NASA: Search for Alien Life Continues - Under the Laser Microscope

MICROSCOPES revolutionised the study of life on Earth. Now a rugged, easy-to-use instrument is aiming to be equally influential in the search for alien life in locations such as the oceans beneath the icy surface of Jupiter's moon Europa.

The hunt for signs of extraterrestrial life usually focuses on detecting molecules associated with living organisms. Direct observation through optical imaging would be more conclusive, so Hans Kreuzer and Manfred Jericho at Dalhousie University in Halifax, Nova Scotia, Canada, and their colleagues have taken a different approach. They have built a robust microscope that can be dunked into water to detect any microscopic life forms that may be swimming or floating there.

Called the digital inline holographic microscope, it consists of a pair of watertight compartments separated by a chamber into which water can flow. One compartment contains a blue laser that is focused onto a pinhole-sized window facing into the water. Opposite the pinhole, in the second compartment, is a digital camera.

As the laser light hits the pinhole, it generates a spherical light wave that spreads out through the water. If it hits a microscopic object - a bacterium, say - further diffraction occurs. The spherical wave and the diffraction pattern created by the microscopic object interfere to create a pattern that is captured by the camera. This interference pattern is essentially a hologram of whatever is in front of the pinhole.

Kreuzer has patented an algorithm that can reconstruct the objects that created the interference pattern within milliseconds. In this way the camera can produce real-time images of any object in the water if they are larger than about 100 nanometres across.

To test the instrument, the team took it to the extreme environment of Axel Heiberg island in the Arctic, where a robotic vessel immersed it in a lake (Planetary and Space Science, DOI: 10.1016/j.pss.2009.07.012). "We saw all sorts of critters we didn't know were there," says team member Jay Nadeau of McGill University in Montreal, Canada.

Nadeau says that the rugged, lightweight device can be easily transported, and does not require constant intervention to obtain clear images. It has a wide angle of view and a large depth of field, which together allow it to follow objects as they float in the 7-cubic-millimetre chamber in front of the pinhole. "You can be absolutely certain if something is alive and swimming," says Nadeau.

Chris McKay of NASA's Ames Research Center in Moffett Field, California, who worked on the Phoenix mission to Mars, is intrigued by the work. "While I would not argue that a microscope is the next instrument to send to Mars or Europa, it is clear that eventually we must send microscopes," he says. "The design here is pretty clever and well suited for a flight instrument."