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Surrounding Earth is a powerful magnetic field created by swirling liquid iron in the planet’s core. Earth’s magnetic field may be nearly as old as the Earth itself – and stands in stark contrast to the Moon, which completely lacks a magnetic field today.
But did the Moon’s core generate a magnetic field in the past?
In the 1980s, geophysicists studying rocks brought back by Apollo astronauts concluded the Moon once had a magnetic field that was as strong as Earth’s. But a robust magnetic field requires a power source, and the Moon’s core is relatively small. For decades, scientists have struggled to resolve this conundrum: how could such a small core create a strong magnetic field?
I’m a professor of geophysics and have been studying Earth’s magnetic field for more than 30 years. I recently assembled a team to use new scientific techniques to reexamine the evidence for lunar magnetization. We found that the Moon did not in fact have a long-lived magnetic field. Not only does this finding change the modern understanding of the Moon’s geologic history, it also has major implications for the presence of resources on the Moon that could be critical to future human exploration.
Why a magnetic Moon?
Certain rocks have the extraordinary ability to preserve records of past magnetic fields when they contain minerals with iron atoms that align with a magnetic field as the rock cools and solidifies. The best magnetic minerals at preserving evidence of a field are tiny – a thousand times smaller than the width of a human hair – because it takes a lot of energy to rearrange their atoms.
Geophysicists who study ancient magnetism recreate this process, reheating rock samples in the presence of known magnetic fields and comparing the new alignment of the iron atoms with the orientation of iron atoms before the rock was reheated. This allows researchers to learn about past magnetic fields.
Early researchers studying the first rocks brought back from the Moon by U.S. astronauts wanted to use this method to study the Moon’s magnetism. But they faced problems. Lunar rocks contain a certain type of iron – called native iron – that is easily altered by heat. Additionally, the native iron grains in lunar rocks are sometimes relatively large, making them less likely to reliably record past magnetic fields.
From the 1970s onward, geophysicists used alternative, nonheating methods to study the Moon’s magnetism. They found that some lunar samples had recorded strong magnetic fields, suggesting that the Moon had a magnetic field for over 2 billion years.
But this result only deepened the conundrum. The question of how the Moon’s core could produce a strong magnetic field remained unsolved.
An alternative theory
In the experiments, some Apollo samples showed evidence of strong magnetic fields but other samples did not. Some researchers attributed the missing magnetization to the presence of large native iron grains that were poor magnetic recorders. But many of the samples also contained small iron grains that should have recorded a field.
There have been long-standing doubts about the nonheating techniques researchers used on the Apollo samples. Some scientists have called them methods of “last resort” and conclude that the uncertainties in data collected in this way were so large that any interpretation must be viewed as speculation.
Alternatively, another group of scientists has suggested for decades that when meteorites strike the Moon, they create a dusty plasma – a gas of ions and electrons – that could generate a strong magnetic field and magnetize lunar rocks near the impact zone.
In 2008, geophysicist Kristin Lawrence decided to revisit the question of lunar magnetization using an improved reheating technique. In contrast to the researchers who originally studied the samples, she was unable to detect any definitive evidence for a past magnetic field. The approach Lawrence and her team used was better than the nonheating tests, but her results were still not conclusive. She felt she was on to something, though, and that is when she turned to me and my lab for help.
In 2011, Lawrence brought us a collection of lunar samples to test. We had been developing techniques to identify individual millimeter-size silicate crystals that contain only very small iron grains and have ideal recording properties. We then used an ultrasensitive superconducting magnetometer and a special carbon dioxide laser to rapidly heat those samples in a way that avoids altering their iron minerals. We found that nearly all the rocks had profoundly weak magnetic signals.
At the time of this first test we were still improving the method, so we couldn’t say with certainty whether the samples had formed on a Moon without a magnetic field. But we have been improving our testing methods, and last year we decided to revisit the Apollo samples.
We definitively found that some of the samples did indeed contain magnetic minerals capable of preserving high-fidelity signals of ancient magnetic fields. But the rocks had recorded no such signals. This suggests that the Moon lacked a magnetic field for nearly all of its history.
So, what explains the previous findings of a magnetic Moon? The answer was in one of the samples: a small, dark piece of glass containing tiny iron-nickel particles.
The glass was made by a meteorite impact and showed clear evidence of a strong magnetic field. But it was formed only about 2 million years ago. Nearly all geophysicists agree the Moon did not have a magnetic field at that time, because after 4.5 billion years of cooling there was not enough heat left to power the churning of iron in the Moon’s core to generate a field. The magnetic signature of the glass matched simulations of magnetic fields that can be generated by meteor impacts. This showed that meteorite impacts alone can create strong magnetic fields that magnetize rocks nearby. This could explain the high values previously reported from some Apollo rocks.
Taken together, I believe these findings resolve the mystery of a seemingly magnetic Moon.
Magnetic shielding and lunar resources
This new view of lunar magnetism has huge implications for the potential presence of valuable resources as well as information about the ancient Sun and Earth that may be buried in lunar soils.
Magnetic fields act as shields that prevent solar particles from reaching a planet or moon. Without a magnetic field, solar wind can hit the surface of the Moon directly and implant elements like helium-3 and hydrogen into the soil.
Helium-3 has many applications, but importantly, it could be a fuel source for nuclear fusion and future planetary exploration. The value of hydrogen comes from the fact that it can combine with oxygen to form water, another crucial resource in space.
Since the Moon did not have a long-lived magnetic field, these elements could have been accumulating in soils for billions of years longer than previously thought.
There is also scientific value. Elements embedded by solar wind could shed light on the evolution of the Sun. And as the Moon passes through Earth’s magnetic field, elements from Earth’s atmosphere can be deposited on the lunar surface, and these may hold clues about the earliest Earth.
The absence of a long-lived magnetic field on the Moon might strike some as a loss, but I believe it may unlock a scientific bonanza and a valuable stash of potential resources.
[Get the best of The Conversation, every weekend. Sign up for our weekly newsletter.]
John Tarduno, Professor of Geophysics, University of Rochester
This article is republished from The Conversation under a Creative Commons license. Read the original article.
LAKE COUNTY, Calif. — The National Weather Service has issued a weekend heat advisory for Lake County, while the Lake County Air Quality Management District is warning of continued smoky air conditions due to large wildland fires around the region and Oregon.
The weather advisory is in effect from 1 p.m. Saturday to 8 p.m. Sunday.
The local forecast calls for daytime highs of between 104 and 108 on Saturday and Sunday, with higher temperatures expected in Middletown.
Nighttime temperatures are forecast to be in the low 60s, with light winds of around 10 miles per hour in the afternoons and evenings.
On Monday, temperatures are expected to be around the century mark before rolling back into the 90s through Friday.
At the same time, the National Weather Service forecast says those hot temperatures will be paired with widespread haze through the start of the week.
The Lake County Air Quality Management District said the source of the smoke and haze continues to be the Dixie, McFarland, Monument the River Complex fires, as well as other fires burning in Northern California and Oregon.
The district said overall air quality late this week has remained “moderate” to “unhealthy for sensitive groups.”
The air quality forecast for the weekend will range from “moderate” to “unhealthy for sensitive groups.” There is a moderate potential for “unhealthy for all” conditions when strong inversion conditions develop in the overnight hours, the district reported.
The regional weather patterns are expected to keep the heaviest smoke concentrations north of the air basin, according to the district report.
While the smoke event continues, area residents are encouraged to minimize outdoor activities, especially exercise, not to use fans that bring smoky air inside, run air conditioners on the “recirculate” or “recycle” setting and change standard air filters to medium or high efficiency filters.
Links for air quality conditions and air monitoring are available at the Lake County Air Quality Management District website.
Email Elizabeth Larson at
The City of Clearlake Animal Association is asking for wet food and long lasting treats such as bully sticks for dogs, and wet food for mama cats and kittens as well as disposable litter boxes.
A wish list has been posted at Amazon and on Chewy. For those who wish to shop local and drop off items, call 707-273-9440 to schedule a delivery or donate at the association’s Facebook page.
Here are this week’s adoptable dogs.
‘Dusty’
“Dusty” is a male American Pit Bull Terrier with a tan and white coat.
He is dog No. 4750.
‘Bear’
“Bear” is a male American Staffordshire terrier mix with a short brown coat.
He has been neutered.
He is dog No. 3476.
‘Blue Eyed Jack’
“Blue Eyed Jack” is a male German shepherd mix.
He is dog No. 5046.
‘Cleo’
“Cleo” is a female Doberman pinscher mix with a short gray coat who is new to the shelter.
She has been spayed.
She is dog No. 4865.
‘Gizmo’
“Gizmo” is a senior male Chihuahua mix with a short tan and white coat.
He is dog No. 4902.
‘Mara’
“Mara” is a female Rottweiler mix.
She has a short black and tan coat.
He is house-trained.
She is dog No. 4628.
‘Mary J’
“Mary J” is a female pit bull terrier mix.
She has a white and tan coat.
She is house-trained.
She is dog No. 4927.
‘Mitzy’
“Mitzy” is a female shepherd mix with a medium-length black and white coat.
She is dog No. 4648.
‘Mojo’
“Mojo” is a male Chihuahua mix with a short black and tan coat.
He has been neutered.
He is dog No. 4881.
‘Oakley’
“Oakley” is a male pit bull terrier mix.
He has a short red and white coat.
He is dog No. 4934.
‘Patches’
“Patches” is a male Chihuahua mix with a short tricolor coat.
He is dog No. 4903.
‘Petey’
“Petey” is a male American Staffordshire terrier mix with a black and white coat.
He is dog No. 4963.
‘Sassy’
“Sassy” is a female American bully mix with a short black coat.
She has been spayed.
She is dog No. 4602.
‘Sissy’
“Sissy” is a female American Staffordshire terrier mix with a black coat.
She is dog No. 4964.
‘Tanisha’
“Tanisha” is a female shepherd mix with a short orange and white coat.
She is dog No. 4647.
‘Terry’
“Terry” is a male Dutch shepherd mix with a smooth brindle coat.
He is dog No. 4880.
‘Tinsel’
“Tinsel” is a female American pit bull terrier mix with a short brindle and brown coat.
She is dog No. 4433.
‘Trixie’
“Trixie” is a female German shepherd mix with a short black and tan coat.
She is dog No. 5056.
‘Yule’
“Yule” is a male husky with a medium-length black and white coat.
He is dog No. 4432.
Call the Clearlake Animal Control shelter at 707-273-9440, or email
Visit Clearlake Animal Control on Facebook or on the city’s website.
Email Elizabeth Larson at
The Glass fire started in Napa County on Sept. 27, 2020, at 3:48 a.m., and burned a total of 67,484 acres and destroyed 1,555 structures in Napa and Sonoma counties.
Cal Fire said its investigators were immediately dispatched to the Glass fire and began working to determine the origin and cause of the fire.
“After a very meticulous and thorough investigation, which included months of follow-up on information provided by the public, not enough evidence was available to conclusively identify the cause,” Cal Fire said in the Friday statement.
Cal Fire said the fire’s cause is currently undetermined pending any additional information or evidence that could lead to the determination of the cause.
Tinder dry vegetation and strong winds combined with low humidity and warm temperatures contributed to extreme rates of fire spread which contributed to the difficulty in determining the cause of the fire, Cal Fire said.
July 2021 has earned the unenviable distinction as the world’s hottest month ever recorded, according to new global data released Friday by the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information.
“In this case, first place is the worst place to be,” said NOAA Administrator Rick Spinrad, Ph.D. “July is typically the world’s warmest month of the year, but July 2021 outdid itself as the hottest July and month ever recorded. This new record adds to the disturbing and disruptive path that climate change has set for the globe.”
July 2021 by the numbers
— Around the globe: the combined land and ocean-surface temperature was 1.67 degrees F (0.93 of a degree C) above the 20th-century average of 60.4 degrees F (15.8 degrees C), making it the hottest July since records began 142 years ago. It was 0.02 of a degree F (0.01 of a degree C) higher than the previous record set in July 2016, which was then tied in 2019 and 2020.
— The Northern Hemisphere: the land-surface only temperature was the highest ever recorded for July, at an unprecedented 2.77 degrees F (1.54 degrees C) above average, surpassing the previous record set in 2012.
— Regional records: Asia had its hottest July on record, besting the previous record set in 2010; Europe had its second-hottest July on record — tying with July 2010 and trailing behind July 2018; and North America, South America, Africa and Oceania all had a top-10 warmest July.
Extreme heat and global climate change
With last month’s data, it remains very likely that 2021 will rank among the world’s 10-warmest years on record, according to NCEI’s Global Annual Temperature Rankings Outlook.
Extreme heat detailed in NOAA’s monthly NCEI reports is also a reflection of the long-term changes outlined in a major report released this week by the Intergovernmental Panel on Climate Change.
“Scientists from across the globe delivered the most up-to-date assessment of the ways in which the climate is changing,” Spinrad said in a statement. “It is a sobering IPCC report that finds that human influence is, unequivocally, causing climate change, and it confirms the impacts are widespread and rapidly intensifying.”
Other notable highlights from NOAA’s July global climate report
— Sea ice coverage varied by hemisphere: The Arctic sea ice coverage (extent) for July 2021 was the fourth-smallest for July in the 43-year record, according to analysis by the National Snow and Ice Data Center. Only July 2012, 2019 and 2020 had a smaller sea ice extent. Antarctic sea ice extent was above average in July — the largest July sea ice extent since 2015 and the eighth highest on record.
— The tropics were busier than average: In the Atlantic basin, the season’s earliest fifth-named storm, Elsa, formed on July 1. The Eastern North and Western Pacific basins each logged three named storms. Overall, global tropical cyclone activity this year so far (through July) has been above-normal for the number of named storms.
In a study released Wednesday, NASA researchers used precision-tracking data from the agency’s Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer, or OSIRIS-REx, spacecraft to better understand movements of the potentially hazardous asteroid Bennu through the year 2300, significantly reducing uncertainties related to its future orbit, and improving scientists’ ability to determine the total impact probability and predict orbits of other asteroids.
The study, titled “Ephemeris and hazard assessment for near-Earth asteroid (101955) Bennu based on OSIRIS-REx data,” was published in the journal Icarus.
“NASA’s Planetary Defense mission is to find and monitor asteroids and comets that can come near Earth and may pose a hazard to our planet,” said Kelly Fast, program manager for the Near-Earth Object Observations Program at NASA Headquarters in Washington. “We carry out this endeavor through continuing astronomical surveys that collect data to discover previously unknown objects and refine our orbital models for them. The OSIRIS-REx mission has provided an extraordinary opportunity to refine and test these models, helping us better predict where Bennu will be when it makes its close approach to Earth more than a century from now.”
In 2135, asteroid Bennu will make a close approach with Earth. Although the near-Earth object will not pose a danger to our planet at that time, scientists must understand Bennu’s exact trajectory during that encounter in order to predict how Earth’s gravity will alter the asteroid’s path around the Sun – and affect the hazard of Earth impact.
Using NASA’s Deep Space Network and state-of-the-art computer models, scientists were able to significantly shrink uncertainties in Bennu’s orbit, determining its total impact probability through the year 2300 is about 1 in 1,750 (or 0.057%). The researchers were also able to identify Sept. 24, 2182, as the most significant single date in terms of a potential impact, with an impact probability of 1 in 2,700 (or about 0.037%).
Although the chances of it hitting Earth are very low, Bennu remains one of the two most hazardous known asteroids in our solar system, along with another asteroid called 1950 DA.
Before leaving Bennu May 10, 2021, OSIRIS-REx spent more than two years in close proximity to the asteroid, gathering information about its size (it is about one-third of a mile, or 500 meters, wide), shape, mass, and composition, while monitoring its spin and orbital trajectory. The spacecraft also scooped up a sample of rock and dust from the asteroid’s surface, which it will deliver to Earth on Sept. 24, 2023, for further scientific investigation.
“The OSIRIS-REx data give us so much more precise information, we can test the limits of our models and calculate the future trajectory of Bennu to a very high degree of certainty through 2135,” said study lead Davide Farnocchia, of the Center for Near Earth Object Studies (CNEOS), which is managed by NASA’s Jet Propulsion Laboratory in Southern California. “We’ve never modeled an asteroid’s trajectory to this precision before.”
Gravitational keyholes
The precision measurements on Bennu help to better determine how the asteroid’s orbit will evolve over time and whether it will pass through a “gravitational keyhole” during its 2135 close approach. These keyholes are areas in space that would set Bennu on a path toward a future impact with Earth if the asteroid were to pass through them at certain times, due to the effect of Earth’s gravitational pull.
To calculate exactly where the asteroid will be during its 2135 close approach – and whether it might pass through a gravitational keyhole – Farnocchia and his team evaluated various types of small forces that may affect the asteroid as it orbits the Sun. Even the smallest force can significantly deflect its orbital path over time, causing it to pass through or completely miss a keyhole.
Among those forces, the Sun’s heat plays a crucial role. As an asteroid travels around the Sun, sunlight heats up its dayside. Because the asteroid spins, the heated surface will rotate away and cool down when it enters the nightside. As it cools, the surface releases infrared energy, which generates a small amount of thrust on the asteroid – a phenomenon called the Yarkovsky effect. Over short timeframes, this thrust is minuscule, but over long periods, the effect on the asteroid’s position builds up and can play a significant role in changing an asteroid’s path.
“The Yarkovsky effect will act on all asteroids of all sizes, and while it has been measured for a small fraction of the asteroid population from afar, OSIRIS-REx gave us the first opportunity to measure it in detail as Bennu travelled around the Sun,” said Steve Chesley, senior research scientist at JPL and study co-investigator. “The effect on Bennu is equivalent to the weight of three grapes constantly acting on the asteroid – tiny, yes, but significant when determining Bennu’s future impact chances over the decades and centuries to come.”
The team considered many other perturbing forces as well, including the gravity of the Sun, the planets, their moons, and more than 300 other asteroids, the drag caused by interplanetary dust, the pressure of the solar wind, and Bennu’s particle-ejection events.
The researchers even evaluated the force OSIRIS-REx exerted when performing its Touch-And-Go, or TAG, sample collection event Oct. 20, 2020, to see if it might have slightly altered Bennu’s orbit, ultimately confirming previous estimates that the TAG event had a negligible effect.
“The force exerted on Bennu’s surface during the TAG event were tiny even in comparison to the effects of other small forces considered,” said Rich Burns, OSIRIS-REx project manager at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “TAG did not alter Bennu’s likelihood of impacting Earth.”
Tiny risk, huge gain
Although a 0.057% impact probability through the year 2300 and an impact probability of 0.037% on Sept. 24, 2182, are low, this study highlights the crucial role that OSIRIS-REx operations played in precisely characterizing Bennu’s orbit.
“The orbital data from this mission helped us better appreciate Bennu’s impact chances over the next couple of centuries and our overall understanding of potentially hazardous asteroids – an incredible result,” said Dante Lauretta, OSIRIS-REx principal investigator and professor at the University of Arizona. “The spacecraft is now returning home, carrying a precious sample from this fascinating ancient object that will help us better understand not only the history of the solar system but also the role of sunlight in altering Bennu’s orbit since we will measure the asteroid’s thermal properties at unprecedented scales in laboratories on Earth.”