Giuseppe Colombo helped NASA go to Mercury. Now it's his turn.
The Italian mathematician, who died in 1984, performed the orbital calculations that allowed the Mariner 10 spacecraft to visit Mercury, the innermost planet. In his honor, the European Space Agency (ESA) has named a craft planned for a trip to the rocky planet BepiColombo.
The mission is designed to withstand the rigors of a trip to the planet closest to the Sun, in search of its hot secrets and also to look for ice.
Yes, ice. Mercury is a mysterious planet of extremes and the least explored planet in the solar system (besides Pluto, which many astronomers argue is not even a planet).
Mariner 10's three Mercury flybys in 1974 and 1975 imaged only 40 percent of Mercurys surface because timing and the planet's complicated orbital dynamics resulted in it showing the same face to the camera each time. Those pictures revealed a Sun-beaten, crater-ridden surface.
able --> Today, there is much scientists still need to learn about Mercury, amounting to much to more than just peeking at the other 60 percent of the planet.
Mariner 10 revealed several intriguing features of Mercury, and not all are superficial. Beneath its surface, Mercury is hiding a core that seems to be denser than Earth's, unexpected given the planet's size (about the same as the Moon). Also unexpectedly, Mercury has a relatively strong magnetic field, but possibly not strong enough to fully repel the charged particles of the solar wind, which may be continually bombarding the surface and continually changing its chemistry.
Mercurys location makes it inherently important to solar system evolution theories.
"What we need to know is how particularly the planet is capable of evolving so close to the Sun," says Marcello Coradini, ESA's coordinator for solar system missions. "It's important in order to put boundary conditions on the model of the evolution of the solar system, to know all the possible manifestations and in particular the limiting cases."
The problem: Getting there
Mercury's proximity to the Sun has also made it difficult to go back. The amount of fuel any vessel must carry to make the trip, scientists used to think, made a mission there prohibitively expensive. There is also the issue of solar radiation. "Its surface is extremely hot, so when you go there, you get the solar radiation from the top and from the bottom," Coradini says.
Now both NASA and ESA have solved these problems. Technological improvements in heat shield technology will guarantee that no vessel will be roasted during its mission.
NASA will launch its
, which launches in March and will be only the second of its kind, after NASA's Deep Space 1. Solar-electric, or ion propulsion engines use electrons generated by solar panels to strip xenon atoms of one electron. The positively charged xenon atoms are then pushed out of the chamber in a continuous stream. Physics conservation laws stipulate that if the ions go out one way, the spacecraft goes the other.
The power is nothing compared to a conventional rocket, but over time a spacecraft can be propelled to significant speeds at tremendous cost savings. The setup cuts BepiColombo's travel time in half, to 2.5 years.
"This allows for less degradation of the experiments," Coradini says. "Secondly, the solar electric propulsion allows us to carry a much heavier payload, and also to carry a heavier spacecraft, which is better protected against the solar radiation. And so in principal, all of this will allow a higher resiliency, a higher reliability of the mission."
Looking for ice?
Both missions will help researchers understand Mercury, and scientists from both teams have met to coordinate their objectives and instruments. But, Coradini contends, "Messenger is an exploratory mission while BepiColombo is a consolidation mission, in the sense that Messenger will probably open up more questions than provide answers, while BepiColombo is designed to give final answers on the origin and evolution of Mercury."
And to do so, ESA is designing what will essentially be three spacecraft delivered through two separate launches, Coradini says. One launch will send the Planetary Orbiter and the Magnetospheric Orbiter over to Mercury. Within the same year, the Surface Element will be launched. Both units will arrive at the same time because of slight differences in the paths taken.
The Planetary Orbiter will enter a polar orbit around Mercury. Its instruments will include cameras and other remote sensing tools that should, in part, confirm the presence of ice.
Even though the temperatures on Mercury can swing 1,100 Fahrenheit degrees (600 Celsius) in one day (from 467 to -183 degrees Celsius) Mercury has no atmosphere. Therefore, the Sun only heats up whatever its radiation falls directly upon. "If you are protected or screened against the solar radiation, then you are incredibly cold. You are as cold as deep space," Coradini said.
In 1991, ground-based radar observations detected something shiny near the poles. Scientists suspect the highly reflective material to be ice.
To find ice on Mercury would not only be interesting because the planet is so hot and seemingly barren, but because of where the ice may have come from.
Mercury does not make ice. Its axis of rotation does not precess like Earth's, so its poles have been pointing in the same direction ever since the planet was formed. Therefore, scientists figure that ice might have been deposited on Mercury by comets and other remnants of the early solar system and might have survived for a long time out of direct sunlight in the shadowy corners of deep craters.
The Planetary Orbiter's counterpart, the Magnetospheric Orbiter, will also enter into a polar orbit around Mercury. Its suite of instruments will be designed to pin down and measure Mercury's mysterious magnetic field and interactions with the solar wind.
Both the Orbiters are expected to collect data for one year.
The harsh surface
The Surface Lander, however, will survive only one week in the harsher conditions on the planet. It will land near a pole and investigate the area with a camera and a seismometer, to determine if Mercury is geologically active. Other instruments will look into the composition, temperature and density of the soil.
ESA recently completed feasibility studies for the mission. During the next phase, BepiColombo scientists will investigate ways to minimize the cost and weight of the mission through "special technologies," Coradini says. And they will specify the actual instruments that will be on board all three components by 2004, which will initiate Phase B of the mission planning.
"Between 2004 and 2009, it will be six years of Phases B, C, D, which means final design, construction and launch," Coradini says. "Which for three spacecraft is not that long."
Either via traditional chemical propulsion or the nifty and new ion propulsion, either with one craft or three, by the time a human-crafted vessel returns to Mercury, it will have been more than 30 years since Mariner 10 first beamed back its images of the planet. In that time, humans have sent machines to visit every other planet (again, except Pluto), and some are on the verge of leaving the solar system. One has landed on an asteroid.
All the while, more than half of Mercury remains a complete mystery.
"My generation had already started its career when most of the planets had already been explored at least once," Coradini says. "And this is the last one for which you can say, 'Oh my God, I'm seeing this for the first time!' And I think this is extremely exciting."
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