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."
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Have your say
If life in Martian or Europan moonwater is present but common, then it might not be captured in a 7 cubic millimeter space in a sample. They should work on a way to image a larger volume of water.
It's also not clear how well this device would visualize bacteria or whatever's there. Would it be an image or an interference pattern?
But it's a nice step. This device might be used to cheaply monitor drinking water for contaminants, or automatically classify bacteria from rapid scans or assays. Or have industrial applications.
That should read "present but uncommon".
Rarer Life
Sat Oct 24 01:19:33 BST 2009 by Dennis
http://freetubetv.net
interesting points.
Good questions, Jeremy.
The article states "the camera can produce real-time images of any object in the water if they are larger than about 100 nanometres across." This microscope definitely creates images.
The article states it will take milliseconds to create the images, so it sounds like it can make maybe 100 images per second. Googling "frame rate" tells me movies and TV are around 25 to 30 images per seceond, so you get pretty good videos out of this microscope.
Googling "bacteria size" tells me the smallest bacteria are 0.2 micrometers in size. 1 micrometer = 1000 nanometers, so the smallest bacteria are 200 nanometers in size. The article says the microscope can see things bigger than 100 nanometers, so it can all bacteria.
This microscope can sample 7 cubic millimeters at a time, which is pretty small. But if you can create 100 images per second, then you could get 10 images in 0.1 seconds. So you get 10 images of any bacteria if you flow water through at 7 cubic millimeters per 0.1 second, or 70 cubic millimeters per second, or 4200 cubic millimeters per minute = 4.2 cubic centimeters per minute.
There are 24 times 60 minutes per day, so this microscope could do 4.2 times 60 times 24 = 3456 cubic centimeters per day = 3.456 liters per day, which isn't so shabby.
Steady On There. . .
Thu Oct 22 22:39:31 BST 2009 by sciencebod
http://www.colinb-sciencebuzz.blogspot.com
If one is looking to detect life at the microscopic level, using a microscope, then the crucial test is to detect organisms in the act of reproduction, eg binary fission - the key criterion of life. It's not clear whether the device described, sophisticated though it may be, would have sufficient image resolution to be able to do that.
The Arctic tests seem somewhat premature if they spot "all sorts of critters we didn't know were there". One would have thought the first step would be to introduce the instrument into places where the microorganisms are well characterised by conventional microscopy, to be certain one was able to detect and distinguish those 'critters' that we did know were there...
Only problem with Europa is that even assuming the presence of a liquid ocean, the ice crust is usually estimated to be at least 20 kilometres thick. On earth the deepest we've drilled so far is 12km deep, taking 15 years effort. So getting the instrument into the Europan ocean could be a challenge
But the crust on Europa is water ice. So a hot power source could melt its way down. Though considering the specific heat of water you would need a lot of heat. Also the depth of the ice is unknown. Two comments I would make about that.
First, even on the Earth the crust varies dramatically in thickness. We should look for thin spots in the ice ... I wonder if infra red imaging would show the escaping heat from sub-ice ocean?
Secondly, the extreme flatness of the surface of Europa seems to me to be strong hint that the ice isn't that deep. Say 5-ish km rather than 20. But then again I haven't looked at recent ideas on that.
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