Research: holograms could help find extraterrestrial life
Scientists from The California Institute of Technology and NASA say a technology that uses lasers to create 3D images could be used to discover extraterrestrial microbes. The technology could theoretically be used on space probes.
The technology is called digital holographic microscopy and works by aiming a laser at an object, reflecting the light back. That light is then measured and analyzed, including the intensity of the light and the distance traveled by the light rays after reflecting off the object. This can be used to create a single 3D image of a collected sample.
Software can be used to reconstruct what can be seen on each focal plane. By creating a series of holograms with a certain interval between shots, even the smallest movements can be seen, according to researcher Jay Nadeau. Marking any microbes with fluorescent material that adheres to a broad class of molecules, which are good indicators of life, can also determine what the microbes are made of.
Compared to traditional microscopy, digital holographic microscopy has a number of important advantages. Traditional microscopes use multiple lenses that need to be focused. Getting the right focus is quite a problem; the idea is that a space probe collects samples and analyzes them on the spot, but if that’s done with a traditional microscope, it has to be controlled from Earth, with a delay in the signals. With hologram technology there is no need to focus. Also, a larger surface area can be studied and fewer moving parts are needed, which means there is less chance of the equipment breaking down.
The researchers consider two locations in our solar system the most interesting places to look for extraterrestrial microbes. In addition to the moon Europa, which orbits Jupiter, the small moon Enceladus near Saturn seems to be an interesting location. The surface of Enceladus consists of a layer of ice, and underneath it is most likely an ocean. In the ice are cracks and geyser-like fountains that blow material from the interior of the moon into space; in April, the Cassini spacecraft discovered hydrogen in the geyser fountains. That points to hydrothermal activity in the ocean. The presence of water, an energy source and organic molecules makes Enceladus one of the best places to search for life forms. It is likely that there is not enough energy for multicellular organisms, but unicellular organisms such as bacteria may be present.
Collecting any alien microbes from Enceladus, which can then be found via holograms, is not easy. A space probe like Cassini has to fly through the geyser fountains, collect material and analyze it. The problem is that the plumes have a similar density to smog in cities on Earth. This means that a spacecraft has to fly through the plumes of Enceladus about 12 to 20 times to collect just a femtoliter of liquid. During the fly-by, the probe’s speed is likely to be around one to five kilometers per second, creating a risk that the collected material will be pulverized before it can be examined. To prevent this, special collection techniques must be developed in order to study as many usable samples as possible.
The hologram technology has already been tested in some locations on Earth with extreme conditions. For example, in the spring of 2015 the researchers drilled into the polar ice in Greenland to look for bacteria. The scientists also examined Searl Lake, a very salty lake in the Mojave Desert that contains hostile chemicals such as arsenic and boron. At both locations, the hologram technology appeared to work and bacteria were actually visible.
The research was published in the scientific journal Astrobiology under the title Digital Holographic Microscopy, a Method for Detection of Microorganisms in Plume Samples from Enceladus and Other Icy Worlds.