Artist's impression of the exoplanet Proxima Centauri b shown as arid (but not completely water-free) rocky Super-Earth. ESO/M. Kornmesser - https://www.eso.org/public/images/ann16056a/

Artist's impression of the system Gliese 667. ESO/L. Calçada - https://www.eso.org/public/images/eso0939a/

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    A many-parameter approach to habitability (M-PAtH)

    We are standing on the cusp of a major discovery in planetary sciences. Three new space missions targeting transiting planets are expected to launch in the next two years: the Transiting Exoplanet Survey Satellite (TESS), the CHaracterising ExOPlanet Satellite (CHEOPS), and the James Webb Space Telescope (JWST). The 2020’s will bring three 20-40 meter-class ground-based telescopes: the 24.5-meter Giant Magellan Telescope (GMT), the Thirty Metre Telescope (TMT), and the 39.3-meter European-Extremely Large Telescope (E-ELT). The 2020’s will also see space missions such as the Wide-Field InfraRed Survey Telescope (WFIRST), and the PLAnetary Transits and Oscillations of stars (PLATO-2) mission, which will further survey exoplanets. For the first time in human history, these surveys and telescopes working together will be able to remotely detect potential biosignatures in exo-Earth atmospheres and discover signs of life beyond our Solar System.

    Life can be inferred by the presence of atmospheric biomarkers - gases produced by life that can accumulate to detectable levels in an exoplanet atmosphere. The conviction that these biosignatures will be detected by remote sensing from space telescopes is moderated by current time limitations and observational opportunities. The cancellation a decade ago of both the Terrestrial Planet Finder and Darwin missions means that it is unlikely that a space telescope dedicated to the search for biosignatures in exoplanet atmospheres will be launched within the next 15 years (Snellen et al., 2013). While TESS is predicted to significantly increase the number of detections, unfortunately, none of the new space- and ground-telescopes will be solely dedicated to the characterization of exoplanet atmospheres. In order to make the most of the limited observational resources available, optimal target selection will be of the utmost importance. Selection of targets for this characterisation relies on ambiguously defined concepts of habitability, which are currently constrained by only the density of the planet and the distance from its host star. With the expected increase in the number of detected exoplanets from TESS, we might end up with hundreds of planets that suit these criteria and are accordingly all equally likely to host life. Therefore, it is imperative that we rethink our classification of what makes a planet habitable and improve the habitability model using known planetary and astronomical features that offer a broader and more accessible approach than a narrow focus on specific atmospheric signatures.

    My current research aims to examine the effect that a diverse range of astronomical and planetary parameters have on an exoplanet’s ability to sustain liquid water.

Artist's impression of of the exoplanet 51 Pegasi b. ESO/M. Kornmesser/Nick Risinger (skysurvey.org) - https://www.eso.org/public/images/eso1517a/

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Abiotic chemical disequilibria in Exo-Earth atmospheres:
improving remote biosignature detections by identifying false positives

Sarah R.N. McIntyre
Conference Papers Astronomical Society of Australia's Annual Scientific Meeting 2017, Canberra, ACT, Australia (talk, 13 July 2017)

Abstract

The discovery and characterization of exoplanets has the potential to lead to the identification of life beyond Earth. It has been hypothesised that life can be inferred by the presence of atmospheric biomarkers – biologically produced gases that accumulate in sufficient quantities to result in detectable atmospheric chemical disequilibrium (Krissansen-Totton et al., 2016; Seager et al., 2016). To determine whether exoplanets like Proxima b and the TRAPPIST-1 system are likely to support life, we need to extend our exploration into the potential biological characteristics of their atmospheres. It is important to acknowledge that extraterrestrial life, provided it exists, could be quite unlike the forms of life we are familiar with (Sagan, 1993). For this reason, chemical disequilibrium as a biosignature is appealing because it is a generalized life-detection metric which relies solely on the notion that distinct metabolisms in a biosphere produce waste gases that, with sufficient fluxes, will alter atmospheric composition and result in disequilibrium (Krissansen-Totton et al., 2016). Unfortunately, the gases expected to be produced in abundance by life are ones that are also rife with false positives. The worth of a biosignature is not only determined by the probability of life creating it, but equally by the improbability of non-biological (abiotic) processes producing it (Des Marais, 2013). If all abiotic abundances (O2, N2, N2O, CO2, H2O, O3, CO, CO2, CH4, H2S etc…) can be identified, quantified and eliminated from the spectroscopic data, we will be one step closer to potentially detecting the life on another planet.

Abiotic chemical disequilibria in Exo-Earth atmospheres:
improving remote biosignature detections by identifying false positives

Sarah R.N. McIntyre
Master Thesis Australian National University

Abstract

We are on the cusp of a technological revolution where near-future space- and ground-based observatories will allow an unprecedented opportunity to explore the atmospheres of potentially habitable exo-Earths for signs of life. Unfortunately, detections of the most significant gases produced by life are also susceptible to false positives. A spectral biosignature can only be positively identified when we know both the probability of life forming it, and perhaps more crucially, the improbability of non-biological (abiotic) processes creating it. Likewise, false negatives in biosignatures are influenced by our bias towards signatures of life on Earth since the Cambrian period. Our understanding of the influence of early life forms on Earth is based on a combination of biochemistry and phylogenetic analyses. In this thesis, we present a comprehensive study of the abiotic chemical disequilibrium discriminators for several proposed biosignature atmospheric gases – O2, O3, CH4, N2O, NH3, SO2, CO2 and H2O. Abiotic environmental factors producing these gases have been identified and will improve our ability to select optimal targets and methods to reduce the effect of false positives. We find that the majority of these false-positive mechanisms are contingent on characteristics of the parent star, particularly the photochemical implications for variation in UV intensity, and are generally strongest for planets orbiting M dwarfs. Additionally, a review of future ground- and space-based projects was conducted to determine exoplanet properties that will become observable over the next decade as these new facilities come on line. In advance of the next generation of telescopes, this appraisal of potential biosignatures and the environmental factors and context that could create false positives, will increase our confidence in the detection of extraterrestrial life.

Global Biogeography Since Pangaea

Sarah R.N. McIntyre, Charles H. Lineweaver, Colin P. Groves, Aditya Chopra
Journal Paper Proceedings Of The Royal Society B: Biological Sciences 284 (1856): 20170716. doi:10.1098/rspb.2017.0716.

Abstract

The break-up of the supercontinent Pangaea around 180 Ma has left its imprint on the global distribution of species and resulted in vicariance-driven speciation. Here, we test the idea that the molecular clock dates, for the divergences of species whose geographical ranges were divided, should agree with the palaeomagnetic dates for the continental separations. Our analysis of recently available phylogenetic divergence dates of 42 pairs of vertebrate taxa, selected for their reduced ability to disperse, demonstrates that the divergence dates in phylogenetic trees of continent-bound terrestrial and freshwater vertebrates are consistent with the palaeomagnetic dates of continental separation.

Terrestrial Constraints on Extraterrestrial Intelligence

Sarah R.N. McIntyre, Charles H. Lineweaver
Conference Papers Astrobiology Science Conference 2017, Mesa, Arizona, USA (talk, 24 April 2017)

Abstract

To understand our place in the cosmos, one question rises above all others: “Are we alone in the universe?” Astronomical research on habitable planets has shown that there are billions of prospective Earth-like planets that could all potentially support complex life forms. It is often assumed that once life is present, even as a single-celled organism, an evolution towards humanlike intelligence and subsequent technological development is inevitable. If this convergent evolution hypothesis were to hold up in outer space, it should be applicable to the one planet that we know for certain harbours life – the Earth. Putting a terrestrial spin on Fermi’s paradox, we can ask: If human-like intelligence is convergent, why are we the only species with human-like intelligence on Earth?

Terrestrial Constraints on Extraterrestrial Intelligence

Sarah R.N. McIntyre, Charles H. Lineweaver, Colin Groves
Manuscript in Preparation

Abstract

In the pursuit to understand the cosmos and our place within, one question rises above all others: “Are we alone in the universe?” Astronomical research on habitable planets has shown that there are billions of prospective Earth-like planets that could all potentially support complex life forms. However, there is an assumption that permeates through reasoning regarding evolution of life in space that once life is present, even as a single-celled organism, evolution towards human-like intelligence and subsequent technological development is inevitable. This research experimentally investigated the convergent evolution hypothesis to explore if there is an "intelligence niche" towards which, or into which species evolve, and extrapolate how "rare" occurrence of human-like intelligent life is.

Terrestrial Constraints on Extraterrestrial Intelligence

Sarah R.N. McIntyre, Charles H. Lineweaver
Conference Papers Mt Stromlo Annual Student Seminar, Canberra, Australia (talk, 2 Dec 2016)

Abstract

In the pursuit to understand the cosmos and our place within, one question rises above all others: “Are we alone in the universe?” Astronomical research on habitable planets has shown that there are billions of prospective Earth-like planets that could all potentially support complex life forms. However, there is an assumption that permeates through reasoning regarding evolution of life in space that once life is present, even as a single-celled organism, evolution towards human-like intelligence and subsequent technological development is inevitable. This research experimentally investigated the convergent evolution hypothesis to explore if there is an "intelligence niche" towards which, or into which species evolve, and extrapolate how "rare" occurrence of human-like intelligent life is.

Hearing Harmonies in Newton’s Laws

Sarah R.N. McIntyre
Journal Paper Australian Physics Journal, Volume 51, Issue 4, Jul - Aug 2014, Pages 122-124

Abstract

This year, the Australian Institute of Physics Congress theme “The Art of Physics” sets the stage for further investigation into the intrinsic connection between physics and music. This article describes the author’s physics inspired dance suite that will be performed at the AIP Congress in December.

Artist’s impression of the planet around Alpha Centauri B. ESO/L. Calçada/Nick Risinger (skysurvey.org) - https://www.eso.org/public/images/eso1241a/

 

  • PhD 2020

    Doctor of Philosophy (Astronomy and Astrophysics)

    Australian National University

    Supervisors: Charles Lineweaver, Michael Ireland

    Thesis: A many-parameter approach to habitability (M-PAtH)


  • AFHEA 2017

    Associate Fellowship of the Higher Education Academy

    ANU Educational Fellowship Scheme



  • B.A.2015

    Bachelor of Arts

    Australian National University

    Major: Biological anthropology
    Major: Music

  • MAA 2017

    Masters Astronomy and Astrophysics (Ad)

    Australian National University

    Supervisor: Charles Lineweaver

    Thesis: Abiotic chemical disequilibria in Exo-Earth atmospheres: improving remote biosignature detections by identifying false positives

  • B.Sc.2015

    Bachelor of Science

    Australian National University

    Major: Physics
    Minor: Mathematics
    Specialization: Astronomy and astrophysics

  • Exchange2015

    Global Programs Exchange

    Niels Bohr Institute University of Copenhagen

    Undergraduate course: Atomic Physics
    Masters course: Origin and Evolution of the Solar System

Artist’s impression of CoRoT-7b. ESO/L. Calçada - https://www.eso.org/public/images/eso0933a/

 

Teaching

  • Jul-Nov 2017

    Lab Demonstrator

    Laboratory Demonstrator for Advanced Physics course (Physics 1201) for First Year students at the Australian National University

  • Feb-Jun 2017

    Lab Demonstrator

    Laboratory Demonstrator for Advanced Physics course (Physics 1101) for First Year students at the Australian National University

Professional Activities

  • Jan-Dec 2018

    RSAA Colloquium Committee member

  • Dec 2017

    FAAbExo 2017 LOC Chair

    Franco-Australian Astrobiology and Exoplanet School and Workshop 16 - 20 Dec 2017, Canberra

Artist’s impression of the planet Beta Pictoris b. ESO L. Calçada/N. Risinger (skysurvey.org) - https://www.eso.org/public/images/eso1414a/