Water vapor hints at planet formation
Molecules detected in spinning disks that surround two newly formed stars
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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Water detected in alien planet's atmosphere
Crucial element for life can exist around planets orbiting other stars
Astronomers have detected water in the atmosphere of a planet outside our solar system for the first time.
The finding, to be detailed in an upcoming issue of Astrophysical Journal, confirms previous theories that say water vapor should be present in the atmospheres of nearly all the known extrasolar planets. Even hot Jupiters, gaseous planets that orbit closer to their stars than Mercury to our Sun, are thought to have water.
The discovery, announced today, means one of the most crucial elements for life as we know it can exist around planets orbiting other stars.
“We know that water vapor exists in the atmospheres of one extrasolar planet and there is good reason to believe that other extrasolar planets contain water vapor,” said Travis Barman, an astronomer at the Lowell Observatory in Arizona who made the discovery.
HD209458b is a world well-known among planet hunters. In 1999, it became the first planet to be directly observed around a normal star outside our solar system and, a few years later, was the first exoplanet confirmed to have oxygen and carbon in its atmosphere.
HD209458b is separated from its star by only about 4 million miles (7 million kilometers)—about 100 times closer than Jupiter is to our sun—and is so hot scientists think about it is losing about 10,000 tons of material every second as vented gas.
"Water actually survives over a broad range of temperatures," Barman explained. "It would need to get quite a bit hotter to completely break the water molecules apart."
Using a combination of previously published Hubble Space Telescope measurements and new theoretical models, Barman found strong evidence for water absorption in the atmosphere of the extrasolar planet HD209458b.
Barman took advantage of the fact that HD209458b is a so-called “transiting planet,” meaning it passes directly in front of its star as seen from Earth. It transits every three-and-a-half days.
When this happens, water vapor in the planet’s atmosphere causes the planet to appear slightly larger in the infrared part of the starlight than in the visible portion.
Barman found the water signature after applying new theoretical models he developed to visible and infrared Hubble data collected by Harvard student Heather Knutson last year, which measured the perceived size of the planet over a broad range of wavelengths.
I simulated the passage of starlight through the atmosphere of the planet, and was able to reproduce the variation that they saw," Barman told SPACE.com. "And since I know exactly what physics and chemistry went into my simulation, I know precisely what caused those variations, and I can attribute those variations to water" or other molecules.
Barman said his discovery would not have been possible without the observations made by the Harvard team. "This is an example of theoretical modeling and observations coming together to help identify something new and interesting about this planet," he said.
