Data from MESSENGER spacecraft reveals new insights on planet Mercury
Scientists have discovered that the core of the innermost planet is larger and more complex than expected and that Mercury’s formation wasn’t as orderly as some assumed.
By University of California, Santa Barbara — Published: March 22, 2012
Mercury, as taken from the spacecraft MESSENGER.Thanks to the MErcury Surface, Space Environment, GEochemistry, and Ranging (MESSENGER) spacecraft, and a mission that took more than 10 years to complete, scientists now have a good picture of the solar system's innermost planet. On March 17, MESSENGER completed its one-year primary mission, orbiting Mercury, capturing nearly 100,000 images, and recording data that reveals new information about the planet's core, topography, and the mysterious radar-bright material in the permanently shadowed areas near the poles.
"Mercury is the last unexplored planet," said Stanton Peale from the University of California, Santa Barbara. The way Mercury was formed, he said, may show some constraints on the formation of the solar system.
For one thing, Mercury's core is larger than expected — almost 85 percent of the planetary radius. The Earth's core, in contrast, is just over half of the planet's radius. Additionally, Mercury appears to have a more complex core than Earth's — a solid iron sulfide layer that is now part of the mantle that encases a liquid core, which may float on a solid inner core.
The scientists also found that Mercury's solid outer core and liquid inner core contain more iron than Earth, relative to the whole planet, which influences the way Mercury's magnetic field was generated. However, Peale noted that the surface is comprised of lighter elements.
"We didn't expect so much sulfur," he said, adding that there was almost no iron found on the surface of the planet. With no iron, the volcanic surface rocks are too light to have come from a mantle with the large average density derived for the internal structure. This led to the concept of a two-layer mantle — a light upper silicate layer that could provide the low-density surface material over a dense iron sulfide layer.
In the larger picture, the presence of inordinately large amounts of sulfur on the surface indicates that Mercury's formation was not as orderly as some scientists had previously assumed, according to Peale. "Mercury is composed of material that had condensed over a wide range from the Sun," he said.
Other findings include a precise topographic model of the planet's northern hemisphere, which reveals a smaller spread in elevations compared to those of Mars or the Moon. Additionally, radar-bright features at the poles located in areas of permanent shadow have been found to be consistent with a water-ice hypothesis; however, the notion has yet to be tested further with MESSENGER's neutron spectrometer.
MESSENGER is already on the next phase of its investigations: an extended yearlong mission that includes more comprehensive and more targeted measurements.
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Can Science Prove Anything?
By Andrew Zimmerman Jones
What does it mean to prove a scientific theory? What's the role of mathematics in science? How do you define the scientific method? A recent e-mail conversation with a reader brings up some great questions about the fundamental way people look at science.
The Conversation Begins
Several days ago, I received an e-mail which seemed to criticize my support of the big bang theory which is, after all, unprovable. The author of the e-mail indicated that he thought this was tied into the fact that in my Introduction to the Scientific Method article, I have the following line:
Analyze the data - use proper mathematical analysis to see if the results of the experiment support or refute the hypothesis.
He implied that placing an emphasis on "mathematical analysis" was misleading. He claimed that mathematics was tacked on later, by theoreticians believed that science could be better explained using equations and arbitrarily assigned constants. According to the writer, mathematics can be manipulated to get the results desired, based on the scientist's preconceptions, such as what Einstein did with the cosmological constant.
There are a lot of great points in this explanation, and several which I feel are far wide of the mark. Let's consider them point by point over the next few days.
Point 1: Unprovable
This is an excellent point. The big bang theory is absolutely unprovable. In fact, all scientific theories are unprovable, but the big bang does suffer from this a bit more than most.
When I say that all scientific theories are unprovable, I'm referencing the ideas of famed philosopher of science Karl Popper, who is well known for discussing the idea that a scientific idea must be falsifiable. In other words, there has to be some way (in principle, if not in actual practice) that you could have an outcome which contradicts a scientific idea.
Any idea which can be constantly shifted around so that any sort of evidence would fit it is, by Popper's definition, not a scientific idea. (This is why the concept of God, for example, is not scientific. Those who believe in God use pretty much everything to support their claim and cannot come up with evidence -- at least short of dying and finding that nothing's happened, which unfortunately yields little in the way of empirical data in this world -- which could, even in theory, refute their claim.)
One consequence of Popper's work with falsifiability is the understanding that you never really prove a theory. What scientists do is instead come up with implications of the theory, make hypotheses based on those implications, and then try to prove that specific hypothesis true or false through either experiment or careful observation. If the experiment or observation matches the prediction of the hypothesis, the scientist has gained support for the hypothesis (and therefore the underlying theory), but has not proven it. It's always possible that there's another explanation for the result.
However, if the prediction is proven false, then the theory might have serious flaws. Not necessarily, of course, because there are three potential stages that could contain the flaw:
• the experimental set-up
• the reasoning that led to the hypothesis
• the underlying theory itself
Evidence which contradicts the prediction may just be a result of an error in running the experiment, or it could mean that the theory is sound, but the way the scientist (or even scientists in general) interpreted it has some flaws. And, of course, it's possible that the underlying theory is just flat out wrong.
So let me state categorically that the big bang theory is completely unprovable ... but it is consistent, by and large, with everything else we know about the universe. There are still many mysteries, but very few scientists believe that they will be answered without some variation of the big bang in the distant past.