Messenger orbital trajectory…..Credit: NASA
For the first time in perhaps two billion years the planet Mercury has a satellite. This moonless planet, which is itself smaller than many moons in the solar system and whose surface looks very much like Earth’s Moon, now has a tiny metallic canister in orbit around it, the Messenger space probe. Human science, engineering and money put it there, and it wasn’t easy. It’s a pity the achievement will be underappreciated.
Launch a rocket in Florida (USA) in 2004; lofting it through Earth’s atmosphere and send it on a trajectory consisting of a dozen enormous concentric orbits around the Sun covering 9.9 billion kilometers (6.2 billion miles) over 6 ½ years. Along the way fly by the Earth, Venus (twice), Mercury (three times), all the while chasing the orbit of Mercury and trying to use the planets and Sun to brake the Messenger spacecraft so that after a final burn of its main engines, it slips neatly into a complex elliptical (egg shaped) orbit around Mercury – close enough at one point to take good pictures (about 200 km/124 mi) but also far enough out (15,160 km/9,420 mi) at the other point to cool off.
All this Messenger completed March 17, 2011, and did it perfectly.
I think the achievement deserves a little ‘Huzzah!’ Not all space probes reach their destination and few had as lengthy a journey or were even remotely as complicated in trajectory. Oh, and of course, all the instruments, computers, and communications must work when it gets there.
Price tag: $446 million. Fortunately Messenger launched while the United States still had a taste for science and NASA still had a workable budget.
Thinking about that ‘taste for science,’ there are many people who wonder why so much money is spent on space exploration. This is kind of a cyclic question. It understandably surfaces in times of economic hardship (like now) and under certain political circumstances. The questioning occurs in all nations engaged in space exploration – the U.S., Europe, China, Japan, Russia, Brazil, India. There are many answers to the questioning, none of which is sufficient to end the controversies, because in the final analysis space exploration is a judgment on the way to use a country’s resources, and that’s a dynamic issue under constant change.
Some of the problem is created by the high visibility of space exploration; in effect, it can be the victim of its own success – or failure. In the western world far more money is spent on pet food than space exploration, but few pay any attention to the expenditure for pet food. Then too, this expenditure for space is at the moment mostly governmental – paid by taxes. This makes it more obvious, and in the minds of some, controversial – per se.
Why Mercury? It’s not just because it’s there, or just because we can. In the broadest terms, it’s because Mercury has many mysteries. It’s been photographed once, by the space probe Mariner 10 – but only 45% of the surface was covered. Mercury is difficult to study because it is so close to the Sun. It’s the smallest planet and the fastest moving. From Earth it’s seen only briefly at sunrise or sunset and usually enveloped in the glare of the Sun. Sensitive telescopes don’t even try to view Mercury for risk of burnout from sunlight.
Yet Mercury is a celestial ‘neighbor’ and a kindred planet. The Earth, Mars, Venus and Mercury are the ‘inner planets’ (nearest the Sun) and also the ‘rocky planets’ that have a metallic core and a mantle of ‘rocky’ (mostly silicate) material. As far as is known, Mercury is the oldest planet with an age of approximately 4.8 billion years. After Earth, it is the planet with the highest density – approximately 42% of its volume is the core and the core is composed mostly of iron and other metals. Consequently, Mercury has a magnetic field. These are all factoids about Mercury with some intrinsic interest, but for science the interest is how these came about. What is the geologic history of Mercury? Why is it so dense? What is the nature and origin of the magnetic field? It is believed that answering these questions will be important in piecing together theories on the formation of planets (rocky planets like Earth in particular). Now that rocky planets outside the solar system are regularly discovered, these theories will (finally) have real data for comparison.
Finally, there is the matter of water. Now that it is confirmed the Moon has substantial water and other ices preserved in the bottom of craters near the poles, it will not be surprising to find similar conditions on Mercury. The presence of ice was already suspected from radar imaging and Messenger should be able to confirm it. The presence of water on a planet so close to the Sun, and in fact in an area not subjected to the intense heat of direct sunshine, makes Mercury a potential location for human activity – mining operations, for example – however far off that seems now. Tourist packages to the planet Mercury might be a tough sell.
Tourism aside, the knowledge gained by studying Mercury presents a great challenge – piecing together the history of our solar system and by extrapolation the possible history of countless other solar systems we may observe elsewhere in the universe. It’s part of a massive intellectual feedback system where solving problems and gaining insight leads to asking more questions and more insight. Some of this has immediate practical impact, much of it has potential for the future – and some of it becomes trivial or superseded. On balance, what it does is keep mankind curious, thinking, and learning. This is arguably worth a tiny bit of a nation’s wealth.