FIR Solar System Proposals Stefanie Milam August 5, 2016

28. Planetary Origins and Evolution of the Solar System Goal: To measure accurate isotopic ratios and abundances of trace gases, to constrain models and inform understanding of solar system origin and evolution. Importance: 12C/13C, 14N/15N, 16O/17O/18O provide valuable information about both planetary formation and evolution. The D/H is an indicator of core/envelope fraction needed to discriminate between models of planetary formation. Uniqueness: The measurements possible in the far-IR will permit unique science. Small molecules such as CO2, H2O, HD, and H2 are only visible in this spectral region. Measurement approach: This goal requires spectroscopy (R≥1000) from micron. This will enable a sensitive study of HD lines at  m, CO2 at 15 micron and rotational lines of HCN, CO, NH 3 and PH 3 and isotopes at  m. Spectral resolution should equal or exceed those of previous telescopes to improve S/N, while an aperture size of m is desirable for S/N, and less so for spatial resolution.

29. Thermo-Chemical History of Comets and Water Delivery to Earth Goal: Determining the distribution of D/H values in 100s of comets will reveal their thermo- chemical history and determine their role in delivery of water to the early Earth. Importance: Water has been detected now towards short period comets with a terrestrial D/H, prompting some to suggest that ocean water was delivered by ecliptic comets – though recent Rosetta results suggest an enriched value. A comprehensive survey of the D/H ratio in comets is necessary to address this question. Uniqueness: No current facility is be able to observe low energy water vapor and resolve the lines. Measurement approach: This goal requires intermediate to high resolution spectroscopy (R>1,000) from micron to measure line fluxes and widths of water lines. The goal requires efficient survey capabilities of ~ sources. With a 20m aperture (2e-21 W/m 2 ) we can observe nearly ALL short and long period comets at multiple epochs. NOTE: Figure of Merit (FOM) = [ log10 (Delta) mV Q(H2O)/  (AU)*10 28 ]/Delta.

30. Survey of Small Bodies in the Outer Solar System Goal: A FIR-Survey of TNOs and Related Outer Solar System Small Bodies. Importance: TNO and outer solar system small body size distributions, down to scales of 10s of km or a few km provide tests of the formation scales of planetesimals and evolutionary models of the early Solar system. The ability to derive large quantities of size measurements is a unique value of such FIR surveys. Uniqueness: Only a FIR imaging survey can reach the sensitivity and the speed that may be able to meet the cadence requirements. A 20m FIRS can reach a sensitivity (~13uJy) in ~14s of integration, multiple epochs, covering 2000 square degrees of sky. Measurement approach: The main requirement is to image a large area of the sky multiple times and capture large numbers of TNOs and related outer solar system objects. A single band near 125  m and with sensitivities ~13-50 uJy would reach large numbers (thousands) and small (~7-20 km) sizes. Other bands, ~70 um and 250 um, with comparable sensitivities, would provide better temperature, and therefore size, constraints.

31. Comparative Climate and Thermal Evolution of Giant Planets Goal: Explore the thermal history, present-day climate and circulation patterns of the four Giant Planets as archetypes for brown dwarf and exoplanetary atmospheres. Importance: Sounding far-IR emission, which probes the bulk of the radiated internal energy, can reveal the spatial and temporal variability of temperature, winds, aerosols, and chemical species. This traces the redistribution of energy and material throughout the different atmospheric layers, which governs the internal thermal evolution of a planet as it cools over billions of years. Furthermore, the abundance of helium remains poorly understood the giant planets, reveals formation details. Uniqueness: Thermal mapping Giant Planets can be achieved from large ground-based telescopes, but (i) these do not access the collision-induced H2-He continuum; (ii) they do not permit sounding of He, H2 and other volatiles mentioned; and (iii) they cannot be accurately calibrated. Measurement approach: Broadband far-IR spectral mapping covering the µm range with moderate spectral resolution (R~300) is required for atmospheric studies and abundances of He and H2. Spatial resolutions of <0.2” are required to map these variables on Neptune. Far-IR spectra of Saturn as measured by Cassini/CIRS, showing the lines and the collision-induced continuum that allows temperature, windshear, aerosol, para-H2 and helium sounding.

32. Find Planet IX Goal: Do we really understand our outer backyard?: Find Planet Nine (from Outer Space!) Importance: Numerous groups have proposed the existence of a massive body orbiting the Sun at AU based on the statistics of orbits of KBOs with large perihelia. The required mass for the perturber is around 10 Earth masses. The existence of such an object in the Solar system would have profound consequences for the formation history of planets and comets. Uniqueness: No other facility can come close to the required mapping speed to search the entire sky for Planet IX in 6 months. Assumptions in proposal. Measurement approach: The position of the object is not certain, so the driving requirement is to survey a large area of the sky relatively quickly. The survey will have to cover the area several times so motion can be detected and confirmed. Over a six month interval, the full parallactic motion of 40 arc- sec would be seen. A survey speed of 10 sq.deg per hour is required. Even a 2 Earth Radius Planet 9, with Teff=37K has ~4 mJy flux at 80um is detectable with a 5 meter FIRS architecture. FIRS 5 meter (10 meter), 5-sigma, 1second sensitivity at 80um as 0.6 (0.15) mJy.