Monthly Archives: July 2021

Among the terrestrial planetssolar systemAnd Mercury is an exception. In its contrasting interior in silicate shell and metal core, the latter represents three quarters of its total mass! Much higher in the case of Venus and Earth – a third – as for Mars – a quarter. Even more surprising is its density, given the generally higher iron content, which exceeds all other planets. To explain this difference, two theories have followed one another. The first imagined a gradient of the fraction of iron available to form the planets according to the distance from the sun. The vision was then replaced by the idea of ​​collision (s) which blew up the rock mantle of Mercury. However, a new paradigm seems to dust off the oldest theory by tilting in its favor. But has the mystery of iron mercury really been solved?

The magnetic field of the young sun. The solar dynamo creates a strong magnetic field (green lines) that attracts the iron-rich magnetic particles to the Sun in a planetary accretion disk. Source: NASA / JPL-Caltech.

The magnetic field of the young sun

Researchers at the University of Maryland and the University of Tohoku have developed a model that represents the chemical makeup of planets as a function of heliocentric position. As a starting point for their study, they postulated that the density, mass and iron content of the planet vary with its distance from the solar magnetic field. Specifically, about the young Sun, at the time when planets were still forming in a protoplanetary disk. “The Sun is made of plasma, highly conductive, capable of supporting and amplifying the magnetic field”, describes Joao Pedro Marquez, lecturer at the IAS and at the University of Paris-Saclay. However, macroscopic movements such as convection or rotation have been shown to amplify them more, which is called the dynamo effect. That is why young stars, spinning very quickly, have a strong magnetic field. But this electromagnetic dance is in reality a waltz, in which the partner of the solar star is only the disc that surrounds it …

Much like a spinning disc, the sun is absorbed into plasma, through which electric currents pass. “These two astrophysical bodies interact and create instability in the disc,” notes the astrophysicist. The resulting magnetic field will attract iron particles to the center of the solar system, producing a gradient visible on both planets and meteorites. Then the accumulated iron sinks into the core under the influence of gravity, at the same time expelling oxygen from the lighter. But is this process enough to get an iron core like Mercury? I am not entirely sure according to Joao Pedro Marquez: “Such a scenario does not exclude the addition of a celestial collision, because Mercury still contains a lot of iron! “.

How the Mercury Credits were formed: Left: NASA / JPL-Caltech Right: Reprinted with permission from Macmillan Publishers Ltd: Nature [4737348: 460-461,© 2011]Nasa.

From iron to earthly life

However, the results presented by the researchers raise questions according to Matthew Finsendon, who is also a lecturer at the IAS and the University of Paris-Saclay. Thus, the planetary orientation presented in the research mainly depends on the state of Mercury, which clearly stands out in terms of intensity. The scale used also curiously flattens the state of Venus which, unlike the defended scenario, is less dense than Earth – but more distant. A problem that seems to be solved by the unexpected absence of Venus in several characters … but it is not the only anomaly to count. “According to this model, the formation of Mercury will be completed in just two million years, which seems fast,” notes Matthew Finsendon. In addition, the migration of giant planets should be at the origin of important movements of matter, which would distort the appearance of the gradient. The reasons for questioning are piling up… However, there is one point in particular that looks promising: the state of exoplanets.

To validate their findings, the researchers propose to observe other star systems similar to ours, in order to see if the planetary iron gradient in our system is located elsewhere. If the density of the planets decreased with the distance from the star, they would be right… really? “There are still potential biases. Perhaps near the star, the outer layers of the planet risk disappearing after the collision, in which case the theory of the collision of Mercury remains plausible, ”suggests the astrophysicist. With its unusual nucleus, Mercury is one of the few planets that still has a magnetic field. The core of a planet is truly crucial to sustaining life… as we know it! The blue planet therefore has a magnetosphere through the liquid part of its iron core. Cosmic rays refract there before seriously damaging the health of living organisms. What if life existed without a magnetic field? With organisms living exclusively underground or resistant to radiation. Matthew Finsendon insists: “If there is life, it must adapt as much as possible to its development environment.

Calcutta: Unprecedented iron ore and pellet prices are forcing small secondary steel units in various states, including West Bengal, to shut down or cut production, officials said on Sunday. In West Bengal, at least five of those MSME units have closed while another 100 to 115 have cut production by 15 to 50 percent, Steel Re-rolling Mills Association chairman Vivek Adukia said.

“Secondary steel MSMEs are also waiving the power requirements of DVC and WBSEDCL (West Bengal State Electricity Distribution Company Limited),” Adukia said.

In Bengal, about 500 units are engaged in sponge iron, rolling mills and steelmaking through induction furnace. All of these units, along with factories in other states, are suffering from unprecedented iron ore prices, pellet prices due to the unhindered export of the ore.

The secondary steel associations of West Bengal, Odhisha, Madhya Pradesh, Chhattisgarh, Jharkhand, Karnataka, Maharashtra and Andhra Pradesh jointly asked the Prime Minister and the Minister of Steel for their intervention and the imposition of a 50 percent export duty on pellets.

Secondary steelmakers have argued their demand for pellet export duties for a year without any effective action from the government, Adukia said.

West Bengal Sponge Iron Manufacturers Association President Shankar Lal Agarwal said the price of pellets rose from Rs 4,500 per tonne in May 2020 to Rs 15,000 per tonne in June of this year, impacting costs a ton of steel of 20,800 Rs.

Officials claimed that 50,000 secondary steel MSMEs plunged into losses despite such high steel prices.

“Companies with their own sources of pellets and iron ore are making a profit,” Adukia said.

Advocating the government to make raw materials available for domestic industry, Agarwal called on the government to allow a consortium of smaller units (up to 5 members per consortium) to bid in auctions that will help reduce dependence on the free market.

Mercury’s disproportionately massive core could be the result of the Sun’s powerful magnetic influence rather than the consequence of a cataclysmic collision with another body in the ancient past, according to the results of a new study.

Since the advent of spaceflight, humanity has sent only three spaceships to unravel the secrets held by Mercury, the innermost planet in our solar system. In the 1970s, NASA’s Mariner 10 spacecraft made three separate overflights of the planet, capturing high-resolution images and capturing data about Mercury’s magnetic field.

Decades later, on March 17, 2011, the agency’s MESSENGER spacecraft became the first probe to orbit Mercury. He then spent four years characterizing the alien world in unprecedented detail. Meanwhile, the joint European / Japanese mission BepiColombo is still on its way to the planet and is expected to arrive at the end of 2025.

As a result of these efforts, astronomers have learned a lot about Mercury, but it still holds a plethora of mysteries that the scientific community has yet to solve.

One of these mysteries is related to the internal structure of the planet. Analysis of data collected by orbiting spacecraft taking detailed readings of Mercury’s gravitational signature had in the past revealed that the planet had an iron core of disproportionate mass to the size of its mantle.

To be more precise, it is estimated that the core is about three-quarters of the mass of Mercury and has a radius of about 1,289 miles (2,074 km), while the outer rocky shell of the planet is only 250 miles (400 km). in depth. This makes it the second densest planet in the solar system.

Until now, the main theory as to why Mercury has such an unusually large nucleus for such a small planet has centered on the idea that it was in fact a much larger planet that had fallen victim to a planetary collision in the distant past. According to this theory, the cataclysmic force of the interaction was sufficient to remove much of Mercury’s outer shell, leaving behind a shallow mantle to cover the core of the once larger planet.

However, according to the new study, Mercury’s unusual structure may actually be the result of the natural influence of the Sun’s magnetic field.

The authors created a new computer model of the primordial cloud of dust and gas from which planets in the solar system would eventually form, and simulated the effect of a young Sun’s magnetic field on the swirling mass. It was discovered that the magnetic influence of our mother star brought the iron grains embedded in the cloud closer together. This resulted in the planets that formed closest to the Sun to have a much larger iron core than those that would one day orbit in the most distant regions of the solar system.

The researchers combined their model with previous research on planetary formation, in order to calculate the speed at which the material would be attracted to the Sun. They found that the planetary compositions predicted by their model correlated well with the actual planets that make up our solar system today.

As well as shedding light on how our home solar system came to merge and subsequently mature, the new research could also have important implications for astronomers hoping to better understand distant exoplanets spread across the galaxy.

“You can’t just say, ‘Oh, a star’s makeup looks like this anymore, so the planets around it have to look like this,” said William McDonough, professor of geology at the University of Maryland and one of the authors. of the new study. “Now you have to say, ‘Each planet might have more or less iron depending on the star’s magnetic properties when the solar system starts growing.'”

The team is now looking for an alien star system in which rocky planets are known to orbit, with which they can further test their theory.

The article was published in the journal Advances in Earth and Planetary Sciences.

Source: University of Maryland