Session 1

Space astronomy missions to detect ingredients for life and exoplanets in the universe: status of current and future approved missions and new proposals

09/11 – Monday

Afternoon

15:00 - 15:30 Water and ice in the universe: from clouds to planets (Ewine van Dishoeck)

Authors
  1. Ewine van Dishoeck (Leiden Observatory, Leiden University)
Abstract

Water is one of the most abundant chemical species in the universe, and essential for the origin of life (as we know it) on Earth and on the many exoplanets that have now been identified. But where does all the water in our oceans come from? Molecules such as water are formed in the very tenuous clouds between the stars that are present throughout the entire Milky Way and even in galaxies at the edge of the universe. Thanks to the launch of the Spitzer Space Telescope and the Herschel Space Observatory, our understanding of the physics and chemistry of water in space has dramatically improved (see www.strw.leidenuniv.nl/WISH for summary). With Herschel and Spitzer, a comprehensive set of data on water gas and ice has been obtained toward a large sample of well-characterized protostars, covering a wide range of masses as well as evolutionary stages -from the earliest stages represented by pre-stellar cores to the late stages represented by the pre-main sequence stars surrounded only by disks. The new Atacama Large Millimeter/submillimeter Array (ALMA) is providing exciting new insight, zooming in to the planet-forming zones of disks. The latest results from Herschel and ALMA will be presented and the evolution of water and the oxygen reservoir from clouds to new stars and planets will be discussed. New insight into the origin of the water in oceans on Earth comes from observations of deuterated water and comparison with comets, including the Rosetta mission.

References:

van Dishoeck et al. 2014, Water from clouds to planets, Protostars & Planets VI, ed. H. Beuther et al. (University of Arizona Press), p. 835-858.
http://arxiv.org/abs/1401.8103

van Dishoeck et al. 2013, Interstellar water chemistry: from laboratory to observations, Chemical Reviews 113, 9043-9085

Bergin & van Dishoeck 2012, Water in star- and planet-forming regions,
Philosophical transactions of Royal Society A, 370, 2778-2802

15:30 - 16:00 Radioactive isotopes from nucleosynthesis as water­‐controlling heat sources (Roland Diehl)

Authors
  1. Roland Diehl (Max Planck Institut für extraterrestrische Physik)
Abstract

In protoplanetary disks, melting of small bodies is largely controlled by heating from longlived (My) radioactive isotopes. The amount and distribution of radioactivities in solids therefore determines the water content that eventually ends up in planets. Nucleosynthesis in massive stars and their supernovae creates candidate isotopes 26 Al and 60 Fe, which are partly ingested into protostellar material from the surrounding interstellar gas. The decay of these isotopes are studied in the Galaxy through gamma-­‐ray telescopes, measuring the sources of those radioactivities and how they distribute their ejecta. We discuss the interstellar reservoirs of those radioactivities, as we learn through such gamma-­‐ray surveys to originate from the population of massive stars in the Galaxy. Then we will use the constraints from the early solar system to discuss how water in protoplanetary disks may be constrained from Galactic nucleosynthesis.

16:00 - 16:20 Infrared spectroscopy- a method for remote sensing of water and other biosignature gases on earth-like planets (Shivom Gupta)

Authors
  1. Shivom Gupta (Uttar Pradesh Technical University)
  2. Afraz Khan (Uttar Pradesh Technical University)
Abstract

Discovery of exoplanets disproved the old belief that there are no planets orbiting other stars. As more exoplanets were found by modern scientific methods the focus shifted to another question which was – life. There is life on Earth which is a part of planets belonging to the Solar System and since newer planets were being discovered it led scientists and astrobiologists to find better and improved methods to search for more exoplanet in the hopes of finding earth like planets which may support life.
Present techniques developed for searching and studying physical parameters of exoplanets include radial velocity method, transit method, microlensing, direct imaging etc. Direct imaging of earth like planet has not been proved successful in studying their atmosphere. One of the most promising method is transit spectroscopy, in which transmitted light from an exoplanet transiting in front of a K or M type star is analysed in near infrared region in high resolution narrow band looking for specific absorption lines of water and other biosignature gases in the atmosphere under study. Biosignature gases have been divided in to two categories Type I and Type III. The first category includes byproduct gases produced as a result of metabolic reaction and the second category includes chemicals produced by lifeforms. This technique has been used to study the atmosphere of a few exoplanets and especially the hot Jupiters. Infrared spectroscopy revealed a great diversity in their atmosphere with some hot jupiters showing no sign of cloud and some cooler one with hazes and clouds. The problem which limits the study of exo-atmosphere of a super earth is noise in the signal. It is somewhat compensated by atmosphere modelling and simulations. For simulating observations and finding the exoplanet transmission spectrum, three components are required, steller spectra, planet transmission spectrum and telluric transmittance. For the simulation of observation, the intensity corresponding to the area covered by the planet is required and can be obtained by integrating the specific intensity over the area covered by the planet’s atmosphere. For earth like planet the transmission spectra are created using the model LinePak with increase in impact parameter up to 100 km above the surface. The telluric transmittance is calculated by the same atmospheric modelling code LinePak. High resolution spectroscopy instruments are required which can provide a high signal to noise ratio. The current best spectrograph at Keck II and Subaru telescope have resolution of 25000 and 20000 respectively. Resolutions higher than these with a broad range of wavelength is needed so that multiple biosignature gases could be detected.
Future missions like Transiting Exoplanet Survey Satellite and near-infrared spectroscopy with very high ranges of wavelength and resolution by James Webb Space Telescope may provide an opportunity to peak into the atmosphere of an earth like planet at distances of tens of parsec and could help us find life on other planets in the next two decades which may change our perception of life in the universe.

17:30 - 18:00 Water Contents on Rocky Planets in the Habitable Zones of M dwarfs and Biosignature Detection (Feng Tian)

Authors
  1. Feng Tian (Tsinghua University)
Abstract

The searches for habitable planets currently focus on M dwarfs because of observation feasibility considerations. However, the early evolution of M dwarfs are quite different from that of Sun-like stars: the total luminosities of M dwarfs decrease by a factor of 10 during their PMS phase. As a result of this luminosity evolution, rocky planets in the habitable zones of main sequence M dwarfs were too close to the host stars during the first 100 Myrs and were in the runaway and moist greenhouse states.

This scenario has been studied by three groups of researchers recently (Ramirez and Kaltenegger 2014, Tian and Ida, Luger and Barnes 2015), and their consensus is that massive amount of water could have been lost during this time — early evolution of M dwarfs could have changed the water contents of rocky planets around them, which could strongly influence the habitability of rocky planets around low mass stars.

It has been proposed that oxygen could build up in the atmospheres of rocky planets in the habitable zones of low mass stars because of the unique UV environments and the consequent atmospheric photochemistry (Hu et al. 2014, Tian et al. 2014, Domagal-Goldman et al. 2015). In addition, dense oxygen dominant atmospheres (up to 2000 bars, Luger and Barnes 2015) might form because of efficient loss of hydrogen from these exoplanets. Because O2 and its photolysis product ozone are potentially important biosignature gases, what biosignature should be used for the atmosphere on rocky planets around M dwarfs is in debate.

In this talk we will present new research developments regarding habitability, water contents, and biosignature detection related to rocky planets in the habitable zones of M dwarfs.

18:00 - 18:20 Starshade Missions and the Search for Life (Webster Cash)

Authors
  1. Webster Cash (University of Colorado at Boulder)
Abstract

Ground testing of starshades has confirmed that they they achieve ultra high contrast at low angles in a robust manner. The US community is now moving into a demonstration phase for starshades. A program of ground and atmospheric based demos of small starshades to achieve contrast of better than 10^10 at inner working angles pushing in toward one arcsecond will be described. A low cost orbital mission that could be implemented in the next few years will described as well, reaching in to a quarter of an arcsecond. These efforts will allow a flagship-scale starshade to move forward early in the next decade.

Starshades, with their high efficiency and excellent contrast, will allow direct imaging of planetary systems, revealing major planets plus debris disks down to the level of our zodiacal light. Placing a spectrograph entrance slit over the image of an exoplanet will then enable high quality spectroscopy. The low cost orbital mission should be able to perform the first searches for biomarkers on Earth-like planets in nearby planetary systems like Tau Ceti and Epsilon Eridani.

By detecting exozodiacal light signals in a statistical sample of nearby stars, the orbital demo mission would be able to establish the net background against which exoplanetary spectra must be taken. This in turn would allow the requirement on the angular resolution and hence aperture of a future Lifefinder mission to be set.