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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
Ian J. O’Neill
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Earth (ESD) Earth Home Explore Climate Change Science in Action Multimedia Data For Researchers 14 Min Read NASA’s Brad Doorn Brings Farm Belt Wisdom to Space-Age Agriculture
This image shows corn cultivation patterns across the U.S. Midwest in 2020, with lands planted in corn marked in yellow. Credits:
NASA Earth Observatory/ Lauren Dauphin Bradley Doorn grew up in his family’s trucking business, which hauled milk and animal feed across the sprawling plains of South Dakota. Home was Mitchell, a small town famous for its Corn Palace, where murals crafted from corn kernels and husks have adorned its facade since 1892—a tribute to the abundance of the surrounding farmland.
Trucking was often grueling work for the family, the day breaking early and ending in headlights. Like farming, driving a truck wasn’t just a job; it was the engine of daily life, thrumming through nearly every conversation and decision.
Brad loved the outdoors, and by the time he started college in the early 1980s, studying geological engineering felt like a natural fit. “I wanted to be out in the field somewhere, working under the big skies of the West,” Brad recalled. But in his sophomore year at the South Dakota School of Mines and Technology, the tuition money dried up.
Dean Doorn, Brad Doorn’s father, stands beside a milk truck used in the family’s business of hauling milk across South Dakota in the 1960s and ’70s. Credit: B. Doorn Doorn found himself at a crossroads familiar to many in rural America: return to the certainty of a family trade or chart a new route. “That’s when the Army stepped in,” he said. The ROTC program offered a way to continue with school and a path into the world of remote sensing—a field that would come to define his career.
Brad’s choice to join the Army would eventually place him at the forefront of a mapping revolution, equipping him to see and analyze Earth in ways never possible before the advent of satellites. But more than the technical skills, the military showed him the allure of a life anchored to mission and team.
Even as his career took him far from Mitchell, Doorn would remain connected to his rural America roots. Today, he leads NASA’s agriculture programs within the agency’s Earth Science Division. “My family wasn’t made up of farmers, but farming was a part of everything growing up,” said Brad. “Even now, working with NASA, that connection to the land—the sense of how weather, crops, and people are tied together—it’s still in everything I do.”
Amid the dazzle of NASA’s feats exploring the solar system and universe, it’s easy to miss the agency’s quiet work in fields of soy and wheat. But for more than 60 years, the agency has harnessed the power of its satellites to deliver crucial data on temperature, precipitation, crop yields, and more to farmers, policymakers, and food security experts worldwide.
The Landsat 9 satellite captured this false-color image of Louisiana rice fields in February 2023. Dark blue shows flooded areas, while green indicates vegetation. Grid-like levees separate fields pre-planting. Louisiana is the third largest producer of rice in the U.S. Credit: NASA Earth Observatory/ Lauren Dauphin From orbit, satellites beam down streams of data—numbers and pixels that, when paired with farmers’ knowledge of the land, can guide growers as they adjust irrigation levels or plan for the next planting. But the satellites don’t just yield data; they tell stories that call for action, enabling nations to brace for droughts, floods, and the prospect of empty grain silos.
“Under Brad’s guidance, NASA’s agriculture program has become a global leader for satellite-driven solutions, tackling food security and sustainability head-on,” said Lawrence Friedl, the senior engagement officer for NASA Earth Science. Reflecting on years of collaboration, he added: “I am so impressed and grateful for what he and his teams have accomplished.”
Boots Meet Satellites in the First Gulf War
Long before Brad began guiding NASA’s agricultural initiatives, he was already navigating tricky terrain, both literal and figurative, with satellite imagery. His career in remote sensing didn’t start with crops, but with the deserts of Iraq and Kuwait.
As part of the Army’s 18th Airborne Corps, Brad led a company at Fort Bragg (now Fort Liberty) in North Carolina that had just returned from operations in the First Gulf War, in the early 1990s. “I loved being part of a unit, part of something bigger than just me,” Brad recalled. “It felt good to have that purpose and mission.”
Far from the combat zone, Doorn’s company became cartographers of the invisible. Their task: merge data from the Landsat satellite with the gritty reality of desert warfare depicted on military maps.
Brad Doorn, then a U.S. Army officer, sits at his desk during his early career in remote sensing. His military experience would later shape his work at NASA, applying satellite technology to real-world challenges. Credit: B. Doorn Landsat, a civilian satellite built by NASA and operated by the U.S. Geological Survey, could see what the soldiers on the ground could not. Its thermal infrared sensor—a camera with a penchant for temperature and moisture—read the desert floor like an ancient script, picking out the cold, soggy signature of mud lurking beneath the desert’s deceptive crust. Each pixel of satellite data became a brushstroke in a new kind of map, keeping tanks out of the mire and the missions on track.
“It was so neat to see the remote sensing techniques I’d learned about in school actually making a difference,” Doorn said.
With this knowledge, he helped guide his unit’s shift from analog maps—paper grids and grease pencils—to the emerging world of digital mapping, a leap that sharpened the military’s ability to read the landscape and steer clear of trouble.
From Desert Muck to Farm Fields
Brad’s military experience gave him an early look at how satellite data could address tangible, on-the-ground challenges. In the Army, he saw how integrating satellite data into military maps could offer soldiers critical information. That experience set the foundation for his later work at NASA, where he would help develop technology with lasting, practical impacts.
Consider OpenET, a NASA-funded initiative that uses Landsat data to give farmers insights into water use and irrigation needs at field scale. The ET in OpenET stands not for the little alien who phoned home, but for evapotranspiration. It’s a combination of water evaporating from the ground and water released by plants into the air.
The program relies on the same thermal technology Doorn used during the Gulf War. Just as cooler, wetter areas in the desert hint at muddy spots, cooler patches in farm fields show where there’s more moisture or plants are releasing more water. These data are key to managing water resources wisely and keeping crops healthy.
“OpenET has transformed our understanding of water demand,” explained Doorn.
To better manage water, state officials and farmers in California are using satellite data through OpenET to track evapotranspiration. Here, the colors represent total evapotranspiration for 2023 as the equivalent depth of water in millimeters. Dark blue regions have higher evapotranspiration rates, such as in the Central Valley. Credit: NASA Earth Observatory using openetdata.org In the late 2000s, when a new generation of Landsat satellites was being planned, the thermal infrared imagers were initially left off the drawing board. “Landsat 8’s design caused a lot of consternation in some Western states that were beginning to use the instrument for measuring and monitoring water use,” said Tony Willardson, the executive director of the Western States Water Council, a government entity that advises western governors on water policy.
Brad played a key role in conveying to NASA the critical need for this technology, both for agriculture and water management, Willardson said. The thermal imager was eventually reinstated and has since “helped to close a gap in western water management.”
“A lot of the technologies that we are using more and more were developed by NASA,” said Willardson. “We need NASA to be doing even more in Earth science.”
Sowing Global Food Stability from Space
Brad ended up serving in the Army for nearly a decade. “You hit that 10-year mark in the military, and you sort of have to decide if you’re staying in for 20 or if you’re getting out,” said Brad. “My wife, Kristen, was able to manage her career as a registered dietician through the first four moves in six years, but eventually it was too much. So, I told her: ‘Your choice. You decide where we go next.’”
She chose southern Pennsylvania to be closer to her family. Brad was 32 years old, and the couple had two small children at the time—one of whom had had open-heart surgery at 6 weeks old to fix a heart defect. They would go on to have another child.
In the late 1990s, within a few years of leaving the military, Doorn found himself someplace he had never imagined: sitting behind a desk at the U.S. Department of Agriculture. For a boy who had grown up driving trucks across the plains of South Dakota—who had vowed never to work in an office, much less live east of the Mississippi—this was an unexpected detour. But he had long since learned that the best paths are often the ones you don’t see coming.
At USDA, he moved forward not with a grand plan, but with an instinctive trust in where curiosity and challenge might lead. He rose through the ranks, from a programmer to directing the agency’s international food production analysis program. He was increasingly driven by a conviction that satellite data, if used the right way, could transform how we see the land and the way we feed the world.
While at USDA, and later at NASA, which he joined in 2009, Brad was instrumental in developing and overseeing the Global Agricultural Monitoring (GLAM) system. This real-time interactive satellite platform delivers massive amounts of ready-to-use satellite data directly to USDA crop analysts, eliminating the burden of data processing and enabling them to focus on rapid crop analysis across the globe. It was a pioneering tool, said Inbal Becker-Reshef, a research professor at University of Maryland’s Department of Geographical Sciences, who played a central role in developing the GLAM system.
At a 2022 Kansas gathering, Brad Doorn presents to farmers about NASA’s Earth Science Division and its activities supporting agriculture. Credit: A. Whitcraft GLAM set the stage for GEOGLAM, a separate, international initiative launched in 2011 by agriculture ministers from the G20—a group of the world’s major economies—partly as a response to global food price volatility. GEOGLAM, which stands for Group on Earth Observations Global Agricultural Monitoring, uses satellite data to monitor global crop conditions, from drought stress to excessive rain, around the world.
Joseph Glauber, a former USDA chief economist, noted that there was initial uncertainty within USDA about the initiative’s longevity, but he credited Brad’s background with rallying support. Today, GEOGLAM’s monthly crop assessments, produced by over 40 organizations including USDA and NASA, serve as a global consensus on crop conditions, helping governments and humanitarian organizations anticipate food shortages.
“Even today, the G20 points to GEOGLAM and its sister initiative, the Agricultural Market Information System—which tracks how crop conditions affect markets—as major successes,” Glauber said.
Harvesting Data Amid Conflict
Doorn’s work crosses continents. When war broke out between Russia and Ukraine in 2022, it rattled global food markets. The Ukrainian government turned to NASA Harvest—a global food security and agriculture consortium led by the University of Maryland and funded by NASA—for help. As manager of NASA’s agriculture program, Brad was a driving force behind the launch of NASA Harvest in 2017, envisioning it as a program that would harness satellite data to provide timely, actionable insights for global agriculture.
From orbit, satellites could observe the sown and the harvested wheat, sunflowers, and barley, offering some of the only reliable estimates for fields in the war zone. Satellite imagery revealed that, despite the conflict, more cropland had been planted and harvested in Ukraine than anyone had expected, a finding that helped stabilize volatile global food prices.
“Brad and the team recognized that providing that type of rapid agricultural assessment for policy support is what NASA Harvest exists for,” said Becker-Reshef, who is the director of the consortium.
NASA Harvest’s reach stretches well beyond Europe. In sub-Saharan Africa, the consortium collaborates with local and international partners, tracking the health of crops and the creeping spread of drought. This information helps equip governments, aid organizations, and farmers to act before disaster strikes, making each data point a crucial defense against hunger.
NASA Harvest has since been joined by NASA Acres, founded in 2023 to provide satellite data and tools that help farmers make well-informed decisions for healthier crops and soil in the United States. One project, for example, involves working with farmers in Illinois to manage nitrogen use more effectively, leveraging satellite data to enhance crop yields while reducing environmental impact.
This image shows corn cultivation patterns across the U.S. Midwest in 2020, with lands planted in corn marked in yellow. The map was built from the Cropland Data Layer product provided by the National Agricultural Statistics Service, which includes data from the USGS National Land Cover Database and from satellites such as Landsat 8. Credit: NASA Earth Observatory/ Lauren Dauphin Friedl noted that Doorn understands the missions of both NASA and the USDA, and with his agricultural roots, he knows the needs of farmers and agricultural businesses firsthand. “Often in meetings, Brad would remind us that the margins for a farmer are in the pennies,” Friedl said. “They wouldn’t be able to afford remote sensing,” so making sure NASA’s satellite information was free and accessible was that much more important.
“It’s hard to imagine that NASA would have the agriculture program it does without somebody like Brad continuing to advocate and push for this to exist,” said Alyssa Whitcraft, the director of NASA Acres. “He knows how critical it is for satellite data to be accessible and useful to those on the ground. He makes sure we never lose sight of that.”
An Emissary Between Worlds
Colleagues say Doorn’s strength lies in his ability to bridge worlds, whether it’s making connections between agencies like NASA and USDA, or connecting such agencies to state water councils or farming communities. His fluency in translating complex science into simple terms makes him equally at ease in whichever world he finds himself.
“There’s NASA language and there’s farm language,” says Lance Lillibridge, who farms about 1,400 acres of corn and soybeans in Benton County, Iowa, and has helped lead the Iowa Corn Growers Association. “Sometimes you need an interpreter, and Brad’s that guy.” He recalled a meeting where some farmers were skeptical, wary of NASA’s “big brother” eyes in the sky, “but Brad had a way of putting people at ease, keeping everyone focused on the shared goal of better data for better decisions.”
Brad Doorn speaks during NASA’s “Space for Ag” roadshow in Iowa, July 2023, highlighting NASA’s role in supporting sustainable farming practices. Credit: N. Pepper “One of my favorite memories of Brad,” said Forrest Melton, the OpenET project scientist at NASA’s Ames Research Center, “is an afternoon spent visiting with farmers in western Nebraska, drinking iced tea and talking with them about the challenges facing their family farm.”
Colleagues describe Brad as a nearly unflappable guide, one who knows the agricultural landscape so well that he makes the impossible seem manageable. They say his calm, approachable style, paired with a ready smile, puts people at ease whether in Washington conference rooms or Midwestern barns. And he listens closely to understand where there may be opportunities to help.
“Few people in the water and agriculture communities, from the small-scale farmer to the federal government appointee, aren’t familiar with some aspect of the work Brad has enabled over the decades,” said Sarah Brennan, a former deputy program manager for NASA’s water resources programs. “He has supported the development of some of the greatest advancements in using remote sensing in these communities.”
It’s About the People and the Team
Doorn’s leadership is less about issuing directives, colleagues say, and more about cultivating growth—in crops, in data systems, and in people. Like a farmer tending to his fields, he nurtures the potential in every project and person he encounters. “Almost everyone who has worked for Brad can point back to the opportunities he provided them that launched their successful careers,” said Brennan.
Over the years, he’s added layers to this work of creating paths for others to succeed: as president of the American Society of Photogrammetry and Remote Sensing, as an adjunct professor at Penn State, and as a youth basketball league director.
“What I’ve learned, probably in the military and I’ve carried it forward, is that it’s the people that matter,” Brad said. “I had great mentors who believed it’s just as important to help others grow as it is to meet the day’s demands. Those roles shift your focus toward the people around you, and often, the more you give of your time, the more you end up getting back.”
Young Brad Doorn (front center) stands with his siblings, capturing a family moment in 1960s South Dakota. His youngest brother isn’t pictured. Credit: B. Doorn It has been a long journey from hauling milk and animal feed across the South Dakota plains to surveying them now as a scientist. The tools of his career have changed—from truck routes to satellite orbits, from paper maps to digital data—but his mission remains the same: helping farmers feed the world.
“Growing up in South Dakota, I saw firsthand the challenges farmers face. Today, I’m proud to help provide the tools and data that can make a real difference in their lives,” Doorn added. “Whether it’s a farmer, an economist, or a military analyst, if you give them the right tools, they’ll take them to places you never even thought about. That’s what excites me—seeing where they go.”
By Emily DeMarco
NASA’s Earth Science Division, Headquarters
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NASA, ESA, R. Kirshner (Harvard-Smithsonian Center for Astrophysics and Gordon and Betty Moore Foundation), and M. Mutchler and R. Avila (STScI) This image, released on Feb. 24, 2017, shows Supernova 1987a (center) surrounded by dramatic red clouds of gas and dust within the Large Magellanic Cloud. This supernova, first discovered on Feb. 23, 1987, blazed with the power of 100 million Suns. Since that first sighting, SN 1987A has continued to fascinate astronomers with its spectacular light show. Located in the nearby Large Magellanic Cloud, it was the nearest supernova explosion observed in hundreds of years and the best opportunity yet for astronomers to study the phases before, during, and after the death of a star.
Image credit: NASA, ESA, R. Kirshner (Harvard-Smithsonian Center for Astrophysics and Gordon and Betty Moore Foundation), and M. Mutchler and R. Avila (STScI)
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Preparations for Next Moonwalk Simulations Underway (and Underwater)
New findings using data from NASA’s IXPE (Imaging X-ray Polarimetry Explorer) mission offer unprecedented insight into the shape and nature of a structure important to black holes called a corona.
A corona is a shifting plasma region that is part of the flow of matter onto a black hole, about which scientists have only a theoretical understanding. The new results reveal the corona’s shape for the first time, and may aid scientists’ understanding of the corona’s role in feeding and sustaining black holes.
This illustration of material swirling around a black hole highlights a particular feature, called the “corona,” that shines brightly in X-ray light. In this depiction, the corona can be seen as a purple haze floating above the underlying accretion disk, and extending slightly inside of its inner edge. The material within the inner accretion disk is incredibly hot and would glow with a blinding blue-white light, but here has been reduced in brightness to make the corona stand out with better contrast. Its purple color is purely illustrative, standing in for the X-ray glow that would not be obvious in visible light. The warp in the disk is a realistic representation of how the black hole’s immense gravity acts like an optical lens, distorting our view of the flat disk that encircles it. NASA/Caltech-IPAC/Robert Hurt Many black holes, so named because not even light can escape their titanic gravity, are surrounded by accretion disks, debris-cluttered whirlpools of gas. Some black holes also have relativistic jets – ultra-powerful outbursts of matter hurled into space at high speed by black holes that are actively eating material in their surroundings.
Less well known, perhaps, is that snacking black holes, much like Earth’s Sun and other stars, also possess a superheated corona. While the Sun’s corona, which is the star’s outermost atmosphere, burns at roughly 1.8 million degrees Fahrenheit, the temperature of a black hole corona is estimated at billions of degrees.
Astrophysicists previously identified coronae among stellar-mass black holes – those formed by a star’s collapse – and supermassive black holes such as the one at the heart of the Milky Way galaxy.
“Scientists have long speculated on the makeup and geometry of the corona,” said Lynne Saade, a postdoctoral researcher at NASA’s Marshall Space Flight Center in Huntsville, Alabama, and lead author of the new findings. “Is it a sphere above and below the black hole, or an atmosphere generated by the accretion disk, or perhaps plasma located at the base of the jets?”
Enter IXPE, which specializes in X-ray polarization, the characteristic of light that helps map the shape and structure of even the most powerful energy sources, illuminating their inner workings even when the objects are too small, bright, or distant to see directly. Just as we can safely observe the Sun’s corona during a total solar eclipse, IXPE provides the means to clearly study the black hole’s accretion geometry, or the shape and structure of its accretion disk and related structures, including the corona.
“X-ray polarization provides a new way to examine black hole accretion geometry,” Saade said. “If the accretion geometry of black holes is similar regardless of mass, we expect the same to be true of their polarization properties.”
IXPE demonstrated that, among all black holes for which coronal properties could be directly measured via polarization, the corona was found to be extended in the same direction as the accretion disk – providing, for the first time, clues to the corona’s shape and clear evidence of its relationship to the accretion disk. The results rule out the possibility that the corona is shaped like a lamppost hovering over the disk.
The research team studied data from IXPE’s observations of 12 black holes, among them Cygnus X-1 and Cygnus X-3, stellar-mass binary black hole systems about 7,000 and 37,000 light-years from Earth, respectively, and LMC X-1 and LMC X-3, stellar-mass black holes in the Large Magellanic Cloud more than 165,000 light-years away. IXPE also observed a number of supermassive black holes, including the one at the center of the Circinus galaxy, 13 million light-years from Earth, and those in galaxies NGC 1068 and NGC 4151, 47 million light-years away and nearly 62 million light-years away, respectively.
Stellar mass black holes typically have a mass roughly 10 to 30 times that of Earth’s Sun, whereas supermassive black holes may have a mass that is millions to tens of billions of times larger. Despite these vast differences in scale, IXPE data suggests both types of black holes create accretion disks of similar geometry.
That’s surprising, said Marshall astrophysicist Philip Kaaret, principal investigator for the IXPE mission, because the way the two types are fed is completely different.
“Stellar-mass black holes rip mass from their companion stars, whereas supermassive black holes devour everything around them,” he said. “Yet the accretion mechanism functions much the same way.”
That’s an exciting prospect, Saade said, because it suggests that studies of stellar-mass black holes – typically much closer to Earth than their much more massive cousins – can help shed new light on properties of supermassive black holes as well.
The team next hopes to make additional examinations of both types.
Saade anticipates there’s much more to glean from X-ray studies of these behemoths. “IXPE has provided the first opportunity in a long time for X-ray astronomy to reveal the underlying processes of accretion and unlock new findings about black holes,” she said.
The complete findings are available in the latest issue of The Astrophysical Journal.
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 Marshall. 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
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Lane Figueroa
NASA’s Marshall Space Flight Center
256-544-0034
lane.e.figueroa@nasa.gov
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In October 1604, a new star appeared in the sky, puzzling astronomers of the day. First observed on Oct. 9, German astronomer Johannes Kepler (1571-1630) began his observations on Oct. 17 and tracked the new star for over a year. During that time, it brightened to magnitude -2.5, outshining Jupiter, and for several weeks remained visible in the daytime. Publication of his detailed observations in 1606 led astronomers to call the star Kepler’s Supernova, today formally designated as supernova SN 1604. Astronomers of the day did not know what caused the star’s sudden appearance and eventual disappearance, but the phenomenon helped shape European cosmology toward the heliocentric model proposed by Polish astronomer Nicolaus Copernicus half a century earlier. Today, astronomers designate SN 1604 as a Type Ia supernova, resulting from the explosion of a white dwarf star, and use ground-based and space-based telescopes to study its remnants.
Left: Portrait of Johannes Kepler by August Köhler. Middle: Kepler’s book about his observations of the 1604 supernova open to the page depicting the location of the new star. Right: Closeup of Kepler’s illustration of the location of the new star, designated N, in the constellation Ophiuchus near the right foot of the serpent-bearer.
Italian astronomer Lodovico delle Colombo first observed the supernova in the constellation Ophiuchus on Oct. 9. Kepler, then working in Prague, heard rumors of the new star but did not observe it until Oct. 17. He continued to monitor the star for over a year, inspired by the earlier work of Danish astronomer Tycho Brahe’s observations of a similar phenomenon, the 1572 supernova. The new star quickly brightened to magnitude -2.5, outshining Jupiter, and for three weeks could be seen in the daytime before finally fading into obscurity in March 1606. Kepler could only make naked eye observations, since Italian astronomer Galileo Galilei didn’t turn his newly invented telescope to the skies for another four years after SN 1604 faded from view.
Later in 1606, Kepler summarized his observations in his book De Stella nova in pede Serpentarii (On the New Star in Ophiuchus’ Foot), published in Prague. SN 1604 is believed to be about 20,000 light years away, near the edge of a dark nebula complex. Kepler and his contemporaries observed not only the last known supernova to occur in the Milky Way Galaxy but also the last supernova visible to the naked eye until 1987. That one, Supernova 1987A, appeared in the Large Magellanic Cloud, a small satellite galaxy of the Milky Way.
A Type Ia supernova results from a white dwarf drawing in material from a nearby red giant star, the additional mass leading to a runaway thermonuclear explosion.
Astronomers today understand that what Kepler and others believed as the birth of a new star actually represented the violent death of a star. Astronomers today classify supernovas according to their characteristics, and SN 1604 belongs to the group known as Type Ia supernovas, typically found in binary star systems composed of a white dwarf and a red giant. The gravitation force of the white dwarf draws in material from its larger less dense companion until it reaches a critical mass, around 1.4 times the mass of our Sun. At that point, a runaway thermonuclear chain reaction begins, causing a release of tremendous amounts of energy, including light, that we see as a sudden brightening of an otherwise dim star.
Images of Kepler’s supernova remnants in different portions of the electromagnetic spectrum. Left: X-ray image from the Chandra X-ray Observatory. Middle: Visible image from the Hubble Space Telescope. Right: Infrared image from the Spitzer Space Telescope.
Supernova explosions leave remnants behind and those of SN 1604 remain visible today. Ground-based and space-based instruments using different parts of the electromagnetic spectrum study these remnants to gain a better understanding of their origins. The remnants of SN 1604 emit energy most strongly in the radio and X-ray parts of the electromagnetic spectrum. In recent years, astronomers have used Type Ia supernovas to determine the rate of expansion of the universe. Because Type Ia supernovas all occur in stars of about 1.4 solar masses, they give out about the same amount of light. This makes them useful as distance indicators – if one Type Ia supernova is dimmer than another one, it is further away by an amount that astronomers can calculate. Based on this information, astronomers believe that the expansion of the universe is accelerating, possibly caused by the presence of a mysterious substance called dark energy.
Events in world history in 1604:
January 1 – First performance of William Shakespeare’s play A Midsummer’s Night’s Dream.
March 22 – Karl IX begins his rule as King of Sweden.
August 5 – Sokolluzade Mehmed Pasha becomes the new Ottoman Grand Vizier in Constantinople.
August 18 – England and Spain sign the Treaty of London, ending their 20-year war.
September 1 – Sri Guru Granth Sahib, Sikhism’s religious text, is installed at Hamandir Sahib in Amritsar, India.
October 4 – Emperor of Ethiopia Za Dengel is killed in battle with the forces of Za Sellase, who restores his cousin Yaqob to the throne.
November 1 – First performance of William Shakespeare’s tragedy Othello.
December 29 – A magnitude 8.1 earthquake shakes the Taiwan Strait causing significant damage.
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