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

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.

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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.

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).

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.


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