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Sunken ruins of a 11,000-year-old megastructure found in the Baltic Sea
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By European Space Agency
Video: 00:15:30 Meet Arnaud Prost—aerospace engineer, professional diver, and member of ESA’s Astronaut Reserve. From flying aircraft to getting a taste of spacewalk simulation, his passion for exploration knows no bounds.
In this miniseries, we take you on a journey through the ESA Astronaut Reserve, diving into the first part of their Astronaut Reserve Training (ART) at the European Astronaut Centre (EAC) near Cologne, Germany. Our “ARTists” are immersing themselves in everything from ESA and the International Space Station programme to the European space industry and institutions. They’re gaining hands-on experience in technical skills like spacecraft systems and robotics, alongside human behaviour, scientific lessons, scuba diving, and survival training.
ESA’s Astronaut Reserve Training programme is all about building Europe’s next generation of space explorers—preparing them for the opportunities of future missions in Earth orbit and beyond.
This interview was recorded in November 2024.
You can listen to this episode on all major podcast platforms.
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Learn more about Arnaud’s PANGAEA training here.
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By NASA
3 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
Ice cover ebbs and flows through the seasons in the Arctic (left) and the Antarctic (right). Overall, ice cover has declined since scientists started tracking it half a century ago. Download this visualization from NASA’s Scientific Visualization Studio: https://svs.gsfc.nasa.gov/5099Trent Schindler/NASA’s Scientific Visualization Studio Winter sea ice cover in the Arctic was the lowest it’s ever been at its annual peak on March 22, 2025, according to NASA and the National Snow and Ice Data Center (NSIDC) at the University of Colorado, Boulder. At 5.53 million square miles (14.33 million square kilometers), the maximum extent fell below the prior low of 5.56 million square miles (14.41 million square kilometers) in 2017.
In the dark and cold of winter, sea ice forms and spreads across Arctic seas. But in recent years, less new ice has been forming, and less multi-year ice has accumulated. This winter continued a downward trend scientists have observed over the past several decades. This year’s peak ice cover was 510,000 square miles (1.32 million square kilometers) below the average levels between 1981 and 2010.
In 2025, summer ice in the Antarctic retreated to 764,000 square miles (1.98 million square kilometers) on March 1, tying for the second lowest minimum extent ever recorded. That’s 30% below the 1.10 million square miles (2.84 million square kilometers) that was typical in the Antarctic prior to 2010. Sea ice extent is defined as the total area of the ocean with at least 15% ice concentration.
The reduction in ice in both polar regions has led to another milestone — the total amount of sea ice on the planet reached an all-time low. Globally, ice coverage in mid-February of this year declined by more than a million square miles (2.5 million square kilometers) from the average before 2010. Altogether, Earth is missing an area of sea ice large enough to cover the entire continental United States east of the Mississippi.
“We’re going to come into this next summer season with less ice to begin with,” said Linette Boisvert, an ice scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “It doesn’t bode well for the future.”
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Observations since 1978 show that ice cover has declined at both poles, leading to a downward trend in the total ice cover over the entire planet. In February 2025, global ice fell to the smallest area ever recorded. Download this visualization from NASA's Scientific Visualization Studio: https://svs.gsfc.nasa.gov/5521Mark Subbaro/NASA's Scientific Visualization Studio Scientists primarily rely on satellites in the Defense Meteorological Satellite Program, which measure Earth’s radiation in the microwave range. This natural radiation is different for open water and for sea ice — with ice cover standing out brightly in microwave-based satellite images. Microwave scanners can also penetrate through cloud cover, allowing for daily global observations. The DMSP data are augmented with historical sources, including data collected between 1978 and 1985 with the Nimbus-7 satellite that was jointly operated by NASA and the National Oceanic and Atmospheric Administration.
“It’s not yet clear whether the Southern Hemisphere has entered a new norm with perennially low ice or if the Antarctic is in a passing phase that will revert to prior levels in the years to come,” said Walt Meier, an ice scientist with NSIDC.
By James Riordon
NASA’s Earth Science News Team
Media contact: Elizabeth Vlock
NASA Headquarters
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Last Updated Mar 27, 2025 LocationNASA Goddard Space Flight Center Related Terms
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1 min read Arctic Sea Ice Near Historic Low; Antarctic Ice Continues Decline
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By NASA
X-ray: NASA/CXC/Technion/N. Keshet et al.; Illustration: NASA/CXC/SAO/M. Weiss People often think about archaeology happening deep in jungles or inside ancient pyramids. However, a team of astronomers has shown that they can use stars and the remains they leave behind to conduct a special kind of archaeology in space.
Mining data from NASA’s Chandra X-ray Observatory, the team of astronomers studied the relics that one star left behind after it exploded. This “supernova archaeology” uncovered important clues about a star that self-destructed – probably more than a million years ago.
Today, the system called GRO J1655-40 contains a black hole with nearly seven times the mass of the Sun and a star with about half as much mass. However, this was not always the case.
Originally GRO J1655-40 had two shining stars. The more massive of the two stars, however, burned through all of its nuclear fuel and then exploded in what astronomers call a supernova. The debris from the destroyed star then rained onto the companion star in orbit around it, as shown in the artist’s concept.
This artist’s impression shows the effects of the collapse and supernova explosion of a massive star. A black hole (right) was formed in the collapse and debris from the supernova explosion is raining down onto a companion star (left), polluting its atmosphere.CXC/SAO/M. Weiss With its outer layers expelled, including some striking its neighbor, the rest of the exploded star collapsed onto itself and formed the black hole that exists today. The separation between the black hole and its companion would have shrunk over time because of energy being lost from the system, mainly through the production of gravitational waves. When the separation became small enough, the black hole, with its strong gravitational pull, began pulling matter from its companion, wrenching back some of the material its exploded parent star originally deposited.
While most of this material sank into the black hole, a small amount of it fell into a disk that orbits around the black hole. Through the effects of powerful magnetic fields and friction in the disk, material is being sent out into interstellar space in the form of powerful winds.
This is where the X-ray archaeological hunt enters the story. Astronomers used Chandra to observe the GRO J1655-40 system in 2005 when it was particularly bright in X-rays. Chandra detected signatures of individual elements found in the black hole’s winds by getting detailed spectra – giving X-ray brightness at different wavelengths – embedded in the X-ray light. Some of these elements are highlighted in the spectrum shown in the inset.
The team of astronomers digging through the Chandra data were able to reconstruct key physical characteristics of the star that exploded from the clues imprinted in the X-ray light by comparing the spectra with computer models of stars that explode as supernovae. They discovered that, based on the amounts of 18 different elements in the wind, the long-gone star destroyed in the supernova was about 25 times the mass of the Sun, and was much richer in elements heavier than helium in comparison with the Sun.
This analysis paves the way for more supernova archaeology studies using other outbursts of double star systems.
A paper describing these results titled “Supernova Archaeology with X-Ray Binary Winds: The Case of GRO J1655−40” was published in The Astrophysical Journal in May 2024. The authors of this study are Noa Keshet (Technion — Israel Institute of Technology), Ehud Behar (Technion), and Timothy Kallman (NASA’s Goddard Space Flight Center).
NASA’s Marshall Space Flight Center in Huntsville, Alabama, manages the Chandra program. The Smithsonian Astrophysical Observatory’s Chandra X-ray Center controls science operations from Cambridge, Massachusetts, and flight operations from Burlington, Massachusetts.
Read more from NASA’s Chandra X-ray Observatory.
Learn more about the Chandra X-ray Observatory and its mission here:
https://www.nasa.gov/chandra
https://chandra.si.edu
Visual Description
This release features an artist’s rendering of a supernova explosion, inset with a spectrum graph.
The artist’s illustration features a star and a black hole in a system called GRO J1655-40. Here, the black hole is represented by a black sphere to our upper right of center. The star is represented by a bright yellow sphere to our lower left of center. In this illustration, the artist captures the immensely powerful supernova as a black hole is created from the collapse of a massive star, with an intense burst of blurred beams radiating from the black sphere. The blurred beams of red, orange, and yellow light show debris from the supernova streaking across the entire image in rippling waves. These beams rain debris on the bright yellow star.
When astronomers used the Chandra X-ray Observatory to observe the system in 2005, they detected signatures of individual elements embedded in the X-ray light. Some of those elements are highlighted in the spectrum graph shown in the inset, positioned at our upper lefthand corner.
The graph’s vertical axis, on our left, indicates X-ray brightness from 0.0 up to 0.7 in intensity units. The horizontal axis, at the bottom of the graph, indicates Wavelength from 6 to 12 in units of Angstroms. On the graph, a tight zigzagging line begins near the top of the vertical axis, and slopes down toward the far end of the horizontal axis. The sharp dips show wavelengths where the light has been absorbed by different elements, decreasing the X-ray brightness. Some of the elements causing these dips have been labeled, including Silicon, Magnesium, Iron, Nickel, Neon, and Cobalt.
News Media Contact
Megan Watzke
Chandra X-ray Center
Cambridge, Mass.
617-496-7998
mwatzke@cfa.harvard.edu
Lane Figueroa
Marshall Space Flight Center, Huntsville, Alabama
256-544-0034
lane.e.figueroa@nasa.gov
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By NASA
Researchers analyzing pulverized rock onboard NASA’s Curiosity rover have found the largest organic compounds on the Red Planet to date. The finding, published Monday in the Proceedings of the National Academy of Sciences, suggests prebiotic chemistry may have advanced further on Mars than previously observed.
Scientists probed an existing rock sample inside Curiosity’s Sample Analysis at Mars (SAM) mini-lab and found the molecules decane, undecane, and dodecane. These compounds, which are made up of 10, 11, and 12 carbons, respectively, are thought to be the fragments of fatty acids that were preserved in the sample. Fatty acids are among the organic molecules that on Earth are chemical building blocks of life.
Living things produce fatty acids to help form cell membranes and perform various other functions. But fatty acids also can be made without life, through chemical reactions triggered by various geological processes, including the interaction of water with minerals in hydrothermal vents.
While there’s no way to confirm the source of the molecules identified, finding them at all is exciting for Curiosity’s science team for a couple of reasons.
Curiosity scientists had previously discovered small, simple organic molecules on Mars, but finding these larger compounds provides the first evidence that organic chemistry advanced toward the kind of complexity required for an origin of life on Mars.
This graphic shows the long-chain organic molecules decane, undecane, and dodecane. These are the largest organic molecules discovered on Mars to date. They were detected in a drilled rock sample called “Cumberland” that was analyzed by the Sample Analysis at Mars lab inside the belly of NASA’s Curiosity rover. The rover, whose selfie is on the right side of the image, has been exploring Gale Crater since 2012. An image of the Cumberland drill hole is faintly visible in the background of the molecule chains. NASA/Dan Gallagher The new study also increases the chances that large organic molecules that can be made only in the presence of life, known as “biosignatures,” could be preserved on Mars, allaying concerns that such compounds get destroyed after tens of millions of years of exposure to intense radiation and oxidation.
This finding bodes well for plans to bring samples from Mars to Earth to analyze them with the most sophisticated instruments available here, the scientists say.
“Our study proves that, even today, by analyzing Mars samples we could detect chemical signatures of past life, if it ever existed on Mars,” said Caroline Freissinet, the lead study author and research scientist at the French National Centre for Scientific Research in the Laboratory for Atmospheres and Space Observations in Guyancourt, France
In 2015, Freissinet co-led a team that, in a first, conclusively identified Martian organic molecules in the same sample that was used for the current study. Nicknamed “Cumberland,” the sample has been analyzed many times with SAM using different techniques.
NASA’s Curiosity rover drilled into this rock target, “Cumberland,” during the 279th Martian day, or sol, of the rover’s work on Mars (May 19, 2013) and collected a powdered sample of material from the rock’s interior. Curiosity used the Mars Hand Lens Imager camera on the rover’s arm to capture this view of the hole in Cumberland on the same sol as the hole was drilled. The diameter of the hole is about 0.6 inches. The depth of the hole is about 2.6 inches. NASA/JPL-Caltech/MSSS Curiosity drilled the Cumberland sample in May 2013 from an area in Mars’ Gale Crater called “Yellowknife Bay.” Scientists were so intrigued by Yellowknife Bay, which looked like an ancient lakebed, they sent the rover there before heading in the opposite direction to its primary destination of Mount Sharp, which rises from the floor of the crater.
The detour was worth it: Cumberland turns out to be jam-packed with tantalizing chemical clues to Gale Crater’s 3.7-billion-year past. Scientists have previously found the sample to be rich in clay minerals, which form in water. It has abundant sulfur, which can help preserve organic molecules. Cumberland also has lots of nitrates, which on Earth are essential to the health of plants and animals, and methane made with a type of carbon that on Earth is associated with biological processes.
Perhaps most important, scientists determined that Yellowknife Bay was indeed the site of an ancient lake, providing an environment that could concentrate organic molecules and preserve them in fine-grained sedimentary rock called mudstone.
“There is evidence that liquid water existed in Gale Crater for millions of years and probably much longer, which means there was enough time for life-forming chemistry to happen in these crater-lake environments on Mars,” said Daniel Glavin, senior scientist for sample return at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and a study co-author.
The recent organic compounds discovery was a side effect of an unrelated experiment to probe Cumberland for signs of amino acids, which are the building blocks of proteins. After heating the sample twice in SAM’s oven and then measuring the mass of the molecules released, the team saw no evidence of amino acids. But they noticed that the sample released small amounts of decane, undecane, and dodecane.
Because these compounds could have broken off from larger molecules during heating, scientists worked backward to figure out what structures they may have come from. They hypothesized these molecules were remnants of the fatty acids undecanoic acid, dodecanoic acid, and tridecanoic acid, respectively.
The scientists tested their prediction in the lab, mixing undecanoic acid into a Mars-like clay and conducting a SAM-like experiment. After being heated, the undecanoic acid released decane, as predicted. The researchers then referenced experiments already published by other scientists to show that the undecane could have broken off from dodecanoic acid and dodecane from tridecanoic acid.
The authors found an additional intriguing detail in their study related to the number of carbon atoms that make up the presumed fatty acids in the sample. The backbone of each fatty acid is a long, straight chain of 11 to 13 carbons, depending on the molecule. Notably, non-biological processes typically make shorter fatty acids, with less than 12 carbons.
It’s possible that the Cumberland sample has longer-chain fatty acids, the scientists say, but SAM is not optimized to detect longer chains.
Scientists say that, ultimately, there’s a limit to how much they can infer from molecule-hunting instruments that can be sent to Mars. “We are ready to take the next big step and bring Mars samples home to our labs to settle the debate about life on Mars,” said Glavin.
This research was funded by NASA’s Mars Exploration Program. Curiosity’s Mars Science Laboratory mission is led by NASA’s Jet Propulsion Laboratory in Southern California; JPL is managed by Caltech for NASA. SAM (Sample Analysis at Mars) was built and tested at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. CNES (the French Space Agency) funded and provided the gas chromatograph subsystem on SAM. Charles Malespin is SAM’s principal investigator.
By Lonnie Shekhtman
NASA’s Goddard Space Flight Center, Greenbelt, Md.
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By NASA
3 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
Communities in coastal areas such as Florida, shown in this 1992 NASA image, are vulnerable to the effects of sea level rise, including high-tide flooding. A new agency-led analysis found a higher-than-expected rate of sea level rise in 2024, which was also the hottest year on record.NASA Last year’s increase was due to an unusual amount of ocean warming, combined with meltwater from land-based ice such as glaciers.
Global sea level rose faster than expected in 2024, mostly because of ocean water expanding as it warms, or thermal expansion. According to a NASA-led analysis, last year’s rate of rise was 0.23 inches (0.59 centimeters) per year, compared to the expected rate of 0.17 inches (0.43 centimeters) per year.
“The rise we saw in 2024 was higher than we expected,” said Josh Willis, a sea level researcher at NASA’s Jet Propulsion Laboratory in Southern California. “Every year is a little bit different, but what’s clear is that the ocean continues to rise, and the rate of rise is getting faster and faster.”
This graph shows global mean sea level (in blue) since 1993 as measured by a series of five satellites. The solid red line indicates the trajectory of this increase, which has more than doubled over the past three decades. The dotted red line projects future sea level rise.NASA/JPL-Caltech In recent years, about two-thirds of sea level rise was from the addition of water from land into the ocean by melting ice sheets and glaciers. About a third came from thermal expansion of seawater. But in 2024, those contributions flipped, with two-thirds of sea level rise coming from thermal expansion.
“With 2024 as the warmest year on record, Earth’s expanding oceans are following suit, reaching their highest levels in three decades,” said Nadya Vinogradova Shiffer, head of physical oceanography programs and the Integrated Earth System Observatory at NASA Headquarters in Washington.
Since the satellite record of ocean height began in 1993, the rate of annual sea level rise has more than doubled. In total, global sea level has gone up by 4 inches (10 centimeters) since 1993.
This long-term record is made possible by an uninterrupted series of ocean-observing satellites starting with TOPEX/Poseidon in 1992. The current ocean-observing satellite in that series, Sentinel-6 Michael Freilich, launched in 2020 and is one of an identical pair of spacecraft that will carry this sea level dataset into its fourth decade. Its twin, the upcoming Sentinel-6B satellite, will continue to measure sea surface height down to a few centimeters for about 90% of the world’s oceans.
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This animation shows the rise in global mean sea level from 1993 to 2024 based on da-ta from five international satellites. The expansion of water as it warms was responsible for the majority of the higher-than-expected rate of rise in 2024.NASA’s Scientific Visualization Studio Mixing It Up
There are several ways in which heat makes its way into the ocean, resulting in the thermal expansion of water. Normally, seawater arranges itself into layers determined by water temperature and density. Warmer water floats on top of and is lighter than cooler water, which is denser. In most places, heat from the surface moves very slowly through these layers down into the deep ocean.
But extremely windy areas of the ocean can agitate the layers enough to result in vertical mixing. Very large currents, like those found in the Southern Ocean, can tilt ocean layers, allowing surface waters to more easily slip down deep.
The massive movement of water during El Niño — in which a large pool of warm water normally located in the western Pacific Ocean sloshes over to the central and eastern Pacific — can also result in vertical movement of heat within the ocean.
Learn more about sea level:
https://sealevel.nasa.gov
News Media Contacts
Jane J. Lee / Andrew Wang
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-0307 / 626-379-6874
jane.j.lee@jpl.nasa.gov / andrew.wang@jpl.nasa.gov
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Last Updated Mar 13, 2025 Related Terms
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