Image Credit: ESA artist impression
By: Sarah Cruddas
To date only two robotic spacecraft have ever explored the planet Mercury. The closest planet to our Sun is also the least visited of the inner rocky worlds. Instead it is often overlooked, in favor of the seemingly more exciting counterparts – Venus, with its choking thick atmosphere, and Mars, the next destination for human explorers.
But on October 20, a new mission will launch to this barren world at the inner reaches of our Solar System. Known as BepiColombo, it is named in honor of the man who made our first ever mission to Mercury possible, Italian Mathematician and Engineer Giuseppe Colombo – better know by his nickname Bepi Colombo.
While the two previous missions to Mercury had been carried out by NASA, this is the first mission to the planet for the European Space Agency (ESA). Together with the Japanese Space Agency (JAXA), they have developed not one, but two spacecraft which will operate in different orbits around the planet. The Mercury Planetary Orbiter (provided by ESA) which is designed for remote sensing, while the Mercury Magnetospheric Orbiter (provided by JAXA) is designed for the study of the magnetosphere.
Together these spacecraft are designed to provide mission scientists with data to help draw conclusions on the formation and evolution of Mercury and build a complete description of the planet and its environment. “The BepiColombo mission shall provide the detailed information necessary to understand Mercury and its magnetosphere environment, to find clues to the origin and evolution of a planet close to its parent star,” explains BepiColombo Project Scientist Johannes Benkhoff.
With its comprehensive instrumentation, BepiColombo will provide high-resolution global mapping of the planet surface. It is a flagship mission for ESA, with a goal of building on the achievements of NASA’s MESSENGER mission to Mercury, which ended in 2015.
Like with almost all missions exploring new frontiers and making huge discoveries – such as providing support for the hypothesis that Mercury harbors abundant frozen water in its permanently shadowed frozen craters – NASA’s MESSENGER mission left scientists with many more questions about the planet (e.g. why there is so much volatile material on the surface of the planet, something which is incompatible with current formation theories). “I strongly believe that the instrumentation of BepiColombo is perfectly suited to obtain our science goals and to deliver answers to the necessary and also new questions raised by MESSENGER.” Adds Benkhoff, “We also have several missions on both spacecraft which were not present on MESSENGER.” Among the instruments on BepiColombo is an accelerometer to correct the disturbance of the spacecraft by the solar wind which will allow high precision measurements of Mercury’s gravity field.
Yet with so many tantalizing places to visit in our Solar System, why go to Mercury again? “While a trip to Mercury may not be on the bucket list of many astronauts, learning more about this small world is most definitely of interest to astronomers. This is only partly because of the natural curiosity we have for a neighboring planet,” explains Senior Astronomer for the SETI Institute Seth Shostak.
We know that Mercury on the inside resembles Earth, with an iron core much larger than our own and undergoing strong solar influence. It is the only inner planet other than Earth with a strong magnetic di-pole. According to ESA’s Chief Scientist and Senior Exploration Officer Bernard Foing, “Mercury can give clues on the structure and evolution of inner planets. Being the planet closest to the sun, it represents the inner end-member of the four terrestrial planets. As such, it plays a fundamental role in constraining and testing the competing theories explaining dynamical and compositional aspects of the formation and evolution of the whole group. Its evolution history is therefore an important piece in the puzzle.”
Added to this is the fact that Mercury has a negligible atmosphere – meaning what happens on Mercury stays on Mercury. The closest rock from our sun is a time capsule for events more than 4.5 billion years ago when our Solar System was formed. According to Shostak, “A solution to the great puzzle of planet formation may be written in its ‘craggy face’.”
Knowing more about Mercury’s surface composition will also help to provide a key test of competing models for the formation and evolution of the planet as well as the other terrestrial worlds, including our Earth. “Mercury’s interior structure will be investigated by the radio science experiment in combination with the laser altimeter and the high-resolution camera,” says Benkhoff. Together these instruments will, for the first time, provide an accurate determination of the global gravity field and the rotational state of the planet. “Mercury can be seen as one end-member of our planetary system. Thus, understanding Mercury’s evolution will for sure contribute to a better understanding about solar system formation.”
Understanding more about Mercury could also help scientists in their quest for life beyond Earth. While it is safe to say that Mercury is likely to have never supported life, that doesn’t mean there couldn’t be something similar to Mercury, elsewhere in our Universe, but in just the right place and with slightly different conditions that could harbor some form of life. “The really compelling reason to check out this neglected world is because of what we might learn about many of the trillion or so other planets that clog the Milky Way,” says Shostak. On Earth we have now learned that our own magnetic field is essential – not just for aligning compass needles, but for shielding Earth’s flora and fauna from deadly high-energy particles. “But no-one expected Mercury, whose iron core is presumably as solid as the Bank of England, to have a magnetic field. How does this happen, and would this bode well for the chance that small planets around other stars could be suitable for life?”
Yet this eagerly-awaited third mission to the ‘first rock’ from the Sun is only possible because of the learnings and successes of the first missions to the planet. Like with so much of what we do in space, the team behind BepiColombo will be standing on the shoulders of giants. Among those giants, the missions’ namesake who implemented the interplanetary gravity assist maneuver during the 1974 Mariner 10 mission when it became the first spacecraft to visit Mercury. An incredible achievement when you think that Sputnik had become the first human-made object in space less than two decades beforehand.
It would take until 2015 for our reconnaissance of the classical planets to be complete when New Horizons preformed its flyby of Pluto. In terms of becoming a spacefaring species, we are still in our infancy. There will be challenges with BepiColombo, hard technical challenges because of the travel, the close proximity to the Sun, and the high temperatures the spacecraft will face. But it is BepiColombo and this new era of planetary science missions which will truly help push us forward in our understanding of the Solar System, as well as inspiring many more to reach for the stars.