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Astrochemistry and the Origin of Planetary Systems

Final Report Summary - CHEMPLAN (Astrochemistry and the Origin of Planetary Systems)

When interstellar clouds collapse to form new stars and planets, the surrounding gas and dust become part of the infalling envelopes and rotating disks, thus providing the basic material from which new solar systems are made. Instrumentation to probe the physics and chemistry in low-mass star-forming regions had so far lacked spatial resolution, but changed with the inauguration of the Atacama Large Millimeter/submillimeter array (ALMA) in 2013. The A-ERC program CHEMPLAN was centered on using ALMA to survey protostars and disks on the relevant scales of 1-50 AU where planet formation takes place for the first time, and to follow the chemistry of water and complex organic molecules from cores to disks, comets and ultimately planets. These observational projects have been complemented by state-of-the-art models of the physical and chemical evolution from cloud to disk and planets, and by surface science laboratory experiments that simulate the chemistry on icy dust grains in space.

Highlights of CHEMPLAN include (i) The first detection of a dust trap in a circumstellar disk, the likely site of future planetesimal and comet formation; (ii) Imaging of the CO snowlines in protoplanetary disks; such snowlines control the ultimate composition of comets and planets in disks that form from the icy grains; (iii) The detection of simple sugars and amides, the precursors of biologically relevant molecules, around a solar-type young star, and elucidating their formation pathways through laboratory experiments. These molecules are found on scales corresponding to the orbit of Uranus and are moving in the right direction to be incorporated into future solar systems. (iv) Determination of the deuterium fractionation of water on solar-system scales in protostars, providing clues to the origin of water on Earth; (v) Models following the chemistry of O2 and organic molecules from cloud to disk and planets, showing that the surprisingly abundant O2 in comets must be primordial, i.e. made in the cloud out of which our solar system formed. This cloud was somewhat warmer than most pre-stellar clouds. (vi) Demographics of disks in a single star-forming region, showing that most mature disks only have enough mass to form a Neptune-like planet. This implies that planet formation must start at an earlier stage.