In less than a week, a machine from another planet will arrive on an alien world, soon to start zeroing in on targets and zapping them with its heat ray.
War of the Worlds? Not quite.
It's the Mars rover Curiosity, the robotic star of NASA's $2.5-billion Mars Science Laboratory mission. Any zapping serves to answer a question that has captured the imagination of generations of scientists and the public: Has Mars ever hosted life?
Curiosity is slated to arrive on Mars early in the morning Eastern time on Aug. 6. If the landing goes well, Curiosity will explore the red planet's Gale Crater and its imposing Mt. Sharp. Both show tantalizing geological evidence that the dent in Mars' surface once might have sported environments capable of supporting at least simple forms of life.
The story is written in the chemical make-up of the rocks Curiosity examines. And a first cut at determining which rocks to drive to for analyzing in detail will be made from information gathered by ChemCam, an infrared laser and telescope package that sits atop Curiosity's extendable "neck."
The device, one of 10 science instruments on the rover, also will be hunting for water, either bound up in minerals or as ices in the soil Curiosity traverses. Researchers have identified water as a key requirement for the emergence and survival of life as they've come to know it on Earth.
ChemCam's approach, using a laser and mini telescope to identify atoms present in a distant object, already has found wide use on Earth in situations that would be dangerous for humans, says Darby Dyar, an astronomer at Mt. Holyoke College in Hadley, Mass., and a member of the ChemCam team.
Nuclear-power-plant operators use similar technology as a kind of fuel gauge for the uranium-oxide fuel rods in commercial nuclear reactors. The rods' composition changes as they are used up, she explains. Archaeologists have used the technique to identify the composition of artifacts. Scrap-metal recyclers use it to identify the types of steel they receive. And security specialists are eying it as a tool that could help screen for explosives at airports and along US borders.
The technology was adapted for space missions by a team led by Los Alamos National Laboratory geochemist Roger Wiens, ChemCam's lead scientist. The Mars Science Laboratory's mission marks the instrument's maiden flight.
On Mars, ChemCam represents the Annie Oakley among the rover's science packages. It can place its powerful laser beam on a spot the size of a period on a printed page at 23 feet – farther in the lab, Dr. Dyar acknowledges, but for Mars, 23 feet will do.
The beam plants 1-million-watt pulses on the spot for about five-billionths of a second each, heating the rock or dust it encounters to more than 3,500 degrees Fahrenheit, vaporizing the material.
From a hypothetical Martian's standpoint, the beam's encounter with rock looks like the spark from a butane barbecue lighter. But the spectrum from that tiny bit of light carries an enormous amount of information about the types of atoms present in the material vaporized and their relative abundance.
Indeed, the device is the only one aboard the rover that can identify atoms across the entire periodic table of elements, giving researchers more opportunity to test the makeup of rock types they didn't anticipate finding.
By comparing the results ChemCam delivers from Mars with the spectra of up to 2,000 so-called calibration samples on Earth, researchers will be able to identify the rocks and minerals ChemCam zaps.
And if the rock of interest is covered with dust? No worries. A series of pulses from ChemCam's laser becomes the high-tech whisk broom that exposes the rock surface scientists really want to analyze.
Yet even before ChemCam reaches the Martian surface, researchers are trying to tailor the approach to provide dates for rocks on other planets, much as geochemists date rocks on Earth.
The idea is to detect a sample's spectrum in even finer detail than ChemCam does, so that it picks up not just the signatures of atoms, but their variants, known as isotopes.
By comparing the relative abundance of specific isotopes, researchers will have a more precise tool for gauging the age of rock formations they encounter with future rovers. Currently, they get merely a qualitative estimate of age by counting craters or mapping the relative positions of different geologic features.
On Earth with state-of-the-art technology, dating rocks with a high degree of precision is still a difficult process, says Ralph Milliken, a planetary scientist at Brown University in Providence, R.I., and a member of the Mars Science Laboratory science team. It's highly unlikely for rover-based approaches to match the precision of measurements made on labs on Earth, he says.
Still, "even if you could get the absolute age of something plus or minus 500 million years, that would be huge for Mars," he says.
Gale Crater, Curiosity's landing site, "is a good example. There is a debate as to the age of the material inside that crater" – a debate that yields an estimate that ranges over a billion years.
The latter half of that estimate bumps up against the end of the planet's earliest, and presumably wettest, period. With rock ages uncertain to within a billion years, did the rocks of interest in the crater really come from a wetter period, or from later dryer period?
It's a debate that bears directly on whether a young Mars – at least at this location – hosted potential habitats for life. It's a debate that the technology behind ChemCam eventually could help answer.