Several times I was asked about the methods of sterilization of the Soviet apparatus sent to Venus, and whether microorganisms could have been introduced onto them. I decided to give a detailed answer.
But first I decided to lay out a table from my book on the structure of the cloud layer of Venus. In addition to the data on pressure and temperature, I also placed there data from the nephelometer and the IFP "Vegi-2" device, which obtained the distribution of gases containing phosphorus / sulfur / chlorine over height. I would like to note that the maximum in the cloud layer of Venus according to the nephelometer data and the IFP differ due to the fact that the nephelometer received data on the daytime side of Venus, and the IFP on the night side. At night, the clouds dropped slightly.
The table with the most accurate data on the pressure / temperature ratio, again according to the data from Vega-2, can be downloaded here.
Now to sterilization. Since the main model of Venus, when developing our first descent vehicles, was adopted the so-called "ionospheric" model, which implied the presence of life, the question of sterilization was one of the first.
Here I would like to note that the main problem was in the sealed volume of the descent vehicle. The outer surface of the descent vehicle withstood the entrance to the dense layers of the atmosphere, during which no living organism would have survived. The transfer module generally burned up in the atmosphere. But inside the descent vehicle, during the flight, sufficiently comfortable conditions for bacteria were maintained, so it was him who needed to be sterilized.
Our first interplanetary stations sent to other planets were sterilized on the recommendation of the Institute of Microbiology of the USSR Academy of Sciences with a mixture of ethylene oxide with carbon dioxide, respectively, 10-12% ethylene oxide and 90-88% carbon dioxide, used to reduce the explosiveness of ethylene oxide.
However, in 1964, the Central Scientific Research Disinfection Institute of the USSR Ministry of Health recommended a more effective bactericidal gas mixture of ethylene oxide (60%) and methyl bromide (40%), called the OB mixture. The high efficiency of the OB mixture is achieved due to the bactericidal action of both of its components.
Also, the study of LZTK-2 and LZTK-3 liquids used in thermostating systems for spacecraft of the 3MV type showed that these liquids are seeded with spore microbes and do not possess bactericidal and bacteriostatic properties. E. coli and Staphylococcus aureus retained their viability in these fluids for 30 days. The research results showed that these fluids need to be sterilized. For example, when heated to 180 degrees Celsius for 45 minutes.
The new rules were approved in May 1966. The only thing is that the first Earth descent vehicle entered the Venusian atmosphere as early as March 1, 1966 (Venera-3 station), and I cannot say whether the sterilization of the liquid was carried out on this SC.
Little is known about the design of the Venera-3 spacecraft. Despite the fact that this station was the first to reach Venus, no signal was received from it. The next station is better known - "Venera-4". At that station, they generally abandoned the gas-liquid thermoregulation system, using a more reliable gas one. Sterilization of this station was also carried out. Here is an extract from the technical description of this station:
“The internal cavities of the finally assembled descent vehicle AMS are subjected to gas sterilization with a mixture of OB in the amount provided by OKB-1 in the instruction IN-53A1. During sterilization, the CA is heated to 35 degrees C for ~ 20 hours, followed by repeated evacuation and filling with dry nitrogen. ”
Analogue of the CA“ Venus-4 ”in the Memorial Museum of Cosmonautics
After "Venera-4", having learned about the difficult conditions on its surface, the sterilization of the apparatus was stopped. At least, this is not mentioned in the documents.
The question arises, could our SAs have brought microorganisms into the cloudy layer of Venus? This could be done only by those stations that were destroyed in the cloud layer of Venus due to high pressure, without having time to reach the surface. These were four stations (in brackets the temperature at which they collapsed): "Venera-3" (unknown), "Venera-4" (262º ), "Venera-5/6" (326º ).
It can be seen that Venera-5/6 collapsed at a sufficiently high temperature. Terrestrial microorganisms would not survive at this temperature. The same can be said about "Venus-4". Plus it's guaranteed to be thoroughly sterilized.
So the question remains only about Venera-3. In comparison with "Venus-4" it had a less durable hull, and it had to collapse at a higher altitude, approximately, at a temperature of about 130 ° C. Which, of course, is also quite a lot. Plus, he went through gas sterilization for sure, we can't only say whether it was not sterilized liquid. Unfortunately, without telemetry it is impossible to tell at what height it collapsed. So the question remains. And it will hardly ever be possible to give an exact answer to it.