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Standard Definition and Evaluation Team

Overview

Two of the four large mission concept studies for the Astrophysics Decadal Survey were designed to directly image and spectrally characterize earth-like exoplanets. In 2016, the Astrophysics Division chartered an Exoplanet Standard Definition and Evaluation Team (ExSDET) for the purpose of providing an unbiased science yield analysis of the multiple large mission concepts using a transparent and documented set of common inputs, assumptions and methodologies.

Over the course of the past three years, the ExSDET has responded to the direction provided in the charter and the required deliverables by performing the following tasks:

  • Develop analysis tools that will allow quantification of the science metrics of the mission studies
  • Incorporate physics-based instrument models to evaluate both internal and external occulter designs
  • Establish the science metrics that define the yield criteria
  • Cross validate the various analytical methodologies and tools
  • Provide complete evaluations using common assumptions and inputs of the exoplanet yields for each mission concept.

The primary goal of the SDET Final Report is to present the best understanding of the exoplanet imaging and characterization capabilities of the current STDT observatory and instrument designs, along with their nominal operating plans, using common input assumptions and analysis methodologies. This report is explicitly not intended to present an exploration of the capabilities of the full design spaces available to the various mission concepts. Due to large uncertainties in the astrophysics inputs, particularly exo-earth occurrence rate, the yield values should be considered relative rather than absolute.

Figure 1. Characterization metric A facilitates a quick search for the water line at 940 nm with a single coronagraph observation with 20% BW. Characterization metric C2 is the full spectra used in the HabEx Final Report to compare the architectures of a starshade-only, coronagraph-only, and hybrid starshade/coronagraph.
Figure 1. Characterization metric A facilitates a quick search for the water line at 940 nm with a single coronagraph observation with 20% BW. Characterization metric C2 is the full spectra used in the HabEx Final Report to compare the architectures of a starshade-only, coronagraph-only, and hybrid starshade/coronagraph.
NASA/JPL-Caltech

H20 Line: metric A		Broad (metric C1)Broad (metric C2)
ScenarioAYOEXO SIMSOmniAYOEXO SIMSOmniAYOEXO SIMSOmni
HabEx 4H-9298598717
LUVOIR A54-50------
LUVOIR B281828-46-710
HabEx 4C-612-23535
HabEx 4S-318-395313
Table 1. The Common Comparison of Yield. Omni stands for the omniscient upperbound found by EXOSIMS when all exo-earths were promoted to characterization at mission start.

We present here key plots from four cases evaluated in the Final Report. Each case has two interactive plots in star luminosity versus distance format, with user selectable quantity to be plotted, such as the number of earths detected or characterized, the mean integration time, and the first time the star was observed. Hovering over the star reveals the star name and statistics of the plotted quantity.

The video below shows one design reference mission Monte Carlo realization for the HabEx baseline hybrid architecture. The HabEx 4-meter hybrid case consists of a coronagraph used in a blind search for the detection of exoplanets and a starshade for the spectral characterization of exoplanets.

While the starshade repositions (black arrows), the coronagraph searches for exoplanets. The synthetic planets are ‘observed’ and ‘detected’ if the goal SNR is reached: green for rocky planets in the HZ, purple for all other planets including rocky planets not in the HZ, red for insufficient SNR to detect any planets, grey for an unobserved star, all from a broad list of 760 potential target stars. The size of the circle indicates the number of repeat detections or characterizations, with the case of 4 detections shown in the legend for scale. Three detections spaced over half a period are required to promote the target for spectral characterization. The discovery, repeated imaging, and eventual spectral characterization can be seen on the star near (-35, 190). Spectral characterizations with the starshade are distinguished by a black edge around the circle marker and are at the tip of a black slew arrow. The white annulus is the region of observability for the starshade. The central grey circle with yellow boarder is the solar keepout zone for both the coronagraph and the starshade. The position of the Sun is labeled 'S' and denoted by a grey cross. The yellow dots are the Earth (E), the moon (L), and the outer planets.

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