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NASA NTRS1985

Review of methodology and technology available for the detection of extrasolar planetary systems

Four approaches exist for the detection of extrasolar planets. According to the only direct method, the planet is imaged at some wavelength in a manner which makes it possible to differentiate its own feeble luminosity (internal energy source plus reflected starlight) from that of the nearby host star. The three indirect methods involve the detection of a planetary mass companion on the basis of the observable effects it has on the host star. A search is conducted regarding the occurrence of regular, periodic changes in the stellar spatial motion (astrometric method) or the velocity of stellar emission line spectra (spectroscopic method) or in the apparent total stellar luminosity (photometric method). Details regarding the approaches employed for implementing the considered methods are discussed.

Tarter, J. C.↗

NASA NTRS2010

Detection of Planetary Emission from the Exoplanet TrES-2 Using Spitzer/IRAC

We present here the results of our observations of TrES-2 using the Infrared Array Camera on Spitzer. We monitored this transiting system during two secondary eclipses, when the planetary emission is blocked by the star. The resulting decrease in flux is 0.127% +/- 0.021%, 0.230% +/- 0.024%, 0.199% +/- 0.054%, and 0.359% +/- 0.060% at 3.6 microns, 4.5 microns, 5.8 microns, and 8.0 microns, respectively. We show that three of these flux contrasts are well fit by a blackbody spectrum with T(sub eff) = 1500 K, as well as by a more detailed model spectrum of a planetary atmosphere. The observed planet-to-star flux ratios in all four lRAC channels can be explained by models with and without a thermal inversion in the atmosphere of TrES-2, although with different atmospheric chemistry. Based on the assumption of thermochemical equilibrium, the chemical composition of the inversion model seems more plausible, making it a more favorable scenario. TrES-2 also falls in the category of highly irradiated planets which have been theoretically predicted to exhibit thermal inversions. However, more observations at infrared and visible wavelengths would be needed to confirm a thermal inversion in this system. Furthermore, we find that the times of the secondary eclipses are consistent with previously published times of transit and the expectation from a circular orbit. This implies that TrES-2 most likely has a circular orbit, and thus does not obtain additional thermal energy from tidal dissipation of a non-zero orbital eccentricity, a proposed explanation for the large radius of this planet. Key words: eclipses - infrared: stars - planetary systems - stars: individual (OSC 03549-02811) - techniques: photometric

Donovan, Francis T.↗

NASA NTRS2020

Solar System Escape Trajectories Using Outer Planetary Gravity Assists

A broad search of outer planet gravity assist sequences reveals flyby conditions that are naturally amenable for solar system escape. The optimal flyby conditions depend on the arrival velocity at the final body and provide the maximum possible escape speed for purely ballistic sequences. Trajectories in the 2030-2060 time frame are categorized by their encounter year with an emphasis on solar system escape speed and direction. All resulting sequences require a Jupiter gravity assist, and a considerable increase in escape speed is found in trajectories that utilize an additional Saturn, Uranus, or Neptune flyby. However, these solutions are limited by their availability and range of right ascensions. All cataloged trajectories are able to escape the solar system at least 3 au/year, and the highest energy sequences are in excess of 5.5 au/year. The search space is then used to find outer planet gravity assist trajectories to Kuiper Belt Objects (KBOs), and several cases are optimized.

Lam, Try↗

NASA NTRS2024

The CARMENES Search for Exoplanets Around M Dwarfs: Revisiting the GJ 581 Multi-Planetary System With New Doppler Measurements From CARMENES, HARPS, and HIRES

Context.GJ 581 is a nearby M dwarf known to host a packed multiple planet system composed of two super-Earths and a Neptune-mass planet. We present new orbital analyses of the GJ 581 system, utilizing recent radial velocity (RV) data obtained from the CARMENES spectrograph combined with newly reprocessed archival data from the HARPS and HIRES spectrographs. Aims.Our aim was to analyze the post-discovery spectroscopic data of GJ 581, which were obtained with CARMENES. In addition, we used publicly available HIRES and HARPS spectroscopic data to seek evidence of the known and disputed exoplanets in this system. We aimed to investigate the stellar activity of GJ 581 and update the planetary system’s orbital parameters using state-of-the-art numerical models and techniques. Methods.We performed a periodogram analysis of the available precise CARMENES, HIRES, and HARPS RVs and of stellar activity indicators. We conducted detailed orbital analyses by testing various orbital configurations consistent with the RV data. We studied the posterior probability distribution of the parameters fit to the data and we explored the long-term stability and overall orbital dynamics of the GJ 581 system. Results. We refined the orbital parameters of the GJ 581 system using the most precise and complete set of Doppler data available. Consistent with the existing literature, our analysis confirms that the system is unequivocally composed of only three planets detectable in the present data, dismissing the putative planet GJ 581 d as an artifact of stellar activity. Our N-body fit reveals that the system’s inclination is i=47.0+14.6−13.0deg, which implies that the planets could be up to 30% more massive than their previously reported minimum masses. Furthermore, we report that the GJ 581 system exhibits long-term stability, as indicated by the posterior probability distribution, characterized by secular dynamical interactions without the involvement of mean motion resonances.

Satellites↗

NASA NTRS1993

Planet formation

Models of planetary formation are developed using the present single example of a planetary system, supplemented by limited astrophysical observations of star-forming regions and circumstellar disks. The solar nebula theory and the planetesimal hypothesis are discussed. The latter is found to provide a viable theory of the growth of the terrestrial planets, the cores of the giant planets, and the smaller bodies present in the solar system. The formation of solid bodies of planetary size should be a common event, at least around young stars which do not have binary companions orbiting at planetary distances. Stochastic impacts of large bodies provide sufficient angular momentum to produce the obliquities of the planets. The masses and bulk compositions of the planets can be understood in a gross sense as resulting from planetary growth within a disk whose temperature and surface density decreased with distance from the growing sun.

Lissauer, Jack J.↗

NASA NTRS1990

Astrophysics from the moon

Ideas presented at the Workshop on Astrophysics from the moon, held in Annapolis, Maryland, in February 1990, are discussed. Consideration is given to the formation of stars and planetary systems, the possibility of earthlike planets among the nearby stars, the possible existence of life and intelligence elsewhere, the current status of the sun and other stars, the evolution of the early universe, and environmental and site considerations for initial observatories.

Mumma, Michael J.↗

NASA NTRS2016

Astrobiology: Life on Earth (and Elsewhere?)

Astrobiology investigates the origins, evolution and distribution of life in the universe. Scientists study how stellar systems and their planets can create planetary environments that sustain biospheres. They search for biosignatures, which are objects, substances and or patterns that indicate the presence of life. Studies of Earth's early biosphere enhance these search strategies and also provide key insights about our own origins.

Evolution↗

NASA NTRS2004

Precursor Science for the Terrestrial Planet Finder

This document outlines a path for the development of the field of extrasolar planet research, with a particular emphasis on the goals of the Terrestrial Planet Finder (TPF). Over the past decade, a new field of research has developed, the study of extrasolar planetary systems, driven by the discovery of massive planets around nearby stars. The planet count now stands at over 130. Are there Earth-like planets around nearby stars? Might any of those planets be conducive to the formation and maintenance of life? These arc the questions that TPF seeks to answer. TPF will be implemented as a suite of two space observatories, a 6-m class optical coronagraph, to be launched around 20 14, and a formation flying mid-infrared interferometer, to be launched sometime prior to 2020. These facilities will survey up to 165 or more nearby stars and detect planets like Earth should they be present in the 'habitable zone' around each star. With observations over a broad wavelength range, TPF will provide a robust determination of the atmospheric composition of planets to assess habitability and the presence of life. At this early stage of TPF's development, precursor observational and theoretical programs are essential to help define the mission, to aid our understanding of the planets that TPF could discover, and to characterize the stars that TPF will eventually study. This document is necessarily broad in scope because the significance of individual discoveries is greatly enhanced when viewed in thc context of the field as a whole. This document has the ambitious goal of taking us from our limited knowledge today, in 2004, to the era of TPF observations in the middle of the next decade. We must use the intervening years wisely. This document will be reviewed annually and updated as needed. The most recent edition is available online at http://tpf.jpl.nasa.gov/ or by email request to lawson@hucy.jpl.nasa.gov

Lawson, P. R.↗

NASA NTRS2004

Precursor science for the Terrestrial Planet Finder

Beichman, C. A.↗

NASA NTRS1990

Impact delivery and erosion of planetary oceans in the early inner solar system

The terrestrial planets may have acquired oceans of water (and other surface volatiles) as a late-accreting veneer from impacts of comets and carbonaceous asteroids during the period of heavy bombardment 4.5 to 3.5 Gyr ago. On any given body, the efficiency of this mechanism depended on a competition between impact delivery of new volatiles and impact erosion of those already present. For the larger worlds of the inner Solar System, this competition strongly favored the net accumulation of planetary oceans.

Chyba, Christopher F.↗

NASA NTRS2012

The Johnson Space Center Experimental Impact Lab: Contributions Toward Understanding the Evolution of the Solar System

Impact is the most common and only weathering phenomenon affecting all the planetary bodies (e.g., planets, satellites, asteroids, comets, etc.) in the solar system. NASA Johnson Space Center s Experimental Impact Laboratory (EIL) includes three accelerators that are used in support of research into the effects of impact on the formation and evolution of the solar system. They permit researchers to study a wide variety of phenomena associated with high-velocity impacts into a wide range of geologic targets and materials relevant to astrobiological studies. By studying these processes, researchers can investigate the histories and evolution of planetary bodies and the solar system as a whole. While the majority of research conducted in the EIL addresses questions involving planetary impacts, work involving spacecraft components has been performed on occasion. An example of this is the aerogel collector material flown on the Stardust spacecraft that traveled to Comet Wild-2. This capture medium was tested and flight qualified using the 5 mm Light-Gas Gun located in the EIL.

See, T. H.↗

NASA NTRS2012

Gas and Dust in Debris Disks: Clues to the Late Stages of Planet Formation

The basic character of debris disks was established soon after their discovery in the mid- 1980's. These disks around nearby main sequence stars are composed of material (mostly dust) produced by collisions and/or evaporation of extrasolar asteroids and comets. However, fundamental observational questions about debris disks remain unanswered. How much material do debris disks typically contain and how does it evolve with time? What is the composition of their dust and gas? Are planets present or forming in the disks? Answers to these questions will provide insights into the late stages of planetary system formation and the origins of terrestrial planet atmospheres. In this talk, I will explain our current understanding of the place of debris disks in the planet formation process. Progress toward addressing the questions given above will be discussed, with emphasis on recent studies of the small but important gas component. Finally, I will outline the implications of debris dust for future efforts to directly image and characterize extrasolar terrestrial planets.

Roberge, Aki↗

NASA NTRS1965

Planetary structure.

Probable interior structure of planets in solar system and Moon, based on data relative to terrestrial theory

SOLAR SYSTEM↗

NASA NTRS2010

Gas and Dustin Debris Disks: Clues to the Late Stages of Planet Formation

The basic character of debris disks was established soon after their discovery in the mid- 1980's. These disks around nearby main sequence stars are composed of material (mostly dust) produced by collisions and/or evaporation of extrasolar asteroids and comets. However, fundamental observational questions about debris disks remain unanswered. How much material do debris disks typically contain and how does it evolve with time? What is the composition of their dust and gas? Are planets present or forming in the disks? Answers to these questions will provide insights into the late-stages of planetary system formation and the origins of terrestrial planet atmospheres. In this talk, I will explain our current understanding of the place of debris disks in the planet formation process. Progress toward addressing the questions given above will be discussed, with emphasis on recent studies of the small but important gas component. Finally, I will outline the implications of debris dust for future efforts to directly image and characterize extrasolar terrestrial planets.

Roberge, Aki↗

NASA NTRS2018

Multi-Planetary Systems: Observations and Models of Dynamical Interactions

More than 600 multi-planet systems are known. The vast majority of these systems have been discovered by NASA's Kepler spacecraft, but dozens were found using the Doppler technique, the first multi-exoplanet system was identified through pulsar timing, and the most massive system has been found using imaging. More than one-third of the 4000+ planet candidates found by NASA's Kepler spacecraft are associated with target stars that have more than one planet candidate, and the large number of such Kepler "multis" tells us that flat multiplanet systems like our Solar System are common. Virtually all of Kepler candidate multis are stable, as tested by numerical integrations that assume a physically motivated mass-radius relationship. Statistical studies performed on these candidate systems reveal a great deal about the architecture of planetary systems, including the typical spacing of orbits and flatness. The characteristics of several of the most interesting confirmed multi-exoplanet systems will also be discussed.HR 8799's four massive planets orbit tens of AU from their host star and travel on nearly circular orbits. PSR B1257+12 has three much smaller planets orbiting close to a neutron star. Both represent extremes and show that planet formation is a robust process that produces a diversity of outcomes. Although both exomoons and Trojan (triangle Lagrange point) planets have been searched for, neither has yet been found.

planet candidates↗

NASA NTRS2000

Computing Needs for Astrobiology: Models of Planetary Formation

Theories of planet formation indicate that a diverse range of physical and chemical processes determine the characteristics of a planetary system. Extensive numerical modeling is required to understand how planetary systems form, and to make quantitative assessments of the factors which determine the masses, spacings and volatile compound inventories of planets and small bodies within a planetary system. Fluid flow problems associated with the formation and evolution of protoplanetary disks include specific local calculations to provide physical insight, which are best performed on workstations, and large multifaceted simulations which require supercomputers with large memories. Formation and early growth of planetesimals display a similar range of computational requirements. Modeling the late stages of planetary accumulation is very CPU intensive, as it requires following a simple system of approx. hundreds of bodies for millions of dynamical (orbital) times. These varied computational needs could be met in the most cost-effective manner by a diverse set of computers, including workstations for individual PI's and dedicated time on various types of supercomputers which are specialized for differing tasks.

Lissauer, Jack J.↗

NASA NTRS2008

Taking the Measure of the Universe : Precision Astrometry with SIM PlanetQuest

Precision astrometry at microarcsecond accuracy has application to a wide range of astrophysical problems. This paper is a study of the science questions that can be addressed using an instrument with flexible scheduling that delivers parallaxes at about 4 microarcsec (microns)as) on targets as faint as V = 20, and differential accuracy of 0.6 (microns)as on bright targets. The science topics are drawn primarily from the Team Key Projects, selected in 2000, for the Space Interferometry Mission PlanetQuest (SIM PlanetQuest). We use the capabilities of this mission to illustrate the importance of the next level of astrometric precision in modern astrophysics. SIM PlanetQuest is currently in the detailed design phase, having completed in 2005 all of the enabling technologies needed for the flight instrument. It will be the first space-based long baseline Michelson interferometer designed for precision astrometry. SIM will contribute strongly to many astronomical fields including stellar and galactic astrophysics, planetary systems around nearby stars, and the study of quasar and AGN nuclei. Using differential astrometry SIM will search for planets with masses as small as an Earth orbiting in the 'habitable zone' around the nearest stars, and could discover many dozen if Earth-like planets are common. It will characterize the multiple-planet systems that are now known to exist, and it will be able to search for terrestrial planets around all of the candidate target stars in the Terrestrial Planet Finder and Darwin mission lists. It will be capable of detecting planets around young stars, thereby providing insights into how planetary systems are born and how they evolve with time. Precision astrometry allows the measurement of accurate dynamical masses for stars in binary systems. SIM will observe significant numbers of very high- and low-mass stars, providing stellar masses to 1%, the accuracy needed to challenge physical models. Using precision proper motion measurements, SIM will probe the Galactic mass distribution, and through studies of tidal tails, the formation and evolution of the Galactic halo. SIM will contribute to cosmology through improved accuracy of the Hubble Constant. With repeated astrometric measurements of the nuclei of active galaxies, SIM will probe the dynamics of accretion disks around supermassive black holes, and the relativistic jets that emerge from them.

Quasars and Active Galactic Nuclei↗

NASA NTRS2012

Planetary Protection Concerns During Pre-Launch Radioisotope Power System Final Integration Activities

The Advanced Stirling Radioisotope Generator (ASRG) is a next-generation radioisotope-based power system that is currently being developed as an alternative to the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG). Power sources such as these may be needed for proposed missions to solar system planets and bodies that have challenging Planetary Protection (PP) requirements (e.g. Mars, Europa, Enceladus) that may support NASA s search for life, remnants of past life, and the precursors of life. One concern is that the heat from the ASRG could potentially create a region in which liquid water may occur. As advised by the NASA Planetary Protection Officer, when deploying an ASRG to Mars, the current COSPAR/NASA PP policy should be followed for Category IVc mission. Thus, sterilization processing of the ASRG to achieve bioburden reduction would be essential to meet the Planetary Protection requirements. Due to thermal constraints and associated low temperature limits of elements of the ASRG, vapor hydrogen peroxide (VHP) was suggested as a candidate alternative sterilization process to complement dry heat microbial reduction (DHMR) for the assembled ASRG. The following proposed sterilization plan for the ASRG anticipates a mission Category IVc level of cleanliness. This plan provides a scenario in which VHP is used as the final sterilization process. Keywords: Advanced Stirling Radioisotope Generator (ASRG), Planetary Protection (PP), Vapor hydrogen peroxide (VHP) sterilization.

Chen, Fei↗