For the first time, phosphorus, a key ingredient of life, has been pinpointed in a cloud of gas and dust surrounding a newborn star.
Astronomers spotted a bright infant star shooting powerful jets of energy that created cavities in the gas and dust cocoon from which it formed. Different types of molecules in the cloud, including two simple phosphorus-bearing ones — phosphorus monoxide and phosphorus mononitride — were detected along the cavities’ walls, researchers report in the February Monthly Notices of the Royal Astronomical Society. Ultraviolet radiation from the newborn star helped form these molecules, the team suspects.
“Essentially, the young star is digging away at its natal cloud,” says Maria Drozdovskaya, an astrochemist at the University of Bern in Switzerland. Though phosphorus has been spotted around young stars before, its exact location had never been pinpointed, Drozdovskaya says. Her team showed that phosphorus monoxide dominated the dust regions closest to the infant star.
Molecules of phosphorus monoxide were also detected in a comet in our solar system, the team reports, helping link faraway star-forming regions where the molecules are created all the way to our part of the galaxy.
The findings add to evidence that comets may have helped deliver phosphorus, which is essential to DNA and many key organic chemicals, to the early Earth.
Observations of the young star were made using the Atacama Large Millimeter/submillimeter Array, or ALMA, an enormous collection of radio dishes in Chile’s Atacama Desert. With its high-resolution instruments, ALMA was able to look in detail at the star, found in a star-forming region known as AFGL 5142 located about 7,000 light-years away from Earth.
Finding phosphorus in the earliest phases of a star’s life doesn’t necessarily mean it sticks around for long enough to become incorporated into planets. So the researchers turned to evidence closer to home, taking a second look at data from the European Space Agency’s now-defunct Rosetta spacecraft, which studied the comet 67P/Churyumov-Gerasimenko from 2014 to 2016 (SN: 8/6/14).
Comets are thought to be pristine relics from the solar system’s past. Rosetta had already detected phosphorus as well as the simplest amino acid glycine in the atmosphere of comet 67P (SN: 5/27/16). But clued in by the presence of phosphorus monoxide in the protostellar cloud, the spacecraft’s scientists looked at their data again and found that phosphorus monoxide was the main form of phosphorus in the icy body.
“It’s clearly telling us that comets contain the ingredients of life in their most basic form,” Drozdovskaya says.
Though essential for life, most of the phosphorus on Earth is locked up in minerals in its crust. Organisms tend to get the amount they need through their diet. Phosphorus monoxide, however, has the advantage of being soluble in water, making it far more biologically available than phosphorus locked in minerals, says study coauthor Víctor Rivilla of the Arcetri Astrophysical Observatory in Florence. If comets delivered phosphorus to the young Earth in the form of phosphorus monoxide, perhaps that helps explain how early life was able to access the element.
It’s still unclear exactly how the phosphorus molecules were created or if comets actually delivered them to Earth. “As much as we’re making enormous progress — and this paper is an example of that — there are still these giant gaps,” says George Cody, a geochemist at the Carnegie Institution for Science in Washington, D.C., who was not involved in the work.
A sample return mission that collects ice from a comet and brings it to terrestrial laboratories would allow scientists to do much more detailed analyses of such simple molecules and perhaps start to fill in a few details, he says. While missions are under way to retrieve samples from asteroids (SN: 1/15/19), NASA’s most recent comet sample–retrieval proposal, the Comet Astrobiology Exploration Sample Return (CAESAR), was not selected in the agency’s last round of funding.