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By NASA
Scientists have hypothesized since the 1960s that the Sun is a source of ingredients that form water on the Moon. When a stream of charged particles known as the solar wind smashes into the lunar surface, the idea goes, it triggers a chemical reaction that could make water molecules.
Now, in the most realistic lab simulation of this process yet, NASA-led researchers have confirmed this prediction.
The finding, researchers wrote in a March 17 paper in JGR Planets, has implications for NASA’s Artemis astronaut operations at the Moon’s South Pole. A critical resource for exploration, much of the water on the Moon is thought to be frozen in permanently shadowed regions at the poles.
“The exciting thing here is that with only lunar soil and a basic ingredient from the Sun, which is always spitting out hydrogen, there’s a possibility of creating water,” Li Hsia Yeo, a research scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “That’s incredible to think about,” said Yeo, who led the study.
Solar wind flows constantly from the Sun. It’s made largely of protons, which are nuclei of hydrogen atoms that have lost their electrons. Traveling at more than one million miles per hour, the solar wind bathes the entire solar system. We see evidence of it on Earth when it lights up our sky in auroral light shows.
Computer-processed data of the solar wind from NASA’s STEREO spacecraft. Download here: https://svs.gsfc.nasa.gov/20278/ NASA/SwRI/Craig DeForest Most of the solar particles don’t reach the surface of Earth because our planet has a magnetic shield and an atmosphere to deflect them. But the Moon has no such protection. As computer models and lab experiments have shown, when protons smash into the Moon’s surface, which is made of a dusty and rocky material called regolith, they collide with electrons and recombine to form hydrogen atoms.
Then, the hydrogen atoms can migrate through the lunar surface and bond with the abundant oxygen atoms already present in minerals like silica to form hydroxyl (OH) molecules, a component of water, and water (H2O) molecules themselves.
Scientists have found evidence of both hydroxyl and water molecules in the Moon’s upper surface, just a few millimeters deep. These molecules leave behind a kind of chemical fingerprint — a noticeable dip in a wavy line on a graph that shows how light interacts with the regolith. With the current tools available, though, it is difficult to tell the difference between hydroxyl and water, so scientists use the term “water” to refer to either one or a mix of both molecules.
Many researchers think the solar wind is the main reason the molecules are there, though other sources like micrometeorite impacts could also help by creating heat and triggering chemical reactions.
In 2016, scientists discovered that water is released from the Moon during meteor showers. When a speck of comet debris strikes the moon, it vaporizes on impact, creating a shock wave in the lunar soil. With a sufficiently large impactor, this shock wave can breach the soil’s dry upper layer and release water molecules from a hydrated layer below. NASA’s LADEE spacecraft detected these water molecules as they entered the tenuous lunar atmosphere. NASA’s Goddard Space Flight Center Conceptual Image Lab Spacecraft measurements had already hinted that the solar wind is the primary driver of water, or its components, at the lunar surface. One key clue, confirmed by Yeo’s team’s experiment: the Moon’s water-related spectral signal changes over the course of the day.
In some regions, it’s stronger in the cooler morning and fades as the surface heats up, likely because water and hydrogen molecules move around or escape to space. As the surface cools again at night, the signal peaks again. This daily cycle points to an active source — most likely the solar wind—replenishing tiny amounts of water on the Moon each day.
To test whether this is true, Yeo and her colleague, Jason McLain, a research scientist at NASA Goddard, built a custom apparatus to examine Apollo lunar samples. In a first, the apparatus held all experiment components inside: a solar particle beam device, an airless chamber that simulated the Moon’s environment, and a molecule detector. Their invention allowed the researchers to avoid ever taking the sample out of the chamber — as other experiments did — and exposing it to contamination from the water in the air.
“It took a long time and many iterations to design the apparatus components and get them all to fit inside,” said McLain, “but it was worth it, because once we eliminated all possible sources of contamination, we learned that this decades-old idea about the solar wind turns out to be true.”
Using dust from two different samples picked up on the Moon by NASA’s Apollo 17 astronauts in 1972, Yeo and her colleagues first baked the samples to remove any possible water they could have picked up between air-tight storage in NASA’s space-sample curation facility at NASA’s Johnson Space Center in Houston and Goddard’s lab. Then, they used a tiny particle accelerator to bombard the dust with mock solar wind for several days — the equivalent of 80,000 years on the Moon, based on the high dose of the particles used.
They used a detector called a spectrometer to measure how much light the dust molecules reflected, which showed how the samples’ chemical makeup changed over time.
In the end, the team saw a drop in the light signal that bounced to their detector precisely at the point in the infrared region of the electromagnetic spectrum — near 3 microns — where water typically absorbs energy, leaving a telltale signature.
While they can’t conclusively say if their experiment made water molecules, the researchers reported in their study that the shape and width of the dip in the wavy line on their graph suggests that both hydroxyl and water were produced in the lunar samples.
By Lonnie Shekhtman
NASA’s Goddard Space Flight Center, Greenbelt, Md.
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By NASA
NASA astronauts (left to right) Christina Koch, Victor Glover, Reid Wiseman, Canadian Space Agency Astronaut Jeremy Hansen. Credit: NASA/Josh Valcarcel The Artemis II test flight will be NASA’s first mission with crew under Artemis. Astronauts on their first flight aboard NASA’s Orion spacecraft will confirm all of the spacecraft’s systems operate as designed with crew aboard in the actual environment of deep space. Through the Artemis campaign, NASA will send astronauts to explore the Moon for scientific discovery, economic benefits, and to build the foundation for the first crewed missions to Mars – for the benefit of all.
The unique Artemis II mission profile will build upon the uncrewed Artemis I flight test by demonstrating a broad range of SLS (Space Launch System) and Orion capabilities needed on deep space missions. This mission will prove Orion’s critical life support systems are ready to sustain our astronauts on longer duration missions ahead and allow the crew to practice operations essential to the success of Artemis III and beyond.
Leaving Earth
The mission will launch a crew of four astronauts from NASA’s Kennedy Space Center in Florida on a Block 1 configuration of the SLS rocket. Orion will perform multiple maneuvers to raise its orbit around Earth and eventually place the crew on a lunar free return trajectory in which Earth’s gravity will naturally pull Orion back home after flying by the Moon. The Artemis II astronauts are NASA’s Reid Wiseman, Victor Glover, and Christina Koch, and CSA (Canadian Space Agency) astronaut Jeremy Hansen.
The initial launch will be similar to Artemis I as SLS lofts Orion into space, and then jettisons the boosters, service module panels, and launch abort system, before the core stage engines shut down and the core stage separates from the upper stage and the spacecraft. With crew aboard this mission, Orion and the upper stage, called the interim cryogenic propulsion stage (ICPS), will then orbit Earth twice to ensure Orion’s systems are working as expected while still close to home. The spacecraft will first reach an initial orbit, flying in the shape of an ellipse, at an altitude of about 115 by 1,400 miles. The orbit will last a little over 90 minutes and will include the first firing of the ICPS to maintain Orion’s path. After the first orbit, the ICPS will raise Orion to a high-Earth orbit. This maneuver will enable the spacecraft to build up enough speed for the eventual push toward the Moon. The second, larger orbit will take approximately 23.5 hours with Orion flying in an ellipse between about 115 and 46,000 miles above Earth. For perspective, the International Space Station flies a nearly circular Earth orbit about 250 miles above our planet.
After the burn to enter high-Earth orbit, Orion will separate from the upper stage. The expended stage will have one final use before it is disposed through Earth’s atmosphere—the crew will use it as a target for a proximity operations demonstration. During the demonstration, mission controllers at NASA’s Johnson Space Center in Houston will monitor Orion as the astronauts transition the spacecraft to manual mode and pilot Orion’s flight path and orientation. The crew will use Orion’s onboard cameras and the view from the spacecraft’s windows to line up with the ICPS as they approach and back away from the stage to assess Orion’s handling qualities and related hardware and software. This demonstration will provide performance data and operational experience that cannot be readily gained on the ground in preparation for critical rendezvous, proximity operations and docking, as well as undocking operations in lunar orbit beginning on Artemis III.
Checking Critical Systems
Following the proximity operations demonstration, the crew will turn control of Orion back to mission controllers at Johnson and spend the remainder of the orbit verifying spacecraft system performance in the space environment. They will remove the Orion Crew Survival System suit they wear for launch and spend the remainder of the in-space mission in plain clothes, until they don their suits again to prepare for reentry into Earth’s atmosphere and recovery from the ocean.
While still close to Earth, the crew will assess the performance of the life support systems necessary to generate breathable air and remove the carbon dioxide and water vapor produced when the astronauts breathe, talk, or exercise. The long orbital period around Earth provides an opportunity to test the systems during exercise periods, where the crew’s metabolic rate is the highest, and a sleep period, where the crew’s metabolic rate is the lowest. A change between the suit mode and cabin mode in the life support system, as well as performance of the system during exercise and sleep periods, will confirm the full range of life support system capabilities and ensure readiness for the lunar flyby portion of the mission.
Orion will also checkout the communication and navigation systems to confirm they are ready for the trip to the Moon. While still in the elliptical orbit around Earth, Orion will briefly fly beyond the range of GPS satellites and the Tracking and Data Relay Satellites of NASA’s Space Network to allow an early checkout of agency’s Deep Space Network communication and navigation capabilities. When Orion travels out to and around the Moon, mission control will depend on the Deep Space Network to communicate with the astronauts, send imagery to Earth, and command the spacecraft.
After completing checkout procedures, Orion will perform the next propulsion move, called the translunar injection (TLI) burn. With the ICPS having done most of the work to put Orion into a high-Earth orbit, the service module will provide the last push needed to put Orion on a path toward the Moon. The TLI burn will send crew on an outbound trip of about four days and around the backside of the Moon where they will ultimately create a figure eight extending over 230,000 miles from Earth before Orion returns home.
To the Moon and “Free” Ride Home
On the remainder of the trip, astronauts will continue to evaluate the spacecraft’s systems, including demonstrating Earth departure and return operations, practicing emergency procedures, and testing the radiation shelter, among other activities.
The Artemis II crew will travel approximately 4,600 miles beyond the far side of the Moon. From this vantage point, they will be able to see the Earth and the Moon from Orion’s windows, with the Moon close in the foreground and the Earth nearly a quarter-million miles in the background.
With a return trip of about four days, the mission is expected to last about 10 days. Instead of requiring propulsion on the return, this fuel-efficient trajectory harnesses the Earth-Moon gravity field, ensuring that—after its trip around the far side of the Moon—Orion will be pulled back naturally by Earth’s gravity for the free return portion of the mission.
Two Missions, Two Different Trajectories
Following Artemis II, Orion and its crew will once again travel to the Moon, this time to make history when the next astronauts walk on the lunar surface. Beginning with Artemis III, missions will focus on establishing surface capabilities and building Gateway in orbit around the Moon.
Through Artemis, NASA will explore more of the Moon than ever before and create an enduring presence in deep space.
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