A new study led by scientists at the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Maryland, shows that exhaust from a mid-sized lunar lander can quickly spread around the Moon and potentially contaminate scientifically vital ices at the lunar poles.
Computer simulations of water vapor emitted by a 2,650-pound (1,200-kilogram) lander—about a quarter of the dry mass of the Apollo Lunar Module—touching down near the Moon’s south pole showed exhaust takes only a few hours to disperse around the entire Moon. From 30% to 40% of the vapor persisted in the lunar atmosphere and surface two months later, and roughly 20% would ultimately freeze out near the poles a few months after that.
Those results, published online Aug. 11 in the Journal of Geophysical Research: Planets, show that researchers’ interest in studying the native ices in the Moon’s poleward craters—ices that may date back several billion years—will need to be carefully considered during increased efforts to return humans to the Moon.
Dealing with spacecraft exhaust on the Moon isn’t a new problem. Researchers appreciated this issue during NASA’s Apollo missions in the ’60s and ’70s, when they developed early models to predict the spread of exhaust throughout the lunar atmosphere and contamination of the surface.
“Exhaust during the Apollo mission didn’t complicate measurements in the same ways that it might now,” said Parvathy Prem, a researcher at APL and the lead author on the study.
During the Apollo era, most of the interest was in collecting lunar samples. While that’s still true today, the more recent discovery of ices preserved in permanently shadowed craters near the lunar poles has shifted scientific interest to understanding the origin and dispersion of water and other volatile molecules on the Moon’s surface and in its thin atmosphere.
“These are some of the only places where we can find traces of the origin of water in the inner solar system,” Prem said. Reading that record requires measuring the composition of those ices as well as their various isotopes to deduce where they likely came from and how they may have gotten there. Frozen-out exhaust gases from robotic or human exploration that collect on those ices could confound those measurements, even if the lander touches down hundreds of miles away.
“The interesting thing about Parvathy’s work is that it shows very well that the effect, while small and temporary, is global,” said Dana Hurley, a planetary scientist at APL and coauthor on the study.
Space organizations can expect volatile gases to significantly coat the lunar surface at well over 60 miles (100 kilometers) from the landing site.
The residue exhaust does eventually fade away, but Hurley points out that current plans for human lunar exploration mean it will happen more frequently and with much heavier landers.
“The results of this study drive the critical need to conduct the research we want to do about the lunar atmosphere and volatile deposits while they are relatively pristine,” Hurley said.
Prem cautions that the model isn’t foolproof. Among its most salient limitations are that it assumes the degree to which water interacts and “sticks” to the lunar surface, which is still uncertain but of great interest for understanding how easily water is transported around the Moon. The model also tracks only water vapor, which comprises about a third of the composition of most landers’ exhaust. Other exhaust molecules, such as hydrogen, ammonia and carbon monoxide, may behave differently and perhaps persist even longer.
Follow-up work should include measuring the amount of exhaust that’s around the Moon during and after future landings, Prem said, which would help narrow in on an answer to how much these exhaust gases “stick” to the surface. “But I would also suggest that modeling and monitoring the fate of exhaust gases should be a routine part of lunar mission development and planning.”
Conversations about mitigating exhaust gases have only just started, Prem explained.
In January, NASA finalized 16 science and technology demonstration payloads that it had selected to be delivered to the Moon through the Artemis program, including the Surface Exosphere Alterations by Landers (SEAL), an instrument that will investigate the chemical response of the lunar surface during a landing as well as any contaminants that may have been injected.
“Whether we intend to or not, we’re going to do this experiment of bringing exhaust gases with us,” Prem said. It’s now a matter of deciding how we deal with them.
Parvathy Prem et al. The Evolution of a Spacecraft‐Generated Lunar Exosphere, Journal of Geophysical Research: Planets (2020). DOI: 10.1029/2020JE006464
Johns Hopkins University
Simulations show lander exhaust could cloud studies of lunar ices (2020, August 14)
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2020 could be on track to be another record-setting warm year, despite global lockdowns – CBC.ca
People around the world participated in the Global Day of Climate Action on Friday, a reminder that even though we’re in the midst of one of the biggest health issues to face humanity, climate change stands to pose an even bigger threat — with increased chances of drought, wildfires, hurricanes, flooding and heat waves.
At the start of the COVID-19 pandemic earlier this year, businesses shuttered and people went into lockdown. As a result, greenhouse gas emissions dropped, including both nitrogen dioxide and carbon dioxide (CO2), two drivers of global warming.
There was some hope that this could be the silver lining to a tragic situation, but the fact is, it’s unlikely to make a dent in the upward trend of Earth’s rising temperatures.
In fact, the U.S. National Atmospheric and Oceanic Administration’s National Centers for Environmental Information (NCEI) recorded that globally, August’s land and sea temperatures were the second-highest on record. For North America, it was the hottest August on record, at 1.52 C above average. August also marked the 428th-consecutive month with temperatures above the 20th-century average.
The issue is that CO2 has already accumulated in our atmosphere, and Earth is playing a game of catch-up.
“Carbon dioxide can last thousands and thousands of years in the atmosphere,” said Ahira Sanchez-Lugo, a physical scientist who compiles global temperature data at NCEI. “So just because with the pandemic we’ve seen a reduction in emissions, that doesn’t mean that we will see a reduction in global temperatures any time soon.”
Climatologist Michael Mann, a professor of atmospheric science at Penn State University, said there’s likely to be a drop in emissions but that it won’t make a large difference.
“It will probably lead to a roughly four to five per cent reduction in carbon emissions for 2020. That means a very slightly lower rate of warming,” he said.
Too many blankets
Sanchez-Lugo likes to use the analogy of CO2 acting as Earth’s blanket: It’s needed in order to regulate the planet’s temperature, but additional accumulation is like throwing more and more blankets on top.
“So that’s what’s happening right now in that sense: Right now, Earth already has several layers of blankets, and just because we stopped or we’ve reduced carbon greenhouse emissions recently, that doesn’t mean that we’re peeling off those blankets,” she said.
Year-to-date, the temperature is 1.03 C higher than the average and is only behind 2016’s record warmth of 1.08 C above average.
The hottest year on record was 2016, reaching 0.94 C above the average. It also marked the third-consecutive year a record was set. But that was also the year of a moderate to strong El Nino, a natural phenomenon that is characterized by warming in the Pacific Ocean — which in turn causes higher temperatures in some regions and greater precipitation in others.
This year, however, has not been a year of El Nino.
So does this mean we might break the 2016 record without its warming effect?
“Right now, there is about a 55 per cent chance of  being the second warmest,” Sanchez-Lugo said, “and … about a 39 per cent chance of it being the warmest year on record.”
While 2020 may not be on top of the list, it’s likely that more and more records will be set in the coming years.
A study published in May in the Bulletin of the American Meteorological Society, of which Sanchez-Lugo was a co-author suggested that “there’s a greater than a 99 per cent chance that most of the next 10 years through 2028 will be ranked among the top 10 warmest.”
The pandemic might be a way of illustrating that countries can reduce their emissions by altering their lifestyles, such as by not commuting to work five days a week, which would be one way to continue to see emissions decrease.
But Mann said big changes need to be made in order to see significant improvement in the decades to come.
“If we can reduce carbon emissions a bit more — about seven per cent a year — for each of the next 10 years, we can stay on a path that stabilizes global warming below 1.5 C, preventing the most damaging and dangerous impacts of climate change,” he said.
“However, simple behavioural changes won’t get us there. We need systematic change, i.e. policies to rapidly decarbonize our economy.”
New measurements show moon has hazardous radiation levels – FOX 8 Live WVUE
Wimmer-Schweingruber said the radiation levels are close to what models had predicted. The levels measured by Chang’e 4, in fact, “agree nearly exactly” with measurements by a detector on a NASA orbiter that has been circling the moon for more than a decade, said Kerry Lee, a space radiation expert at Johnson Space Center in Houston.
China's Chang'e-4 detects hazardous radiation levels on the Moon – CGTN
Space radiation on the moon is two to three times higher than that on the International Space Station (ISS). This could be one of the biggest dangers for future moon explorers, the Chinese moon probe discovered.
A Chinese-German team reported on the radiation data collected by the moon lander – named Chang’e-4 for the Chinese moon goddess – in the U.S. journal Science Advances. Chang’e-4 made the first ever soft-landing on the far side of the Moon in January, 2019.
The discovery provides the first full measurements of radiation exposure from the lunar surface, vital information for NASA and others aiming to send astronauts to the moon, the study noted.
“This is an immense achievement in the sense that now we have a data set which we can use to benchmark our radiation” and better understand the potential risk to people on the moon, said Thomas Berger, a physicist with the German Space Agency’s medicine institute.
Though Apollo missions in the 1960s and 1970s proved it was safe for people to spend a few days on the lunar surface, NASA did not take daily radiation measurements that would help scientists quantify just how long crews could stay.
The question is now answered.
Astronauts would get 200 to 1,000 times more radiation on the moon than what we experience on Earth – or five to 10 times more than passengers on a trans-Atlantic airline flight, noted Robert Wimmer-Schweingruber of Christian-Albrechts University in Kiel, Germany.
“The radiation levels we measured on the Moon are about 200 times higher than on the surface of the Earth and five to 10 times higher than on a flight from New York to Frankfurt,” added Wimmer-Schweingruber.
That means humans can stay at most two months on the surface of the Moon without special protection measures, according to Robert Wimmer-Schweingruber, an astrophysicist at the University of Kiel.
Sources of radiation
There are several sources of radiation exposure: galactic cosmic rays, sporadic solar particle events (for example from solar flares), and neutrons and gamma rays from interactions between space radiation and the lunar soil.
Radiation is measured using the unit sievert, which quantifies the amount absorbed by human tissues.
The team found that the radiation exposure on the Moon is 1,369 microsieverts per day – about 2.6 times higher than the International Space Station crew’s daily dose.
The reason for this is that the ISS is still partly shielded by the Earth’s protective magnetic bubble, called the magnetosphere, which deflects most radiation from space.
Earth’s atmosphere provides additional protection for humans on the surface, but we are more exposed the higher up we go.
NASA is planning to bring humans to the Moon by 2024 under the Artemis mission and has said it has plans for a long term presence that would include astronauts working and living on the surface.
For Wimmer-Schweingruber there is one work-around if we want humans to spend more than two or three months: build habitats that are shielded from radiation by coating them with 80 centimeters (30 inches) of lunar soil.
(With input from agencies)
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