Astrobiologia: Marte custodisce i segreti della vita sulla Terra

Un’antichissima sorgente idrotermale sottomarina su Marte potrebbe aver ospitato forme di vita in passato e oggi potrebbe svelarci le caratteristiche ambientali in cui si è sviluppata la vita sulla Terra. Si tratterebbe di un antico sistema che avrebbe funzionato come una sorta di ‘incubatrice’, descritta sulla rivista Nature Communications e ubicata nel bacino Eridania, nella parte meridionale del Pianeta Rosso, scoperta dalla sonda Mars Reconnaissance Orbiter (Mro) della Nasa.

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Serpentino, carbonati, talco e altri depositi minerali scoperto dallo spettrometro “Crism” che risalirebbero a 3,7 miliardi di anni fa e che potrebbero diventare il bersaglio di nuovi studi di astrobiologia alla ricerca di tracce di vita, come sottolineano gli autori dello studio coordinati da Joseph Michalski, prima geologo del Museo di storia naturale di Londra e ora in forza all’Università di Hong Kong.

“Anche se non dovessimo mai trovare tracce di vita passata su Marte, questo sito ci potrà svelare il tipo di ambiente in cui si è sviluppata la vita sulla Terra”, spiega Paul Niles, del Johnson Space Center della Nasa a Houston. “L’attività vulcanica combinata con l’acqua stagnante potrebbe aver creato le stesse condizioni che a quel tempo esistevano sulla Terra quando sono comparse le prime forme di vita”.

Osservarle direttamente oggi è molto difficile, poiché le tracce geologiche di quel tempo sono state ormai confuse dal continuo ‘riciclo’ della crosta terrestre, mentre il bacino marziano, con la sua antica crosta conservata, potrebbe rappresentare un modello da studiare.

“Ricorda gli ambienti idrotermali terrestri, simili a quelli dove potremmo trovare la vita su altri pianeti. La vita che non ha bisogno di un’atmosfera gradevole o di una superficie temperata, ma – conclude Niles – solo di rocce, calore e acqua”.

Qui dimostriamo che questi vincoli osservazionali, sebbene non coerenti con molti attori in precedenza proposti per i climi che formano il lago, sono coerenti con uno scenario di scoppio di metano. In questo scenario, le transizioni caotiche in obliquità media fanno passare latitudini a temperature e carichi di ghiaccio che destabilizzano il clatrato di metano. Utilizzando simulazioni numeriche, si scopre che il metano in eccesso può svilupparsi a livelli atmosferici sufficienti per i climi di formazione del lago, se il clatrato di metano occupa inizialmente più del 4% del volume totale in cui è stabile termodinamicamente.

Tali frazioni di occupazione sono coerenti con la produzione di metano da reazioni di acqua-roccia a causa della circolazione idrotermale nei primi anni marziani. Si stima inoltre che la distruzione fotochemica del metano atmosferico riduca la durata dei singoli climi di formazione del lago a meno di un milione di anni, in linea con le osservazioni. Le esplosioni di metano rappresentano un percorso potenziale per escursioni intermittenti a uno stato climatico caldo e umido ritenute presenti alle origini di Marte.

Lo studio su nature.com – qui sotto i riferimenti scientifici dello studio:

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Author information

Affiliations

  1. Department of Geophysical Sciences, University of Chicago, Chicago, Illinois 60637, USA

    • Edwin S. Kite &
    • David P. Mayer
  2. NASA Ames Research Center, Mountain View, California 94035, USA

    • Peter Gao
  3. Astronomy Department, University of California, Berkeley, California 94720, USA

    • Peter Gao
  4. School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia V8P 5C2, Canada

    • Colin Goldblatt
  5. Jet Propulsion Laboratory, Pasadena, California 91109, USA

    • Michael A. Mischna
  6. US Geological Survey, Astrogeology Science Center, Flagstaff, Arizona 86001, USA

    • David P. Mayer
  7. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125, USA

    • Yuk L. Yung

Contributions

E.S.K. designed research; M.A.M., Y.L.Y. and D.P.M. contributed new models, model output, and analyses; E.S.K., C.G. and P.G. carried out research; and E.S.K. wrote the paper.

Competing financial interests

The authors declare no competing financial interests.

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