Scientists find evidence Mercury has a solid inner core

Related Articles

Related Articles

Scientists have long known that Earth and Mercury have metallic cores. Like Earth, Mercury’s outer core is composed of liquid metal, but there have only been hints that Mercury’s innermost core is solid.

Now, in a new study, scientists report evidence that Mercury’s inner core is indeed solid and that it is very nearly the same size as Earth’s solid inner core.

Some scientists compare Mercury to a cannonball because its metal core fills nearly 85 percent of the volume of the planet. This large core — huge compared to the other rocky planets in our solar system — has long been one of the most intriguing mysteries about Mercury. Scientists had also wondered whether Mercury might have a solid inner core.

The findings of Mercury’s solid inner core, published in AGU’s journal Geophysical Research Letters, help scientists better understand Mercury but also offer clues about how the solar system formed and how rocky planets change over time.

“Mercury’s interior is still active, due to the molten core that powers the planet’s weak magnetic field, relative to Earth’s,” said Antonio Genova, an assistant professor at Sapienza University of Rome who led the research while at NASA Goddard Space Flight Center in Greenbelt, Maryland. “Mercury’s interior has cooled more rapidly than our planet’s. Mercury may help us predict how Earth’s magnetic field will change as the core cools.”

To figure out what Mercury’s core is made of, Genova and his colleagues had to get, figuratively, closer. The team used several observations from NASA’s MESSENGER mission to probe Mercury’s interior. The researchers looked, most importantly, at the planet’s spin and gravity.


Subscribe to more articles like this by following our Google Discovery feed - Click the follow button on your desktop or the star button on mobile. Subscribe

The MESSENGER spacecraft entered orbit around Mercury in March 2011 and spent four years observing this nearest planet to our Sun until it was deliberately brought down to the planet’s surface in April 2015.

Scientists used radio observations from MESSENGER to determine Mercury’s gravitational anomalies (areas of local increases or decreases in mass) and the location of its rotational pole, which allowed them to understand the orientation of the planet.

Each planet spins on an axis, also known as the pole. Mercury spins much more slowly than Earth, with its day lasting about 58 Earth days. Scientists often use tiny variations in the way an object spins to reveal clues about its internal structure. In 2007, radar observations made from Earth revealed small shifts in Mercury’s spin, called librations, that proved some of the planet’s core must be liquid-molten metal. But observations of the spin rate alone were not sufficient to give a clear measurement of what the inner core was like. Could there be a solid core lurking underneath, scientists wondered?

Gravity can help answer that question. “Gravity is a powerful tool to look at the deep interior of a planet because it depends on the planet’s density structure,” said Sander Goossens, a researcher at NASA Goddard and co-author of the new study.

As MESSENGER orbited Mercury over the course of its mission and got closer and closer to the surface, scientists recorded how the spacecraft accelerated under the influence of the planet’s gravity. The density structure of a planet can create subtle changes in a spacecraft’s orbit. In the later parts of the mission, MESSENGER flew about 120 miles above the surface, and less than 65 miles during its last year. The final low-altitude orbits provided the best data yet and allowed for Genova and his team to make the most accurate measurements about the internal structure of Mercury yet taken.

Genova and his team put data from MESSENGER into a sophisticated computer program that allowed them to adjust parameters and figure out what the interior composition of Mercury must be like to match the way it spins and the way the spacecraft accelerated around it. The results showed that for the best match, Mercury must have a large, solid inner core. They estimated that the solid, iron core is about 1,260 miles (2,000 kilometers) wide and makes up about half of Mercury’s entire core (about 2,440 miles, or nearly 4,000 kilometers, wide). In contrast, Earth’s solid core is about 1,500 miles (2,400 kilometers) across, taking up a little more than a third of this planet’s entire core.

“We had to pull together information from many fields: geodesy, geochemistry, orbital mechanics and gravity to find out what Mercury’s internal structure must be,” said Erwan Mazarico, a planetary scientist at NASA Goddard and co-author of the new study.

The fact that scientists needed to get close to Mercury to find out more about its interior highlights the power of sending spacecraft to other worlds, according to the researchers. Such accurate measurements of Mercury’s spin and gravity were simply not possible to make from Earth. New discoveries about Mercury are practically guaranteed to be waiting in MESSENGER’s archives, with each discovery about our local planetary neighborhood giving us a better understanding of what lies beyond.

“Every new bit of information about our solar system helps us understand the larger universe,” Genova said.

AMERICAN GEOPHYSICAL UNION

Header Image Credit : NASA

- Advertisement -

Download the HeritageDaily mobile application on iOS and Android

More on this topic

LATEST NEWS

Drones Map High Plateaus Basin in Moroccan Atlas to Understand Human Evolution

Researchers from the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH) have been using drones to create high-resolution aerial images and topographies to compile maps of the High Plateaus Basin in Moroccan Atlas.

The Kerguelen Oceanic Plateau Sheds Light on the Formation of Continents

How did the continents form? Although to a certain extent this remains an open question, the oceanic plateau of the Kerguelen Islands may well provide part of the answer, according to a French-Australian team led by the Géosciences Environnement Toulouse laboratory.

Ancient Societies Hold Lessons for Modern Cities

Today's modern cities, from Denver to Dubai, could learn a thing or two from the ancient Pueblo communities that once stretched across the southwestern United States. For starters, the more people live together, the better the living standards.

Volubilis – The Ancient Berber City

Volubilis is an archaeological site and ancient Berber city that many archaeologists believe was the capital of the Kingdom of Mauretania.

Pella – Birthplace of Alexander The Great

Pella is an archaeological site and the historical capital of the ancient kingdom of Macedon.

New Argentine fossils uncover history of celebrated conifer group

Newly unearthed, surprisingly well-preserved conifer fossils from Patagonia, Argentina, show that an endangered and celebrated group of tropical West Pacific trees has roots in the ancient supercontinent that once comprised Australia, Antarctica and South America, according to an international team of researchers.

High-tech CT reveals ancient evolutionary adaptation of extinct crocodylomorphs

The tree of life is rich in examples of species that changed from living in water to a land-based existence.

Fish fossils become buried treasure

Rare metals crucial to green industries turn out to have a surprising origin. Ancient global climate change and certain kinds of undersea geology drove fish populations to specific locations.

Archaeologists Discover Viking Toilet in Denmark

Archaeologists excavating a settlement on the Stevns Peninsula in Denmark suggests they have discovered a toilet from the Viking Age.

Innovation by ancient farmers adds to biodiversity of the Amazon, study shows

Innovation by ancient farmers to improve soil fertility continues to have an impact on the biodiversity of the Amazon, a major new study shows.

Popular stories