Phosphorus, present in our DNA and cell membranes, is an essential element for life. But how it became available on the early Earth when life appeared here about 4 billion years ago is something of a mystery. For the first time, astronomers — among them researchers from the University of Bern — have now been able to show that molecules with phosphorus are formed in star-forming regions and probably came to Earth with comets.
New stars and planetary systems arise in cloud-like regions of gas and dust in between stars, making these interstellar clouds the ideal place to start the search for life’s building blocks. “Life appeared on Earth about 4 billion years ago, but we still do not know the processes that made it possible,” says the lead-author of a new study Víctor Rivilla from the National Institute of Astrophysics INAF in Florence. The new study, which was published today in Monthly Notices of the Royal Astronomical Society, shows that phosphorus monoxide is a key piece in the origin-of-life puzzle. Researchers from the University of Bern were also involved in the study, including Professor Emeritus Kathrin Altwegg from the Institute of Physics and Maria Drozdovskaya from the Center for Space and Habitability (CSH).
View with a giant telescope to star-forming regions
High on the Chajnantor plateau in the Chilean Andes, the European Southern Observatory (ESO), together with its international partners, is operating the Atacama Large Millimeter/submillimeter Array (ALMA) (see info box below). ALMA comprises 66 high-precision antennas working together in what is known as an interferometer. It allows a detailed look into the star-forming region called “AFGL 5142”.
The ALMA observations showed, for the first time, that phosphorus-bearing molecules such as phosphorus monoxide are formed as massive stars come to life. Maria Drozdovskaya explains: “Flows of gas from young massive stars open up cavities in interstellar clouds. Molecules with phosphorus form along the cavity walls through photochemistry.” The researchers have also shown that phosphorus monoxide is the most abundant phosphorus-bearing molecule in these regions.
In the star-forming regions phosphorus monoxide can freeze out and get trapped in ice surrounding interstellar dust grains, as new Solar Systems come to life. Even before Sun-like stars are fully-fledged, icy dust grains come together to form pebbles, planetesimals and ultimately comets.
Interstellar journey from the stars via comets to the Earth
In order to follow the trail of these phosphorus-bearing compounds the researchers combined the data from ALMA with those from the Bern mass spectrometer ROSINA on board of the Rosetta probe of the European Space Agency (ESA), which had collected data from the comet 67P/Churyumov-Gerasimenko (see info box below).
Kathrin Altwegg, the Principal Investigator for ROSINA and an author in the new study, explains: “We had had found hints of phosphorus in the ROSINA data before, but we did not know what molecule had carried it there.” She got a clue for what this molecule could be after being approached at a conference by an astronomer studying star-forming regions with ALMA: “She said that phosphorus monoxide would be a very likely candidate, so I went back to our data and there it was!”
“Phosphorus is essential for life as we know it,” adds Altwegg. “As comets most probably delivered large amounts of organic compounds to the Earth, the phosphorus monoxide found in comet 67P may strengthen the link between comets and life on Earth.” This intriguing journey of phosphorus monoxide could be documented because of the collaborative efforts between astronomers. “The detection of phosphorus monoxide was clearly thanks to an interdisciplinary exchange between the data of the telescope ALMA on Earth by ESO and the data of the ROSINA-instrument in space by ESA,” says Altwegg.
Reference: “ALMA and ROSINA detections of phosphorus-bearing molecules: the interstellar thread between star-forming regions and comets,” V. M. Rivilla et al., 2020 February, Monthly Notices of the Royal Astronomical Society [available at https://doi.org/10.1093/mnras/
