The Beginning

A Philosophical Position

Life may have come from non-life as one big accident. This seems highly unlikely, at least given the way our universe is set up, so if it's that way, then we are probably the only intelligent life in the universe, maybe the only life at all.

Or maybe the origin of life was directed, in which case it has happened as few or many times as the director deigns, but at least once, at least here.

Or maybe the origin of life occurs due to necessary physical principles acting on conditions that are, in certain regions of our universe, inevitable. Put some likely simple chemicals and rocks near enough to a star and pop! Life. Every time. In this case, life is very likely all over the place.

Or maybe life arises from incremental chances, incremental steps, maybe with some or all of the chance steps the numbers are fixed a bit, the dice are weighted by particular physical laws and conditions. After all, random isn't truly random. Even a coin flip is absolutely fixed by basic Newtonian physics. There might be a physical selection after these steps, choosing the structures that replicate however inefficiently over those that don't replicate at all. In this case, life might be unique to the Earth, all over the place, or in very few places, depending on how unique the steps are and what the probabilities of the steps happen to be.

Which one of these is it? I don't know! No one knows! That's why I and many others do the research. Because we don't know the answer, but with research, maybe we can find it. I approach my work in light of this hypothetical: If we ever find life on other worlds, something we can possibly do even within other solar systems within the next 25-50 years, that will strongly suggest that it wasn't a big accident, and will help strongly constrain how many little accidents and how likely they would have been. Or that discovery, along with the exploration of prebiotic chemistry in the lab, might point to life being inevitable given ubiquitous starting conditions.

No experiment or observation can rule in or rule out a generic designer. If we find life, that's consistent with the designer, and if we don't, also consistent. However interesting the design hypothesis may be to a theologian, it is of no consequence to the scientist.

Even if intelligent design, as a scientific hypothesis, happens to be true (and how would we know?), it's a terribly boring answer.

The Origin and Evolution of
Life on Earth and other

How did life first arise on Earth? Did life start on other planets, and if so, must it have started the same way? Answering this question involves a combination of three interdisciplinary approaches: (1) laboratory prebiotic chemistry experiments, (2) Early Earth geochemistry, and (3) exoplanet characterization for determining how universal the chemical pathways toward life's origin actually are.

These three projects are discussed below (details to be added:)

Looking Where the Light is Good

Gold's Propane-Rich Early Earth Reborn

Life after Light

Universal Life

Planets and

I am interested in characterizing exoplanet atmospheres and understanding the chemical processes that occur within them, and whether this information, about exoplanets of any composition and character, can tell us about the plausibility of life on the surfaces of rocky extrasolare planets.

Chemistry on Exoplanets
The STAND2015 Network The chemical network used in Rimmer & Helling (2015) can be found at the end of the arxiv preprint, or can be found in a text layout set up to be read by the Argo code here. An updated version, with updated rates (from May 2016) used in Shami Tsai's paper is here. Please consult the paper, or send me an e-mail if you have questions about the format or the letter codes. The format is based on the OSU astrochemistry chemical network formats, which you can find here.

The ARGO Model The 1D photochemistry/diffusion code used in Rimmer & Helling (2015). It has been extensively tested and is in the process of being commented, and a guidebook is being written. The plan is to make a version of this code publicly available by end of 2018. This will include a github python wrapper used to run the Fortran code.

Extrasolar Planets
I am work on the chemistry of extrasolar planet atmospheres. This work centers around four questions (including examples of my efforts to address these questions in the literature):

  • How can the chemical composition of extrasolar planets be determined spectroscopically? (Casewell et al. 2015)
  • What does atmospheric chemistry on exoplanets tell us about the physical conditions on these worlds? (Rimmer & Helling 2015)
  • Does planet formation leave an impact on the exoplanet chemistry? Are the initial conditions important for the atmospheres? (Helling et al 2014)
  • Can the observed character of an exoplanet help us constrain whether life could have arisen there? How so?

My fosus is primarily on the chemistry of hot Jupiters and directly imaged planets, because these are the exoplanets that can be best characterized by their spectra. As observational data improves, I plan to transition the focus of my work more toward water worlds and super-earths. Hot Jupiters and directly imaged gas giants will probably always be the best characterized exoplanets, and they are very different objects than those found in our solar system. They command my enduring interest

HD 209458 b is the first exoplanet detected via the transit method, and is currently one of the best characterized exoplanets. I have used it as a benchmark case to compare my models with those of other researchers, esp. Moses et al (2011) and Lavvas et al (2014). Below is my comparison of my results (Rimmer & Helling (2015), solid lines) to the results of Moses et al (2011, dotted lines) for some relevant species.

HR 8799 d: A member of the first directly imaged exoplanet system, HR8799b, like all directly imaged exoplanets, has the great advantage of possessing a detectable emission spectrum. Presently, directly imaged gas giants are detected far from their host stars, making them ideal candidates for studying cosmic ray chemistry in exoplanet atmospheres. The effect of a cosmic ray flux impinging on the atmosphere, being sheilded only by the planet's own (assumed Jupiter-like) magnetic field, can be seen in our results (Rimmer et al 2014) where the dotted lines represent thermochemical equlibrium, the dashed lines dynamically-driven chemical quenching, and the solid lines a combination of dynamically driven quenching and cosmic ray chemistry.

The Early Earth: I have applied this model to the Early Earth (the Earth within its first billion years). With just photochemistry, my results are more or less consistent with the seminal Kasting (1993) paper. It definitely confirms that photochemistry alone is not sufficient to produce a large amount of molecular oxygen on the Early Earth. ${\rm CO_2}$ is stable in this model, and it does not appear that photochemistry would be able to convert a strongly oxidizing atmosphere at the surface boundary into a reducing environment higher in the atmosphere. The next step is to apply this same analysis in combination with (a) different hydrogen fluxes, (b) a temperature profile appropriate to another stellar type and (c) lightning-driven chemistry on a cloudy Early Earth, where the products of this chemistry can build up before becoming photochemically processed. The results in the simple case are shown here (Rimmer & Helling, 2015):

Present-Day Earth: I have compared my results to present-day Earth measurements mostly for benchmarking purposes. Earth's atmosphere is the best studied, and it is important to make sure that the atmospheric chemistry predicted by models comes into at least a broad agreement with present-day Earth chemistry. This work, in combination with the cosmic ray work, has lead me to a hobbyist's interest in Earth climate modelling and climate change science. Below are my results for the contemporary Earth for certain simple species (Rimmer & Helling, 2015).


Titan is a truly fascinating object within our own solar system, Titan has a rich ion-netural organic nitrogen chemistry. Its atmospheric chemistry has been transformed by several physical effects, UV and X-ray photons, cosmic rays, energetic particles captured in Saturn's magnetic field and solar wind particles. It is the ideal place to test the STAND chemical network, and the STAND chemical network affords the ability to explore tholin production in the upper atmosphere and other tracers of energetic particle driven chemistry expected to produce Titan's upper atmospheric haze. It is a future project goal to construct a comprehensive model for the atmosphere of this moon.

Curriculum Vitae

  • PhD in Physics,
           Ohio State University

  • BS in Physics cum laude,
           University of Colorado
           Health Sciences Center

  • CV

  • Papers
  • Submitted, Accepted and
    Published Papers

    1. Gerin, M., de Luca, M., Black, J., Goicoechea, J. R., Herbst, E., Neufeld, D. A., ... [Rimmer, P. B.]... and Zmuidzinas, J. (2010). Interstellar OH+, H2O+ and H3O+ along the sight-line to G10. 6-0.4. Astronomy and Astrophysics, 518, L110.
    2. Gerin, M., de Luca, M., Goicoechea, J. R., Herbst, E., Falgarone, E., Godard, B., ... [Rimmer, P. B.]... and Ward, J. S. (2010). Interstellar CH absorption in the diffuse interstellar medium along the sight-lines to G10. 6-0.4 (W31C), W49N, and W51. Astronomy and Astrophysics, 521, L16.
    3. Neufeld, D. A., Goicoechea, J. R., Sonnentrucker, P., Black, J. H., Pearson, J., Yu, S., ... [Rimmer, P. B.] ... and Shipman, R. (2010). Herschel/HIFI observations of interstellar OH+ and H2O+ towards W49N: a probe of diffuse clouds with a small molecular fraction. Astronomy and Astrophysics, 521, L10.
    4. Gupta, H., Rimmer, P. B., Pearson, J. C., Yu, S., Herbst, E., Harada, N., ... and Nordh, L. H. (2010). Detection of OH+ and H2O+ towards Orion KL. Astronomy and Astrophysics, 521, L47.
    5. Rimmer, P. B., and Herbst, E. (2011). Propagation of low-energy cosmic rays in molecular clouds: calculations in two dimensions. Memorie della Societa Astronomica Italiana, 82, 933.
    6. Rimmer, P. B., Herbst, E., Morata, O., and Roueff, E. (2012). Observing a column-dependent zeta in dense interstellar sources: the case of the Horsehead nebula. Astronomy and Astrophysics, 537, 7.
    7. Bilger, C., Rimmer, P. B., and Helling, Ch. (2013). Small hydrocarbon molecules in cloud- forming brown dwarf and giant gas planet atmospheres. Monthly Notices of the Royal Astronomical Society, 435(3), 1888-1903.
    8. Rimmer, P. B., and Helling, Ch. (2013). Ionization in Atmospheres of Brown Dwarfs and Extrasolar Planets. IV. The Effect of Cosmic Rays. The Astrophysical Journal, 774(2), 108.
    9. Stark, C. R., Helling, C., Diver, D. A., and Rimmer, P. B. (2013). Ionization in Atmospheres of Brown Dwarfs and Extrasolar Planets. V. Alfvén Ionization. The Astrophysical Journal, 776(1), 11.
    10. Stark, C. R., Helling, Ch., Diver, D. A., and Rimmer, P. B. (2014). Electrostatic activation of prebiotic chemistry in substellar atmospheres. In Press. International Journal of Astrobiology 13(2), 165
    11. Rimmer, P. B., Helling, Ch., and Bilger, C. (2014). The Influence of Galactic Cosmic Rays on Ion-Neutral Hydrocarbon Chemistry in the Upper Atmospheres of Free-Floating Exoplanets. International Journal of Astrobiology 13(2), 173
    12. Helling, C., Woitke, P., Rimmer, P. B., Kamp, I., Thi, W. F., and Meijerink, R. (2014). Disk evolution, element abundances and cloud properties of young gas giant planets. Life, 4(2), 142-173.
    13. Rimmer, P. B., Stark, C. R., and Helling, C. (2014). Jupiter as a Giant Cosmic Ray Detector. The Astrophysical Journal Letters, 787(2), L25.
    14. Casewell, S. L., Lawrie, K. A., Maxted, P. F. L., Marley, M. S., Fortney, J. J., Rimmer, P. B., ... and Helling, C. (2015). Multiwaveband photometry of the irradiated brown dwarf WD0137− 349B. Monthly Notices of the Royal Astronomical Society, 447(4), 3218-3226.
    15. Rimmer, P. B. and Helling, Ch. A Chemical Kinetics Network for Lightning and Life in Planetary Atmospheres. (2016) The Astrophysical Journal Supplement, 224(1), 9.
    16. Helling, Ch., Rimmer, P. B., Rodriguez-Barrera, I. M., Wood, K., Robertson, G. B., and Stark, C. R., (2016). Ionisation and Discharge in Cloud-Forming Atmospheres of Brown Dwarfs and Extrasolar Planets. Plasma Physics and Controlled Fusion, 58(7), 074003.
    17. Tsai, S.-M., Lyons, J., Grosheintz, L., Rimmer, P. B., Kitzmann, D., Heng, K. (2016) VULCAN: An Open-Source, Validated Chemical Kinetics Python code for Exoplanetary Atmospheres. The Astrophysical Journal Supplement Series. 228(2), 20.
    18. Hodosan, G., Rimmer, P. B., and Helling, Ch. (2016) Is lightning a possible source of the radio emission on HAT-P-11b? Monthly Notices of the Royal Astronomical Society. 461.2, 1222.
    19. Hodosán, G., Helling, C., Asensio-Torres, R., Vorgul, I., and Rimmer, P. B. (2016). Lightning climatology of exoplanets and brown dwarfs guided by solar system data. Monthly Notices of the Royal Astronomical Society, 461(4), 3927-3947.
    20. Ardaseva, A., Rimmer, P. B., Hodosan, G., Helling, Ch., Waldman, I., Yurchenko, S., Tennyson, J. (2017) Lightning Chemistry on Contemporary and Early-Earth-Like Planets. Monthly Notices of the Royal Astronomical Society, 470(1), 187.
    21. Ferus, M., Koukal, J., Lenža, L., Srba, J., Kubelík, P., Laitl, V., ... and Rimmer, P. B. (2018). Calibration-free quantitative elemental analysis of meteor plasma using reference laser-induced breakdown spectroscopy of meteorite samples. Astronomy and Astrophysics, 610, A73.
    22. Rimmer, P.B., Xu, J., Thompson, S., Gillen, E., Sutherland, J. D., Queloz, D. (2018) The Origin of RNA Precursors on Exoplanets. Science Advances. 4(8), aar3302.
    23. Kitzmann, D., Heng, K., Rimmer, P.B., et al. (2018) The Peculiar Atmospheric Chemistry of KELT-9b. Astrophysical Journal. 863(2), 183.
    24. Hoeijmakers, J.H., Ehrenreich, D., Heng, K., ... Rimmer, P.B., Molirani, E. and Fabrizio, L.D. (2018) Atomic iron and titanium in the atmosphere of the exoplanet KELT-9b. Nature. 560, 453.
    25. Rimmer, P.B. and Shorttle, O. (2019) Origin of life’s building blocks in Carbon and Nitrogen rich surface hydrothermal vents. Life. 9, 12.
    26. Rimmer, P.B., Shorttle, O. and Rugheimer, S. Geochemical Perspectives Letters. 9, 38.
    27. Civiš, S., Knížek, A. Rimmer, P.B. Ferus, M., Kubelík P., Zukalová M., Kavan, L. and Chatzitheodoridis E. (2019) Formation of perchlorates through methanogenesis on Mars. ACS Earth and Space Chemistry Accepted.
    28. Rimmer, P.B. and Rugheimer, S. Hydrogen Cyanide in Nitrogen-Rich Atmospheres of Rocky Exoplanets. Icarus. Under Review.
    29. Ranjan, S., Todd, Z.R., Rimmer, P.B., Sasselov, D.D., Babbin, A.R. Nitrogen Oxide Concentrations in Natural Waters on Early Earth. Geochemistry, Geophysics, Geosystems. Under Review.
    30. Rimmer, P.B., Ferus, M., Waldmann, I., et al. Identifiable Acetylene Features Predicted for Young Earth-like Exoplanets with Reducing Atmospheres undergoing Late Heavy Bombardment. Nature Astronomy. Submitted.
    31. Günther, M. N., Zhan, Z., Seager, S., Rimmer, P.B. et al. Stellar Flares from the First Tess Data Release: Exploring a New Sample of M-dwarfs. ApJ. Submitted.
    32. Hobbs, R., Shorttle, O., Madhusudhan, N. and Rimmer, P.B. A chemical kinetics code for modelling exoplanet atmospheres. MNRAS. Submitted.
    33. Rimmer, P.B., Gillen, E. and Catling D.C. Icarus. Submitted.


    Department of Earth Sciences, University of Cambridge
    Cavendish Astrophysics
    JJ Thomson Ave, Cambridge CB3 0HE
    +44 (0)1223 346436

    MRC Laboratory of Molecular Biology
    Francis Crick Ave, Cambridge CB2 OQH



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