Source - A Space Mission to Probe the Trail of Water

Water is critical for determining the habitability of planets, and understanding how the Earth became wet is essential for determining the occurrence of ocean worlds. Water is believed to have been accreted onto the Earth well after its formation, plausibly from impacts of comets or asteroids formed during the evolution of the protoplanetary disk. This disk itself collapsed from a dense core in a molecular cloud. The water transferred from core to disk was formed in the dense interstellar medium, so that tracing the trail of water is an overarching goal for both astronomy and planetary science. Tracing the inheritance of water requires observation of the submillimeter rotational lines of water and of its isotopologues H₂¹⁸ O, H₂¹⁷ O, and HDO. The most favorable transitions lie at 500 GHz to 1200 GHz. To observe a statistically meaningful sample of sources in a 3-year mission requires a 3.2 to 4.2 m telescope equipped with highest sensitivity SIS receivers and digital spectrometers. We discuss here the science and mission design of our proposed mission, Source.