Prebiotic Chemistry of Pluto

Area of Science:

• Astrobiology
• Planetary Science
• Organic Chemistry

Background:

• Pluto's surface exhibits a range of colors (yellow to dark brown) consistent with laboratory-produced organic residues known as tholins.
• Tholins are complex macromolecular organic solids with aromatic structures, synthesized in laboratory experiments simulating planetary atmospheric and surface ice conditions.

Purpose of the Study:

• To present evidence for the abiotic formation of complex organic molecules, such as amino acids and nucleobases, on Pluto's surface and near-subsurface regions.
• To investigate the origin and composition of tholins observed on Pluto and their implications for organic chemistry in the outer Solar System.

Main Methods:

• Analysis of spectral data from Pluto to identify surface composition and color variations.
• Laboratory experiments simulating Pluto's surface ice composition (N2, CH4, CO) subjected to photolysis and radiolysis to synthesize organic compounds.
• Laboratory experiments involving pyrimidines and purines in H2O-NH3 ice to form nucleobases.

Main Results:

• Pluto's surface colors match laboratory-produced tholins.
• Tholins are found in both gas- and solid-phase on Pluto, with a distinct variety observed at Virgil Fossae, suggesting subsurface origin.
• Photolysis and radiolysis experiments produced complex, nitrogen-rich organic compounds similar to those found on Pluto.
• Experiments successfully synthesized biologically relevant nucleobases (guanine, cytosine, adenine, uracil, thymine) from relevant precursors.

Conclusions:

• Abiotic processes likely formed complex organic molecules, including amino acids and nucleobases, on Pluto.
• The presence of tholins and nucleobases on Pluto indicates significant organic chemistry occurring on this outer Solar System body.
• Similar organic materials may exist on other Kuiper Belt Objects, highlighting the importance of studying organic molecule origins and evolution across diverse astronomical settings.