https://www.nasa.gov/ixpe
Elizabeth Landau
NASA Headquarters
elizabeth.r.landau@nasa.gov
202-358-0845
Lane Figueroa
NASA’s Marshall Space Flight Center
256-544-0034
lane.e.figueroa@nasa.gov
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Last Updated Dec 06, 2024 Related Terms
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Hubble Space Telescope Home NASA’s Hubble Finds… Hubble Space Telescope Hubble Home Overview About Hubble The History of Hubble Hubble Timeline Why Have a Telescope in Space? Hubble by the Numbers At the Museum FAQs Impact & Benefits Hubble’s Impact & Benefits Science Impacts Cultural Impact Technology Benefits Impact on Human Spaceflight Astro Community Impacts Science Hubble Science Science Themes Science Highlights Science Behind Discoveries Hubble’s Partners in Science Universe Uncovered Explore the Night Sky Observatory Hubble Observatory Hubble Design Mission Operations Missions to Hubble Hubble vs Webb Team Hubble Team Career Aspirations Hubble Astronauts News Hubble News Hubble News Archive Social Media Media Resources Multimedia Multimedia Images Videos Sonifications Podcasts E-books Lithographs Fact Sheets Glossary Posters Hubble on the NASA App More Online Activities 5 Min Read NASA’s Hubble Finds Sizzling Details About Young Star FU Orionis
An artist’s concept of the early stages of the young star FU Orionis (FU Ori) outburst, surrounded by a disk of material. Credits:
NASA-JPL, Caltech In 1936, astronomers saw a puzzling event in the constellation Orion: the young star FU Orionis (FU Ori) became a hundred times brighter in a matter of months. At its peak, FU Ori was intrinsically 100 times brighter than our Sun. Unlike an exploding star though, it has declined in luminosity only languidly since then.
Now, a team of astronomers has wielded NASA’s Hubble Space Telescope‘s ultraviolet capabilities to learn more about the interaction between FU Ori’s stellar surface and the accretion disk that has been dumping gas onto the growing star for nearly 90 years. They find that the inner disk touching the star is extraordinarily hot — which challenges conventional wisdom.
The observations were made with the telescope’s COS (Cosmic Origins Spectrograph) and STIS (Space Telescope Imaging Spectrograph) instruments. The data includes the first far-ultraviolet and new near-ultraviolet spectra of FU Ori.
“We were hoping to validate the hottest part of the accretion disk model, to determine its maximum temperature, by measuring closer to the inner edge of the accretion disk than ever before,” said Lynne Hillenbrand of Caltech in Pasadena, California, and a co-author of the paper. “I think there was some hope that we would see something extra, like the interface between the star and its disk, but we were certainly not expecting it. The fact we saw so much extra — it was much brighter in the ultraviolet than we predicted — that was the big surprise.”
A Better Understanding of Stellar Accretion
Originally deemed to be a unique case among stars, FU Ori exemplifies a class of young, eruptive stars that undergo dramatic changes in brightness. These objects are a subset of classical T Tauri stars, which are newly forming stars that are building up by accreting material from their disk and the surrounding nebula. In classical T Tauri stars, the disk does not touch the star directly because it is restricted by the outward pressure of the star’s magnetic field.
The accretion disks around FU Ori objects, however, are susceptible to instabilities due to their enormous mass relative to the central star, interactions with a binary companion, or infalling material. Such instability means the mass accretion rate can change dramatically. The increased pace disrupts the delicate balance between the stellar magnetic field and the inner edge of the disk, leading to material moving closer in and eventually touching the star’s surface.
This is an artist’s concept of the early stages of the young star FU Orionis (FU Ori) outburst, surrounded by a disk of material. A team of astronomers has used the Hubble Space Telescope’s ultraviolet capabilities to learn more about the interaction between FU Ori’s stellar surface and the accretion disk that has been dumping gas onto the growing star for nearly 90 years. They found that the inner disk, touching the star, is much hotter than expected—16,000 kelvins—nearly three times our Sun’s surface temperature. That sizzling temperature is nearly twice as hot as previously believed. NASA-JPL, Caltech
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The enhanced infall rate and proximity of the accretion disk to the star make FU Ori objects much brighter than a typical T Tauri star. In fact, during an outburst, the star itself is outshined by the disk. Furthermore, the disk material is orbiting rapidly as it approaches the star, much faster than the rotation rate of the stellar surface. This means that there should be a region where the disk impacts the star and the material slows down and heats up significantly.
“The Hubble data indicates a much hotter impact region than models have previously predicted,” said Adolfo Carvalho of Caltech and lead author of the study. “In FU Ori, the temperature is 16,000 kelvins [nearly three times our Sun’s surface temperature]. That sizzling temperature is almost twice the amount prior models have calculated. It challenges and encourages us to think of how such a jump in temperature can be explained.”
To address the significant difference in temperature between past models and the recent Hubble observations, the team offers a revised interpretation of the geometry within FU Ori’s inner region: The accretion disk’s material approaches the star and once it reaches the stellar surface, a hot shock is produced, which emits a lot of ultraviolet light.
Planet Survival Around FU Ori
Understanding the mechanisms of FU Ori’s rapid accretion process relates more broadly to ideas of planet formation and survival.
“Our revised model based on the Hubble data is not strictly bad news for planet evolution, it’s sort of a mixed bag,” explained Carvalho. “If the planet is far out in the disk as it’s forming, outbursts from an FU Ori object should influence what kind of chemicals the planet will ultimately inherit. But if a forming planet is very close to the star, then it’s a slightly different story. Within a couple outbursts, any planets that are forming very close to the star can rapidly move inward and eventually merge with it. You could lose, or at least completely fry, rocky planets forming close to such a star.”
Additional work with the Hubble UV observations is in progress. The team is carefully analyzing the various spectral emission lines from multiple elements present in the COS spectrum. This should provide further clues on FU Ori’s environment, such as the kinematics of inflowing and outflowing gas within the inner region.
“A lot of these young stars are spectroscopically very rich at far ultraviolet wavelengths,” reflected Hillenbrand. “A combination of Hubble, its size and wavelength coverage, as well as FU Ori’s fortunate circumstances, let us see further down into the engine of this fascinating star-type than ever before.”
These findings have been published in The Astrophysical Journal Letters.
The observations were taken as part of General Observer program 17176.
The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.
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NASA Satellites Reveal Abrupt Drop in Global Freshwater Levels
Earth (ESD) Earth Home Explore Climate Change Science in Action Multimedia Data For Researchers GRACE satellites measure gravity as they orbit the planet to reveal shifting levels of water on the Earth (artist’s concept). NASA/JPL-Caltech An international team of scientists using observations from NASA-German satellites found evidence that Earth’s total amount of freshwater dropped abruptly starting in May 2014 and has remained low ever since. Reporting in Surveys in Geophysics, the researchers suggested the shift could indicate Earth’s continents have entered a persistently drier phase.
From 2015 through 2023, satellite measurements showed that the average amount of freshwater stored on land — that includes liquid surface water like lakes and rivers, plus water in aquifers underground — was 290 cubic miles (1,200 cubic km) lower than the average levels from 2002 through 2014, said Matthew Rodell, one of the study authors and a hydrologist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “That’s two and a half times the volume of Lake Erie lost.”
During times of drought, along with the modern expansion of irrigated agriculture, farms and cities must rely more heavily on groundwater, which can lead to a cycle of declining underground water supplies: freshwater supplies become depleted, rain and snow fail to replenish them, and more groundwater is pumped. The reduction in available water puts a strain on farmers and communities, potentially leading to famine, conflicts, poverty, and an increased risk of disease when people turn to contaminated water sources, according to a UN report on water stress published in 2024.
The team of researchers identified this abrupt, global decrease in freshwater using observations from the Gravity Recovery and Climate Experiment (GRACE) satellites, operated by the German Aerospace Center, German Research Centre for Geosciences, and NASA. GRACE satellites measure fluctuations in Earth’s gravity on monthly scales that reveal changes in the mass of water on and under the ground. The original GRACE satellites flew from March 2002 to October 2017. The successor GRACE–Follow On (GRACE–FO) satellites launched in May 2018.
This map shows the years that terrestrial water storage hit a 22-year minimum (i.e., the land was driest) at each location, based on data from the GRACE and GRACE/FO satellites. A significantly large portion of the global land surface reached this minimum in the nine years since 2015, which happen to be the nine warmest years in the modern temperature record. Image by NASA Earth Observatory/Wanmei Liang with data courtesy of Mary Michael O’Neill The decline in global freshwater reported in the study began with a massive drought in northern and central Brazil, and was followed shortly by a series of major droughts in Australasia, South America, North America, Europe, and Africa. Warmer ocean temperatures in the tropical Pacific from late 2014 into 2016, culminating in one of the most significant El Niño events since 1950, led to shifts in atmospheric jet streams that altered weather and rainfall patterns around the world. However, even after El Niño subsided, global freshwater failed to rebound. In fact, Rodell and team report that 13 of the world’s 30 most intense droughts observed by GRACE occurred since January 2015. Rodell and colleagues suspect that global warming might be contributing to the enduring freshwater depletion.
Global warming leads the atmosphere to hold more water vapor, which results in more extreme precipitation, said NASA Goddard meteorologist Michael Bosilovich. While total annual rain and snowfall levels may not change dramatically, long periods between intense precipitation events allow the soil to dry and become more compact. That decreases the amount of water the ground can absorb when it does rain.
“The problem when you have extreme precipitation,” Bosilovich said, “is the water ends up running off,” instead of soaking in and replenishing groundwater stores. Globally, freshwater levels have stayed consistently low since the 2014-2016 El Niño, while more water remains trapped in the atmosphere as water vapor. “Warming temperatures increase both the evaporation of water from the surface to the atmosphere, and the water-holding capacity of the atmosphere, increasing the frequency and intensity of drought conditions,” he noted.
While there are reasons to suspect that the abrupt drop in freshwater is largely due to global warming, it can be difficult to definitively link the two, said Susanna Werth, a hydrologist and remote sensing scientist at Virginia Tech, who was not affiliated with the study. “There are uncertainties in climate predictions,” Werth said. “Measurements and models always come with errors.”
It remains to be seen whether global freshwater will rebound to pre-2015 values, hold steady, or resume its decline. Considering that the nine warmest years in the modern temperature record coincided with the abrupt freshwater decline, Rodell said, “We don’t think this is a coincidence, and it could be a harbinger of what’s to come.”
By James R. Riordon
NASA’s Earth Science News Team
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Last Updated Nov 15, 2024 Editor James Riordon Contact James Riordon james.r.riordon@nasa.gov Location NASA Goddard Space Flight Center Related Terms
Earth Goddard Space Flight Center GRACE (Gravity Recovery And Climate Experiment) GRACE-FO (Gravity Recovery and Climate Experiment Follow-on) Water on Earth Explore More
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