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Planet Mercury Has Solid Inner Core About Same Size as Earth



Mercury's surface
Photo: MESSENGER

A new analysis has found that Mercury has a solid inner core, just like Earth does. And Mercury's core is about the same size as our own planet.

I'm biased here, but Mercury is an incredible, mysterious planet that continues to offer exciting results to scientists. Perhaps most intriguingly, it generates its own magnetic field from the motion deep within the planet, just like the Earth. The discovery of Mercury's solid inner core could help scientists better understand both planets.

"An enhanced knowledge of the size of the solid inner core provides crucial information on the history of the planet's interior and, consequently, its magnetic field" Antonio Genova, an assistant professor at Sapienza Università di Roma and the study's first author, told Gizmodo in an email. "The solidification of the core has a major role in Earth's interior and magnetic field evolution."

The most recent spacecraft to study the planet up close was NASA's MErcury Surface, Space ENvironment, Geochemistry, and Ranging (MESSENGER) Mission , which launched in 2004 and orbited the Mercury from 2011 to 2015. During that mission, it took detailed measurements of the planet's surface, gravity field and rotation, which scientists hoped would reveal what Mercury looked like from the inside. Most recently, scientists reanalyzed the probe's Radio Science instrument, taking into account a new technique in order to precisely determine the planet's orbit.

This led to new estimates for the planet's gravitational field, according to a paper recently published in Geophysical Research Letters . Those results showed that the planet has a solid inner core that makes up about 30 to 70 percent of the total radius of the Mercury core.

"Mercury is now the second rocky planet-after Earth-for which we have evidence of solid Internal core, "Sean Solomon, principal investigator of the MESSENGER mission, told Gizmodo.

It's not a precise value, but the mere presence of a solid core core says something important-it helps scientists better understand how the planet generates its magnetic field. On Earth, the scientists attribute our own magnetic field to the dynamo, the heat from the inner core, combined with the planet's spin driving motion of the metal in the liquid outer core. Mercury's interior is also cooling, as demonstrated by land forms generated by its surface contracting. The size of the solid core core will help scientists better understand that cooling, said Solomon.

If the solid core took half the Mercury core's radius, that's about 1,000 kilometers, according to calculations in the paper-over 40 percent of the planet's total radius of less than 2,500 kilometers. By contrast, Earth's solid core is about 1,200 kilometers in radius, which is less than one-fifth of our planet's total radius of 6,370 kilometers. Scientists wonder about the reasons for these differences.

Thankfully, there's another mission on the way to the rocky inner planet called BepiColombo. Hopefully, scientists will soon solve some of Mercury's mysteries.


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