Exoplanets, -moons, -comets

EarthShine: Observing Our World as an Exoplanet from the Surface of the Moon

By Keith Cowing

Status Report

NASA NTRS

May 29, 2025

Filed under Analog, biosignature, DSCOVR, Earth, EarthShine, exoplanet, imaging, Moon, NASA NTRS

EarthShine: Observing Our World as an Exoplanet from the Surface of the Moon — EPyC-IR spectroscopy complements CHEILS reflected light measurement. Earth’s nadirviewed spectrum from 2.5 to 12.5 μm (modeled) is bracketed by EPyC-IR and includes reflected light for <3 μm (opaque due to water opacity) transitioning to thermal emission at longer wavelengths. Critical gases diagnostic of the habitable Earth-like atmosphere are clear in this range —H2O, CO2, O3, and CH4. These signatures can be measured in exoplanets only from space, and thus methods can be tested only in space observations of Earth. Balance between pure blackbody functions (dotted lines for 260, 270, 300, and 310 K) and calculated atmospheric emission (snow, forest, desert, ocean, and cloud) constrain composition and thermal structure. A cloudy planet presents a colder scene for 3.5 to 4.2 μm and >10 μm; the 300-K vegetation spectrum is dominated by lower emissivity than a 300-K ocean or desert in the LWIR region and is manifest as the dimmest of these three scenarios in this range. The global (disc integrated) spectrum includes contributions from terrains with unique spectral signatures such as visible suppression by savanna vegetation, low-albedo over ocean, and reduced emission due to ice absorption at 3.5 to 4 μm over snow. Models for crescent-phase spectroscopy change the weighting of features and must be tested empirically. — NASA NTRS

NASA’s return to the Moon coincides with explosive growth in exoplanet discovery. Missions are being formulated to search for habitable planets orbiting other stars, making this the ideal time to deploy an instrument suite to the lunar surface to help us recognize a habitable exoplanet when we see it.

We present EarthShine, a technically mature, three-instrument suite to observe the whole Earth from the Moon as an exoplanet proxy. Earth Shine data will validate and improve models critical for designing missions to image and characterize exoplanets, thus informing observing strategies for flagship missions to directly image exoplanets.

The power of EarthShine. Observations would begin at day 0, viewing the waning gibbous Earth at dusk. Lunar noon, day 7, views the “new Earth” at mission mid-point. The payload would go dormant near day 14, with a waxing gibbous Earth at dawn. By comparison, DSCOVR can view only “full Earth,” while EPOXI viewed only a modest range of phase angle on the dawn side. — NASA NTRS

EarthShine will answer interconnected questions in Earth and lunar science, exoplanets, and astrobiology, related to the credo“ follow the water.” Earth Shine can take advantage of current NASA programs to conduct science from the Moon with low-cost, mature space hardware to reduce risk and assure success.

Like the 1968 Apollo Earthrise image of our home planet, lonely in the black sky, the appeal of Earth Shine to a multidisciplinary array of researchers in Earth Science, Planetary Science, and astrophysics will maximize both its scientific impact and its impact on the general public.

EarthShine: Observing Our World as an Exoplanet from the Surface of the Moon, NASA NTRS

Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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