NASA’s Messenger spacecraft has achieved orbit around Mercury. It will remain in orbit for about a year and will circle Mercury 730 times. Its mission includes taking photographs, collecting data about Mercury’s surface and atmosphere, and trying to figure out why the planet is so dense. Scientists currently believe that two-thirds of the planet’s core must be some kind of iron composite.
Mercury’s density is just one of many intriguing aspects of the planet. It is the closest planet to the Sun — if you could stand on Mercury, the Sun would look at least three times larger than it appears from the surface of Earth — and it experiences extraordinary heat variations. When Mercury’s surface is exposed to the Sun, temperatures can reach levels sufficient to melt lead; on the dark side, temperatures can drop to -280 degrees Fahrenheit because there is no atmosphere to retain the heat. Mercury has the fastest orbit of any planet, circling the Sun once every 88 days. In addition to being blasted by heat, its surface is scourged by the solar wind and pockmarked with craters from countless collisions with comets, asteroids, meteors, and other space debris attracted by the Sun’s immense gravity.
The extreme conditions on Mercury posed significant engineering challenges for mission engineers. How do you design a spacecraft that is durable enough to be launched, hardy enough to be flung around planets in order to reach the right velocity and insertion point for orbit, and tough enough to stand up to Mercury’s metal-melting temperatures, yet capable of performing scientific experiments that require delicate measurements by sensitive instruments and then transmitting the results of those experiments back to Earth? One answer was to use ceramic shielding and mirrored surfaces to guard instruments and reflect heat rather than absorb it. Another answer is for the spacecraft to do its transmission duties when it is farthest away from the planet and least exposed to the intense heat.
The Messenger mission is another example of how we get great “bang for the buck” from unmanned space exploration, and how the exceptional engineering work that characterizes such missions can help point the way to technological breakthroughs and creative solutions to engineering problems on Earth.