Tikalon Blog by Dev Gualtieri

Martian Radiation

August 29, 2022

Manufacturers enhance the saleability of even mundane products through the addition of technology. Sometimes, the added technology has no real benefit. Consumer electronics often has a multitude of manual controls and blinking lights that are just eye candy. I remember how early desktop computers would have a digital display showing the change in processor speed when the turbo button was pressed. What was displayed wasn't an actual frequency measurement, just a stored number. This concept goes back to early mainframe computers and der Blinkenlichten (the blinkenlights).

Eye candy and blinkenlights - A Digital Equipment Corporation PDP-10 mainframe computer.

The hundreds of indicator lamps on early models were incandescent, but they were eventually replaced by light-emitting diodes. A now forgotten trick to increase the life of frequently switched incandescent bulbs is to hold them at a low current when "off" and not switch them entirely off.

About 1500 units of the PDP-10 were sold from 1968-1983. Although I wasn't able to find a selling price, a good estimate would be about $140,000 for a typical configuration, which is about a quarter of a million dollars in today's money.

One of the first online service providers, CompuServe, operated more than 200 PDP-10s at its peak. As they say, you need to spend money to make money.

(Wikimedia Commons image by Wolfgang Stief. Click for larger image.)

Sometimes the added technology was intended to satisfy a real need, although its actual implementation was likely not that effective. In the 1960s, our family had a clothes washer with an ultraviolet lamp intended as an antimicrobial aid. In those days, such lamps were fluorescent, and the idea of having something like that inside a water-filled container seems dangerous by today's standards. Clothes washers still have UV lamps, but the UV source is now an array of light-emitting diodes.

During the COVID-19 pandemic, there was a fear that the coronavirus could be transmitted on surfaces, and there were UV devices sold that allowed sterilization of your mail, but my family took a different approach of letting our mail age for a few days before opening. UV radiation is now used effectively for sterilization of hospital rooms. Short-wavelength UV (UV-C), known as germicidal UV, has wavelengths between about 200-280 nanometers, and it's strongly absorbed by nucleic acids. UV-C irradiation has been shown to be a potent antimicrobial for methicillin-resistant Staphylococcus aureus, and vancomycin-resistant enterococci.[1]

Sterilization of bacteria by short-wavelength UV radiation was discovered by Arthur Downes and Thomas P. Blunt in 1878, and Niels Finsen (1860-1904) was awarded the Nobel Prize in Physiology or Medicine in 1903 for his use of UV light in treatment of tuberculosis of the skin (lupus vulgaris). Marseille, France, tried UV sterilization of its drinking water in 1910, but the technology of that time wasn't quite up to the task. A century later, technology has improved to the point at which there are more than 6,000 UV water treatment plant worldwide.

Other ionizing radiations are used in the sterilization of food. These include gamma rays, X-rays, and electron beams. The most widely used method is gamma irradiation from the radioisotope, cobalt-60, a versatile radioisotope used also for industrial radiography. About half a million metric tons of food are sterilized by these means annually.

The preceding serves as background information in the exploration for life on Mars. The NASA's Curiosity Mars rover has been drilling holes into the Martian regolith, its surface soil, looking for signs of past life. A team of planetary scientists from the NASA Goddard Space Flight Center (Greenbelt, Maryland), the Catholic University of America (Washington, District of Columbia),Georgetown University (Washington, District of Columbia), and the University of Wisconsin-Madison (Madison, Wisconsin) have just published a paper in Astrobiology in which they conclude that a shallow hole will yield no result.[2-3] Because of the radiation environment of Mar over the period of time from which Martian life could have been viable, any remaining life signs would exist only at depths of two meters (6.6 feet), or more.[2-3]

Book cover for Thuvia, Maid of Mars by Edgar Rice Burroughs, 1920.

Yes, Thuvia, there is life on Mars - Run!

Book cover for Thuvia, Maid of Mars by Edgar Rice Burroughs (1875-1950), 1920.

Burroughs was influenced in his Mars novels by the astronomical speculations of Percival Lowell (1855-1916). Lowell thought that the Mars environment in its past was much like the present Earth, but it had become less hospitable to life over time. Lowell believed that the inhabitants of Mars had built canals, seen as a network of lines by some observers, to bring water from the polar ice caps to irrigate arable land.

Science fiction authors are inventive people, and Burroughs introduced the ideas of autopilot and collision avoidance for aircraft in Thuvia, Maid of Mars.

(Wikipedia Commons image of cover art by P. J. Monahan. Click for larger image.)

Amino acids are a class of organic chemicals that provide evidence for prebiotic chemistry or chemical of life on Mars.[2] That's because amino acids are fundamental chemicals for life on Earth, since they are the monomers from which proteins and enzymes are made.[2-3] One problem in searching for these on Mars is that small molecules such as amino acids are degraded relatively quickly by ionizing radiation.[3]

Shallow underground places are not safe from ionizing radiation, since cosmic radiation can penetrate meters into solid rock over just the course of 20 million years.[2-3] Life might have appeared on Mars billions of years ago when Mars was more like Earth, having liquid water, a thick atmosphere, and a global magnetic field to shield the surface from most cosmic rays, but such protection has been missing for at least a billion years.[3]

Amino acids haven't been discovered yet on Mars, but they have been discovered in meteorites, including the Martian meteorite, Nakhla.[4] Meteorites from Mars are typically ejected from depths of a meter, or more, but there's a possibility that the amino acids of Nakhla are from terrestrial contamination. The Curiosity and Perseverance rovers have detected organic chemicals on Mars, but these could have been created by non-biological chemical reactions.[3]

NASA's Curiosity Mars rover took this selfie using the Mars Hand Lens Imager, a camera located on the end of its robotic arm. The location was in the Glen Torridon region, a place where conditions on an early Mars would have been favorable to supporting life, if it ever was present. (NASA/JPL-Caltech/MSSS image. Click for larger image.)

In their experiments, the research team exposed several pure amino acids to gamma radiation in vacuum in dry and hydrated silicate mixtures and in mixtures of silicates with perchlorate salts, a mixture that simulates Martian soil.[2-3] The temperature and radiation dosage were representative of the martian near-subsurface.[2-3] The temperature ranged from Earth's room temperature, about the highest temperature on the surface of Mars, to a more typical -55 °C (-67 °F.[3] The gamma radiation dosage was designed to simulate what was seen at Mars over about 80 million years.[3]

These were the first experiments in which amino acids were mixed into simulated Martian soil.[3] Says team member, Alexander Pavlov, a space scientist at the NASA Goddard Space Flight Center, "Our work is the first comprehensive study where the destruction (radiolysis) of a broad range of amino acids was studied under a variety of Mars-relevant factors (temperature, water content, perchlorate abundance) and the rates of radiolysis were compared... It turns out that the addition of silicates and particularly silicates with perchlorates greatly increases the destruction rates of amino acids."[3]

Amino acids mixed with dry silica powder were a factor of 10 more likely to undergo radiolysis than amino acids alone.[2] Adding perchlorate salts to the silicate samples, or hydration of silicate samples, accelerated the radiolysis rate by about 50%.[2] Says Pavlov, "Our results suggest that amino acids are destroyed by cosmic rays in the Martian surface rocks and regolith at much faster rates than previously thought... Current Mars rover missions drill down to about two inches (around five centimeters). At those depths, it would take only 20 million years to destroy amino acids completely. The addition of perchlorates and water increases the rate of amino acid destruction even further."[3]

No evidence of amino acid racemization was detected in the experiments after gamma radiation exposure; this means that the chirality of some surviving amino acids, as produced by Living organisms, might be preserved.[2] Since an effective search for amino acids on Mars appears to require sampling at great depths, a good strategy is to seek recently exposed outcrops, such as recent microcraters with ages less than 10 million years, or the material ejected from such craters.[3] There's even a proposal for a robotic exploration of Martian caves.[5]

Martian Radiation

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