52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548) 1346.pdf Interplanetary exchange in the Solar System – are we really biologically isolated? Margarita Safonova1 and Chandra Sivaram1,2, 1Indian Institute of Astrophysics, Koramangala, 2nd block, Bangalore 560034, India ([email protected]), 2([email protected]). Following the explosion of humanity’s into space. Experiments conducted in the last space exploration, Planetary Protection decades in space and on the ground Policies were introduced in 1950s [1] to confirmed that microorganisms are able to restrict the possibility of introducing survive all stages of associated hazards: terrestrial biota to outer space worlds with our impact shocks, impact ejections, and spacecraft and probes (termed forward interplanetary transfer. Some are capable of contamination). In addition, they were also doing it even without much of the protection, intended to regulate the return of samples but most need just centimetres of rock cover from outer worlds to safeguard the Earth from (e.g. [2]). possible unfriendly organisms (back The Solar System was formed from the contamination). In this regard, the Planetary same protoplanetary disk, and findings of Protection Policies are purely complex organics in meteoroids (including anthropocentric. In case of forward amino acids and even a protein – the first contamination, the basic concern is that if we extra-terrestrial proto-solar protein, named bring terrestrial organisms to another world, it hemolithin due to the presence of iron and would confuse our scientific identification of lithium [3]) indicate that life-building blocks the indigenous life forms. In the case of back were available everywhere from the contamination, it is the Earth life that could beginning. Terrestrial planets, some moons be under the threat of being extinguished. and even some asteroids were potentially This point of view completely ignores the habitable very early on, with water and fact that Solar System objects do not exist in protective magnetic fields. The whole Solar isolation. The Solar System is full of dust: System is thus already contaminated by the remains of asteroids, comets and impact constant interchange of meteoroids, with their ejecta. Every day 100 to 300 tonnes of this water, organics and possible biota content. interplanetary dust with particles masses of Therefore, it follows that it is too late to 10-12 to 1 g accretes on our planet. Larger enforce the Planetary Protection Policies, meteorites of the size big enough to produce a maybe 4 billion years too late. fireball (10 cm to ~few metres) enter Earth atmosphere at the rate of up to 500,000 Acknowledgments: Part of this research is annually. The same happens with other financed by the Department of Science and planets. Ejecta from large impactors goes to Technology (DST), Government of India, under the neighbouring planets, for example, roughly a Women Scientist Scheme (PH), project Ref. No. SR/WOS-A/PM-17/2019. third of impact ejecta from Venus lands on Earth, and about a quarter from all terrestrial References: planets is reprocessed by Jupiter, with reasonable assumption that some lands on the [1] Review and Assessment of Planetary potentially habitable Jovian moons. Protection Policy Development Processes. National Earth itself is inhabited for the last ~4 Academies of Sciences, Engineering, and Medicine, billion years. And in all these years it had its The National Academies Press, Washington DC. share of dramatic impacts, lifting tonnes of [2] Nicholson, W. L. (2009) Trends in Microbiology, rocks, dust and water (with living organisms) 17, 243. [3] M. W. McGeoch et al. (2020) arXiv: 2002.11688s. .