Members Can Post Anonymously On This Site
11 min read
The Universe is Expanding Faster These Days and Dark Energy is Responsible. So What is Dark Energy?
Some 13.8 billion years ago, the universe began with a rapid expansion we call the big bang. After this initial expansion, which lasted a fraction of a second, gravity started to slow the universe down. But the cosmos wouldn’t stay this way. Nine billion years after the universe began, its expansion started to speed up, driven by an unknown force that scientists have named dark energy.
But what exactly is dark energy?
The short answer is: We don’t know. But we do know that it exists, it’s making the universe expand at an accelerating rate, and approximately 68.3 to 70% of the universe is dark energy.
The history of the universe is outlined in this infographic. NASA A Brief History
It All Started With Cepheids
Dark energy wasn’t discovered until the late 1990s. But its origin in scientific study stretches all the way back to 1912 when American astronomer Henrietta Swan Leavitt made an important discovery using Cepheid variables, a class of stars whose brightness fluctuates with a regularity that depends on the star’s brightness.
All Cepheid stars with a certain period (a Cepheid’s period is the time it takes to go from bright, to dim, and bright again) have the same absolute magnitude, or luminosity – the amount of light they put out. Leavitt measured these stars and proved that there is a relationship between their regular period of brightness and luminosity. Leavitt’s findings made it possible for astronomers to use a star’s period and luminosity to measure the distances between us and Cepheid stars in far-off galaxies (and our own Milky Way).
Around this same time in history, astronomer Vesto Slipher observed spiral galaxies using his telescope’s spectrograph, a device that splits light into the colors that make it up, much like the way a prism splits light into a rainbow. He used the spectrograph, a relatively recent invention at the time, to see the different wavelengths of light coming from the galaxies in different spectral lines. With his observations, Silpher was the first astronomer to observe how quickly the galaxy was moving away from us, called redshift, in distant galaxies. These observations would prove to be critical for many future scientific breakthroughs, including the discovery of dark energy.
Redshift is a term used when astronomical objects are moving away from us and the light coming from those objects stretches out. Light behaves like a wave, and red light has the longest wavelength. So, the light coming from objects moving away from us has a longer wavelength, stretching to the “red end” of the electromagnetic.
Discovering an Expanding Universe
The discovery of galactic redshift, the period-luminosity relation of Cepheid variables, and a newfound ability to gauge a star or galaxy’s distance eventually played a role in astronomers observing that galaxies were getting farther away from us over time, which showed how the universe was expanding. In the years that followed, different scientists around the world started to put the pieces of an expanding universe together.
In 1922, Russian scientist and mathematician Alexander Friedmann published a paper detailing multiple possibilities for the history of the universe. The paper, which was based on Albert Einstein’s theory of general relativity published in 1917, included the possibility that the universe is expanding.
In 1927, Belgian astronomer Georges Lemaître, who is said to have been unaware of Friedmann’s work, published a paper also factoring in Einstein’s theory of general relativity. And, while Einstein stated in his theory that the universe was static, Lemaître showed how the equations in Einstein’s theory actually support the idea that the universe is not static but, in fact, is actually expanding.
Astronomer Edwin Hubble confirmed that the universe was expanding in 1929 using observations made by his associate, astronomer Milton Humason. Humason measured the redshift of spiral galaxies. Hubble and Humason then studied Cepheid stars in those galaxies, using the stars to determine the distance of their galaxies (or nebulae, as they called them). They compared the distances of these galaxies to their redshift and tracked how the farther away an object is, the bigger its redshift and the faster it is moving away from us. The pair found that objects like galaxies are moving away from Earth faster the farther away they are, at upwards of hundreds of thousands of miles per second – an observation now known as Hubble’s Law, or the Hubble- Lemaître law. The universe, they confirmed, is really expanding.
This composite image features one of the most complicated and dramatic collisions between galaxy clusters ever seen. Known officially as Abell 2744, this system has been dubbed Pandora’s Cluster because of the wide variety of different structures found. Data from Chandra (red) show gas with temperatures of millions of degrees. In blue is a map showing the total mass concentration (mostly dark matter) based on data from the Hubble Space Telescope, the Very Large Telescope (VLT), and the Subaru telescope. Optical data from HST and VLT also show the constituent galaxies of the clusters. Astronomers think at least four galaxy clusters coming from a variety of directions are involved with this collision. Expansion is Speeding Up, Supernovae Show
Scientists previously thought that the universe’s expansion would likely be slowed down by gravity over time, an expectation backed by Einstein’s theory of general relativity. But in 1998, everything changed when two different teams of astronomers observing far-off supernovae noticed that (at a certain redshift) the stellar explosions were dimmer than expected. These groups were led by astronomers Adam Riess, Saul Perlmutter, and Brian Schmidt. This trio won the 2011 Nobel Prize in Physics for this work.
While dim supernovae might not seem like a major find, these astronomers were looking at Type 1a supernovae, which are known to have a certain level of luminosity. So they knew that there must be another factor making these objects appear dimmer. Scientists can determine distance (and speed) using an objects’ brightness, and dimmer objects are typically farther away (though surrounding dust and other factors can cause an object to dim).
This led the scientists to conclude that these supernovae were just much farther away than they expected by looking at their redshifts.
Using the objects’ brightness, the researchers determined the distance of these supernovae. And using the spectrum, they were able to figure out the objects’ redshift and, therefore, how fast they were moving away from us. They found that the supernovae were not as close as expected, meaning they had traveled farther away from us faster than ancitipated. These observations led scientists to ultimately conclude that the universe itself must be expanding faster over time.
While other possible explanations for these observations have been explored, astronomers studying even more distant supernovae or other cosmic phenomena in more recent years continued to gather evidence and build support for the idea that the universe is expanding faster over time, a phenomenon now called cosmic acceleration.
But, as scientists built up a case for cosmic acceleration, they also asked: Why? What could be driving the universe to stretch out faster over time?
Enter dark energy.
What Exactly is Dark Energy?
Right now, dark energy is just the name that astronomers gave to the mysterious “something” that is causing the universe to expand at an accelerated rate.
Dark energy has been described by some as having the effect of a negative pressure that is pushing space outward. However, we don’t know if dark energy has the effect of any type of force at all. There are many ideas floating around about what dark energy could possibly be. Here are four leading explanations for dark energy. Keep in mind that it’s possible it’s something else entirely.
Some scientists think that dark energy is a fundamental, ever-present background energy in space known as vacuum energy, which could be equal to the cosmological constant, a mathematical term in the equations of Einstein’s theory of general relativity. Originally, the constant existed to counterbalance gravity, resulting in a static universe. But when Hubble confirmed that the universe was actually expanding, Einstein removed the constant, calling it “my biggest blunder,” according to physicist George Gamow.
But when it was later discovered that the universe’s expansion was actually accelerating, some scientists suggested that there might actually be a non-zero value to the previously-discredited cosmological constant. They suggested that this additional force would be necessary to accelerate the expansion of the universe. This theorized that this mystery component could be attributed to something called “vacuum energy,” which is a theoretical background energy permeating all of space.
Space is never exactly empty. According to quantum field theory, there are virtual particles, or pairs of particles and antiparticles. It’s thought that these virtual particles cancel each other out almost as soon as they crop up in the universe, and that this act of popping in and out of existence could be made possible by “vacuum energy” that fills the cosmos and pushes space outward.
While this theory has been a popular topic of discussion, scientists investigating this option have calculated how much vacuum energy there should theoretically be in space. They showed that there should either be so much vacuum energy that, at the very beginning, the universe would have expanded outwards so quickly and with so much force that no stars or galaxies could have formed, or… there should be absolutely none. This means that the amount of vacuum energy in the cosmos must be much smaller than it is in these predictions. However, this discrepancy has yet to be solved and has even earned the moniker “the cosmological constant problem.”
Some scientists think that dark energy could be a type of energy fluid or field that fills space, behaves in an opposite way to normal matter, and can vary in its amount and distribution throughout both time and space. This hypothesized version of dark energy has been nicknamed quintessence after the theoretical fifth element discussed by ancient Greek philosophers.
It’s even been suggested by some scientists that quintessence could be some combination of dark energy and dark matter, though the two are currently considered completely separate from one another. While the two are both major mysteries to scientists, dark matter is thought to make up about 85% of all matter in the universe.
Some scientists think that dark energy could be a sort of defect in the fabric of the universe itself; defects like cosmic strings, which are hypothetical one-dimensional “wrinkles” thought to have formed in the early universe.
A Flaw in General Relativity:
Some scientists think that dark energy isn’t something physical that we can discover. Rather, they think there could be an issue with general relativity and Einstein’s theory of gravity and how it works on the scale of the observable universe. Within this explanation, scientists think that it’s possible to modify our understanding of gravity in a way that explains observations of the universe made without the need for dark energy. Einstein actually proposed such an idea in 1919 called unimodular gravity, a modified version of general relativity that scientists today think wouldn’t require dark energy to make sense of the universe.
Dark energy is one of the great mysteries of the universe. For decades, scientists have theorized about our expanding universe. Now, for the first time ever, we have tools powerful enough to put these theories to the test and really investigate the big question: “what is dark energy?”
NASA plays a critical role in the ESA (European Space Agency) mission Euclid (launched in 2023), which will make a 3D map of the universe to see how matter has been pulled apart by dark energy over time. This map will include observations of billions of galaxies found up to 10 billion light-years from Earth.
NASA’s Nancy Grace Roman Space Telescope, set to launch by May 2027, is designed to investigate dark energy, among many other science topics, and will also create a 3D dark matter map. Roman’s resolution will be as sharp as NASA’s Hubble Space Telescope’s, but with a field of view 100 times larger, allowing it to capture more expansive images of the universe. This will allow scientists to map how matter is structured and spread across the universe and explore how dark energy behaves and has changed over time. Roman will also conduct an additional survey to detect Type Ia supernovae
In addition to NASA’s missions and efforts, the Vera C. Rubin Observatory, supported by a large collaboration that includes the U.S. National Science Foundation, which is currently under construction in Chile, is also poised to support our growing understanding of dark energy. The ground-based observatory is expected to be operational in 2025.
The combined efforts of Euclid, Roman, and Rubin will usher in a new “golden age” of cosmology, in which scientists will collect more detailed information than ever about the great mysteries of dark energy.
Additionally, NASA’s James Webb Space Telescope (launched in 2021), the world’s most powerful and largest space telescope, aims to make contributions to several areas of research, and will contribute to studies of dark energy.
NASA’s SPHEREx (the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer) mission, scheduled to launch no later than April 2025, aims to investigate the origins of the universe. Scientists expect that the data collected with SPHEREx, which will survey the entire sky in near-infrared light, including over 450 million galaxies, could help to further our understanding of dark energy.
NASA also supports a citizen science project called Dark Energy Explorers, which enables anyone in the world, even those who have no scientific training, to help in the search for dark energy answers.
*A brief note*
Lastly, to clarify, dark energy is not the same as dark matter. Their main similarity is that we don’t yet know what they are!
By Chelsea Gohd
NASA’s Jet Propulsion Laboratory
Last Updated Feb 05, 2024 Related Terms
Dark Energy Dark Matter Euclid Galaxies James Webb Space Telescope (JWST) Nancy Grace Roman Space Telescope SPHEREx (Spectro-Photometer for the History of the Universe and Ices Explorer) Stellar Evolution The Big Bang The Universe Explore More
2 min read Hubble Views a Dim but Distinct Galaxy
3 days ago
2 min read Hubble Sees a Merged Galaxy
3 days ago
2 min read Hubble Captures a Suspected Galaxy Encounter
4 days ago
Keep Exploring Discover More Topics From NASA
Humans in Space
View the full article
3 min read
What’s Made in a Thunderstorm and Faster Than Lightning? Gamma Rays!
A flash of lightning. A roll of thunder. These are normal stormy sights and sounds. But sometimes, up above the clouds, stranger things happen. Our Fermi Gamma-ray Space Telescope has spotted bursts of gamma rays – some of the highest-energy forms of light in the universe – coming from thunderstorms. Gamma rays are usually found coming from objects with crazy extreme physics like neutron stars and black holes. So why is Fermi seeing them come from thunderstorms?
About a thousand times a day, thunderstorms fire off fleeting bursts of some of the highest-energy light naturally found on Earth. These events, called terrestrial gamma-ray flashes, last less than a millisecond and produce gamma rays with tens of millions of times the energy of visible light. NASA’s Goddard Space Flight Center Thunderstorms form when warm, damp air near the ground starts to rise and encounters colder air. As the warm air rises, moisture condenses into water droplets. The upward-moving water droplets bump into downward-moving ice crystals, stripping off electrons and creating a static charge in the cloud.
Updrafts and downdrafts within thunderstorms force rain, snow and ice to collide and acquire an electrical charge, which can cause lightning. Under just the right conditions, the fast-moving electrons can create a terrestrial gamma-ray flash. NASA’s Goddard Space Flight Center The top of the storm becomes positively charged, and the bottom becomes negatively charged, like two ends of a battery. Eventually the opposite charges build enough to overcome the insulating properties of the surrounding air – and zap! You get lightning.
This illustration shows electrons accelerating upwards from a thunderhead. NASA’s Goddard Space Flight Center Scientists suspect that lightning reconfigures the cloud’s electrical field. In some cases, this allows electrons to rush toward the upper part of the storm at nearly the speed of light. That makes thunderstorms the most powerful natural particle accelerators on Earth!
Interactions with matter can produce gamma rays and vice versa, as shown here in this illustration. High-energy electrons traveling close to the speed of light can be deflected by passing near an atom or molecule, producing a gamma ray. And a gamma ray passing through the electron shell of an atom transforms into two particles: an electron and a positron. NASA’s Goddard Space Flight Center When those electrons run into air molecules, they emit a terrestrial gamma-ray flash, which means that thunderstorms are creating some of the highest energy forms of light in the universe. But that’s not all – thunderstorms can also produce antimatter! Yep, you read that correctly! Sometimes, a gamma ray will run into an atom and produce an electron and a positron, which is an electron’s antimatter opposite!
NASA’s Fermi Gamma-ray Space Telescope, illustrated here, scans the entire sky every three hours as it orbits Earth. NASA’s Goddard Space Flight Center Conceptual Image Lab Fermi can spot terrestrial gamma-ray flashes within 500 miles (800 kilometers) of the location directly below the spacecraft. It does this using an instrument called the Gamma-ray Burst Monitor which is primarily used to watch for spectacular flashes of gamma rays coming from the universe.
Visualization of ten years of Fermi observations of terrestrial gamma-ray flashes. NASA’s Goddard Space Flight Center There are an estimated 1,800 thunderstorms occurring on Earth at any given moment. Over its first 10 years in space, Fermi spotted about 5,000 terrestrial gamma-ray flashes. But scientists estimate that there are 1,000 of these flashes every day – we’re just seeing the ones that are within 500 miles of Fermi’s regular orbits, which don’t cover the U.S. or Europe.
The map above shows all the flashes Fermi saw between 2008 and 2018. (Notice there’s a blob missing over the lower part of South America. That’s the South Atlantic Anomaly, a portion of the sky where radiation affects spacecraft and causes data glitches.)
Storm clouds produce some of the highest-energy light naturally made on Earth: terrestrial gamma-ray flashes. The tropical disturbance that would later become Hurricane Julio in 2014 produced four flashes within 100 minutes, with a fifth the next day. NASA’s Goddard Space Flight Center Fermi has also spotted terrestrial gamma-ray flashes coming from individual tropical weather systems. In 2014 Tropical Storm Julio produced four flashes in just 100 minutes!
Last Updated Feb 05, 2024 Related Terms
Black Holes Earth Extreme Weather Events Fermi Gamma-Ray Space Telescope Gamma Rays Gamma-Ray Bursts Neutron Stars The Universe Weather and Atmospheric Dynamics Explore More
4 min read When Dead Stars Collide!
In October 2017, for the first time, astronomers observed light and gravitational waves from the…
1 hour ago
2 min read Hubble Views a Dim but Distinct Galaxy
3 days ago
2 min read Hubble Sees a Merged Galaxy
3 days ago
Keep Exploring Discover More Topics From NASA
Dark Matter & Dark Energy
The Big Bang
View the full article
5 min read
How is the 2024 Total Solar Eclipse Different than the 2017 Eclipse?
On April 8, the Moon’s shadow will sweep across the United States, as millions will view a total solar eclipse. For many, preparing for this event brings memories of the magnificent total solar eclipse on Aug. 21, 2017.
The total solar eclipse on Aug. 21, 2017, was photographed from Madras, Oregon. The black circle in the middle is the Moon. Surrounding it are white streams of light belonging to the Sun’s outer atmosphere, called the corona. NASA/Aubrey Gemignani In 2017, an estimated 215 million U.S. adults (88% of U.S. adults) viewed the solar eclipse, either directly or electronically. They experienced the Moon pass in front of the Sun, blocking part or all of our closest star’s bright face. The eclipse in 2024 could be even more exciting due to differences in the path, timing, and scientific research.
Wider, More Populated Path
The path of totality – where viewers can see the Moon totally block the Sun, revealing the star’s outer atmosphere, called the corona – is much wider during the upcoming total solar eclipse than it was during the eclipse in 2017. As the Moon orbits Earth, its distance from our planet varies. During the 2017 total solar eclipse, the Moon was a little bit farther away from Earth than it will be during upcoming total solar eclipse, causing the path of that eclipse to be a little skinnier. In 2017, the path ranged from about 62 to 71 miles wide. During the April eclipse, the path over North America will range between 108 and 122 miles wide – meaning at any given moment, this eclipse covers more ground.
The 2024 eclipse path will also pass over more cities and densely populated areas than the 2017 path did. This will make it easier for more people to see totality. An estimated 31.6 million people live in the path of totality this year, compared to 12 million in 2017. An additional 150 million people live within 200 miles of the path of totality.
This map shows the path of the 2017 total solar eclipse, crossing from Oregon to South Carolina, and the 2024 total solar eclipse, crossing from Mexico into Texas, up to Maine, and exiting over Canada. To see a map showing which areas will experience the partial solar eclipse and which areas will experience the total solar eclipse on April 8, 2024, click the arrows.
Ernest Wright/NASA’s Scientific Visualization Studio This map illustrates the paths of the Moon’s shadow across the U.S. during the 2024 total solar eclipse. On April 8, 2024, a total solar eclipse will cross North and Central America creating a path of totality. During a total solar eclipse, the Moon completely blocks the Sun while it passes between the Sun and Earth. The sky will darken as if it were dawn or dusk and those standing in the path of totality may see the Sun’s outer atmosphere (the corona) if weather permits. To see a map comparing the 2024 eclipse and the 2017 eclipse paths, click the arrows.
NASA/Scientific Visualization Studio/Michala Garrison; Eclipse Calculations By Ernie Wright, NASA Goddard Space Flight Center
You don’t need to live within the path of totality to see the eclipse – in April, 99% of people who reside in the United States will be able to see the partial or total eclipse from where they live. Every contiguous U.S. state, plus parts of Alaska and Hawaii, will experience at least a partial solar eclipse.
Longer Time in Totality
In April, totality will last longer than it did in 2017. Seven years ago, the longest period of totality was experienced near Carbondale, Illinois, at 2 minutes, 42 seconds.
For the upcoming eclipse, totality will last up to 4 minutes, 28 seconds, in an area about 25 minutes northwest of Torreón, Mexico. As the eclipse enters Texas, totality will last about 4 minutes, 26 seconds at the center of the eclipse’s path. Durations longer than 4 minutes stretch as far north as Economy, Indiana. Even as the eclipse exits the U.S. and enters Canada, the eclipse will last up to 3 minutes, 21 seconds.
During any total solar eclipse, totality lasts the longest near the center of the path, widthwise, and decreases toward the edge. But those seeking totality shouldn’t worry that they need to be exactly at the center. The time in totality falls off pretty slowly until you get close to the edge.
Heightened Solar Activity
NASA/ESA’s Solar and Heliospheric Observatory (SOHO) captured this video of a coronal mass ejection on March 13, 2023. NASA/Aubrey Gemignani
Every 11 years or so, the Sun’s magnetic field flips, causing a cycle of increasing then decreasing solar activity. During solar minimum, there are fewer giant eruptions from the Sun, such as solar flares and coronal mass ejections. But during solar maximum, the Sun becomes more active.
In 2017, the Sun was nearing solar minimum. Viewers of the total eclipse could see the breathtaking corona – but since the Sun was quiet, streamers flowing into the solar atmosphere were restricted to just the equatorial regions of the star. The Sun is more magnetically symmetrical during solar minimum, causing this simpler appearance. During the 2024 eclipse, the Sun will be in or near solar maximum, when the magnetic field is more like a tangled hairball. Streamers will likely be visible throughout the corona. In addition to that, viewers will have a better chance to see prominences – which appear as bright, pink curls or loops coming off the Sun.
With lucky timing, there could even be a chance to see a coronal mass ejection – a large eruption of solar material – during the eclipse.
Expanded Scientific Research
The third rocket launched on Oct. 14, 2023, during the annular solar eclipse leaves the launch pad. WSMR Army Photo During the total eclipse in 2024, NASA is funding several research initiatives that build on research done during the 2017 eclipse. The projects, which are led by researchers at different academic institutions, will study the Sun and its influence on Earth with a variety of instruments, including cameras aboard high-altitude research planes, ham radios, and more. In addition to those projects, instruments that were launched during the 2023 annular solar eclipse on three sounding rockets will again be launched during the upcoming total solar eclipse.
Two spacecraft designed to study the Sun’s corona – NASA’s Parker Solar Probe and ESA (European Space Agency) and NASA’s Solar Orbiter – have also launched since the 2017 solar eclipse. These missions will provide insights from the corona itself, while viewers on Earth see it with their own eyes, providing an exciting opportunity to combine and compare viewpoints.
To learn more about the 2024 total solar eclipse and how you can safely watch it, visit NASA’s eclipse website.
By Abbey Interrante
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Special thanks to Michael Zeiler for his calculations on the populations in the eclipse path.
The 2017 total solar eclipse viewing analysis was conducted by Professor Jon D. Miller of the University of Michigan. This study was supported by a collaborative agreement between the University of Michigan and the National Aeronautics and Space Administration (award NNX16AC66A).
View the full article
Jakobshavn Isbrae, a glacier on Greenland’s western coast, is shown in imagery taken on Sept. 5, 1985, by the Landsat 5 satellite. Jakobshavn receded from 1985 to 2022, losing about 97 billion tons (88 billion metric tons) of ice, a recent study of the Greenland Ice Sheet’s glacial retreat found.NASA/USGS A Landsat 8 image from Sept. 4, 2022, shows Jakobshavn Isbrae breaking at its edge. A recent study found that from 1985 to 2022 the Greenland Ice Sheet shed about 1,140 billion tons (1,034 billion metric tons) – one-fifth more mass than previously estimated.NASA/USGS A new, comprehensive analysis of satellite data finds that majority of glaciers on the landmass have retreated significantly.
The Greenland Ice Sheet has shed about one-fifth more ice mass in the past four decades than previously estimated, researchers at NASA’s Jet Propulsion Laboratory in Southern California reported in a new paper. The majority of glaciers on the landmass have retreated significantly, and icebergs are falling into the ocean at an accelerating rate. This additional ice loss has had only an indirect impact on sea levels, but could hold implications for ocean circulation in the future.
Published in Nature on Jan. 17, the analysis offers a comprehensive look at retreat around the edges of the entire ice sheet from 1985 to 2022, drawing from nearly a quarter million pieces of satellite data on glacier positions. Of the 207 glaciers in the study, 179 retreated significantly since 1985, 27 held steady, and one advanced slightly.
Most of the ice loss came from below sea level, in fjords on Greenland’s periphery. Once occupied by ancient glacial ice, many of these deep coastal valleys have filled with seawater – meaning the ice that broke off made little net contribution to sea level. But the loss likely accelerated the movement of ice flowing down from higher elevations, which in turn added to sea level rise.
“When the ice at the end of a glacier calves and retreats, it’s like pulling the plug out of the fjord, which lets ice drain into the ocean faster,” said Chad Greene, a glacier scientist at JPL and the study’s lead author.
Accounting for Glacial Retreat
For decades researchers have studied the Greenland Ice Sheet’s direct contributions to global sea level rise through ice flow and melting. Scientists participating in the international Ice sheet Mass Balance Inter-comparison Exercise (IMBIE) estimated that the ice sheet had lost 5,390 billion tons (4,890 billion metric tons) between 1992 and 2020, adding about 0.531 inches (13.5 millimeters) to global mean sea level, according to the Intergovernmental Panel on Climate Change.
Imagery from the Landsat 7 satellite taken on Aug. 5, 1999, shows Zachariae Isstrom, a glacier in northeast Greenland. This glacier lost about 176 billion tons (160 billion metric tons) of ice during its retreat from 1985 to 2022, a recent study found.NASA/USGS A Landsat 8 image from Aug. 22, 2022, shows icebergs breaking from Zachariae Isstrom. From 1985 to 2022, as icebergs fell into the ocean at an accelerating rate, the Greenland Ice Sheet shed about 1,140 billion tons (1,034 billion metric tons) – one-fifth more mass than previously estimated.NASA/USGS But the IMBIE measurements do not account for ice lost due to the retreat of terminal glaciers along the edges of Greenland. (These glacier edges were already in the water, whether submerged or floating.) The new study quantifies this amount: For the 1985 to 2022 period in the new paper, the ice sheet was estimated to have lost about 1,140 billion tons (1,034 billion metric tons) – 21% more mass lost than in the IMBIE assessment.
Although it doesn’t add to sea levels, the additional ice represents a significant influx of fresh water to the ocean. Recent studies have suggested that changes in the salinity of the North Atlantic Ocean from melting icebergs could weaken the Atlantic Meridional Overturning Circulation, part of the global “conveyor belt” of currents that transport heat and salt around the ocean. This could influence weather patterns worldwide, as well as affect ecosystems, the authors said.
A Comprehensive View of Glacial Retreat
Icebergs have tumbled from Greenland’s glaciers for thousands of years as part of a natural cycle that typically balanced glacier growth in the winter with melting and retreat in the summer. The new study finds that ice retreat has far outpaced growth throughout the 21st century.
The researchers also found that Greenland’s ice extent remained relatively steady from 1985 to 2000, then started a marked recession that continues to this day.
The data showed a glacier in northeast Greenland called Zachariae Isstrom lost the most ice, dropping 176 billion tons (160 billion metric tons) of mass due to retreat. It was followed by Jakobshavn Isbrae on the western coast, which lost an estimated 97 billion tons (88 billion metric tons), and Humboldt Gletscher in the northwest, which lost 96 billion tons (87 billion metric tons).
Only one glacier, Qajuuttap Sermia in southern Greenland, experienced any growth over the study period, but its gains were too small to offset the losses from other glaciers.
The researchers also found that glaciers with the largest seasonal fluctuations in the position of their ice front experienced the greatest overall retreat. The correlation suggests the glaciers that are most sensitive to warming each summer will be most impacted by climate change in the coming decades.
The discovery of a large-scale pattern of glacier retreat and its link to glacier sensitivity on seasonal time scales was the result of a big-data synthesis that looks at all parts of the ice sheet over time, said JPL cryosphere scientist Alex Gardner, a co-author of the paper. Scientists drew from five publicly available datasets that cumulatively tracked the month-to-month positions of 236,328 glacier edges as detected, either manually or by computer algorithms, in images collected by optical and radar satellites.
“Previously, we had bits and pieces – lots of local studies,” Gardner said. “But what this study offers is a systematic and comprehensive view that has led to some pretty significant insights that we didn’t have about the ice sheet before.”
News Media Contacts
Andrew Wang / Jane J. Lee
Jet Propulsion Laboratory, Pasadena, Calif.
626-379-6874 / 818-354-0307
firstname.lastname@example.org / email@example.com
Last Updated Jan 17, 2024 Related Terms
Ice & Glaciers Cryosphere Earth Earth Science Jet Propulsion Laboratory Explore More
7 min read Michael Thorpe Studies Sediment from Source to Sink
Sedimentary and planetary geologist Michael Thorpe finds the stories rocks have to tell, those on…
Article 9 mins ago 8 min read NASA’s PACE To Investigate Oceans, Atmospheres in Changing Climate
Earth’s oceans and atmosphere are changing as the planet warms. Some ocean waters become greener…
Article 6 days ago 6 min read This US-Indian Satellite Will Monitor Earth’s Changing Frozen Regions
Article 7 days ago View the full article
3 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
Graphic depiction of Thin Film Isotope Nuclear Engine Rocket (TFINER)James Bickford James Bickford
Charles Stark Draper Laboratory
New exciting missions, such as a rendezvous with a passing interstellar object, or a multi-target observing effort at the solar gravitational focus, require velocities that are well in excess of conventional rocketry. Exotic solar sail approaches may enable reaching the required distant localities, but are unable to then make the required propulsive maneuvers in deep space. Nuclear rockets are large and expensive systems with marginal capability to reach the location. In contrast, we propose a thin film nuclear isotope engine with sufficient capability to search, rendezvous and then return samples from distant and rapidly moving interstellar objects.
The same technology allows a gravitational lens telescope to be repointed so a single mission could observe numerous high-value targets.
The basic concept is to manufacture thin sheets of a radioactive isotope and directly use the momentum of its decay products to generate thrust. The baseline design is a ~10-micron thick Thorium-228 radioisotope film which undergoes alpha decay with a halflife of 1.9 years. The subsequent decay chain cascade produces daughter products with four additional alpha emissions that have halflives between 300ns and 3 days. A thrust is produced when one side of the thin film is coated with a ~50-micron thick absorber that captures forward emissions. Multiple “stages” consisting of longer half-life isotopes (e.g. Ac-227) can be combined to maximize the velocity over extended mission timelines.
Key differentiators of the concepts are:
• Cascading isotope decay chains (Thorium cycle) increases performance by ~500%
• Multiple ‘stages’ (materials) increases delta-V and lifetime without reducing thrust
• Thrust sheet reconfiguration enables active thrust vectoring and spacecraft maneuvers
• Substrate thermo-electrics can generate excess electrical power (e.g. ~50 kW @ eff=1%)
• A substrate beta emitter can be used for charge neutralization or to induce a voltage bias that preferentially directs exhaust emissions and/or to exploit the outbound solar wind
Leveraging 30kg of radioisotope (comparable to that launched on previous missions) spread over ~250 m^2 of area would provide more than 150 km/sec of delta-V to a 30 kg payload. Multiple such systems could be inserted into a solar escape trajectory with a single conventional launch vehicle allowing local search and rendezvous operations in the outer solar system. The system is scalable to other payloads and missions. Key advantages are:
• Ability to reach a velocity greater than 100 km/sec with spare capacity for rendezvous operations around objects outside the solar
system including options for sample return.
• Simple design based on known physics and well-known materials
• Scalable to smaller payloads (sensors) or to larger missions (e.g., telescopes)
• Novel ability to reach deep space (> 150 AU) very quickly and then continue aggressive maneuvers (> 100 km/sec) for dim object search/rendezvous and/or retargeting telescopes at the solar gravitational focus over a period of years.
2024 Phase I Selection
Keep Exploring Discover More NIAC Topics
Space Technology Mission Directorate
NASA Innovative Advanced Concepts
NIAC Funded Studies
View the full article
Check out these Videos