Mercury has a Solid Inner Core, new study shows

Like Earth, Mercury’s outer core is composed of liquid metal while it has a solid inner core, which accounts for nearly 85% of the planet’s volume.

Mercury is an incredible, mysterious planet that continues to offer some exciting results to scientists. Perhaps most intriguingly, it generates its own magnetic field from the motion deep within the planet, just like the Earth. Planetary researchers have long known that Earth and Mercury have metallic cores but the discovery of Mercury’s solid inner core could help scientists to improve their understanding of both the planets. This core fills nearly 85% of the volume of the planet — huge compared to the other rocky planets in the Solar System. Dr. Antonio Genova, a Researcher at Sapienza University referred to that and said,

“An enhanced knowledge of the size of the solid inner core provides crucial information on the history of the planet’s interior and, consequently, of its magnetic field. Mercury’s interior is still active, due to the molten core that powers the planet’s weak magnetic field, relative to Earth’s and its 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.”

A number of previous theories suggest that Mercury itself was a core of a bigger body and the planet was born once that body was blown off by solar radiation.

The Process

In order to determine the composition of Mercury’s core, researchers took help from the MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) mission of NASA which was launched in 2004 and orbited Mercury from 2011 to 2015. This mission gathered an immense amount of data, including detailed measurements of the planet’s surface, gravitational field, and rotation. Mercury spins much more slowly than Earth, with its day lasting about 58 Earth days. In an attempt to determine the precise orbit of the planet, scientists reanalyzed the Radio Science instrument of MESSENGER by making use of a new technique.

The close approach of the probe allowed the scientists to extrapolate the acceleration of the spacecraft under the influence of the planet’s gravity. The researchers then put all that data into a sophisticated computer program. The results showed that Mercury must have a large, solid inner core of about 1,260 miles (about 2,000 kilometers). Determining gravitational anomalies (areas of local increases or decreases in mass) and the location of its rotational pole enabled the researching team to understand the orientation of Mercury. Sander Goossens, a Researcher at NASA Goddard Center, emphasized the power of gravity as a tool to learn about the interior structure of a planet. Erwan Mazarico, a Planetary Scientist at Goddard, acknowledged his idea by saying,

“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.”

Findings

According to the paper published in Geophysical Research Letters, this research has resulted in new estimates for the planet’s gravitational field. The findings of the study demonstrate that the planet has a solid inner core which fills about 85% of the entire planet. This makes Mercury the second rocky planet after Earth to have a solid core. Although this figure is more of an estimate, the mere presence of a solid inner core says something really important about the magnetic field of the planet. The magnetic field of Earth is attributed to the heat from the inner core combined with the planet’s spin driving motion of metal in the outer core. Similarly, Mercury’s interior is also cooling and the size of the solid inner core will help scientists to better understand that cooling effect.

Significance of Solid Inner Core

The research highlights the importance of sending probes to investigate planets up close. Such accuracy is simply not possible by observing the worlds from Earth. The team thinks many more discoveries remain hidden in the extensive MESSENGER data while another mission (BepiColombo) is on its way to Mercury. This mission is interestingly named after the Italian mathematician and engineer Giuseppe (Bepi) Colombo and scientists are hopeful that it will continue to unravel the mystery of Mercury. Genova summed up the situation in the following words:

“Every new bit of information about our Solar System helps us understand the larger universe.”