Nordic Winter School on Astrobiology Sirkka, Finland January 2006

1. Interstellar chemistry and the conditions for making prebiotic moleculesDavid Field, Department of Physics and Astronomy, Aarhus Nordic Winter School on Astrobiology Sirkka, Finland January 2006 Astronomy and Astrobiology, a synthesis – and some chemical physics: electron collisions in the interstellar medium

2. What is astrobiology for an astronomer? • Astrobiology is the study of the origin of life on Earth • Astrobiology is the study of whether there may exist elsewhere the conditions under which life can develop • Astrobiology is the study of whether life may presently exist elsewhere

3. What are the new areas in Astronomy that have fuelled the field of Astrobiology? • mechanisms of star formation • planet formation • exoplanets (Didier Queloz: 4th and 6th January)

4. there are also discoveries of a more “chemical” nature • chemical analysis of meteorites: high D/H ratio in aminoacids in meteorites – an “interstellar inheritance” • some aminoacids in meteorites may be non-racemic mixtures • photolysis of simulated interstellar ices • electron-induced chemistry in ices

5. Discoveries (or ‘hints’) in these fields are little illuminated patches: it is difficult to link them together into a coherent picture • More questions are raised than are answered: astrobiology is a young subject. We are just beginning to assemble “the pieces of the puzzle” • Andre Brack “The molecular origins of life: assembling pieces of the puzzle”

6. One hundred to one hundred and fifty years ago • The history of the Universe would have been extremely short in the minds of many people • The literal truth of the Bible gave the Earth an age of about 6000 years • Or, to be more precise, the date of creation was Sunday October 23rd, 4004 BC, with Adam and Eve on the 28th October, a Friday

7. the Age of the Sun • But one hundred years ago, we still could not understand how the Sun could be more than 20 million years old, heated by gravity and meteors – this was the view of Lord Kelvin • Geologists – and Darwin – needed hundreds of millions of years for the age of the Earth: how could the Earth be older than the Sun?

8. Creation 10,000 million years later Life on Earth 9000 million years later Galaxies form Solar system forms 1 hundred million years later quasars the first star 1 million years later Gravity takes over Deuterium, helium 1 second Hydrogen nuclei (protons) form 1 microsecond The Big Bang

9. The Universe and Us • What is the connection between the Universe and us -what is the Outer Space-Earth connection? • We are made of star-dust, mostly from our own Galaxy, the Milky Way…… • But also a little bit from the Andromeda galaxy, 2 million light years away. • So we are not just extraterrestrials, we are partly extragalactic, too. Several percent of the hydrogen atoms in your body may have come from Andromeda.

12. Elements for life • O, C, H, N + traces of many others: Mg, Si, Fe, Al, Na, K, Mn, P…even including tungsten (W). • All heavy elements were formed since the Big Bang 13.5 billion years ago. • After the “first star in the Universe” exploded as a mighty supernova, the first galaxies formed • These were composed (it is believed) of massive stars that exploded as supernovae, making heavy elements

13. Elements for life • Later galaxies contained stars more similar to the Sun • Biology was at first not feasible since the abundance of heavy elements was 100 times lower than in the Milky Way • Further generations of stars have turned ~1.7% of all H atoms formed in the Big Bang into elements heavier than He Birgitta Nordström: Friday 6th January • Nucleosynthesis and the chemical conditions for planet formation

14. 9000 million years later… • In a spiral arm of the Milky Way, a galaxy among >1011 others, a particular cloud of gas, the “presolar nebula”, began to undergo gravitational collapse • the nebula contained the elements necessary for life • there was also enough refractory material to make “rocky planets” • a billion years later there were single cell creatures! – a problem for biologists

15. If you had eyes sensitive at radio-wavelengths • then you would see the sky full of blobs of cool gas • many blobs appearing as big as the moon • stretching along the Milky Way

16. the Milky Way seen at radio wavelengths Stars form in these blobs of gas

17. Young stars and planets around other stars • to study how the Sun formed, we observe very young stars which, we believe, may evolve into stars similar to the Sun • The most heavily studied region is Orion • Here, more than one thousand stars have formed in the last one million years

18. Orion Cloud, M42 OMC1 : scale ~ 0.15 pc We can study very young stars in the Orion Molecular Cloud (OMC1) and discover what were the physical conditions prevailing at the time of the formation of the Sun and our planetary system

19. Disks around stars • Very young stars (“protostars”) can be caught in the act of planet formation • Using the Hubble Space Telescope, disks of dusty gas, 50-1000 AU in diameter can be detected (1AU = 1 Earth – Sun distance)

20. a very young star planets forming here! Supersonic outflow of gas Observations of "disks" A propostar in the Orion Molecular Cloud. The disk of dusty material is ~1000 AU in diameter McCaughrean,O’Dell Astr.J. 1997 ~1000 AU 

21. The mass of material in this disk is enough to make >700 Earths (or >2 Jupiters) • The inner, most dense part is where planets must be forming • Our Solar system is about 150 AU in diameter for comparison

22. Exoplanets • >150 exoplanets have been detected, mostly by Doppler techniques: Jupiter's gravitational pull causes the Sun to move in a circle with a velocity of 13 ms-1. • We have not yet been able to image planets around other stars • IAUC 200 Direct Imaging of Exoplanets: Science & Techniques, October 3-7, 2005, Nice, France Some claims of direct imaging with the Spitzer Space Telescope and VLT: not yet firmly established – the “planets” may be brown dwarfs • We may be able to detect planets rather directly with the James Webb Space Telescope and with ALMA (the Atacama Large Millimetre Array)

23. Earth-like planets • present techniques are not able to detect Earth-mass planets (except, in principle, gravitational micro-lensing techniques) • therefore we still do not know if there are Earth-mass planets around other stars • the massive exoplanets found reveal that there are many uncertainties about how planets form

24. Gas around very young stars : “protostars” • 90% H2; 10% He • CO+H2O+NH3+dozens of other molecules and ions = a few ten-thousandths of the total number density • number density: a few hundred particles/cm3 to >1011/cm3 • temperature 10K to 5000K

25. Dust around protostars • dust grains made of Mg, Fe silicates and graphitic composites = 1% of total mass of gas • particle size: “large molecule” (tens of Å) to microns, with many more small dust particles than large : number with mass M, n(M)~M-2.3 • temperature: 10K – but can be higher • coated with a cocktail of molecules CO, H2O, NH3, CO2, methanol etc.

26. Absorption spectrum of ices on dust grains observed against the IR background from a protostar W33A

27. Gas phase molecules: radio fingerprints in Orion Methanol, HCN, sulphur dioxide, methyl cyanide, acetic acid in just 1 GHz Schilke et al. 2001

28. Star and Planet formation • Stars form in the dense cores of dusty molecular clouds • When they “break out”, we can see them

29. star (and planet) formation • Nature does a good job of forming stars. However we do not understand how it works • how is the angular momentum lost? (planets – as Didier Queloz has told you – however…..) • what is the role of turbulence? • the physics and chemistry in the disks where planets are forming are largely unknown

30. star formation • Barnard 68: a molecular cloud with a density of ~105 cm-3, T~16K, 375 light years distant, ~0.375 light years across • B68 is about to form a star: just on the edge of gravitational collapse. Strongly depleted in CO in its cold dark centre

31. star formation • BHR71: a similar clump of gas, but where a star has just formed →

32. How do we get from to ?

33. Material falls into towards the centre and lands on the protostar at supersonics speeds. This causes a ”shock”. • In the shock, gas is warmed up to >1000K. Dust particles will also be warmed, to perhaps a 100-200K depending on size. • The frozen chemical mantles will evaporate releasing water, CO2, CH4, NH3, nitriles etc. into the gas phase.

34. material may be cycled around from the grain mantle to the gas phase, refrozen, re-evaporated • complex gas phase chemistry in protoplanetary disks as a source of prebiotic molecules • solid state chemistry may be a source of prebiotic molecules

35. What can we see when we look at protostellar zones? • Dust obscures protostars: you cannot see them in the visible region of the spectrum • look in the infrared e.g. at 2 microns (and at longer wavelengths) • 2 micron emission of vibrationally excited hydrogen is a beacon of star formation • one can see gas bursting out protostars and smashing into the surrounding material with velocities of 5 to 50 km/s

36. a very young star planets forming here Supersonic outflow

37. lmage in infrared emission from hydrogen: the signpost of star formation Very early stage at which the star is emitting due to accretion and the disk is nearly as massive as the star a star which formed about ten to one hundred thousand years ago scale: thousands of AU

38. OMC1 : scale ~ 0.15 pc

39. OMC1 : scale ~ 0.15 pc

40. H2 emission in OMC1 at 2.121 (v=1-0 J=31) Canada-France-Hawaii Telescope

41. Orion OMC1: measure the radial velocity of the supersonic outflow associated with star formation extensive chemical processing at high temperature in “shocks”: material blasted off the surface of dust, reacts in the gas phase and redeposited on dust Gustafsson et al. 2003

42. material re-deposited after the shock cools from several thousand K to 10K (1-2 years) • chemically processed material is reprocessed on dust grain surfaces by cold electrons: these can be very active in inducing chemistry- see later • chemical processing also by UV photons if majority of the dust is not completely shielded from UV light by other dust

43. The detailed nature of the chemistry during the period of star formation and planet formation must be the key to understanding the formation of aminoacids, bases of DNA etc. in space (analysis of meteorites) • UV irradiation of H2O+methanol+CO+CO2 ices gives 16 different aminoacids (Munoz-Caro et al. Nature 2002)

44. The chemical wealth of meteorites • Meteorites are million year old chips (i.e. recent) off much older “parent bodies” • Murchison: 4.5 billion years old parent body • Matrix = dust remnants from the pre-solar and solar nebula • bases of DNA, RNA + 70 or more aminoacids, 8 of which are those found in biochemistry.

45. The chemical wealth of meteorites • also diaminoacids – constituents of peptide nucleic acids (Nielsen 1999) – suggested as the earliest progenitor of life, predating RNA or DNA • sugars and sugar-related compounds • 50 organic acids up to C10

46. D/H ratios • in cold interstellar clouds at 10K – the presolar nebula – thermochemistry and surface reactions drive molecules to replace H with D • cosmic D/H ~ 2 x 10-5 • even ND3 has been observed (van der Tak et al. 2003) + many other deuterated compounds • aminoacids in Murchison show D/H ratio several times > terrestrial aminoacids: a sign of the interstellar ancestry of the Murchison molecules

47. Delivery of biochemicals from space • does the presence of all these biochemicals in Murchison (and other meteorites) have any bearing on the origin of life on Earth? • the early Earth was subject to intensive bombardment 4.5 – 3.9 billion years ago (decreasing and ending at 3.5 byr)

48. Micrometeorites • tiny meteorites ~100 microns • French scientists (Michel Maurette?) freezing to death in the name of science, extracting pure micrometeorites from icy puddles in the Antarctic

49. Antarctic Micrometeorites AMMs • AMMs are ancient • contain organic carbon • the non-protein amino acid alpha-amino isobutyric acid (AIB) has been detected in MMs. ~14% of the MMs in that study contained AIB. • let’s assume that MMs typically contain aminoacids molecules: chips off the same block as their much larger cousins, meteorites Matrajt et al METEORITICS & PLANETARY SCIENCE 39 1849 (2004)

50. Antarctic Micrometeorites: AMMs • 75% pass through the atmosphere of the Earth without strong melting • molecules in AMMs would not decompose entirely • today 500 tons/yr of organic C falls to Earth in MMs • uncertain extrapolation back in time: the quantity of organic C delivered to the early Earth is 100 times > total budget in biosphere today (where did it go?)