Engineering topics

Karl R Stapelfeldt

Publications and source records attributed to Karl R Stapelfeldt.

3 records

NASA NTRS2019

Imaging Earth-like Exoplanets with a Small Space Telescope

The Cen AB system represents a particularly attractive target for missions to directly image exoplanets. A potentially habitable planet can in theory be imaged in the system with a telescope as small as 40cm, provided it has a powerful enough starlight suppression system. Technology to enable this is rapidly maturing, and there have been several mission concept studies. This technology is relevant to missions like WFIRST, LUVOIR, and HabEx because it enables them to image binary stars. Small coronagraph mission concepts described here would also complement and synergize with all the above missions. We suggest that a stronger ongoing program is needed, perhaps building on the recent Small Sat concept study initiative, to support mission concept and proposal development for Small Sats ($35M), Missions of Opportunity ($75M) and possibly up through Explorer missions.

Ruslan Belikov↗

NASA NTRS2018

Exoplanet Biosignatures: Understanding Oxygen as a Biosignature in the Context of Its Environment

Here we review how environmental context can be used to interpret whether O 2 is a biosignature in extrasolar planetary observations. This paper builds on the overview of current biosignature research discussed in Schwieterman et al. (2017), and provides an in-depth, interdisciplinary example of biosignature identification and observation that serves as a basis for the development of the general framework for biosignature assessment described in Catling et al., (2017). O 2 is a potentially strong biosignature that was originally thought to be an unambiguous indicator for life at high-abundance. In exploring O 2 as a biosignature, we describe the coevolution of life with the early Earth's environment, and how the interplay of sources and sinks in the planetary environment may have resulted in suppression of O 2 release into the atmosphere for several billion years, a false negative for biologically generated O 2 . False positives may also be possible, with recent research showing potential mechanisms in exoplanet environments that may generate relatively high abundances of atmospheric O 2 without a biosphere being present. These studies suggest that planetary characteristics that may enhance false negatives should be considered when selecting targets for biosignature searches. Similarly our ability to interpret O 2 observed in an exoplanetary atmosphere is also crucially dependent on environmental context to rule out false positive mechanisms. We describe future photometric, spectroscopic and time-dependent observations of O 2 and the planetary environment that could increase our confidence that any observed O 2 is a biosignature, and help discriminate it from potential false positives. The rich, interdisciplinary study of O 2 illustrates how a synthesis of our understanding of life's evolution and the early Earth, scientific computer modeling of star-planet interactions and predictive observations can enhance our understanding of biosignatures and guide and inform the development of next-generation planet detection and characterization missions. By observing and understanding O 2 in its planetary context we can increase our confidence in the remote detection of life, and provide a model for biosignature development for other proposed biosignatures.

Victoria S Meadows↗

NASA NTRS2016

Characterizing Rocky and Gaseous Exoplanets with 2 m Class Space-based Coronagraphs

Several concepts now exist for small, space-based missions to directly characterize exoplanets in reflected light. While studies have been performed that investigate the potential detection yields of such missions, little work has been done to understand how instrumental and astrophysical parameters will affect the ability of these missions to obtain spectra that are useful for characterizing their planetary targets. Here, we develop an instrument noise model suitable for studying the spectral characterization potential of a coronagraph-equipped, space-based telescope. We adopt a baseline set of telescope and instrument parameters appropriate for near-future planned missions like WFIRST-AFTA, including a 2 m diameter primary aperture, an operational wavelength range of 0.4–1.0 μm, and an instrument spectral resolution of λ/Δλ =70, and apply our baseline model to a variety of spectral models of different planet types, including Earth twins, Jupiter twins, and warm and cool Jupiters and Neptunes. With our exoplanet spectral models, we explore wavelength-dependent planet–star flux ratios for main-sequence stars of various effective temperatures and discuss how coronagraph inner and outer working angle constraints will influence the potential to study different types of planets. For planets most favorable to spectroscopic characterization—cool Jupiters and Neptunes as well as nearby super-Earths—we study the integration times required to achieve moderate signal-to-noise ratio spectra. We also explore the sensitivity of the integration times required to either detect the bottom or presence of key absorption bands (for methane, water vapor, and molecular oxygen) to coronagraph raw contrast performance, exozodiacal light levels, and the distance to the planetary system. Decreasing detector quantum efficiency at longer visible wavelengths makes the detection of water vapor in the atmospheres of Earth-like planets extremely challenging, and also hinders detections of the 0.89 μm methane band. Additionally, most modeled observations have noise dominated by dark currents, indicating that improving CCD performance could substantially drive down requisite integration times. Finally, we briefly discuss the extension of our models to a more distant future Large UV-Optical-InfraRed (LUVOIR) mission.

Astrobiology↗