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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
Radioisotope Power Systems RPS Home About About RPS About the Program About Plutonium-238 Safety and Reliability For Mission Planners Contact Systems Overview Power Systems Thermal Systems Dynamic Radioisotope Power Missions Overview Timeline News Resources STEM Overview Power to Explore Contest Kid-Friendly Videos FAQ 5 Min Read After 60 Years, Nuclear Power for Spaceflight is Still Tried and True
Workers install one of three Radioisotope Thermoelectric Generators (RTGs) on the Cassini spacecraft. More › Credits:
NASA Editor’s Note: Originally published on June 21, 2021.
Six decades after the launch of the first nuclear-powered space mission, Transit IV-A, NASA is embarking on a bold future of human exploration and scientific discovery. This future builds on a proud history of safely launching and operating nuclear-powered missions in space.
“Nuclear power has opened the solar system to exploration, allowing us to observe and understand dark, distant planetary bodies that would otherwise be unreachable. And we’re just getting started,” said Dr. Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate. “Future nuclear power and propulsion systems will help revolutionize our understanding of the solar system and beyond and play a crucial role in enabling long-term human missions to the Moon and Mars.”
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Space nuclear power to explore the deepest, dustiest, darkest, and most distant regions of our solar system and beyond. NASA From Humble Beginnings: Nuclear Power Spawns an Age of Scientific Discovery
On June 29, 1961, the John’s Hopkins University Applied Physics Laboratory launched the Transit IV-A Spacecraft. It was a U.S. Navy navigational satellite with a SNAP-3B radioisotope powered generator producing 2.7 watts of electrical power — about enough to light an LED bulb. Transit IV-A broke an APL mission-duration record and confirmed the Earth’s equator is elliptical. It also set the stage for ground-breaking missions that have extended humanity’s reach across the solar system.
Since 1961, NASA has flown more than 25 missions carrying a nuclear power system through a successful partnership with the Department of Energy (DOE), which provides the power systems and plutonium-238 fuel.
“The department and our national laboratory partners are honored to play a role in powering NASA’s space exploration activities,” said Tracey Bishop, deputy assistant secretary in DOE’s Office of Nuclear Energy. “Radioisotope Power Systems are a natural extension of our core mission to create technological solutions that meet the complex energy needs of space research, exploration, and innovation.”
There are only two practical ways to provide long-term electrical power in space: the light of the sun or heat from a nuclear source.
We couldn’t do the mission without it. No other technology exists to power a mission this far away from the Sun, even today.
Alan Stern
Principal Investigator, NASA’s New Horizons Mission to Pluto and Beyond
“As missions move farther away from the Sun to dark, dusty, and harsh environments, like Jupiter, Pluto, and Titan, they become impossible or extremely limited without nuclear power,” said Leonard Dudzinski, chief technologist for NASA’s Planetary Science Division and program executive for Radioisotope Power.
That’s where Radioisotope Power Systems, or RPS, come in. They are a category of power systems that convert heat generated by the decay of plutonium-238 fuel into electricity.
“These systems are reliable and efficient,” said June Zakrajsek, manager for NASA’s Radioisotope Power Systems Program office at Glenn Research Center in Cleveland. “They operate continuously over long-duration space missions regardless of sunlight, temperature, charged particle radiation, or surface conditions like thick clouds or dust. They’ve allowed us to explore from the Sun to Pluto and beyond.”
RPS powered the Apollo Lunar Surface Experiment Package. They’ve sustained Voyager 1 and 2 since 1977, and they kept Cassini-Huygens’ instruments warm as it explored frigid Saturn and its moon Titan.
Today, a Multi-Mission Thermoelectric Generator (MMRTG) powers the Perseverance rover, which is captivating the nation as it searches for signs of ancient life on Mars, and a single RTG is sustaining New Horizons as it ventures on its way out of the solar system 15 years after its launch.
“The RTG was and still is crucial to New Horizons,” said Alan Stern, New Horizons principal investigator from the Southwest Research Institute. “We couldn’t do the mission without it. No other technology exists to power a mission this far away from the Sun, even today.”
New Horizons carries seven scientific instruments and a radioisotope thermoelectric generator. The spacecraft weighs 1,060 pounds. NASA/JHUAPL Great Things to Come: Science and Human Exploration
Dragonfly, which is set to launch in 2028, is the next mission with plans to use an MMRTG. Part of NASA’s New Frontiers program, Dragonfly is an octocopter designed to explore and collect samples on Saturn’s largest moon, Titan, an ocean world with a dense, hazy atmosphere.
“RPS is really an enabling technology,” said APL’s Zibi Turtle, principal investigator for the upcoming Dragonfly mission. “Early missions like Voyager, Galileo, and Cassini that relied on RPS have completely changed our understanding and given us a geography of the distant solar system…Cassini gave us our first close-up look at the surface of Titan.”
According to Turtle, the MMRTG serves two purposes on Dragonfly: power output to charge the lander’s battery and waste heat to keep its instruments and electronics warm.
“Flight is a very high-power activity. We’ll use a battery for flight and science activities and recharge the battery using the MMRTG,” said Turtle. “The waste heat from the power system is a key aspect of our thermal design. The surface of Titan is very cold, but we can keep the interior of the lander warm and cozy using the heat from the MMRTG.”
As the scientific community continues to benefit from RPS, NASA’s Space Technology Mission Directorate is investing in new technology using reactors and low-enriched uranium fuel to enable a robust human presence on the Moon and eventually human missions to Mars.
Astronauts will need plentiful and continuous power to survive the long lunar nights and explore the dark craters on the Moon’s South Pole. A fission surface power system could provide enough juice to power robust operations. NASA is leading an effort, working with the DOE and industry to design a fission power system for a future lunar demonstration that will pave the way for base camps on the Moon and Mars.
NASA has also thought about viable ways to reduce the time it takes to travel to Mars, including nuclear propulsion systems.
As NASA advances its bold vision of exploration and scientific discovery in space, it benefits from 60 years of the safe use of nuclear power during spaceflight. Sixty years of enlightenment that all started with a little satellite called Transit IV-A.
News Media Contact
Jan Wittry
NASA’s Glenn Research Center
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By NASA
Teams from NASA and ESA (European Space Agency), including NASA astronaut Stan Love (far right) and ESA astronaut Luca Parmitano (far left) help conduct human factors testing inside a mockup for the Gateway lunar space station. Thales Alenia Space Teams at NASA, ESA (European Space Agency), and Thales Alenia Space, including astronauts Stan Love and Luca Parmitano, came together in Turin, Italy, this summer for a test run of Gateway, humanity’s first space station to orbit the Moon.
The group conducted what is known as human factors testing inside a mockup of Lunar I-Hab, one of four Gateway modules where astronauts will live, conduct science, and prepare for missions to the Moon’s South Pole region. The testing is an important step on the path to launch by helping refine the design of spacecraft for comfort and safety.
Lunar I-Hab is provided by ESA and Thales Alenia Space and is slated to launch on Artemis IV. During that mission, four astronauts will launch inside the Orion spacecraft atop an upgraded version of the SLS (Space Launch System) rocket and deliver Lunar I-Hab to Gateway in orbit around the Moon.
ESA, CSA (Canadian Space Agency), JAXA (Japan Aerospace Exploration Agency), and the Mohammad Bin Rashid Space Centre of the United Arab Emirates are providing major hardware for Gateway, including science experiments, the modules where astronauts will live and work, robotics, and life support systems.
International teams of astronauts will explore the scientific mysteries of deep space with Gateway as part of the Artemis campaign to return to the Moon for scientific discovery and chart a path for the first human missions to Mars and beyond.
A mockup of ESA’s Lunar I-Hab module, one of four elements of the Gateway space station where astronauts will live, conduct science, and prepare for missions to the lunar South Pole Region.Thales Alenia Space An artist’s rendering of ESA’s Lunar I-Hab module in orbit around the Moon, one of four elements of the Gateway space station where astronauts will live, conduct science, and prepare for missions to the lunar South Pole Region.NASA/Alberto Bertolin, Bradley Reynolds Learn More About Gateway Share
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Last Updated Oct 22, 2024 EditorBriana R. ZamoraContactDylan Connelldylan.b.connell@nasa.govLocationJohnson Space Center Related Terms
Gateway Space Station Artemis Artemis 4 Earth's Moon Exploration Systems Development Mission Directorate Gateway Program Humans in Space Johnson Space Center Explore More
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