IV Convegno della Ricerca Italiana in Fisica Solare e Relazione Sole-Terra (18-20 Ottobre 2005) Sessione 6 - Relazione Sole-Terra: Variabilita’ ed Attivita’ del Sole Giovedi’, 19 Ottobre, 2005 CONSTRAINTS ON THE ORIGIN OF LIFE ON EARTH DUE TO THE PHYSICS OF THE ANCIENT SUN J. Chela-Flores The Abdus Salam ICTP, Trieste, Italia & Instituto de Estudios Avanzados, IDEA, Caracas, Venezuela M. Messerotti INAF-Trieste Astronomical Observatory, Basovizza, Trieste and Department of Physics, University of Trieste, Italia

Sources of Space Weather

The Voyayers (1 and 2) The Solar System Family NASA, Europa

Voyager I (94 AU)

Sources of chemical evolution in the Solar System

Compounds observed in the comas of comets The Hale-Bopp comet Someprecursors of the biomolecules

Organic compounds in meteorites The Murchison meteorite

The formation of the Earth

Evolution of the early atmosphere  During the accretional period, the Earth’s volatiles were released on impact, forming a transient steam atmosphere.  At the end of the accretionary phase the Earth’s surface cools and the steam atmosphere produces an early hydrosphere, leaving an atmosphere of some 85 C.

During of the first 100 Myr  A model postulates a large hydrodynamic escape of H. Escaping H carries away heavier atoms by aerodynamic drag.  The lighter isotopes are carried off more easily than the heavy ones. In post-accretion with decreasing EUV flux that was fueling the H escape, this process becomes difficult and eventually stops.  The net effect is that the formation of the early Earth led to ‘isotopic fractionation of the chemical elements’.

The fractionation of sulfur: the delta-34 parameterr (corresponding to the Canyon Diablo meteorite, CDM)  This parameter has zero value when the sample (sa) coincides with the average terrestrial value of 34 S/ 32 S.

Sulfur in the lunar dust from the Apollo missions

The delta 34 S parameter in terrestrial, meteoritic and lunar material Terrestrial Meteoritic Lunar Sulfate coexistenting with sea water According to measurements near the Californian coast: S (insoluble), principally pyrite.

Chemical element fractionation  The delta 34-S parameter on lunar soils (and meteorites) is narrower than the corresponding cases of H, C and N.  Hence, it may be the most reliable element for estimating biological effects.

Solar radiation on the Earth as a challenge to early microorganisms

Microorganisms can survive large doses of radiation Deinococcus radiodurans Bacillus subtilis E. coli bacteria

Life on Earth: resistance to radiation Survival of D. radiodurans after irradiation

Europa (Galileo, 1995)

Is life possible on Europa under Jupiter’s ionizing radiation?  A bacterium with the radioresistance of D. radiodurans would survive in 1 mm depth of the icy surface.  The radiation environment at 40 m is similar to the Earth biosphere.

Non-water ice constituents staining the icy surface of Europa New absorption features (  m) Candidate elements H2O2H2O2 C 2 H 5 SH mercaptan SO 2 CO 2 (CN) 2 cyanogen

Conceivable sources of sulfur stains on the icy surface of Europa  External: Ions may be implanted from the Jovian plasma,  Internal: Sulfur may be due to cryovolcanism, or we can ask: Could sulfur be of biogenic origin?

Measurements from the Ulysses dust detector (3.8 kg/consumes 2.2 W) in a second approach to Jupiter in 2004

Io’s volcanic surface (Galileo)

One way to decide on the S source: Landing on the icy surface of Europa  The lander will have a set of 4 miniprobes.  Mass constraint for the microprobes 1.7 kg. Tirso Velasco and colleagues The Europa Microprobe In Situ Explorer (EMPIE)

Main phases of the descent  Four light landers (350 gm each).  Ejection from the orbiter.  Penetration in ice 72.5 cm.

Discussion  Sulfur bacteria cannot in principle be ruled out as a source of the sulfur stains of the icy surface of Europa.  If the sulfur source is biogenic, significant deviations from the CDM values of the delta 34 S-parameter should take place.  Miniature gas chromatography-mass spectrometry (GC-MS) is appropriate for the detection of such biosignatures.

Conclusions  The collaboration of distinct sectors of the exploration of the Moon, the Galilean satellites and the Sun has taken place.  This approach should lead to the identification of biosignatures of life.  Hence, life’s origin could begin to be understood under the influence of the ancient Sun.