|
|
|
Is Mercury shrinking?
MERCURY, the small world near the very core of the solar system poses many riddles and mysteries for scientists and researchers. One of these mysteries being that the planet might be shrinking.
In other words the planet might be collapsing or contracting into itself while it freezes slowly. The theory is based on images that were brought back by Nasa’s Mariner 10 spacecraft in the 70s. The images showed that scarps of the surface looked like they had buckled from within. This feature was present at random, halfway across the surface. The planet is 4,878 kilometres in diametre, slightly larger than our Moon. Now with a new spacecraft being sent to the tiny planet, scientists hope to get a better idea of what’s really going on.
Mark Robinson, a researcher from the Northwestern University says, “It’s a pretty cool thing. When I first heard it, I thought it was weird.”
The Messenger spacecraft bound for Mercury is expected to not only shed light on the surface features but also give scientists an insight about its metallic core.
Robinson is also a team member of the Messenger mission and hopes that researchers will get a chance to see Mercury’s hidden hemisphere and whether there are signs of surface contraction there including study surface composition. The team hopes to find material on the surface that might have spewed out from the interior of the planet.
Launched on August 3, the MErcury Surface, Space ENvironment, Geochemistry and Ranging, mission, (Messenger) is expected to reach its destination in March 2011. Before finally entering into orbit around Mercury, it will make three successive passes around the planet.
The supposition that Mercury might be “the incredible shrinking planet,” arose from the images taken by Mariner 10 which showed deep scarps which snake across the surface. One such feature named Discovery Rupes, is a mile deep. Such surface scarps on Earth can be compared to the fault lines that run parallel to the US coastline. On Mercury though, these features run randomly across the surface. One theory proposes that these scarps are due to the fact that Mercury’s crust was formed over a huge molten core and that when the core kind of cooled, it shrank somewhat, buckling the surface in from certain places.
Robinson explains that though water expands as it cools most of the other materials contract when they cool down and that is probably what happened with Mercury’s crust. He feels that based on the surface features of the known hemisphere of the planet, the surface buckling in is from 1 to 3 kilometres, which is “not something insignificant.”
Researchers are not sure regarding any of these theories as Mercury’s core holds most of the mystery. “Our understanding of the core is very rudimentary. It’s just based on the fact that Mercury has very high uncompressed density,” admits Robinson.
According to researchers since Mercury has extremely high density, they feel that its core is large and metallic, mostly iron. Robert Gold, payload manager for Messenger of the Johns Hopkins University Applied Physics Laboratory, states, “Mercury is a small enough planet that its core should have frozen about 2.2 billion years ago.”
The Messenger spacecraft might not be able to fully confirm the shrinking planet theory but it is expected to at least strengthen it. The spacecraft is expected to spend a whole year mapping the planet with unprecedented detail. Something the Mariner 10 spacecraft was not capable of doing. It’s cameras can pick out surface features only 60 feet across while Mariner 10 could only resolve surface details up to a mile.
Messenger has a Mercury Laser Altimetre instrument, which will track the wobbling of the planet on its axis. This will help researchers determine the composition of the planet’s core. The spacecraft surface scanning tools will also study ancient lava flows and their composition to give a better understanding of the planet’s exterior.
As Robinson states, “I would be very surprised if Mercury’s unseen hemisphere has features we don’t have hints about on the side we’ve seen.” Since only 40 per cent of the planet has been seen, it would be most interesting to see what features the rest of the 60 per cent surface holds.
Successfully launched after being shot from a Boeing Delta 2 Rocket, the Messenger spacecraft is on its way on a five billion-mile and 7-year journey.
“This was another great Boeing and Nasa success as we bid Messenger farewell,” states Nasa’s launch director at Kennedy Space Centre in Florida, Chuck Dovale.
The spacecraft will take a roundabout route to Mercury after swinging by three inner planets. Messenger science team member, Ralph McNutt of the Johns Hopkins University, explains, “Mercury is very hard to get to. To get there, the MESSENGER spacecraft is about 55 per cent fuel, about the same amount as the Cassini spacecraft to Saturn.”
The spacecraft will swing close to Earth once, Venus twice and three times by Mercury before entering into its final orbit. It will study and observe the small planet for a year as its primary mission. Its fuel tanks are capable of providing propellant for a year around the planet.
“The mission ends with a whimper. By about 2015 or 2016, gravity will crash Messenger into the surface of the planet,” says McNutt.
Another spacecraft to be launched in 2009 is being planned for a trip to Mercury, BepiColombo. Named after the Giuseppe Colombo, the Italian mathematician, whose orbital calculations helped Nasa plan its Mariner 10 mission, the spacecraft will help scientists look for ice.
As strange as it sounds, scientists and researchers feel that there is ice at the poles. Ground-based radars detected something shiny near the poles in their observations made in 1991. If ice is found on the planet closest to the Sun, it will be a most interesting phenomenon as it will be more of a mystery as to where the ice could have come from.
Experts feel that comets or other debris from the early stages of the solar system could have deposited it there. And still survives at the poles out of direct sunlight. According to Marcello Coradini, The European Space Agency’s coordinator for solar system missions: “What we particularly need to know is how the planet is capable of evolving so close to the Sun. 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.” Though both missions, the Messenger as well as the European Space Agency’s, BepiColombo, are being sent to better understand Mercury, Coradini outlines that, “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.” BepiColombo will use solar electric propulsion. Ion propulsion or solar electric propulsion engines use electrons that are generated by solar panels.
If both the missions are successful in giving us a better understanding of the planet closest to the Sun, we might understand a little bit more about the formation of our own solar system. And whether the planet Mercury is actually shrinking or contracting within itself. In that case will it become even tinnier with time? Or maybe cease to exist? It is yet another cosmic mystery waiting to be solved.
The writer
|
|
|
|
