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By NASA
4 min read
Preparations for Next Moonwalk Simulations Underway (and Underwater)
The mystery of why life uses molecules with specific orientations has deepened with a NASA-funded discovery that RNA — a key molecule thought to have potentially held the instructions for life before DNA emerged — can favor making the building blocks of proteins in either the left-hand or the right-hand orientation. Resolving this mystery could provide clues to the origin of life. The findings appear in research recently published in Nature Communications.
Proteins are the workhorse molecules of life, used in everything from structures like hair to enzymes (catalysts that speed up or regulate chemical reactions). Just as the 26 letters of the alphabet are arranged in limitless combinations to make words, life uses 20 different amino acid building blocks in a huge variety of arrangements to make millions of different proteins. Some amino acid molecules can be built in two ways, such that mirror-image versions exist, like your hands, and life uses the left-handed variety of these amino acids. Although life based on right-handed amino acids would presumably work fine, the two mirror images are rarely mixed in biology, a characteristic of life called homochirality. It is a mystery to scientists why life chose the left-handed variety over the right-handed one.
A diagram of left-handed and right-handed versions of the amino acid isovaline, found in the Murchison meteorite.NASA DNA (deoxyribonucleic acid) is the molecule that holds the instructions for building and running a living organism. However, DNA is complex and specialized; it “subcontracts” the work of reading the instructions to RNA (ribonucleic acid) molecules and building proteins to ribosome molecules. DNA’s specialization and complexity lead scientists to think that something simpler should have preceded it billions of years ago during the early evolution of life. A leading candidate for this is RNA, which can both store genetic information and build proteins. The hypothesis that RNA may have preceded DNA is called the “RNA world” hypothesis.
If the RNA world proposition is correct, then perhaps something about RNA caused it to favor building left-handed proteins over right-handed ones. However, the new work did not support this idea, deepening the mystery of why life went with left-handed proteins.
The experiment tested RNA molecules that act like enzymes to build proteins, called ribozymes. “The experiment demonstrated that ribozymes can favor either left- or right-handed amino acids, indicating that RNA worlds, in general, would not necessarily have a strong bias for the form of amino acids we observe in biology now,” said Irene Chen, of the University of California, Los Angeles (UCLA) Samueli School of Engineering, corresponding author of the Nature Communications paper.
In the experiment, the researchers simulated what could have been early-Earth conditions of the RNA world. They incubated a solution containing ribozymes and amino acid precursors to see the relative percentages of the right-handed and left-handed amino acid, phenylalanine, that it would help produce. They tested 15 different ribozyme combinations and found that ribozymes can favor either left-handed or right-handed amino acids. This suggested that RNA did not initially have a predisposed chemical bias for one form of amino acids. This lack of preference challenges the notion that early life was predisposed to select left-handed-amino acids, which dominate in modern proteins.
“The findings suggest that life’s eventual homochirality might not be a result of chemical determinism but could have emerged through later evolutionary pressures,” said co-author Alberto Vázquez-Salazar, a UCLA postdoctoral scholar and member of Chen’s research group.
Earth’s prebiotic history lies beyond the oldest part of the fossil record, which has been erased by plate tectonics, the slow churning of Earth’s crust. During that time, the planet was likely bombarded by asteroids, which may have delivered some of life’s building blocks, such as amino acids. In parallel to chemical experiments, other origin-of-life researchers have been looking at molecular evidence from meteorites and asteroids.
“Understanding the chemical properties of life helps us know what to look for in our search for life across the solar system,” said co-author Jason Dworkin, senior scientist for astrobiology at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and director of Goddard’s Astrobiology Analytical Laboratory.
Dworkin is the project scientist on NASA’s OSIRIS-REx mission, which extracted samples from the asteroid Bennu and delivered them to Earth last year for further study.
“We are analyzing OSIRIS-REx samples for the chirality (handedness) of individual amino acids, and in the future, samples from Mars will also be tested in laboratories for evidence of life including ribozymes and proteins,” said Dworkin.
The research was supported by grants from NASA, the Simons Foundation Collaboration on the Origin of Life, and the National Science Foundation. Vázquez-Salazar acknowledges support through the NASA Postdoctoral Program, which is administered by Oak Ridge Associated Universities under contract with NASA.
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Last Updated Nov 21, 2024 EditorWilliam SteigerwaldContactNancy N. Jonesnancy.n.jones@nasa.govLocationGoddard Space Flight Center Related Terms
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By NASA
Curiosity Navigation Curiosity Home Mission Overview Where is Curiosity? Mission Updates Science Overview Instruments Highlights Exploration Goals News and Features Multimedia Curiosity Raw Images Images Videos Audio Mosaics More Resources Mars Missions Mars Sample Return Mars Perseverance Rover Mars Curiosity Rover MAVEN Mars Reconnaissance Orbiter Mars Odyssey More Mars Missions The Solar System The Sun Mercury Venus Earth The Moon Mars Jupiter Saturn Uranus Neptune Pluto & Dwarf Planets Asteroids, Comets & Meteors The Kuiper Belt The Oort Cloud 3 min read
Sols 4366–4367: One of Those Days on Mars (Sulfate-Bearing Unit to the West of Upper Gediz Vallis)
NASA’s Mars rover Curiosity acquired this image using its Right Navigation Camera on Nov. 14, 2024 — sol 4363, or Martian day 4,363 of the Mars Science Laboratory mission – at 02:55:34 UTC. NASA/JPL-Caltech Earth planning date: Friday, Nov. 15, 2024
The Monday plan and drive had executed successfully, so the team had high hopes for APXS and MAHLI data on several enticing targets in the rover’s workspace. Alas, it was not to be: The challenging terrain had resulted in an awkwardly perched wheel at the end of the drive, so we couldn’t risk deploying the arm from this position. Maybe next drive!
We did plan a busy weekend of non-arm science activities regardless. Due to a “soliday” the weekend has two sols instead of three, but we had enough power available to fit in more than three hours of observations. The two LIBS observations in the plan will measure the composition of the flat, reddish material in the workspace that is fractured in a polygonal pattern (“Bloody Canyon”) and a nearby rock coating in which the composition is suspected to change with depth (“Burnt Camp Creek”). One idea is that the reddish material could be the early stage version of the thicker dark coatings we’ve been seeing.
A large Mastcam mosaic (“Yosemite”) was planned to capture the very interesting view to the rover’s north. Nearby and below the rover is the layer of rocks in which the “Mineral King” site was drilled on the opposite side of the channel back in March. This is a stratum of sulfate-bearing rock that appears dark-toned from orbit and we’re interested to know how consistent its features are from one side of the channel to the other. Higher up, the Yosemite mosaic also captures some deformation features that may reveal past water activity, and some terrain associated with the Gediz Vallis ridge. So there’s a lot of science packed into one mosaic!
Two long-distance RMI mosaics were planned; one is to image back into the channel, where there may be evidence of a late-stage debris flow at the base of the ridge. The second looks “forward” from the rover’s perspective instead, into the wind-shaped yardang unit above us that will hopefully be explored close-up in the rover’s future. This yardang mosaic is intended to form one part of a stereo observation.
The modern environment on Mars will also be observed with dust devil surveys on both sols, line-of-sight and tau observations to measure atmospheric opacity (often increased by dust in the atmosphere), and zenith and suprahorizon movies with Navcam to look for clouds. There will also be standard passive observations of the rover’s environment by REMS and DAN.
We’ll continue driving westward and upward, rounding the Texoli butte to keep climbing through the sulfate-bearing unit. It’s not always easy driving but there’s a lot more science to do!
Written by Lucy Lim, Participating Scientist at NASA’s Goddard Space Flight Center
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Last Updated Nov 18, 2024 Related Terms
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By NASA
8 Min Read Kathryn Sullivan: The First American Woman to Walk in Space
Astronaut Kathryn D. Sullivan checks the latch of the SIR-B antenna in the space shuttle Challenger's open cargo bay during her historic extravehicular activity (EVA) on Oct. 11, 1984. Earlier, America's first woman to perform an EVA and astronaut David C. Leestma, participated in an in-space simulation of refueling a spacecraft in orbit. Credits: NASA Forty years ago, in October 1984, Kathryn D. Sullivan became the first American woman to walk in space. But being the first presented several challenges that started well before she took those historic steps. Things got complicated just after she learned of her assignment.
Questions of Physiology
Biomedical researchers at NASA’s Johnson Space Center (JSC) raised what they believed was a serious issue with women walking in space and alerted George W.S. Abbey, the head of the Flight Crew Operations Directorate. Females, he learned, were more likely than their male counterparts to develop the bends in the low-pressure environment of the extravehicular mobility unit (EMU), the spacesuit she would wear. To alleviate the possibility of developing decompression syndrome, all spacewalkers had to breathe pure oxygen before a spacewalk to eliminate nitrogen from their bloodstream. Researchers insisted Sullivan (and any future women spacewalkers) spend more time than their male counterparts breathing pure oxygen before going outside of the space shuttle. Sullivan quickly learned that there were flaws in the research, which she countered, and Abbey ended up approving the same requirements for men and women doing an extravehicular activity (EVA).
Setting the Record
After the STS-41G crew had been named in the fall of 1983, a colleague—flush with excitement over the recent flight announcement — congratulated Sally K. Ride and Sullivan on their new titles: Ride being the first woman to fly in space twice and Sullivan the first woman to walk in space. Both shook their heads and explained that it would be many months before launch and that a Soviet woman would fly and do a spacewalk well before the space shuttle Challenger and her crew made it to orbit. As expected, the Soviets assigned cosmonaut Svetlana Y. Savitskaya to a second mission in 1983, less than a month after NASA’s crew announcement. In July 1984, Savitskaya, not Ride, went on to become the first woman to enter space twice and earned the distinction of being the first female to walk in space.
Astronauts Sally K. Ride (right) and Kathryn D. Sullivan, two of three mission specialists, synchronize their watches prior to ingressing the Space Shuttle Challenger on the launch pad at Kennedy Space Center on October 5, 1984.NASA Sullivan was not disappointed at losing the title. As she recalled in an oral history interview, being selected for an EVA was an “extraordinary opportunity,” and it did not matter where she was in the queue. She could not understand how people arrived at the idea that the “seventh, tenth, or thirteenth … is [any] less meaningful … than some historical first.”
Others at the Johnson Space Center still thought there was a way they could best the Soviets. Sullivan’s trainers took note of how short Savitskaya’s EVA was. It was only about three and a half hours. “A little bit more than that,” they explained, and “you’ll get the duration record!” But the idea of breaking her record by a few minutes seemed ludicrous. “I’m certainly not going to go tromping around on dinner speeches … saying, ‘Well yes, but I have the duration record.’”
“Hello, I’m right here!”
While the issue of breaking and setting records remained of interest at NASA more than twenty years after the Soviets sent cosmonaut Yuri Gagarin into space, Sullivan found herself grappling with other matters she found equally frustrating. First, there was the sexist media. No journalist asked how she was feeling about her role in the mission. Flying women in space was still new to the American news media in 1983—Ride had only flown her first mission in June, and while Judith A. Resnik had been named to a mission, she had not yet been in orbit. But Ride had not completed an EVA; only men had walked in space, and some found the activity challenging. Astronaut Eugene A. Cernan described his first EVA as the “spacewalk from hell.” Spacewalks can be physically demanding, and it was assumed that women might not have the strength to do so. Reporters asked commander Robert L. Crippen and Ride, “Do you think Kathy can do this?” Sitting at the preflight press conference she reminded reporters that she could speak for herself. “Hello, I’m right here! Hello. Hello.”
The crew assigned to the STS-41G mission included (seated left to right) Jon A. McBride, pilot; mission specialists Sally K. Ride, Kathryn D. Sullivan, and David C. Leestma. Standing in the rear, left to right, are payload specialist Paul D. Scully-Power, mission commander Robert Crippen, and payload specialist Marc Garneau. Launched aboard the Space Shuttle Challenger on October 5, 1984, the STS-41G mission marked the first flight to include two women.NASA There was also the matter of why her spacewalking partner, David C. Leestma, led the EVA. She had two years seniority in the Astronaut Office, arriving in 1978; NASA named Leestma to the corps in 1980. She also worked on spacesuit issues and the mission’s payload longer than he had, but both were rookies on this mission. Sullivan did not think Crippen and Abbey thought she was incapable, but for traditional norms to have been breached in this instance she could not explain why she—the senior ranking astronaut—was playing a support role instead of leading. If anyone asked why, Sullivan told Crippen he—not she—would have to answer the tough questions.
Space Suit Fit
As she prepared for the flight, she began training in the shuttle EMU, which never quite fit her body. The suit’s elbow did not align with hers so when she bent her arm, she had to use extra force. The lower portion of the suit was misaligned, making it difficult to bend her knee. Being the first American woman to do a spacewalk, she decided what was most important was to perform the EVA and demonstrate the EMU worked for women. “I reckoned the wrong thing to do was to turn the first evolution of a woman doing a spacewalk into a controversy. … I just sucked it up and dealt with it.” The suit techs knew the EMU was not quite her size, but she made it work. Later, when assigned to STS-45, one of the techs noticed how poorly the suit fit. “We ought to do something about it. It ought to fit you,” he said. Sullivan responded, “We can start that conversation now, but if you think I was going to make that the conversation on the first EVA you’re crazy.”
Astronaut Kathryn D. Sullivan, STS-41G mission specialist, gets some help with her extravehicular mobility unit (EMU) prior to participating in an underwater simulation of an extravehicular activity (EVA) scheduled for her flight aboard the Columbia in October 1984. Dr. Sullivan and David C. Leestma (out of frame) participated in the rehearsal in NASA’s weightless environment training facility (WET-F) at the Johnson Space Center.NASA A Walk to Remember
Two days after Sullivan’s thirty-third birthday, STS-41G launched on October 5, 1984. Once in orbit, the flight plan changed quickly. A problem with a malfunctioning Ku-band antenna meant that the EVA had to be pushed back to the day before reentry. Sullivan worried that the walk might be scrapped, but when they finally began the pre-breathing protocol, she relaxed. “Challenger, Houston: You are GO for EVA,” Sullivan recalled, “were the sweetest words I had ever heard.” Sullivan and Leestma’s EVA was short—only three hours and twenty-nine minutes—but busy. Leestma demonstrated it was possible to refuel satellites in orbit, while Sullivan monitored his work. When he wrapped up his task, Sullivan finally had the opportunity to “do something, not just watch things.” She stowed the malfunctioning antenna and before they went back inside the shuttle, they filmed a scene for an IMAX film, The Dream is Alive—where the two spacewalkers rose from the bottom of the space shuttle’s windows and waved at the crew inside, mimicking the “Kilroy Was Here” meme. When filming concluded, Sullivan and Leestma returned to Challenger. “My first spacewalking adventure,” Sullivan wrote in her memoir, “was over all too soon.” The next day, President Ronald Reagan called to ask Sullivan about her experience. “Kathy, when we met at the White House, I know you were excited about walking in space. Was it what you expected?” he asked. Sullivan responded affirmatively and added, “I think it was the most fantastic experience of my life.”
I think it was the most fantastic experience of my life.
Kathryn Sullivan
NASA Astronaut
When she returned to JSC she learned that the EVA flight team had tried to figure out how to send her a diplomatic message to stay outside longer to beat Savitskaya’s record. There ended up being a “five-or six-minute difference” between Sullivan and Savitskaya, “and in the wrong direction as far as they were concerned.”
Despite all the challenges she faced as the first American woman to walk in space, Sullivan called the EVA “a fabulously cool experience.” She hoped to do another, but she never received another assignment to walk in space. She recognized what a unique opportunity she had—very few people have flown in space, and even fewer “get to sneak outside. I’m not going to diminish one dose of sneaking outside just because I didn’t get two, three, or four.”
Watch Suit Up – 50 Years of Spacewalks About the Author
Jennifer Ross-Nazzal
NASA Human Spaceflight HistorianJennifer Ross-Nazzal is the NASA Human Spaceflight Historian. She is the author of Winning the West for Women: The Life of Suffragist Emma Smith DeVoe and Making Space for Women: Stories from Trailblazing Women of NASA's Johnson Space Center.
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Last Updated Oct 07, 2024 Related Terms
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