ATGC hat geschrieben: ↑10. Apr 2018, 18:35
Ich denke, je kleiner der Meteorit ist, um so stärker wird die innere Gesteinsmatrix erhitzt, so dass es bei Mikrometeoriten für darin befindliche Mikroben eher schlecht aussieht.
Ja, so wird es wohl sein, besonders der Wiedereintritt durch eine dichte Atomsphäre scheint mir sehr problematisch.
Wobei ich immer noch darüber nachdenke, ob es da nicht Schupflöcher geben könnte. Kleine Körper und Kleinstkörper verhalten sich anders, das Verhältnis von Oberfläche zu Masse/Volumen ist völlig anders (damit auch das Abbremsverhalten), es können plötzlich ganz andere physikalische Effekte relevant werden: elektromagnetische Kräfte (Elektrostatik, Magnetismus: können die als sanfte Bremse beim Wiedereintritt wirken?), Sonnenlicht-Abbremsung (hab vergessen wie der Effekt heißt, jedenfalls gibt es für kleine Körper keine stabile Umlaufbahnen um die Sonne, die fallen immer weiter nach innen -> schnelles Erreichen weiter innen gelegener Planeten), usw.
Ich habe etwas weitergelesen, hier:
Natural Transfer of Viable Microbes in Space from Planets in the Extra Solar Systems to a Planet in our Solar System and Vice Versa
https://arxiv.org/ftp/arxiv/papers/0809/0809.0378.pdf
Das ist interessant, die gehen von folgendem Szenario aus:
Herausgeworfenes Material von Einschlägen wird beim Auswurf (erst ab einer gewissen Mindestgröße, damit fallen die Mikropartikel weg) außen aufgeschmolzen, ohne dass es im Kern zu heiß wird. Dadurch bildet sich eine dichte Versiegelung, die nachfolgend die schnelle Zerstörung von mitgeführten MO per Vakuum und Hydrolyse verhindert; diese würden ansonsten viel schneller zu Sterilisation führen als alle anderen Effekte (Strahlung, ...):
If DNA decay by hydrolysis or vacuum were effective, the viable transfer from planets in extrasolar systems to the Earth would be impossible. The survival time of bacteria due to DNA damage by hydrolysis is of the order of hundred thousand years, not long enough for long space flights considered here, based on available experimental evidence (Nakamura et al. 1998, Lawley and Brookes 1968, Karran et al. 1980). In vacuated ejecta volumes the DNA decay by vacuum-caused damage occurs much faster than damage by hydrolysis or radiation, in tens of years (Dose et al. 1991, Horneck 1993, Horneck et al. 1994).
https://arxiv.org/ftp/arxiv/papers/0809/0809.0378.pdf, S.8
Was dort noch interessant ist (dort geht es ja auch um Panspermie), ist das dortige folgende Ergebnis:
First consider the transfer of life in the galactic star field. Even if there are planetary systems with both a terrestrial-like planet in its habitable zone and a giant planet well positioned to expel into interstellar space ejecta from the terrestrial-like planet, the number n of meteoroid ejecta of critical size or larger from all the planetary systems of the Galactic field stars which impacted Earth during Earth’s first 700 million years was only n ~ 10^-8, i.e. no such meteoroid capable of carrying viable DNA / RNA based microbes impacted Earth.
https://arxiv.org/ftp/arxiv/papers/0809/0809.0378.pdf, S.18, mit Hervorhebungen
Dann wir es interessant, für Sonnen, die gemeinsam aus einer Urwolke entstanden sind, schaut es nämlich anders aus:
A different situation prevails in a cluster of young stars newly born from the same
core of a collapsing molecular cloud. The short distance between the stars and their slow
relative motion is favourable for an exchange of bodies and gives n ≈ 10^(2+2).
https://arxiv.org/ftp/arxiv/papers/0809/0809.0378.pdf, S.19, mit Hervorhebungen
... also ca. 100-10000 Transfers in dem Zeitraum und damit:
Even though this number is uncertain by several orders of magnitude, there is a definite
possibility that bacteria carrying meteoroids of extrasolar origin have landed on the Earth.
In reverse, it is possible that at least one other planetary system in our birth star cluster
received a life-carrying asteroid from the Earth; and it is not excluded that the whole birth
star cluster was “fertilized” in this way by live bacteria from the Earth.
https://arxiv.org/ftp/arxiv/papers/0809/0809.0378.pdf, S.19
!!! Faszinierende Vorstellung!
From our discussion above, it is clear that exchanges of bacteria between planets in
different solar systems are only possible during the birth cluster stage of the systems in
question. As the number of life-carrying bodies received by the Earth may have been in
thousands, so also other planets in other stellar systems may have received their life from
other members of our original star cluster, or even from a single source, the Earth. Thus the
limited form of lithopanspermia inside a star cluster is possible, while the stronger version
of life spreading through the whole Galaxy from a single source could not happen via
mechanisms described in this work. But life-carrying bodies originating from our solar system may have found their way to our original neighbours, and that all conditions being optimal, life seeded by our system could have spread to many other solar systems. Here in our solar system our common ancestor cell most probably originated either on the Earth or on Mars. We cannot say for sure which one since there has been millions of potentially life-carrying transfers between these two planets (Gladman et al.1996). The GAIA (Douglas et al. 2007) mission will perhaps be able to locate the members of the birth cluster of the Sun while the SIM (Unwin et al. 2008) and DARWIN (Cockell et al. 2008) missions will be able to detect planets around them and search for signs of life in the planets. Even before these missions, the currently ongoing search for life in Mars may already give an indication how likely it is that life is transported between planets by natural means.
https://arxiv.org/ftp/arxiv/papers/0809/0809.0378.pdf, S.19