ESA Mission Poised to Probe Mercury’s Mysteries –“With Implications for the Search for Life on Alien Planets”


Mercury’s magnetosphere could have implications for the search for life beyond our solar system. Exoplanets found orbiting cool red dwarf stars could host liquid water, and possibly life. But because they orbit their stars more closely than Mercury orbits the sun, they likely face strong stellar winds and radiation levels inimical to life, unless the planet is protected by a magnetosphere like Mercury’s.

“If we want to understand if life can [survive] on such planets, one of the important bits of information is the magnetosphere,” says Go Murakami, project scientist for ESA’s BepiColombo mission at the Japan Aerospace Exploration Agency’s Institute of Space and Astronautical Science.

Although the field is 100 times weaker than Earth’s, it accelerates electrons from the solar wind to high energy levels, a phenomenon not seen in Earth’s magnetosphere. Magnetometers aboard both the European and Japanese spacecraft should help the team understand the processes behind the energy boost, says James Slavin, a lead MESSENGER investigator at the University of Michigan in Ann Arbor, who expects “definitive answers to the mystery.”

NASA’s MESSENGER mission to Mercury, left off in 2015, “threw into question many theories about how this planet came to be,” says BepiColombo team member Emma Bunce of the University of Leicester in the United Kingdom. BepiColombo “is perfectly timed and set up to answer these questions,” says mission scientist Johannes Benkhoff of the European Space Agency’s (ESA’s) technology center in Noordwijk, the Netherlands.

BepiColombo, named after the Italian professor Giuseppe ‘Bepi’ Colombo, who was instrumental in making the Mariner 10 mission a success, will probe puzzles including Mercury’s skewed magnetic field, its overstuffed iron core, and strange lakelike depressions perhaps carved by escaping volatile elements.

One mystery awaiting the mission is MESSENGER’s discovery of many volatile elements on the planet’s surface, including chlorine, sulfur, potassium, and sodium, which should have been boiled off by the sun’s heat long ago, reports Science.

“There is something odd in the formation history of Mercury,” Benkhoff says. A clue comes from the ratio of potassium to thorium, which indicates a planet’s temperature during formation. Benkhoff says Mercury’s ratio points to a cooler origin, farther out than Mars. Volatiles are more abundant at those distances, and if Mercury formed beyond Mars and drifted in only later, it would have retained a larger supply of volatiles.

A month before the planned October launch of the joint ESA-JAXA BepiColombo mission to Mercury, two new studies shed light on when the innermost planet formed and the puzzle of its chemical composition.

Mercury is the least-studied of the terrestrial planets and is something of an anomaly compared to Venus, Earth and Mars. It is very small, very dense, has an oversized molten core, and formed under chemical conditions that mean it contains much less oxidized material than its neighboring planets.

Research by a team at the University of Aix Marseille suggests that two factors may help explain why Mercury is so strange. Firstly, the planet may have formed very early in the Solar System’s history from condensed vapor from planetesimals. Secondly, that there may be more iron within Mercury’s mantle than might be suggested by measurements of the surface.

“We think that very early in the Solar System, planetesimals in the innermost region of the Solar System could have formed from reprocessed material that was vaporized due to the extreme temperature there and subsequently recondensed,” said Ronnet. “In addition, we are able to rule out a scenario where Mercury formed from a pile-up of planetesimals coming from further out in the Solar System since, in this case, Mercury would contain more oxidized material than we actually find.”

Early studies have suggested that Mercury is very rich in iron, and contains more sulphur than should be available in the material from which the bulk of the Solar System formed. Since then, the MESSENGER mission has greatly improved our view of the bulk composition of Mercury.

Brugger ran computer simulations of Mercury’s interior investigating core and mantle compositions and compared the results with gravity data gathered by the MESSENGER mission. The results suggest that Mercury has a dense mantle that may contain substantial amounts of iron.

“MESSENGER revealed very low abundances of silicate iron on the surface of Mercury, and this element would instead be present in metallic or sulphide phases. Our study suggests that iron abundances in the mantle could be higher than values measured on the surface,” said Brugger. “With the launch of BepiColombo, we will have a whole new suite of instruments to continue the investigation of Mercury’s unique properties, and try to better understand the structure and origin of the planet.”

BepiColombo is Europe’s first mission to Mercury. It is a joint endeavor between ESA and the Japan Aerospace Exploration Agency, JAXA, and consists of two scientific orbiters: ESA’s Mercury Planetary Orbiter and JAXA’s Mercury Magnetospheric Orbiter. They will be carried on a seven year journey to the innermost planet by the Mercury Transfer Module, using a combination of ion propulsion and gravity assist flybys at Earth, Venus and Mercury. The mission will study all aspects of Mercury, building on the achievements of MESSENGER to provide the best understanding of the Solar System’s innermost planet to date.

The four-in-one spacecraft will set off in October on-board Ariane 5 flight VA 245 for its journey to the smallest and least explored rocky planet in our Solar System. The 6.4-metre stacked satellite assembly will be injected into a direct Earth escape trajectory to start its seven years journey towards Mercury.

Power sources for BepiColombo will be the gravity of Earth, Venus and Mercury in combination with the thrust provided by solar-electric propulsion (SEP). During the voyage to Mercury, two orbiters, a transfer module, consisting of electric propulsion and traditional chemical thruster units, and a sun-shield will form one single composite spacecraft. When it arrives at Mercury in late 2025, the transfer module will separate the two science orbiters. They will endure temperatures in excess of 350 C and gather data during its one year nominal mission, with a possible one-year extension.

The Daily Galaxy via ESA, Science, and Europlanet

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