2017 Colorado space grant review -Stratospheric experiment relevant for search for microbes on martian surface
In 2017 I was part of student program funded by NASA for stratospheric balloons called Demosat
introduction :
Our 2017 mission originally had two hypotheses. The first was to determine if gradual
exposure to extreme low-temperatures over many generations increases yeast tolerance to
low temperatures. The second was to document the difference between natural Ultraviolet
Radiation in the stratosphere versus germicidal lamps effects on Halobacterium
salinarum. Both biological samples can help determine if similar microbial cells could be
capable of surviving conditions in a Martian environment.
Recently, several studies have been done to evaluate the presence of microbes in
the upper atmosphere (Hume). Microbes surviving in the harsh conditions of the
stratosphere have implications in both the ability of microbes and pathogens to transfer
across continents. Survival of microbes in very harsh conditions could have implications
in the potential survival of microbes on Mars. Thus, adapting microbes to harsh
conditions suggests our ability to colonize and terraform Mars. To gain further
understanding of the tolerance of microbes to conditions in the stratosphere, the ability of
the yeast Saccharomyces cerevisiae to withstand freezing temperatures can be
tested. Experimental evolution is an established technique used to adapt Saccharomyces
cerevisiae to variable environmental conditions including drug resistance and ethanol
tolerance (Dunham). Serial transfer is known to change both the physiology and genetics
of yeast. To evaluate if the yeast subjected to the freeze-thaw cycles has evolved to
tolerate the low temperatures of the stratosphere live cells are counted before and after
space flight with the cold adapted strain vs. a control strain. Physiological adaptations to
the fermentation process of the yeast subjected to freeze thaw cycles and space flight
sustained will also be evaluated.
Exposing Halophilic archaea to a UVB-UVC radiation in the stratosphere and a
germicidal lamp in lab is related to Mars because Mars surface contains high levels of
UV radiation. Halobacterium salinarum are resistant to UVB and UVC more than other
halophiles. Antioxidants molecules in the archaea resist the DNA-damaging effects. The
idea of this experiment was to determine the ability to survive in the stratosphere.
Design issues
1- first issue lack of clear mechanism to measure the UV dose exposed to the microbe in the stratosphere.
There are many information available on the exposure of microbes using germicidal lamps, germicidal lamps operate usually with one wavelength like 254nm of UVC, The sun is not a lamp that operates on a singular wavelength, the sun produces all the UV spectrum, UVA UVB and UVC, there are little data available on percentage of wavelengths and intensity in the stratosphere in general, and we were not able to find data for that particular location where the payload will be taken.
However we know that in antarctica at 35 km above earth's surface through the SUNRISE mission, the lowest wavelength detected is a UVC of 214 nm for 30 seconds of the observational time, it unclear if 214 nm is possible to be detected at 30 km above Colorado surface. In that SUNRISE experiment a combination of 300 nm,312 nm, 388 nm,397 nm were detected and these wavelengths were 56% of the observational time.
1A-Sparkfun UV sensor ML8511 was designed mainly to be used on earth surface and not on the stratosphere, on sparkfun website they included a graph of the output voltage and UV intensity @365 nm, we have not found any reliable and accurate way of knowing that at
8 April 2017, at the moment where the payload will reach 30 km above earth surface 365nm is the most percentage of UV that were present in the stratosphere, if 214 nm could be detected
1B -calculating UV dose in the stratosphere
UV dose = mW/cm^2* time of exposure to a specific wavelength, because the stratosphere does not contain a singular wavelength but percentages of different wavelengths,
we have to 1-determine the wavelengths detected and their different percentages, 2- determine the intensity of each wavelengths 3- multiply the intensity with time of exposure to get j/cm^2
4- from the list of calculations find which is the highest UV dose of joules per cm^2.
2- second issue lack of suitable test-tube that is made of material that allow UV to pass through the test tube like quartz tubes and be strong enough to withstand the fall from 18 ft-20 ft. We tried to use a cuvette made of quartz that transmit ( 250 nm~3500 nm), we designed 3rd printed parts to protected from the 18 ft drop, however when we dropped it from 18 ft three times and we discovered that the cuvette were too fragile and the container were not able to protect it.
3-Inability to completely shield the payload from the low stratospheric temperature and keep it around 18-24 Celsius.
The halophile need to be kept at room temperature to ensure its survival, but the heater included in the payload is not enough to raise the temperature to 18 Celsius, the added heater need three batteries weights that g (), and because of restriction of 800g we can't add additional heaters.
for more info on full report can be find here
Written by Sami Tariq /Marym Aljumaiah