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By NASA
This artist’s concept shows interstellar object 1I/2017 U1 (‘Oumuamua) after its discovery in 2017. While itself not a dark comet, ‘Oumuamua’s motion through the solar system has helped researchers better understand the nature of the 14 dark comets discovered so far.European Southern Observatory / M. Kornmesser These celestial objects look like asteroids but act like comets now come in two flavors.
The first dark comet — a celestial object that looks like an asteroid but moves through space like a comet — was reported less than two years ago. Soon after, another six were found. In a new paper, researchers announce the discovery of seven more, doubling the number of known dark comets, and find that they fall into two distinct populations: larger ones that reside in the outer solar system and smaller ones in the inner solar system, with various other traits that set them apart.
The findings were published on Monday, Dec. 9, in the Proceedings of the National Academy of Sciences.
Scientists got their first inkling that dark comets exist when they noted in a March 2016 study that the trajectory of “asteroid” 2003 RM had moved ever so slightly from its expected orbit. That deviation couldn’t be explained by the typical accelerations of asteroids, like the small acceleration known as the Yarkovsky effect.
“When you see that kind of perturbation on a celestial object, it usually means it’s a comet, with volatile material outgassing from its surface giving it a little thrust,” said study coauthor Davide Farnocchia of NASA’s Jet Propulsion Laboratory in Southern California. “But try as we might, we couldn’t find any signs of a comet’s tail. It looked like any other asteroid — just a pinpoint of light. So, for a short while, we had this one weird celestial object that we couldn’t fully figure out.”
Weird Celestial Objects
Farnocchia and the astronomical community didn’t have to wait long for another piece of the puzzle. The next year, in 2017, a NASA-sponsored telescope discovered history’s first documented celestial object that originated outside our solar system. Not only did 1I/2017 U1 (‘Oumuamua) appear as a single point of light, like an asteroid, its trajectory changed as if it were outgassing volatile material from its surface, like a comet.
“‘Oumuamua was surprising in several ways,” said Farnocchia. “The fact that the first object we discovered from interstellar space exhibited similar behaviors to 2003 RM made 2003 RM even more intriguing.”
By 2023, researchers had identified seven solar system objects that looked like asteroids but acted like comets. That was enough for the astronomical community to bestow upon them their own celestial object category: “dark comets.” Now, with the finding of seven more of these objects, researchers could start on a new set of questions.
“We had a big enough number of dark comets that we could begin asking if there was anything that would differentiate them,” said Darryl Seligman, a postdoctoral fellow in the department of Physics at Michigan State University, East Lansing, and lead author of the new paper. “By analyzing the reflectivity,” or albedo, “and the orbits, we found that our solar system contains two different types of dark comets.”
Two Kinds of Dark Comets
The study’s authors found that one kind, which they call outer dark comets, have similar characteristics to Jupiter-family comets: They have highly eccentric (or elliptical) orbits and are on the larger side (hundreds of meters or more across).
The second group, inner dark comets, reside in the inner solar system (which includes Mercury, Venus, Earth, and Mars), travel in nearly circular orbits, and are on the smaller side (tens of meters or less).
Like so many astronomical discoveries, Seligman and Farnocchia’s research not only expands on our knowledge of dark comets, but it also raises several additional questions: Where did dark comets originate? What causes their anomalous acceleration? Could they contain ice?
“Dark comets are a new potential source for having delivered the materials to Earth that were necessary for the development of life,” said Seligman. “The more we can learn about them, the better we can understand their role in our planet’s origin.”
For more information about asteroids and comets, visit:
https://www.jpl.nasa.gov/topics/asteroids/
Small Body Research at JPL NASA Learns More About Interstellar Visitor 'Oumuamua Lesson: Comet on a Stick News Media Contacts
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Last Updated Dec 09, 2024 Related Terms
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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
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Lane Figueroa
NASA’s Marshall Space Flight Center
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Last Updated Dec 06, 2024 Related Terms
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By NASA
Through the Artemis campaign, NASA will land the next American astronauts and first international astronaut on the South Pole region of the Moon. On Thursday, NASA announced the latest updates to its lunar exploration plans.
Experts discussed results of NASA’s investigation into its Orion spacecraft heat shield after it experienced an unexpected loss of charred material during re-entry of the Artemis I uncrewed test flight. For the Artemis II crewed test flight, engineers will continue to prepare Orion with the heat shield already attached to the capsule. The agency also announced it is now targeting April 2026 for Artemis II and mid-2027 for Artemis III. The updated mission timelines also reflect time to address the Orion environmental control and life support systems.
“The Artemis campaign is the most daring, technically challenging, collaborative, international endeavor humanity has ever set out to do,” said NASA Administrator Bill Nelson. “We have made significant progress on the Artemis campaign over the past four years, and I’m proud of the work our teams have done to prepare us for this next step forward in exploration as we look to learn more about Orion’s life support systems to sustain crew operations during Artemis II. We need to get this next test flight right. That’s how the Artemis campaign succeeds.”
The agency’s decision comes after an extensive investigation of an Artemis I heat shield issue showed the Artemis II heat shield can keep the crew safe during the planned mission with changes to Orion’s trajectory as it enters Earth’s atmosphere and slows from nearly 25,000 mph to about 325 mph before its parachutes unfurl for safe splashdown in the Pacific Ocean.
“Throughout our process to investigate the heat shield phenomenon and determine a forward path, we’ve stayed true to NASA’s core values; safety and data-driven analysis remained at the forefront,” said Catherine Koerner, associate administrator, Exploration Systems Development Mission Directorate at NASA Headquarters in Washington. “The updates to our mission plans are a positive step toward ensuring we can safely accomplish our objectives at the Moon and develop the technologies and capabilities needed for crewed Mars missions.”
NASA will continue stacking its SLS (Space Launch System) rocket elements, which began in November, and prepare it for integration with Orion for Artemis II.
Throughout the fall months, NASA, along with an independent review team, established the technical cause of an issue seen after the uncrewed Artemis I test flight in which charred material on the heat shield wore away differently than expected. Extensive analysis, including from more than 100 tests at unique facilities across the country, determined the heat shield on Artemis I did not allow for enough of the gases generated inside a material called Avcoat to escape, which caused some of the material to crack and break off. Avcoat is designed to wear away as it heats up and is a key material in the thermal protection system that guards Orion and its crew from the nearly 5,000 degrees Fahrenheit of temperatures that are generated when Orion returns from the Moon through Earth’s atmosphere. Although a crew was not inside Orion during Artemis I, data shows the temperature inside Orion remained comfortable and safe had crew been aboard.
Engineers already are assembling and integrating the Orion spacecraft for Artemis III based on lessons learned from Artemis I and implementing enhancements to how heat shields for crewed returns from lunar landing missions are manufactured to achieve uniformity and consistent permeability. The skip entry is needed for return from speeds expected for lunar landing missions.
“Victor, Christina, Jeremy, and I have been following every aspect of this decision and we are thankful for the openness of NASA to weigh all options and make decisions in the best interest of human spaceflight. We are excited to fly Artemis II and continue paving the way for sustained human exploration of the Moon and Mars,” said Reid Wiseman, NASA astronaut and Artemis II commander. “We were at the agency’s Kennedy Space Center in Florida recently and put eyes on our SLS rocket boosters, the core stage, and the Orion spacecraft. It is inspiring to see the scale of this effort, to meet the people working on this machine, and we can’t wait to fly it to the Moon.”
Wiseman, along with NASA astronauts Victor Glover and Christina Koch and CSA (Canadian Space Agency) astronaut Jeremy Hansen, will fly aboard the 10-day Artemis II test flight around the Moon and back. The flight will provide valuable data about Orion systems needed to support crew on their journey to deep space and bring them safely home, including air revitalization in the cabin, manual flying capabilities, and how humans interact with other hardware and software in the spacecraft.
With Artemis, NASA will explore more of the Moon than ever before, learn how to live and work farther away from home, and prepare for future human exploration of the Red Planet. NASA’s SLS, exploration ground systems, and Orion spacecraft, along with the human landing system, next-generation spacesuits, Gateway lunar space station, and future rovers are NASA’s foundation for deep space exploration.
For more information about Artemis, visit:
https://www.nasa.gov/artemis
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By NASA
4 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
Coastal locations, such as Drakes Bay on the Point Reyes peninsula in Northern California, are increasingly vulnerable to sea level rise.NOAA/NMFS/WCR/CCO The information will help people who live in coastal areas prepare for impacts caused by rising sea levels.
Earth’s ocean is rising, disrupting livelihoods and infrastructure in coastal communities around the world. Agencies and organizations are working to prepare people as their world changes around them, and NASA information is helping these efforts.
The agency’s global data is now available in the sea level section of the Earth Information Center. NASA developed the global sea level change website in collaboration with the U.S. Department of Defense, the World Bank, the U.S. Department of State, and the United Nations Development Programme.
The site includes information on projected sea level rise through the year 2150 for coastlines around the world, as well as estimates of how much flooding a coastal community or region can expect to see in the next 30 years. The projections come from data collected by NASA and its partners and from computer models of ice sheets and the ocean, as well as the latest sea level assessment from the Intergovernmental Panel on Climate Change, and other sources.
“NASA innovates for the benefit of humanity. Our cutting-edge instruments and data-driven information tools help communities and organizations respond to natural hazards and extreme weather, and inform critical coastal infrastructure planning decisions,” said Karen St. Germain, director of the Earth science division at NASA Headquarters in Washington.
Information to Action
International organizations such as the World Bank will use the data from the global sea level change site for tasks including the creation of Climate Risk Profiles for countries especially vulnerable to sea level rise.
The Defense Department will continue to incorporate sea level rise data into its plans to anticipate and respond to hazards posed to its facilities by the effects of rising oceans. Similarly, the State Department uses the information for activities ranging from disaster preparedness to long-term adaptation planning to supporting partners around the world in related efforts.
“We are at a moment of truth in our fight against the climate crisis. The science is unequivocal and must serve as the bedrock upon which decision-making is built. With many communities around the world already facing severe impacts from sea-level rise, this new resource provides a vital tool to help them protect lives and livelihoods. It also illustrates what is at stake between a 1.5-degree-Celsius world and a current-policies trajectory for all coastal communities worldwide,” said Assistant Secretary-General Selwin Hart, special adviser to the United Nations secretary-general on climate action and just transition.
Rising Faster
NASA-led data analyses have revealed that between 1970 and 2023, 96% of countries with coastlines have experienced sea level rise. The rate of that global rise has also accelerated, more than doubling from 0.08 inches (0.21 centimeters) per year in 1993 to about 0.18 inches (0.45 centimeters) per year in 2023.
As the rate of sea level rise increases, millions of people could face the related effects sooner than previously projected, including larger storm surges, more saltwater intrusion into groundwater, and additional high-tide flood days — also known as nuisance floods or sunny day floods.
“This new platform shows the timing of future floods and the magnitude of rising waters in all coastal countries worldwide, connecting science and physics to impacts on people’s livelihoods and safety,” said Nadya Vinogradova Shiffer, director of the ocean physics program at NASA Headquarters in Washington.
Data released earlier this year found that Pacific Island nations will experience at least 6 inches (15 centimeters) of sea level rise in the next 30 years. The number of high-tide flood days will increase by an order of magnitude for nearly all Pacific Island nations by the 2050s.
“The data is clear: Sea levels are rising around the world, and they’re rising faster and faster,” said Ben Hamlington, a sea level researcher at NASA’s Jet Propulsion Laboratory in Southern California and head of the agency’s sea level change science team. “Having the best information to make decisions about how to plan for rising seas is more crucial than ever.”
To explore the global sea level change site:
https://earth.gov/sealevel
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Last Updated Nov 13, 2024 Related Terms
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Preparations for Next Moonwalk Simulations Underway (and Underwater)
The Permafrost Tunnel north of Fairbanks, Alaska, was dug in the 1960s and is run by the U.S. Army’s Cold Regions Research and Engineering Laboratory. It is the site of much research into permafrost — ground that stays frozen throughout the year, for multiple years.NASA/Kate Ramsayer Earth’s far northern reaches have locked carbon underground for millennia. New research paints a picture of a landscape in change.
A new study, co-authored by NASA scientists, details where and how greenhouse gases are escaping from the Earth’s vast northern permafrost region as the Arctic warms. The frozen soils encircling the Arctic from Alaska to Canada to Siberia store twice as much carbon as currently resides in the atmosphere — hundreds of billions of tons — and most of it has been buried for centuries.
An international team, led by researchers at Stockholm University, found that from 2000 to 2020, carbon dioxide uptake by the land was largely offset by emissions from it. Overall, they concluded that the region has been a net contributor to global warming in recent decades in large part because of another greenhouse gas, methane, that is shorter-lived but traps significantly more heat per molecule than carbon dioxide.
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Greenhouse gases shroud the globe in this animation showing data from 2021. Carbon dioxide is shown in orange; methane is shown in purple. Methane traps heat 28 times more effectively than carbon dioxide over a 100-year timescale. Wetlands are a significant source of such emissions.NASA’s Scientific Visualization Studio The findings reveal a landscape in flux, said Abhishek Chatterjee, a co-author and scientist at NASA’s Jet Propulsion Laboratory in Southern California. “We know that the permafrost region has captured and stored carbon for tens of thousands of years,” he said. “But what we are finding now is that climate-driven changes are tipping the balance toward permafrost being a net source of greenhouse gas emissions.”
Carbon Stockpile
Permafrost is ground that has been permanently frozen for anywhere from two years to hundreds of thousands of years. A core of it reveals thick layers of icy soils enriched with dead plant and animal matter that can be dated using radiocarbon and other techniques. When permafrost thaws and decomposes, microbes feed on this organic carbon, releasing some of it as greenhouse gases.
Unlocking a fraction of the carbon stored in permafrost could further fuel climate change. Temperatures in the Arctic are already warming two to four times faster than the global average, and scientists are learning how thawing permafrost is shifting the region from being a net sink for greenhouse gases to becoming a net source of warming.
They’ve tracked emissions using ground-based instruments, aircraft, and satellites. One such campaign, NASA’s Arctic-Boreal Vulnerability Experiment (ABoVE), is focused on Alaska and western Canada. Yet locating and measuring emissions across the far northern fringes of Earth remains challenging. One obstacle is the vast scale and diversity of the environment, composed of evergreen forests, sprawling tundra, and waterways.
This map, based on data provided by the National Snow and Ice Data Center, shows the extent of Arctic permafrost. The amount of permafrost underlying the surface ranges from continuous — in the coldest areas — to more isolated and sporadic patches.NASA Earth Observatory Cracks in the Sink
The new study was undertaken as part of the Global Carbon Project’s RECCAP-2 effort, which brings together different science teams, tools, and datasets to assess regional carbon balances every few years. The authors followed the trail of three greenhouse gases — carbon dioxide, methane, and nitrous oxide — across 7 million square miles (18 million square kilometers) of permafrost terrain from 2000 to 2020.
Researchers found the region, especially the forests, took up a fraction more carbon dioxide than it released. This uptake was largely offset by carbon dioxide emitted from lakes and rivers, as well as from fires that burned both forest and tundra.
They also found that the region’s lakes and wetlands were strong sources of methane during those two decades. Their waterlogged soils are low in oxygen while containing large volumes of dead vegetation and animal matter — ripe conditions for hungry microbes. Compared to carbon dioxide, methane can drive significant climate warming in short timescales before breaking down relatively quickly. Methane’s lifespan in the atmosphere is about 10 years, whereas carbon dioxide can last hundreds of years.
The findings suggest the net change in greenhouse gases helped warm the planet over the 20-year period. But over a 100-year period, emissions and absorptions would mostly cancel each other out. In other words, the region teeters from carbon source to weak sink. The authors noted that events such as extreme wildfires and heat waves are major sources of uncertainty when projecting into the future.
Bottom Up, Top Down
The scientists used two main strategies to tally greenhouse gas emissions from the region. “Bottom-up” methods estimate emissions from ground- and air-based measurements and ecosystem models. Top-down methods use atmospheric measurements taken directly from satellite sensors, including those on NASA’s Orbiting Carbon Observatory-2 (OCO-2) and JAXA’s (Japan Aerospace Exploration Agency)Greenhouse Gases Observing Satellite.
Regarding near-term, 20-year, global warming potential, both scientific approaches aligned on the big picture but differed in magnitude: The bottom-up calculations indicated significantly more warming.
“This study is one of the first where we are able to integrate different methods and datasets to put together this very comprehensive greenhouse gas budget into one report,” Chatterjee said. “It reveals a very complex picture.”
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Written by Sally Younger
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Last Updated Oct 29, 2024 Related Terms
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