When Apollo 11 astronauts Neil Armstrong and Buzz Aldrin stepped onto the lunar surface in 1969, they did more than make history and utter unforgettable words. They also deployed seismic sensors that would allow scientists back on Earth to monitor the activity on the moon. Crews from the 12th, 14th, 15th, and 16th iterations of Apollo also deployed sensors, the lot of which took measurements until 1977. Using recently developed techniques of analysis, two teams working independently say they have gone back into that catalog of data and sorted through the statistical noise that has confounded researchers, creating a clear picture of the moon’s core.
The new study provides the first confirmation of layering of the moon’s core and suggests that the moon, like Earth, has a solid inner core surrounded by a molten outer core, researchers said. But the moon’s interior also has another layer of partially melted material – a ring of magma – around its outer core, the study found. [MSNBC]
The moon shakes with moonquakes, but those are more scattered and weaker than the quakes we experience here on the home world, and the moon’s busted-up surface made the signals difficult for Apollo seismic monitors to read. Through a statistical technique called waveform stacking, the new teams could better identify how seismic waves move through the moon, and especially how the core affects them. That, in turn, shows the size and density of the core.
The two groups, led by Raphaël Garcia and Renee Weber respectively, both presented their research at last month’s American Geophysical Union meeting, and Weber’s paper has just been published in the journal Science.
Garcia and colleagues found a liquid core with a radius of 365 kilometers. Weber and her colleagues reported a core radius of 330 kilometers…. Given the uncertainties, the two estimates are indistinguishable. In addition, Weber found seismic reflections from a solid inner core with a radius of 240 kilometers—a feature Earth has as well—and reflections from a layer of mostly rock with a bit of magma 150 kilometers thick lying above the liquid iron outer core. [ScienceNOW]
While these two teams attempted to peer into the unknown interior of the moon, another study in this week’s Science tries to figure out the peculiar exterior of the sun. Common sense might suggest that the farther one travels from the fusion furnace at the core of the sun, the more temperatures would drop. But as has often been the case with the sun, common sense is not correct.
The heart of the sun registers in the millions of degrees, and the surface is just about 10,000 Fahrenheit. Yet, the sun’s corona, which is beyond the surface, is millions of degrees in temperature. Various possible explanations have been bandied about over the years, but the new paper argues that plasma jets or “spicules” emanating up from the solar interior (which humans have observed for decades) cause the temperature imbalance. But are they hot enough? It depends which ones you look at, lead author Bart De Pontieu says.
Using observations from NASA’s Solar Dynamics Observatory (the craft that’s been sending back those stunning pictures of the sun), De Pontieu contends that while “classical” spicules that are driven by sound waves are too cool to heat the corona to such spectacular temperatures, type II spicules that are driven by the sun’s magnetic field are not. These spicules can reach temperatures in the millions of degrees, and they can blast upward toward the corona at speeds of 60 miles per second.
On the basis of the jets’ frequency and intensity, the researchers estimate that they deliver energy “of the order that is required” for the corona to sustain its high temperature. “We are not saying that this is the only mechanism to heat the corona,” says De Pontieu. “Clearly, however, these events deserve more attention.” [Nature News]
Other solar researchers agree that De Pontieu’s findings are exciting, but say they’ll wait for more evidence before considering the case closed. And De Pontieu himself points to another question raised by the research: How do the type II spicules get so hot in the first place?
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Images: Science / AAAS; NASA