2015 Annual Science Report
Astrobiology Roadmap Objective 1.2 Reports Reporting | JAN 2015 – DEC 2015
Roadmap Objective 1.2—Indirect and direct astronomical observations of extrasolar habitable planets.
Project 1: The Origin of Homochirality
Small biological molecules are frequently chiral, meaning that they can exist in both right-handed and left-handed forms. The two forms are identical except for the mirror symmetry that they break, and so would be expected to participate in chemical reactions in a way that does not depend on their chirality. When assembled into polymers, the resulting chains would therefore be expected to consist of a mixture of right and left-handed forms of the small molecules, a so-called racemic state. The surprise is that this is not true for the molecules of life. All chiral amino acids used by biology are left-handed and all chiral sugars are right-handed. That is, they are homochiral. This project is concerned with trying to find an explanation for this ubiquitous phenomenon, a universal aspect of all life on Earth. The specific question that is addressed is whether homochirality is a generic phenomenon of living systems, one that would be anticipated to arise if life were found elsewhere in the universe. Or is it instead some frozen accident related to the specific way that life arose on Earth? This question has been hotly debated in one form or other for over a hundred years, certainly since the time that Lord Kelvin coined the term “homochirality”. It is important for the Illinois NASA Astrobiology Institute for Universal Biology, because it is one of the two most evident universal phenomena of all life on Earth, the other being the universal genetic code. The phenomenon is important for another reason. The magnitude of the homochirality is 100%. It is not a slight imbalance in the abundance of right-handed vs. left-handed molecules. Thus, it is an unambiguous signal to measure, either from biological samples or remotely due to the effects of homochirality on the scattering of light waves. Specifically, homochiral solutions or suspensions will affect the polarization plane of electromagnetic waves, and so can readily be detected through optical means. The most exciting possibility in this regard is that if homochirality can be firmly established as a biological phenomenon, then its presence can be used as a biosignature of non-terrestrial life.ROADMAP OBJECTIVES: 1.2 3.2 3.4 4.1 4.2 7.1 7.2
Project 2: Cells as Engines and the Serpentinization Hypothesis for the Origin of Life
All life is, and must be, “powered” since all of its most essential and distinguishing processes have to be driven “up-hill” against their natural thermodynamic direction. By the 2nd law of thermodynamics, however, a process can only be made to proceed up-hill by being mechanistically linked, via a molecular device functioning as an engine, to another, more powerful, process that is moving in its natural, down-hill direction. On fundamental principles, we argue, such engine-mediated conversion activities must also have been operating at, and indeed have been the cause of, life’s emergence. But what then were life’s birthing engines, what sources of power drove them, what did they need to produce, and how did they arise in an entirely lifeless world? Promising potential answers to these and other questions related to the emergence of life are provided by the Alkaline Hydrothermal Vent/serpentinization (“AHV”) hypothesis, whose original propounder and lead proponent, Dr. Michael Russell of JPL, is a co-investigator on this project. The goal of the project is specifically to clarify the essential mechanistic modus operandi of all molecular engines that power life, and to see how the most fundamental and prerequisite of these could have arisen, and operated, in the structures and flows produced by the serpentinization process. Importantly, candidate answers to these questions can be put to definitive laboratory tests.ROADMAP OBJECTIVES: 1.1 1.2 3.1 3.2 3.3 3.4
Understanding Past Environments on Earth and Mars
In this task we performed research to understand the evolution of habitable environments on Earth and Mars, both of which serve as potential analogs for habitable environments on extrasolar planets. We are expanding this line of work from past reports to span the entire histories of both planets. On Earth, we have sought to understand environments and time periods spanning the origins of life to the effects of human-generated greenhouse gas emissions on modern-day climate cycles. On Mars, we focus on the ancient conditions that could have allowed liquid water to be stable at the surface; on modern Mars, we focus on the debate on the presence, amount, and variability of methane in the Martian atmosphere.ROADMAP OBJECTIVES: 1.1 1.2 4.1 4.2 5.1 5.2 6.1
Circumstellar Debris and Planetesimals in Exoplanetary Systems
GCA astronomer Marc Kuchner studies the dynamics of debris disks, extrasolar analogs to the Kuiper Belt and the asteroid belt in our solar system, using NASA’s supercomputers. He develops numerical models of the orbits and the interactions of the planetesimals in these disks for use in interpreting images of them made with the Hubble Telescope and other NASA observatories. Together, the images and models teach us about how planetary systems form and evolve – the context within which processes affecting our Solar System are evaluated and extended to exo-planetary systems. An important goal is to extend these studies to a wider range of proto-planetary systems, thereby expanding the range of diversity within which the Solar System must be interpreted. Kuchner’s second initiative targets that objective.
Accordingly, Kuchner invited the public to help him discover new planetary systems through a new website, launched in 2014. At DiskDetective.org, volunteers view data from NASA’s Wide-field Infrared Survey Explorer (WISE) mission and three other surveys. WISE measured more than 745 million objects, representing the most comprehensive survey of the sky at mid-infrared wavelengths ever taken. Among these objects, thousands of planetary systems await discovery – recognizable by the dusty disks that surround them. But galaxies, interstellar dust clouds and asteroids also glow in the infrared, which stymies automated efforts to identify these disks. At Disk Detective.org, the volunteers find the disks by watching 10-second videos of objects seen by WISE, then classifying them by clicking on a selection of buttons on their screens.ROADMAP OBJECTIVES: 1.1 1.2
Astronomical Biosignatures, False Positives for Life, and Implications for Future Space Telescopes
In this task, we identify novel biosignatures and also identify “false positives” for life, which are ways for non-biological processes to mimic proposed biosignatures. Of primary concern are false positives that could mimic easier to detect biosignatures like O2, which we plan to search for with future space-based telescopes. This is a growing area of research that VPL’s past work has motivated, leading to multiple research teams across the planet following our example. Our work continues to be at the forefront of this area of work, as we have identified new non-biological mechanisms for mimicking signs of life. Further, we explained the ways in which these non-biological mechanisms could be identified, and “true positives” from biology confirmed with secondary measurements. Finally, we communicated these lessons to various teams that are studying concepts for future missions that would search for these signs of life. This connection to missions will ensure that our research is incorporated into those missions, so that they will not be “tricked” by these false positives.ROADMAP OBJECTIVES: 1.1 1.2 4.1 4.3 5.2 5.3 7.2
Inv 3 – Planetary Disequilibria: Characterizing Ocean Worlds and Implications for Habitability
INV 3 looks at how, where, and for how long might disequilibria exist in icy worlds, and what that may imply in terms of habitability. A major interest for this work is how ocean composition affects habitability. We are investigating chemistry behaves under conditions of pressure, temperature, and composition not found on Earth. Our simulations of deep ocean world chemistry couple with models for ocean dynamics, ocean ice interaction, and tectonics within the ice. We are examining each of these, how they interact, and how they relate to what future missions may discover. Members of our team are involved in missions to Mars, Jupiter’s moon Europa, Saturn, and Pluto. We are also involved in studies of exoplanets, and are working to understand how ocean worlds like Ganymede and Europa might provide analogues for more distant watery super-earths.ROADMAP OBJECTIVES: 1.1 1.2 2.2 3.1 4.2 6.2 7.1 7.2
Evolution of Protoplanetary Disks and Preparations for Future Observations of Habitable Worlds
The evolution of protoplanetary disks tells the story of the birth of planets and the formation of habitable environments. Microscopic interstellar materials are built up into larger and larger bodies, eventually forming planetesimals that are the building blocks of terrestrial planets and their atmospheres. With the advent of ALMA and continuing use of the Hubble Space Telescope, we are poised to break open the study of young exo-planetesimals, probing their organic content with detailed observations comparable to those obtained for Solar System bodies. Furthermore, studies of planetesimal debris around nearby mature stars are paving the way for future NASA missions to directly observe potentially habitable exoplanets.ROADMAP OBJECTIVES: 1.1 1.2 3.1 7.2
Stellar Effects on Planetary Habitability and the Limits of the Habitable Zone
In this task, VPL team members studied the interaction between stellar radiation (including light) and planetary atmospheres to better understand the limits of planetary habitability and the effects of stellar radiation on planetary evolution. Work this year spanned climate modeling to atmospheric escape. We showed that multiple stable states of climate could exist for water-rich worlds, including both habitable and uninhabitable states, suggesting that water-rich planets in the habitable zone are not necessarily habitable. Atmospheric escape models were used to illustrate how the pre-main sequence evolution of M-dwarf stars could strip the gaseous envelopes from mini-Neptune planets, transforming them into potentially-habitable, Earth-sized rocky bodies. We also showed that pre-main sequence evolution could lead to strong atmospheric escape of water on otherwise habitable worlds, potentially rendering them uninhabitable. We defined the first metric to rank an exoplanet’s potential to support surface liquid water based on fundamental data from transit observations. Observational work was also undertaken to characterize the frequency and characteristics of stellar flares on M dwarf stars from Kepler data, as input to future work on characterizing the effect of stellar flares on habitability.ROADMAP OBJECTIVES: 1.1 1.2 3.4
Planetary Surface and Interior Models and SuperEarths
We use computational and theoretical models to simulate the evolution of the interior and the surface of real and hypothetical planets around other stars. Our goal is to determine the characteristics that are most likely to contribute to making a planet habitable in the long run. Observations in our own Solar System show us that water and other essential materials are continuously consumed via weathering (and other processes: e.g., subduction, sediment burial) and must be replenished from the planet’s interior via volcanic activity to maintain a biosphere. The surface models we are developing will be used to predict how gases and other materials will be trapped through weathering and biological processes over time. Our interior models are designed to predict tidal effects, heat flow, and how much and what sort of materials will come to a planet’s surface through resurfacing and volcanic activity throughout its history.ROADMAP OBJECTIVES: 1.1 1.2 4.1 5.2 6.1
Exploring the Structure and Composition of Exoplanets With Current and Future Telescopes
This project addresses a major frontier of planetary science and astrobiology, namely the identification and characterization of habitable (and inhabited) exoplanets. Measurements of molecular absorption in the atmospheres of these planets offer the chance to explore several outstanding questions regarding the atmospheric structure and composition of hot Jupiters. Targeted questions include the possibility of bulk compositional variations among planets, and the presence or absence of a stratospheric temperature inversion on individual planets. In this reporting period, we emphasized four areas:
1. We improved our modeling and analysis of exoplanet transit and eclipse measurements obtained with the Hubble Space Telescope (HST) and the Spitzer Space Telescope on highly irradiated, Jupiter-mass planets.
2. We improved our data analysis methods to better understand aspects of measuring the chemical composition of the planet’s atmosphere, and we advanced the chemical and thermal modeling of the planet’s hot dayside.
3. We developed simulations of future observations with the James Webb Space Telescope (JWST), and we provided science leadership for a future balloon-borne telescope that can perform transit spectroscopy of hot exoplanet atmospheres.
4. We estimated the discovery yield of future Earth-like exoplanet imaging missions as part of the planning process for the next Astrophysics Decadal Survey, and we are now expanding this effort to estimate the science yield from spectroscopic characterization of them.ROADMAP OBJECTIVES: 1.1 1.2 7.2
Interstellar and Nebular Chemistry: Theory and Observations
We continue to undertake theoretical and observational studies pertaining to the origin and evolution of organics in Planetary Systems, including the Solar System. In this performance period, we have focused on studies aimed at understanding the origin and processing of organics in the earliest evolutionary phases of stars like the Sun. These include formation pathways and related isotopic fractionation effects.
We have continued observational programs designed to explore the chemical composition of comets and establishing their potential for delivering prebiotic organic materials and water to the young Earth and other planets. State-of-the-art international facilities are being employed to conduct multi-wavelength simultaneous studies of comets in order to gain more accurate abundances, distributions, temperatures, and other physical parameters of various cometary species. We are also leading an international collaboration to study the organic composition of Titan with the Atacama Large Millimeter Array (ALMA).ROADMAP OBJECTIVES: 1.1 1.2 2.2 3.1 3.2 7.1 7.2
Habitable Planet Formation and Orbital Dynamical Effects on Planetary Habitability
This task explores how habitable planets form and how their orbits evolve with time. Terrestrial planet formation involves colliding rocks in a thin gaseous disk surrounding a newborn star and VPL’s modeling efforts simulate the orbital and collisional evolution of a few to millions of small bodies to determine the composition, mass, and orbital parameters of planets that ultimately reach the habitable zone. After formation, gravitational interactions with the star and planet can induce short- and long-term changes in orbital properties that can change amount of energy available for the climate and to illuminate the planetary surface. The VPL simulates these effects in known and hypothetical planetary systems in order to determine the range of variations that permit planetary habitability.ROADMAP OBJECTIVES: 1.1 1.2 3.1 4.3
Modeling and Observations of Exoplanets
The focus of this project is to use the Doppler velocity technique to detect and characterize extrasolar planets and use exoplanet data to establish the nature and diversity of planetary systems in the galaxy, with an emphasis on establishing the abundance of habitable planets in the universe.ROADMAP OBJECTIVES: 1.1 1.2
NNX15AT33A Origin and Evolution of Organics and Water in Planetary Systems
Research by the Blake group (CalTech) supported by the NAI has centered on a joint laboratory and observational program, designed with the participation of Goddard node scientists, that aims to investigate the chemistry of water and simple organics in the protoplanetary disk analogs of the early solar nebula, in comets, and in the atmospheres of extrasolar planets. The laboratory work has involved the creation of novel high bandwidth instruments from the microwave to the THz regime that can probe both gaseous and condensed phase (liquid and solid) materials. Particular emphasis has been placed on the study of small chiral (that is, ‘handed’) organic species, with a view toward establishing whether the homochirality exhibited on the Earth is stochastically or deterministically derived. We combine the laboratory studies with astronomical observations at radio (VLA, GBT, ALMA), far-infrared (SOFIA, Herschel archival data), and infrared (Keck/VLT, Spitzer archival data) wavelengths. A recent highlight is the first detection of a chiral species toward the Galactic Center, as is described in this reportROADMAP OBJECTIVES: 1.1 1.2 3.1
Solar System Analogs for Exoplanet Observations
The worlds of our Solar System can provide an important testing ground for ideas and techniques relevant to characterizing exoplanets. In this task, we use observations and simulations of Solar System planets to understand how astronomers and astrobiologists will recognize signs of habitability and life in future observations of rocky exoplanets. Work in this area this past year includes the first-ever direct detection of molecular nitrogen collision-induced absorption in Earth’s whole-disk spectrum, which can be used to indicate atmospheric pressure and, thus, habitability. Also in this task, VPL scientists have proposed techniques for using color to distinguish Earth-like exoplanets from other types of worlds.ROADMAP OBJECTIVES: 1.2 2.2 7.1 7.2
Undergraduate Research Associates in Astrobiology (URAA)
2015 saw the twelfth session of our summer program for talented science students (Under-graduate Research Associates in Astrobiology), a ten-week residential research program tenured at Goddard Space Flight Center and the University of Maryland, College Park (http://astrobiology.gsfc.nasa.gov/education.html). Competition was again very keen, with an over-subscription ratio of 4.7. Students applied from over 19 Colleges and Universities in the United States, and 4 Interns from 4 institutions were selected. Each Intern carried out a defined research project working directly with a GCA scientist at Goddard Space Flight Center or the University of Maryland. As a group, the Associates met with a different GCA scientist each week, learning about his/her respective area of research, visiting diverse laboratories and gaining a broader view of astrobiology as a whole. At summer’s end, each Associate reported his/her research in a power point presentation projected nation-wide to member Teams in NASA’s Astrobiology Institute, as part of the NAI Forum for Astrobiology Research (FAR) Series.ROADMAP OBJECTIVES: 1.1 1.2 2.1 2.2 3.1 6.2 7.1
Charnay NAI NPP PostDoc Report
My project focuses on the modeling of clouds and photochemical haze in the atmospheres of the early Earth and exoplanets. I use a 3D model, developed to simulate any kind of atmosphere, to study the formation, dynamics, climatic impact and observational features of clouds/haze. My first object of interest is GJ1214b, a mini-Neptune whose observations by HST revealed a cloudy/hazy atmosphere. The formation of such high and thick clouds is not understood. My second object of interest is the Archean Earth for periods with a methane-rich atmosphere leading to the formation of organic haze.ROADMAP OBJECTIVES: 1.2 4.1