New research shows the sun’s magnetic field drew iron toward the center of our solar system as the planets formed. That explains why Mercury, which is closest to the sun has a bigger, denser, iron core relative to its outer layers than the other rocky planets like Earth and Mars. Credit: NASA’s Goddard Space Flight Center
New research from the University of Maryland shows that proximity to the sun’s magnetic field determines a planet’s interior composition.
A new study disputes the prevailing hypothesis on why Mercury has a big core relative to its mantle (the layer between a planet’s core and crust). For decades, scientists argued that hit-and-run collisions with other bodies during the formation of our solar system blew away much of Mercury’s rocky mantle and left the big, dense, metal core inside. But new research reveals that collisions are not to blame—the sun’s magnetism is.
William McDonough, a professor of geology at the University of Maryland, and Takashi Yoshizaki from Tohoku University developed a model showing that the density, mass and iron content of a rocky planet’s core are influenced by its distance from the sun’s magnetic field. The paper describing the model was published on July 2, 2021, in the journal Progress in Earth and Planetary Science.
“The four inner planets of our solar system—Mercury, Venus, Earth, and Mars—are made up of different proportions of metal and rock,” McDonough said. “There is a gradient in which the metal content in the core drops off as the planets get farther from the sun. Our paper explains how this happened by showing that the distribution of raw materials in the early forming solar system was controlled by the sun’s magnetic field.”
McDonough previously developed a model for Earth’s composition that is commonly used by planetary scientists to determine the composition of exoplanets. (His seminal paper on this work has been cited more than 8,000 times.)
McDonough’s new model shows that during the early formation of our solar system, when the young sun was surrounded by a swirling cloud of dust and gas, grains of iron were drawn toward the center by the sun’s magnetic field. When the planets began to form from clumps of that dust and gas, planets closer to the sun incorporated more iron into their cores than those farther away.
The researchers found that the density and proportion of iron in a rocky planet’s core correlates with the strength of the magnetic field around the sun during planetary formation. Their new study suggests that magnetism should be factored into future attempts to describe the composition of rocky planets, including those outside our solar system.
The composition of a planet’s core is important for its potential to support life. On Earth, for instance, a molten iron core creates a magnetosphere that protects the planet from cancer-causing cosmic rays. The core also contains the majority of the planet’s phosphorus, which is an important nutrient for sustaining carbon-based life.
Using existing models of planetary formation, McDonough determined the speed at which gas and dust was pulled into the center of our solar system during its formation. He factored in the magnetic field that would have been generated by the sun as it burst into being and calculated how that magnetic field would draw iron through the dust and gas cloud.
As the early solar system began to cool, dust and gas that were not drawn into the sun began to clump together. The clumps closer to the sun would have been exposed to a stronger magnetic field and thus would contain more iron than those farther away from the sun. As the clumps coalesced and cooled into spinning planets, gravitational forces drew the iron into their core.
When McDonough incorporated this model into calculations of planetary formation, it revealed a gradient in metal content and density that corresponds perfectly with what scientists know about the planets in our solar system. Mercury has a metallic core that makes up about three-quarters of its mass. The cores of Earth and Venus are only about one-third of their mass, and Mars, the outermost of the rocky planets, has a small core that is only about one-quarter of its mass.
This new understanding of the role magnetism plays in planetary formation creates a kink in the study of exoplanets, because there is currently no method to determine the magnetic properties of a star from Earth-based observations. Scientists infer the composition of an exoplanet based on the spectrum of light radiated from its sun. Different elements in a star emit radiation in different wavelengths, so measuring those wavelengths reveals what the star, and presumably the planets around it, are made of.
“You can no longer just say, ‘Oh, the composition of a star looks like this, so the planets around it must look like this,’” McDonough said. “Now you have to say, ‘Each planet could have more or less iron based on the magnetic properties of the star in the early growth of the solar system.’”
The next steps in this work will be for scientists to find another planetary system like ours—one with rocky planets spread over wide distances from their central sun. If the density of the planets drops as they radiate out from the sun the way it does in our solar system, researchers could confirm this new theory and infer that a magnetic field influenced planetary formation.
Reference: “Terrestrial planet compositions controlled by accretion disk magnetic field” by William F. McDonough and Takashi Yoshizaki, 2 July 2021, Progress in Earth and Planetary Science. DOI: 10.1186/s40645-021-00429-4
NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
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.
