Scientists
have detected water vapor in the spinning disks that surround two newly formed
stars, where planets are born.
A team of
researchers spotted the water molecules in disks of dust and gas around DR Tau
and AS 205A, which are around 457 light-years and 391 light-years, respectively,
away from Earth.
The spinning
disks of particles may eventually coalesce to form
planets.
The
discovery, set for publication in the March 20 issue of the Astrophysical
Journal Letters, brings scientists one step closer to understanding water's
role in Earth-like
planet formation.
"This
is one of the very few times that water vapor has been detected in the inner
part of a protoplanetary disk – the most likely place for terrestrial planets
to form," said lead researcher Colette Salyk, a graduate student in
geological and planetary sciences at Caltech.
Water
detection
Salyk and
her colleagues analyzed light-emission data captured by NASA's Spitzer Space
Telescope, finding spikes of brightness at certain wavelengths known to signal
the presence of water vapor. "Only Spitzer is capable of observing these
particular lines in a large number of disks because it operates above Earth's
obscuring water-vapor-rich atmosphere," Salyk said.
Using this
data along with more detailed information collected with instruments on the
Keck II Telescope in Hawaii, the team estimated the speed and location of the water
vapor molecules. "They were moving at fast speeds," Salyk said,
"indicating that they came from close to the stars, which is where Earth-like
planets might be forming."
As to how
much water, the researchers have detected only a small amount so far, they say.
"While
we don't detect nearly as much water as exists in the oceans on Earth, we see
only a very small part of the disk – essentially only its surface – so the
implication is that the water is quite abundant," said co-researcher
Geoffrey Blake, professor of cosmochemistry and planetary sciences at Caltech.
Forming
planets
The
water-vapor findings could indicate that planets are forming around the stars.
For
instance, Jupiter formed in our solar
system as its gravitational field trapped icy solids spinning in the outer
part of the sun's planetary disk. Before Jupiter gained much mass, these same
icy solids could have traveled toward the star and evaporated to produce water
vapor such as that seen around DR Tau and AS 205A.
The
researchers have not detected icy solids around the recently studied stars.
"Our observations are possible evidence for the migration of solids in the
disk," Salyk said. "This is an important prediction of planet-forming
models."
These
initial observations portend more to come. "We were surprised at how easy
it is to find water in planet-forming disks once we had learned where to look,"
said study team member Klaus Pontoppidan, a Caltech postdoctoral scholar and
planetary scientist. "It will take years of work to understand the details
of what we see."
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