LIVERMORE — Space exploration often involves bringing the seemingly impossible to fruition, but when leaders of a NASA mission to Mercury approached a group of physicists at Lawrence Livermore National Laboratory in 2002 for help, the numbers were particularly daunting.
Could the team find a way to get measurements near the surface of Mercury, which reaches about 800 degrees Fahrenheit, from an instrument that operates at about -330 degrees?
The answer will be revealed next week, when the team’s gamma-ray spectrometer is scheduled to begin sending back information after nearly seven years aboard the Mercury Messenger spacecraft.
The craft, which launched from Cape Canaveral, Fla., between a hurricane and a tropical storm in August 2004, is expected to reach planetary orbit Thursday.
The Lawrence Livermore crew’s spectrometer is one of seven instruments aboard the craft sending back data that scientists will use to learn more about Mercury’s magnetic field and planetary formation. The information likely will lead to insight about our own planet, the researchers said.
“We’ve done every test possible, and (the spectrometer) has passed every test. But until it performs in orbit, you’re nervous,” said Morgan Burks, a Lawrence Livermore physicist who worked on the instrument’s cooling system.
The spectrometer resembles an elaborate gold coffee can with a hunk of silver metal — the element germanium — inside.
The germanium measures gamma rays emitted by Mercury’s surface so scientists can determine the elemental composition, but germanium comes with benefits and complications.
The substance produces clearer, more precise results but has to operate at cryogenic, or ultralow, temperatures — no small feat near the surface of Mercury, which is hot enough in some places to melt lead.
Scientists will turn on the spectrometer a week after the Messenger — short for Mercury Surface Space Environment, Geochemistry and Ranging — begins orbiting the solar system’s smallest planet, and data should start to come in a day or two later, Burks said.
Messenger, a $446 million mission funded by NASA and managed by the Applied Physics Laboratory at Johns Hopkins University, is the first to Mercury since 1975.
The planet has a highly radioactive surface that gives off gamma rays — waves of energy that act like fingerprints of the elements that emit them — when cosmic rays hit.
The spectrometer will measure gamma rays emitted from Mercury, and the information will be used to evaluate theories about how the planet’s surface formed, said Ed Rhodes, a Johns Hopkins instrument scientist for the gamma-ray spectrometer.
“Some elements are much more abundant depending on the model you choose,” said Rhodes, who does everything from sending commands to the instrument to analyzing the spectral data it produces.
For example, iron is more volatile than titanium, so detecting more iron would provide evidence for a different model of planetary formation than detecting more titanium, Rhodes said.
He said the mission command brought the Lawrence Livermore physicists into the picture because of their expertise with the more precise germanium detectors.
“At the outset, it was not clear that this would be possible due to the harsh thermal environment found at Mercury,” Burks wrote in a 2004 technical paper.
The Livermore team spent about a year developing a spectrometer that could withstand the extreme conditions of a Mercury orbit, Burks said.
Messenger will complete an orbit of Mercury once every 12 hours for the next year, flying within 124 miles of the surface on each circumnavigation.
“It gets a big heat pulse every 12 hours,” Burks said. “We had to prove the instrument could handle that.”
Between the cooler and various electronics, the spectrometer package is about the size of a soccer ball and weighs just over 20 pounds.
Burks has spent the years since the launch adapting the technology developed for the Messenger craft for the Department of Homeland Security.
Gamma-ray spectrometers can be used to detect bomb-making materials such as uranium and plutonium, he said, and Lawrence Livermore’s team had previously developed a handheld device for use at shipping ports and border-patrol checkpoints.
The low-resolution radiation detectors currently don’t use germanium, which is difficult to cool in a handheld device because the entire system is powered by battery.
Burks is using the cooling developments from the NASA mission to create smaller, lighter handheld devices that use less power and perform better, he said.
The new handheld spectrometers will use germanium to produce more accurate readings and will weigh about nine pounds, compared to the older 30-pound model.
The new technology has been licensed to a company and is undergoing field tests, Burks said.
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