Astronomers have gathered some of the best data on the composition of a planet known as HR 8799c – a new giant gas planet about 7 times the mass of Jupiter revolving around its star every 200 years.
The team used state-of-the-art instruments at the W. M. Keck Observatory for Hawaii's Maunakea to confirm the existence of water in the atmosphere of the planet as well as the lack of methane.
While other researchers had previously made similar measurements on this planet, these new, more powerful data demonstrate the power of combining high resolution spectroscopy with a technique known as adaptive optics, which corrects the blurry effect of the Earth's atmosphere.
"This kind of technology is exactly what we want to use in the future to look for signs of life on a planet resembling Earth, we are not there yet, but we are moving forward," says Dimitris Mawet, associate professor of astronomy at Caltech and researcher of JPL, which Caltech manages for NASA.
Mawet co-authored a new document on the findings published today at Astronomical Journal. The main writer is Ji Wang, a former postdoctoral scholar at Caltech and now an assistant professor at Ohio State University.
Taking pictures of planets revolving around other stars – exoplanets – is a huge project. The light from the stars of the host is far from the planets, making them hard to see.
More than twelve exoplanets have been depicted directly, including HR 8799c and its three planetary comrades. In fact, HR 8799 is the only multi-planet system to capture its image. Discovering the use of adaptive optics on the Keck II telescope, the direct images of HR8799 are the first in a planetary system that rotates around a star different from our sun.
Once an image is taken, astronomers can use instruments, called spectrometers, to break the light of the planet, such as a prism turning sunlight into a rainbow, thus revealing the fingerprints of chemicals. So far, this strategy has been used to learn about the atmosphere of many giant exoplanets.
The next step is to do the same thing for smaller planets that are closest to their stars (the closer a planet is to its star and the smaller its size, the harder it is to see).
The ultimate goal is to search for chemicals in the Earth-like planets that revolve around the star's habitable zone – including life-bearing businesses such as water, oxygen and methane.
The Mawet team hopes to do this with an instrument in the upcoming three-digit telescope, a giant telescope designed by the end of 2020 by various national and international partners, including Caltech.
But for now, scientists are perfecting their technique using the Keck Observatory – and, in the process, they learn about the syntheses and dynamics of the giant planets.
"Right now, with Keck, we can already learn about the physics and dynamics of these giant exotic planets, which are nothing like our own solar system planets," says Wang.
In the new study, researchers used a Keck II telescope called a NIRSPEC (infrared ray cryogenic spectrometer), a high resolution spectrometer that works in infrared light.
They correlated the instrument with the powerful adaptive visual system of the Keck Observatory, a method for creating clearer images using a star guide in the sky as a means of measuring and correcting the turbulence of Earth's atmosphere turbulence.
This is the first time the technique has been demonstrated on planets with direct imaging using the so-called L-band, a kind of infrared light with a wavelength of about 3.5 microns and a spectrum region with many detailed chemical fingerprints.
"L has been overlooked in the past because the sky is brighter at this wavelength," says Mawet. "If you were an alien with eyes tuned to the L-band, you will see an extremely bright sky. It's hard to see exoplanets through this veil."
Researchers say the addition of adaptive optics makes the L movie more accessible to the study of the planet HR 8799c. In their study, they made the most accurate measurements of even the atmospheric components of the planet, confirming that it has water and has no methane as it had previously thought.
"We are now more confident about the lack of methane on this planet," says Wang. "This may be due to mixing in the atmosphere of the planet. Methane, which one would expect on the surface, could be thinned if the transport process carries deeper layers of the planet that do not have methane."
Lane L is also good for making measurements of the carbon-oxygen ratio of a planet – a tracker of where and how a planet is formed. The planets are formed by rotating discs of material around the stars, especially a mixture of hydrogen, oxygen and carbon-rich molecules, such as water, carbon monoxide and methane.
These molecules froze out of the discs that form planets at different distances from the star – at the limits called snowlines. By measuring the carbon-to-oxygen ratio of a planet, astronomers can learn about its origins.
The Mawet team is seeking to activate the newest instrument at the Keck Observatory, called Keck Planet Imager and Characterizer (KPIC). It will also use adaptive optics with high-resolution spectroscopy, but it can see planets that are weaker than HR 8799c and closer to their stars.
"KPIC is a springboard for our future three-way remote control," says Mawet. "We currently learn a lot about the myriad ways in which planets are formed in our universe."