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By NASA
NASA Technicians do final checks on NASA’s Spirit rover in this image from March 28, 2003. The rover – and its twin, Opportunity – studied the history of climate and water at sites on Mars where conditions may once have been favorable to life. Each rover is about the size of a golf cart and seven times heavier (about 405 pounds or 185 kilograms) than the Sojourner rover launched on the Mars Pathfinder to Mars mission in 1996.
Spirit and Opportunity were sent to opposite sides of Mars to locations that were suspected of having been affected by liquid water in the past. Spirit was launched first, on June 10, 2003. Spirit landed on the Martian surface on Jan. 3, 2004, about 8 miles (13.4 kilometers) from the planned target and inside the Gusev crater. The site became known as Columbia Memorial Station to honor the seven astronauts killed when the space shuttle Columbia broke apart Feb. 1, 2003, as it returned to Earth. The plaque commemorating the STS-107 Space Shuttle Columbia crew can be seen in the image above.
Spirit operated for 6 years, 2 months, and 19 days, more than 25 times its original intended lifetime, traveling 4.8 miles (7.73 kilometers) across the Martian plains.
Image credit: NASA
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By NASA
A chevron nozzle is installed on NASA’s Learjet for a mid-March 2001 flight test at Lorain Country Airport to verify that in an emergency, the aircraft could be flown using only the experimental engine. Credit: NASA/Marvin Smith
Shortly after dawn on March 27, 2001, NASA pilot Bill Rieke took off from an airfield just outside of Phoenix in NASA’s blue-and-white Learjet 25 and flew low over a series of microphones for the first flight test of a groundbreaking NASA technology.
On one of the plane’s engines was an experimental jagged-edged nozzle that researchers at Glenn Research Center in Cleveland had discovered made aircraft significantly quieter. These initial flight tests were an important step toward using these “chevron nozzles” on modern aircraft, lowering noise levels for communities.
NASA Glenn has been exploring ways of reducing engine noise since the first jet airliners appeared in the 1950s. New turbofan engines in the 1960s were quieter, but the expansion of the overall airline industry meant that noise was still an issue. With the introduction of noise-limiting mandates in the 1970s, NASA and engine manufacturers embarked on a decades-long search for technologies to lower noise levels.
NASA researchers discovered that the military’s use of rectangular notches, or tabs, along an engine nozzle’s exit – to help disguise a jet fighter’s infrared signature – could also reduce engine noise by helping mix the hot air from the engine core and the cooler air blowing through the engine fan. In the 1990s, Glenn researcher Dennis Huff and his colleagues discovered that a serrated, or sawtooth, shape, referred to as a chevron, offered more promise.
Dennis Huff explains chevron nozzles, seen on a table, to U.S. Senator George Voinovich and other visitors inside the Aero-Acoustic Propulsion Laboratory facility in 2006. Huff was head of NASA Glenn Research Center’s Acoustics Branch at this point.Credit: NASA/Marvin Smith NASA contracted with General Electric and Pratt & Whitney to develop an array of tab and chevron designs to be analyzed in Glenn’s unique Aero-Acoustic Propulsion Laboratory (AAPL). Extensive testing in the spring of 1997 showed the possibilities for reducing noise with these types of nozzles.
Engine manufacturers were impressed with the findings but wary of any technology that might impact performance. So, in 1998, NASA funded engine tests of the 14 most promising designs. The tests revealed the chevron nozzle had a negligible 0.25% reduction of thrust. It was a major development for jet noise research.
In September 2000, Glenn’s Flight Operations Branch was contacted about the logistics of flight-testing chevron nozzles on the center’s Learjet 25 to verify the ground tests and improve computer modeling. Nothing further came of the request, however, until early the next year when Huff informed Rieke, chief of Flight Operations, that the researchers would like to conduct flight tests in late March—with just eight weeks to prepare.
Glenn’s Acoustics Branch worked with colleagues at NASA’s Langley Research Center in Hampton, Virginia, and the Arizona-based engine manufacturer Honeywell on the effort. They planned to conduct testing at Estrella Sailport just outside of Phoenix from March 26 to 28, 2001.
Bill Rieke and Ellen Tom with the chevron nozzle installed on the Learjet. NASA Glenn Research Center’s small Flight Operations team was heavily involved with icing research and solar cell calibration flights during this period, so arrangements were made for Tom, a Federal Aviation Administration pilot, to assist with the chevron flights. Credit: Courtesy of Bill Rieke With the required safety and design reviews, the eight-week target date would be difficult to meet for any test flight, but this one was particularly challenging as it involved modifications to the engine nacelle. While the special nozzle engineers created for the flights would allow them to switch between a six- and a 12-chevron design during testing, it also got hot quickly. This necessitated the installation of new sensors, rewiring of fire alarm cables, and the presence of an onboard test engineer to monitor the temperatures. The short turnaround also required expedited efforts to obtain flight plan approvals, verify the plane’s airworthiness, and perform normal maintenance activities.
Despite the challenges, Rieke and a small team delivered the Learjet to Estrella on March 25, as planned. The next day was spent coordinating with the large Langley and Honeywell team and acquiring baseline noise data. The pilots idled the unmodified engine as the Learjet flew over three perpendicular rows of microphones at an altitude of 500 feet and speed of 230 miles per hour.
View from below as NASA Glenn Research Center’s Learjet 25 passes overhead at the Estrella airfield with the experimental chevron nozzle visible on the left wing.Credit: Courtesy of Bill Rieke The flight patterns were repeated over the next two days while alternately using the two variations of the chevron nozzle. The researchers anecdotally reported that there was no perceptible noise reduction as the aircraft approached, but significant reductions once it passed. Recordings supported these observations and showed that sideline noise was reduced, as well.
The flights of the Learjet, which was powered by a variation of GE’s J-85 turbojet, were complemented by Honeywell’s turbofan-powered Falcon 20 aircraft. These flights ultimately confirmed the noise reduction found in earlier AAPL tests.
Overall, the flight tests were so successful that just over a year later the FAA began certifying GE’s CF34–8, the first commercial aircraft engine to incorporate chevron technology. The engine was first flown on a Bombardier CRJ900 in 2003. Continued studies by both NASA and industry led to the improved designs and the incorporation of chevrons into larger engines, such as GE’s GEnx.
According to Huff, the chevron’s three-decibel noise decrease was analogous to the difference between running two lawnmowers and one. Their comparatively easy integration into engine design and minimal effect on thrust made the chevron a breakthrough in noise-reduction technology. In 2002, NASA presented an innovation award to the Glenn, Langley, and Honeywell team that carried out the flights. Today, airliners such as the 737 MAX and 787 Dreamliner use chevron nozzles to lower noise levels for communities near airports.
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By NASA
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NASA’s Curiosity Mars rover captured these drifting noctilucent, or twilight, clouds in a 16-minute recording on Jan. 17. (This looping clip has been speeded up about 480 times.) The white plumes falling out of the clouds are carbon dioxide ice that would evaporate closer to the Martian surface.NASA/JPL-Caltech/MSSS/SSI While the Martian clouds may look like the kind seen in Earth’s skies, they include frozen carbon dioxide, or dry ice.
Red-and-green-tinted clouds drift through the Martian sky in a new set of images captured by NASA’s Curiosity rover using its Mastcam — its main set of “eyes.” Taken over 16 minutes on Jan. 17 (the 4,426th Martian day, or sol, of Curiosity’s mission), the images show the latest observations of what are called noctilucent (Latin for “night shining”), or twilight clouds, tinged with color by scattering light from the setting Sun.
Sometimes these clouds even create a rainbow of colors, producing iridescent, or “mother-of-pearl” clouds. Too faint to be seen in daylight, they’re only visible when the clouds are especially high and evening has fallen.
Martian clouds are made of either water ice or, at higher altitudes and lower temperatures, carbon dioxide ice. (Mars’ atmosphere is more than 95% carbon dioxide.) The latter are the only kind of clouds observed at Mars producing iridescence, and they can be seen near the top of the new images at an altitude of around 37 to 50 miles (60 to 80 kilometers). They’re also visible as white plumes falling through the atmosphere, traveling as low as 31 miles (50 kilometers) above the surface before evaporating because of rising temperatures. Appearing briefly at the bottom of the images are water-ice clouds traveling in the opposite direction roughly 31 miles (50 kilometers) above the rover.
Dawn of Twilight Clouds
Twilight clouds were first seen on Mars by NASA’s Pathfinder mission in 1997; Curiosity didn’t spot them until 2019, when it acquired its first-ever images of iridescence in the clouds. This is the fourth Mars year the rover has observed the phenomenon, which occurs during early fall in the southern hemisphere.
Mark Lemmon, an atmospheric scientist with the Space Science Institute in Boulder, Colorado, led a paper summarizing Curiosity’s first two seasons of twilight cloud observations, which published late last year in Geophysical Research Letters. “I’ll always remember the first time I saw those iridescent clouds and was sure at first it was some color artifact,” he said. “Now it’s become so predictable that we can plan our shots in advance; the clouds show up at exactly the same time of year.”
Each sighting is an opportunity to learn more about the particle size and growth rate in Martian clouds. That, in turn, provides more information about the planet’s atmosphere.
Cloud Mystery
One big mystery is why twilight clouds made of carbon dioxide ice haven’t been spotted in other locations on Mars. Curiosity, which landed in 2012, is on Mount Sharp in Gale Crater, just south of the Martian equator. Pathfinder landed in Ares Vallis, north of the equator. NASA’s Perseverance rover, located in the northern hemisphere’s Jezero Crater, hasn’t seen any carbon dioxide ice twilight clouds since its 2021 landing. Lemmon and others suspect that certain regions of Mars may be predisposed to forming them.
A possible source of the clouds could be gravity waves, he said, which can cool the atmosphere: “Carbon dioxide was not expected to be condensing into ice here, so something is cooling it to the point that it could happen. But Martian gravity waves are not fully understood and we’re not entirely sure what is causing twilight clouds to form in one place but not another.”
Mastcam’s Partial View
The new twilight clouds appear framed in a partially open circle. That’s because they were taken using one of Mastcam’s two color cameras: the left 34 mm focal length Mastcam, which has a filter wheel that is stuck between positions. Curiosity’s team at NASA’s Jet Propulsion Laboratory in Southern California remains able to use both this camera and the higher-resolution right 100 mm focal length camera for color imaging.
The rover recently wrapped an investigation of a place called Gediz Vallis channel and is on its way to a new location that includes boxwork — fractures formed by groundwater that look like giant spiderwebs when viewed from space.
More recently, Curiosity visited an impact crater nicknamed “Rustic Canyon,” capturing it in images and studying the composition of rocks around it. The crater, 67 feet (20 meters) in diameter, is shallow and has lost much of its rim to erosion, indicating that it likely formed many millions of years ago. One reason Curiosity’s science team studies craters is because the cratering process can unearth long-buried materials that may have better preserved organic molecules than rocks exposed to radiation at the surface. These molecules provide a window into the ancient Martian environment and how it could have supported microbial life billions of years ago, if any ever formed on the Red Planet.
More About Curiosity
Curiosity was built by NASA’s Jet Propulsion Laboratory, which is managed by Caltech in Pasadena, California. JPL leads the mission on behalf of NASA’s Science Mission Directorate in Washington. Malin Space Science Systems in San Diego built and operates Mastcam.
For more about Curiosity, visit:
science.nasa.gov/mission/msl-curiosity
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Andrew Good
Jet Propulsion Laboratory, Pasadena, Calif.
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Karen Fox / Molly Wasser
NASA Headquarters, Washington
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Last Updated Feb 11, 2025 Related Terms
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By NASA
u0022The really interesting thing to me is how time theoretically acts strangely around black holes. According to Albert Einstein’s theory of gravity, black holes change the flow of time,u0022 said Jeremy Schnittman, Goddard research astrophysicist. u0022So much of how we experience the world is based on time, time marching steadily forward. Anything that changes that is a fascinating take on reality.u0022u003cstrongu003eu003cemu003eCredits: NASA’s Goddard Space Flight Center / Rebecca Rothu003c/emu003eu003c/strongu003e Name: Jeremy Schnittman
Formal Job Classification: Research astrophysicist
Organization: Gravitational Astrophysics Laboratory, Astrophysics Division (Code 663)
What do you do and what is most interesting about your role here at Goddard? How do you help support Goddard’s mission?
I try to understand the formation and properties of black holes. I also help develop ideas for new missions to study black holes.
What drew you to astrophysics?
I always liked science and math. The great thing about astrophysics is that it involves a little bit of everything – math, computer programming, physics, chemistry and even philosophy to understand the big picture, the enormity of space.
I have a B.A. in physics from Harvard, and a Ph.D. in physics from MIT. I came to Goddard in 2010 after two post-doctoral fellowships.
Explore how the extreme gravity of two orbiting supermassive black holes distorts our view. In this visualization, disks of bright, hot, churning gas encircle both black holes, shown in red and blue to better track the light source. The red disk orbits the larger black hole, which weighs 200 million times the mass of our Sun, while its smaller blue companion weighs half as much. Zooming into each black hole reveals multiple, increasingly warped images of its partner. Watch to learn more.
Credits: NASA’s Goddard Space Flight Center/Jeremy Schnittman and Brian P. Powell
Download high-resolution video and images from NASA’s Scientific Visualization Studio As an astrophysicist, what do you think about?
I think of myself as a computational physicist as opposed to an experimental or observational physicist. I write many computer programs to do computer simulations of black holes. I also do a lot of theoretical physics, which is pencil and paper work. I think a lot about equations and math to understand black holes.
What is most philosophical about black holes to me is not so much what people most often think about, that their gravity is so strong that even light cannot escape. The really interesting thing to me is how time theoretically acts strangely around black holes. According to Albert Einstein’s theory of gravity, black holes change the flow of time. If you could get close enough to a black hole, theoretically you could go back and forth in time. All our experiments and observations seem to indicate that is how black holes might behave.
So much of how we experience the world is based on time, time marching steadily forward. Anything that changes that is a fascinating take on reality.
Related Link: Gravity Assist: Black Hole Mysteries, with Jeremy Schnittman What do you tell the people you mentor?
I mentor undergraduate, graduate, and post graduate students in astrophysics. Since we are working remotely, I have students from all over the country. I help them with their research projects which mostly relate to black holes in some way. I also offer career advice and help them with their work-life balance. When possible, family comes first.
There are more people coming out of graduate school in astrophysics than there are jobs, so there are going to be many people who will not work for NASA or as a professor. Fortunately, there are a lot of other fascinating, related jobs, and I help guide the students there.
What do you do for fun?
I have a woodshop in our basement where I build furniture, dollhouses, toys, and other items for gifts. As a theoretical physicist, I don’t get to work in a lab. So it is nice to have some hands on experience.
I do a lot of hiking and cycling to exercise. I also enjoy spending time with my family.
Who is your favorite author?
Andy Weir is probably my favorite sci-fi author. I also love the epic naval historical fiction by Patrick O’Brian.
Who inspires you?
My childhood hero, who is still my scientific hero, is Albert Einstein. The more I work in astrophysics, the more he impresses me. Every single one of his predictions that we have been able to test has proven true. It may be a while, but someday I hope we prove his theories about time travel.
Also, I admire Kip Thorne, an American physicist from Cal Tech and recent Nobel laureate, who is “the man” when it comes to black holes. He is also a really nice, good guy, a real mensch. Very humble and down-to-earth. He is always extremely patient, kind and encouraging especially to the younger scientists. He is a good role model as I transition from junior to more senior status.
What is your one big dream?
I make a lot of predictions, so it would be exciting if one of my theories was proven correct. Hopefully someday.
By Elizabeth M. Jarrell
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Conversations with Goddard Conversations With Goddard is a collection of question and answer profiles highlighting the breadth and depth of NASA’s Goddard Space Flight Center’s talented and diverse workforce. The Conversations have been published twice a month on average since May 2011. Read past editions on Goddard’s “Our People” webpage.
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Last Updated Feb 10, 2025 Related Terms
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By NASA
NASA/Michael DeMocker The full moon rises over the Superdome and the city of New Orleans, Louisiana on Monday evening, January 13, 2025.
New Orleans is home to NASA’s Michoud Assembly Facility where several pieces of hardware for the SLS (Space Launch system) are being built. For more than half a century, NASA Michoud has been “America’s Rocket Factory,” the nation’s premiere site for manufacturing and assembly of large-scale space structures and systems.
See more photos from NASA Michoud.
Image credit: NASA/Michael DeMocker
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