For decades, scientists have held that the Earth-Moon system formed as a result of a collision between Earth and a Mars-sized object roughly 4.5 billion years ago. Known as the Giant Impact Hypothesis, this theory explains why Earth and the Moon are similar in structure and composition. Interestingly enough, scientists have also determined that during its early history, the Moon had a magnetosphere – much like Earth does today.
However, a new study led by researchers at MIT (with support provided by NASA) indicates that at one time, the Moon’s magnetic field may have actually been stronger than Earth’s. They were also able to place tighter constraints on when this field petered out, claiming it would have happened about 1 billion years ago. These findings have helped resolve the mystery of what mechanism powered the Moon’s magnetic field over time.
The study, which recently appeared in the journal Science Advances, was led by Saied Mighani, an experimental rock physicist with MIT’s Department of Earth, Atmospheric, and Planetary Sciences. He was joined by members of the Berkeley Geochronology Center at UC Berkeley and the China University of Geosciences, with additional support provided by famed EAPS professor, Dr. Benjamin Weiss.
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To recap, Earth’s magnetic field is essential to life as we know it. When incoming solar wind particles reach Earth, they are deflected by this field and form a bow shock in front of Earth and magnetotail behind it. The remaining particles are deposited on the magnetic poles where they interact with our atmosphere, which causes the Aurorae seen in the far northern and southern hemispheres.
Were it not for this magnetic field, Earth’s atmosphere would have been slowly stripped away by solar wind over the course of billions of years and rendered a cold, dry place. This is believed to be what happened on Mars, where a once-thicker atmosphere was depleted between 4.2 and 3.7 billion years ago and all of the liquid water on its surface was either lost or froze as a result.
Over the years, Weiss’ group has helped demonstrate through the study of lunar rocks that roughly 4 billion years ago, the Moon also had a strong magnetic field of about 100 microteslas in strength (whereas Earth’sis around 50 microteslas today). In 2017, they studied samples collected by the Apollo astronauts that were dated to about 2.5 billion years ago and found a much weaker field (less than 10 microteslas).
In other words, the Moon’s magnetic field weakened by a factor of five between 4 and 2.5 billion years ago, then disappeared entirely about 1 billion years ago. At the time, Weiss and his colleagues theorized that perhaps there were two dynamo mechanisms in the Moon’s interior that were responsible for this change.
Measurements of lunar rocks have demonstrated that the ancient moon generated a dynamo magnetic field in its liquid metallic core (innermost red shell). Credit: Hernán Cañellas/Benjamin Weiss
In short, they argued that a first dynamo effect could have generated a much stronger magnetic field around 4 billion years ago. Then, 2.5 billion years ago, it was replaced by a second dynamo that was more long-lived but sustained a much weaker magnetic field. As Dr. Weiss explained in an MIT News release:
“There are several ideas for what mechanisms powered the lunar dynamo, and the question is, how do you figure out which one did it? It turns out all these power sources have different lifetimes. So if you could figure out when the dynamo turned off, then you could distinguish between the mechanisms that have been proposed for the lunar dynamo. That was the purpose of this new paper.”
Until now, obtaining lunar rocks that are less than 3 billion years old has been a major challenge. The reason for this has to do with the fact that volcanic activity, which was common on the Moon 4 billion years ago, ceased roughly 3 billion years ago. Luckily, the MIT team was able to identify two samples of lunar rock obtained by the Apollo astronauts that were created by an impact 1 billion years ago.
While these rocks were melted by the impact and then resolidified, thus erasing their magnetic record in the process, the team was able to perform tests on them to reconstruct their magnetic signature. First, they analyzed the orientation of the rock’s electrons, which Weiss describes as “little compasses” since they would either align in the direction of an existing magnetic field or appear in random orientations in the absence of one.
Moon rocks from the Apollo 11 mission. Credit: NASA
In both samples, the team observed the latter, which suggested that the rocks formed in an extremely weak magnetic field of no more than 0.1 microteslas (possibly none at all). This was followed by a radiometric dating technique that was adapted for this study by Weiss and David L. Shuster (a Berkeley Geochronology Center researcher and co-author of the study). These results confirmed that the rocks were indeed 1 billion years old.
Finally, the team conducted heat tests on the samples to determine if they could provide a good magnetic record at the time of the impact. This consisted of placing both samples in an oven and exposing them to the kinds of high temperatures that would have been created by an impact. As they cooled, they exposed them to an artificially-generated magnetic field in the laboratory and confirmed that they were able to record it.
These results confirm that the magnetic strength initially measured by the team (0.1 microteslas) is accurate and that by 1 billion years ago, the dynamo powering the Moon’s magnetic field had likely ended. As Weiss expressed:
“The magnetic field is this nebulous thing that pervades space, like an invisible force field. We’ve shown that the dynamo that produced the moon’s magnetic field died somewhere between 1.5 and 1 billion years ago, and seems to have been powered in an Earth-like way.”
Lunar footprint from the Apollo missions. Credit: NASA
As noted, this study also helps to resolve the debate surrounding what drove the lunar dynamo in its later stages. While multiple theories have been suggested, these new findings are consistent with the theory that core crystallization is responsible. Basically, this theory states that the Moon’s inner core crystallized over time, slowing the flow of electrically-charged fluid and arresting the dynamo.
Weiss suggests that prior to this, precession may have been responsible for powering a much stronger (but short-lived) dynamo which would have produced the strong magnetic field. This is consistent with the fact that 4 billion years ago, the Moon is thought to have orbited much closer to Earth. This would have resulted in Earth’s gravity having a far greater effect on the Moon, causing its mantle to wobble and stirring up activity in the core.
As the Moon slowly migrated away from Earth, the effect of precession decreased and the magnetic field-producing dynamo would weaken. By about 2.5 billion years ago, crystallization became the dominant mechanism by which the lunar dynamo continued, producing a weaker magnetic field that persisted until the outer core finally crystallized a billion years ago.
Studies like this could also help resolve the mystery of why planets like Venus and Mars lost their magnetic fields (contributing to cataclysmic climate change) and how Earth could lose its own someday. Considering its importance to habitability, a greater understanding of dynamos and magnetic fields could also help in the search for habitable exoplanets.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
The European Space Agency is fast-tracking a new mission called Ramses, which will fly to near-Earth asteroid 99942 Apophis and join the space rock in 2029 when it comes very close to our planet — closer even than the region where geosynchronous satellites sit.
Ramses is short for Rapid Apophis Mission for Space Safety and, as its name suggests, is the next phase in humanity’s efforts to learn more about near-Earth asteroids (NEOs) and how we might deflect them should one ever be discovered on a collision course with planet Earth.
In order to launch in time to rendezvous with Apophis in February 2029, scientists at the European Space Agency have been given permission to start planning Ramses even before the multinational space agency officially adopts the mission. The sanctioning and appropriation of funding for the Ramses mission will hopefully take place at ESA’s Ministerial Council meeting (involving representatives from each of ESA’s member states) in November of 2025. To arrive at Apophis in February 2029, launch would have to take place in April 2028, the agency says.
This is a big deal because large asteroids don’t come this close to Earth very often. It is thus scientifically precious that, on April 13, 2029, Apophis will pass within 19,794 miles (31,860 kilometers) of Earth. For comparison, geosynchronous orbit is 22,236 miles (35,786 km) above Earth’s surface. Such close fly-bys by asteroids hundreds of meters across (Apophis is about 1,230 feet, or 375 meters, across) only occur on average once every 5,000 to 10,000 years. Miss this one, and we’ve got a long time to wait for the next.
When Apophis was discovered in 2004, it was for a short time the most dangerous asteroid known, being classified as having the potential to impact with Earth possibly in 2029, 2036, or 2068. Should an asteroid of its size strike Earth, it could gouge out a crater several kilometers across and devastate a country with shock waves, flash heating and earth tremors. If it crashed down in the ocean, it could send a towering tsunami to devastate coastlines in multiple countries.
Over time, as our knowledge of Apophis’ orbit became more refined, however, the risk of impact greatly went down. Radar observations of the asteroid in March of 2021 reduced the uncertainty in Apophis’ orbit from hundreds of kilometers to just a few kilometers, finally removing any lingering worries about an impact — at least for the next 100 years. (Beyond 100 years, asteroid orbits can become too unpredictable to plot with any accuracy, but there’s currently no suggestion that an impact will occur after 100 years.) So, Earth is expected to be perfectly safe in 2029 when Apophis comes through. Still, scientists want to see how Apophis responds by coming so close to Earth and entering our planet’s gravitational field.
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“There is still so much we have yet to learn about asteroids but, until now, we have had to travel deep into the solar system to study them and perform experiments ourselves to interact with their surface,” said Patrick Michel, who is the Director of Research at CNRS at Observatoire de la Côte d’Azur in Nice, France, in a statement. “Nature is bringing one to us and conducting the experiment itself. All we need to do is watch as Apophis is stretched and squeezed by strong tidal forces that may trigger landslides and other disturbances and reveal new material from beneath the surface.”
The Goldstone radar’s imagery of asteroid 99942 Apophis as it made its closest approach to Earth, in March 2021. (Image credit: NASA/JPL–Caltech/NSF/AUI/GBO)
By arriving at Apophis before the asteroid’s close encounter with Earth, and sticking with it throughout the flyby and beyond, Ramses will be in prime position to conduct before-and-after surveys to see how Apophis reacts to Earth. By looking for disturbances Earth’s gravitational tidal forces trigger on the asteroid’s surface, Ramses will be able to learn about Apophis’ internal structure, density, porosity and composition, all of which are characteristics that we would need to first understand before considering how best to deflect a similar asteroid were one ever found to be on a collision course with our world.
Besides assisting in protecting Earth, learning about Apophis will give scientists further insights into how similar asteroids formed in the early solar system, and, in the process, how planets (including Earth) formed out of the same material.
One way we already know Earth will affect Apophis is by changing its orbit. Currently, Apophis is categorized as an Aten-type asteroid, which is what we call the class of near-Earth objects that have a shorter orbit around the sun than Earth does. Apophis currently gets as far as 0.92 astronomical units (137.6 million km, or 85.5 million miles) from the sun. However, our planet will give Apophis a gravitational nudge that will enlarge its orbit to 1.1 astronomical units (164.6 million km, or 102 million miles), such that its orbital period becomes longer than Earth’s.
It will then be classed as an Apollo-type asteroid.
Ramses won’t be alone in tracking Apophis. NASA has repurposed their OSIRIS-REx mission, which returned a sample from another near-Earth asteroid, 101955 Bennu, in 2023. However, the spacecraft, renamed OSIRIS-APEX (Apophis Explorer), won’t arrive at the asteroid until April 23, 2029, ten days after the close encounter with Earth. OSIRIS-APEX will initially perform a flyby of Apophis at a distance of about 2,500 miles (4,000 km) from the object, then return in June that year to settle into orbit around Apophis for an 18-month mission.
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Furthermore, the European Space Agency still plans on launching its Hera spacecraft in October 2024 to follow-up on the DART mission to the double asteroid Didymos and Dimorphos. DART impacted the latter in a test of kinetic impactor capabilities for potentially changing a hazardous asteroid’s orbit around our planet. Hera will survey the binary asteroid system and observe the crater made by DART’s sacrifice to gain a better understanding of Dimorphos’ structure and composition post-impact, so that we can place the results in context.
The more near-Earth asteroids like Dimorphos and Apophis that we study, the greater that context becomes. Perhaps, one day, the understanding that we have gained from these missions will indeed save our planet.
