Another Key Amino Acid Found in Space: Tryptophan

Astrochemistry is the study of how molecules can form and react in space. Its roots trace back to the 1800s when astronomers such as William Wollaston and Joseph von Fraunhofer began identifying atomic elements from the spectral lines of the Sun. But it wasn’t until recent decades that the field began to mature.

The first identification of a molecule in space was in 1910 during a close approach of Halley’s Comet. Astronomers detected the presence of cyanogen (CN)₂ in the comet’s tail. Also known as poisonous cyanide, the discovery caused a bit of a panic among the public. Other simple molecules were discovered by radio astronomers in the 1940s and 1950s, but it wasn’t until 1969 that the more complex molecule formaldehyde (CH₂O) was discovered. Formaldehyde is one of the simplest carbohydrates. Since complex carbohydrates are central to life on Earth, this discovery opened the door to the possibility of other organic molecules in space.

Studies of meteorites showed the presence of lots of complex molecules, including amino acids. Amino acids are often referred to as the building blocks of life, since 22 of them are found in DNA and RNA, and living organisms use amino acids to build proteins. But identifying them in space is difficult. The more complex the molecule, the more complex its spectral line pattern, making it difficult to distinguish particular molecules.

But thanks to high-resolution spectroscopy, we’ve gotten better at it. In 2003, astronomers detected the presence of the first amino acid in an interstellar nebula. Glycine (C₂H₅NO₂) is the simplest stable amino acid and an inhibitory neurotransmitter. It was later observed in the tails of comets and in stellar nurseries, further suggesting that the amino acids of life first formed in space through abiotic processes.

Now another amino acid has been discovered in space. As published in the Monthly Notices of the Royal Astronomical Society, a team of astronomers has discovered C₁₁H₁₂N₂O₂, also known as tryptophan. You’re probably familiar with it thanks to Thanksgiving dinners and the apocryphal idea that turkey meat makes you drowsy. It is found in various types of meat, as well as plants such as oats and chickpeas. Since humans cannot produce tryptophan, and we need it to live, it’s one of the essential amino acids.

The molecule was identified in the Perseus Molecular Complex, which is a cluster of molecular clouds and star-forming regions about 1,000 light years from Earth. Using data from the Spitzer infrared telescope, the team identified 20 spectral emission lines unique to tryptophan. It was found in a rather warm region of a star-forming region, at about 280 Kelvin. This suggests that other amino acids are likely to be found in warm molecular clouds.

Reference: Iglesias-Groth, Susana. “A search for tryptophan in the gas of the IC 348 star cluster of the Perseus molecular cloud.” Monthly Notices of the Royal Astronomical Society 523.2 (2023): 2876-2886.