  We present self-consistent three-dimensional climate simulations of possible
habitable states for the newly discovered Habitable Zone Earth-sized planet,
TOI-700 d. We explore a variety of atmospheric compositions, pressures, and
rotation states for both ocean-covered and completely desiccated planets in
order to assess the planet's potential for habitability. For all 20 of our
simulated cases, we use our climate model outputs to synthesize transmission
spectra, combined-light spectra, and integrated broadband phase curves. These
climatologically-informed observables will help the community assess the
technological capabilities necessary for future characterization of this planet
- as well as similar transiting planets discovered in the future - and will
provide a guide for distinguishing possible climate states if one day we do
obtain sensitive spectral observations of a habitable planet around a M-star.
We find that TOI-700 d is a strong candidate for a habitable world and can
potentially maintain temperate surface conditions under a wide variety of
atmospheric compositions. Unfortunately, the spectral feature depths from the
resulting transmission spectra and the peak flux and variations from our
synthesized phase curves for TOI-700 d do not exceed 10 ppm. This will likely
prohibit the James Webb Space Telescope (JWST) from characterizing its
atmosphere; however, this motivates the community to invest in future
instrumentation that perhaps can one day reveal the true nature of TOI-700 d,
and to continue to search for similar planets around less distant stars.
