Detection of Terrestrial Extra-Solar Planets via Gravitational Microlensing Talk Outline A Definitive list of Requirements as long as a habitable or Earth-like planet The Physics of -lensing Mission Design
Taylor, Allen, News Director has reference to this Academic Journal, PHwiki organized this Journal Detection of Terrestrial Extra-Solar Planets via Gravitational Microlensing David Bennett University of Notre Dame Talk Outline What do we need to know to determine the abundance of Earth-like planets What does Earth-like mean The basics of microlensing Microlensing Planet Search Mission Design The proposed GEST mission as an example The Scientific Return Simulated planetary light curves planet detection sensitivity Lens star detection What we learn from the planets that are detected Why is a Space mission needed as long as microlensing Resolve main sequence stars continuous coverage A Definitive list of Requirements as long as a habitable or Earth-like planet A 1 M planet at 1 AU orbiting a G-star How about a 1 M planet at 1.5 or 2 AU with a greenhouse atmosphere Is a gas giant at 5 or 10 AU needed, as well Are planets orbiting M-stars more or less habitable than those orbiting G-stars Moons of giant stars Is a large moon important as long as the development of life Is it possible that life could be based upon NH3 instead of H2O It seems prudent to design a exoplanet search program that reveals the basic properties of planetary systems rather than focusing too closely on current ideas on habitability.
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The Physics of -lensing Foreground lens star + planet bend light of source star Multiple distorted images Total brightness change is observable Sensitive to planetary mass Low mass planet signals are rare not weak Peak sensitivity is at 2-3 AU: the Einstein ring radius Microlensing Rates are Highest Towards the Galactic Bulge High density of source in addition to lens stars is required. Mission Design 1m telescope 3 mirror anastigmat ~2 sq. deg. FOV shutter as long as camera 0.2/pixel => 6108 pixels continuous view of Galactic bulge as long as 8 months per year 60 degree Sun avoidance 1200km polar or high Earth Orbit Images downloaded every 10 minutes 5 Mbits/sec mean data rate <0.03 pointing stability maintained >95% of the time Polar Orbit as long as GEST MIDEX proposal Galactic Exoplanet Survey Telescope
Wide FOV CCD Camera Bulge stars are highly reddened, so Lincoln or LBL IR optimized CCDs improve sensitivity. IR detector arrays might be even better. Focal Plane layout: 32 Labs 3k 6k CCDs, 10m pixels; 600 Mpix total GEST shutter concept no single point failure mode. Simulated Planetary Light Curves Planetary signals can be very strong There are a variety of light curve features to indicate the planetary mass ratio in addition to separation Exposures every 10 minutes moon signal more light curves Low S/N visible G-star lenses with typical S/N
Planet Detection Sensitivity Comparison most sensitive technique as long as a 1 AU -lensing + Kepler gives abundance of Earths at all distances habitable planets in Mars-like orbits Mass sensitivity is 1000 better than vr Assumes 12.5 detection threshold Sensitivity to all Solar System-like planets Except as long as Mercury & Pluto Lens Star Identification Flat distribution in mass assuming planet mass star mass 33% are visible within 2 I-mag of source not blended w/ brighter star Solar type (F, G or K) stars are visible 20% are white, brown dwarfs (not shown) Visible lens stars allow determination of stellar type in addition to relative lens-source proper motion Planetary Semi-major Axes For faint lens stars, separation determination yields a to factor-of-2 accuracy, but the brightest ~30% of lens stars are detectable. For these stars, we can determine the stellar type in addition to semi-major axis to ~10-20%.
Microlensing From the Ground vs. Space Ground-based Images of a Microlensing Event GEST Single Frame GEST Dithered Image Target main sequence stars are not resolved from the ground. Lens stars cannot be identified from the ground Lens-source proper motion cant be measured Ground surveys can only find events with a RE No measurement of planetary abundance vs. semi-major axis Light curves from a LSST or VISTA Survey Simulations use real VLT seeing in addition to cloud data, in addition to realistic sky brightness estimates as long as the bulge. The lightcurve deviations of detectable ~1 M planets have durations of ~1 day, so full deviation shapes are not measured from a single observing site – except as long as unusually short events. Rare, well sampled event Predicted Ground-Based Results as long as Terrestrial Planets Planet Discoveries 12.5 detection threshold deviation region varies by 0.3% or more from stellar lens curve includes baseline require 80% of deviation region measured Assumes 4 year bulge surveys from LSST & VISTA – very optimistic! Lens stars not detected Little sensitivity to separation Cheap ground based programs are sensitive to failed Jupiters
Space-Based Microlensing Planetary Results Planets detected rapidly – even in ~20 year orbits average number of planets per star down to Mmars = 0.1M Separation, a, is known to a factor of 2. planetary mass function, f(=Mplanet/M,a) as long as 0.3Msun M 1 Msun planetary abundance as a function of M in addition to distance planetary abundance as a function of separation (known to ~10%) abundance of free-floating planets down to Mmars the ratio of free-floating planets to bound planets. Abundance of planet pairs high fraction of pairs => near circular orbits Abundance of large moons () ~50,000 giant planet transits Space-Based Microlensing Summary Straight- as long as ward technique with existing technology Low cost MIDEX level or possible shared mission Low-mass planets detected with strong signals Sensitive to planetary mass Sensitive to a wide range of separations Venus-Neptune Combination with Kepler gives planetary abundance at all separations Should be done!
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