Water Vapor Discovery Provides Clues to Planet Formation
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by Dave Smith
Astronomers using the Keck Observatory have found water vapor and other tell-tale signs of planet formation in a distant world.
Using a high-resolution spectrograph named OSIRIS on Keck II, one of a pair of 10-meter telescopes atop Mauna Kea, scientists have obtained what they described as the finest analysis yet of a planet outside our solar system.
“This is the sharpest spectrum ever obtained of an extrasolar planet,” Bruce Macintosh, an astronomer at Lawrence Livermore National Laboratory and a co-author of the study, said in a news release. “This shows the power of directly imaging a planetary system — the exquisite resolution afforded by these new observations has allowed us to really begin to probe planet formation.”
The spectrograph allows astronomers to identify the chemical fingerprints of specific molecules.
In the case of a planet orbiting a star called HR 8799, that showed the presence of a cloudy atmosphere containing water vapor and carbon monoxide.
Astronomers say the ratio of the two substances suggests that the planet grew by gradually drawing in surrounding gas – the same way our own solar system formed.
“Once the solid cores grew large enough, their gravity quickly attracted surrounding gas to become the massive planets we see today,” said lead author Quinn Konopacky of the University of Toronto.
According to another theory, planets in other solar systems may form from the collapse of part of the disk of gas left over after the birth of a star.
However, this planet has a high ratio of carbon to oxygen, one of the two elements in water, which leads astronomers to believe it was formed by gradual formation rather sudden collapse.
“Since that gas had lost some of its oxygen, the planet ends up with less oxygen and less water than if it had formed through a gravitational instability,” Konopacky said.
The planet under study is one of four orbiting the star 130 light years from Earth which were discovered by the authors and collaborators back in 2008 and 2010.
Unlike most planets outside our solar system, whose presence is indicated by interactions with their parent star, these four can be directly observed because they are young and very far from their star.
This makes the system an excellent laboratory for studying exoplanet atmospheres,” said co-author Christian Marois, an astronomer at the National Research Council of Canada.
But despite the presence of the water vapor, don’t expect to find life on it – at least as we know it. The planet, like the three others, is a gaseous giant like our own Jupiter but at least several times larger.
It also has a temperature of more than 1,000 degrees Fahrenheit, far above the boiling point of water. Scientists say the heat is the byproduct of the planet’s formation.
Still, the discovery gives astronomers hope for the discovery of Earth-like planets in other solar systems.
“The fact that the HR8799 giant planets may have formed the same way our own giant planets did is a good sign – that same process also made the rocky planets close to the Sun,” Macintosh said.
The study was posted online today on Science Express and appears March 22 in the journal Science.