Finding the Needles in the Haystacks

Introduction Further Details Model Downloads Simulated Data

Further Details

Finding evidence for life on an exoplanet is an extremely difficult technical challenge. The Earth is about 10 billion times fainter than the Sun at visible wavelengths and its angular separation from the Sun is at most 0.1 arcseconds when viewed from a distance of 10 parsec. For reference, the angular size of the Moon viewed from the surface of Earth is about 1900 arcseconds. Taking a direct image of the Earth from a 10 parsec distance is like taking a picture of a firefly hovering 1 meter to the side of a searchlight that's 2000 kilometers away. Directly imaging the planets and obtaining spectra of their atmospheres will require very high contrast observations, where the bright central star is suppressed. Cartoon of the Earth and Sun viewed from a distance of 10 parsecs Cartoon of the Earth and Sun viewed from a distance of 10 parsecs. Image credit: NASA / A. Roberge

Several designs for large space telescopes with these capabilities are in development. However, these efforts are hampered by unknowns about the target systems, including the fraction of stars with terrestrial planets in their habitable zones (ηEarth) and the characteristics of the exozodiacal dust in the system. Mission performance is typically evaluated by making simple assumptions about the target system properties, and these input assumptions can lead to wildly different expectations for the mission results. Artist's conceptions of a space telecsope capable of directly observing the Earth around the Sun at a distance of 10 parsecs (LUVOIR). Artist's conception of a future space telescope capable of directly observing the Earth around the Sun at a distance of 10 parsecs (LUVOIR). Image credit: NASA GSFC

The Haystacks Project has set out to make a database of high-fidelity planetary system models, based on current observational and theoretical knowledge. The models include spectroscopic as well as spatial information for all components within each exoplantary system (e.g., star, planets, interplanetary dust), resulting in spectral image cubes. They can also incorporate a realistic simulation of background sources that will provide further confusion when obtaining real data on sky. The models will be used by us and other teams to create the first truly realistic simulations of exoEarth direct images and spectra, in order to rigorously investigate the complex sources of noise and confusion that will inevitably be present. The steps in the project are as follows.

1. Produce a complete, high-fidelity model of the modern Solar System, which remains the benchmark for a planetary system containing habitable planets. This step is finished; spectral image cubes available on the Downloads page.

2. Create a representative scene of expected background sources, upon which planetary system models can be overlaid. This is needed because each image deep enough to directly image the Earth at a distance of 10 parsecs will also be deep enough to detect distant galaxies fainter than those in the Hubble Ultra Deep Field (HUDF).

While an exoplanet imaging field will be much smaller than the HUDF, it could still contain background galaxies and stars that might be mistaken for planets (aka. confusion sources). This step is finished; spectral image cubes available on the Downloads page.
The Hubble Ultra Deep Field The Hubble Ultra Deep Field, showing a sea of distant galaxies. Image credit: NASA

3. Create a suite of detailed planetary system models. They will include different planet types, as well as a range of stellar types that encompasses the most likely target stars for future exoEarth observations (F, G, & K stars). Interplanetary dust (also known as exozodiacal dust or “exozodi”) will be carefully handled, as it is expected to be the largest source of noise in direct observations of terrestrial planets. The models will incorporate a range of plausible exozodi structures, brightness levels, and colors. As the models are completed, they will be made available for download.

4. Finally, we will use the models to create simulated exoEarth observations, then test data analysis techniques and characterize possible systematic errors. We will examine the severity of the various sources of confusion and develop observing strategies to remove them. Simulated observations will be available on the Simulations page.
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