27Feb2014

Water Vapor Found In Atmosphere Of A Hot Jupiter

The planet, Tau Boötis b, is located about 51 light-years away and orbits the primary star of a binary system in the Boötes constellation. - See more at: http://www.iflscience.com/space/water-vapor-detected-exoplanet%E2%80%99s-atmosphere#sthash.czK2WbCc.dpuf

Photo credit: David Aguilar, Harvard-Smithsonian Center for Astrophysics

The planet, Tau Boötis b, is located about 51 light-years away and orbits the primary star of a binary system in the Boötes constellation. It interests astronomers for many reasons.

Although liquid water covers a majority of Earth’s surface, scientists are still searching for planets outside of our solar system that contain water. Researchers at Caltech and several other institutions have used a new technique to analyze the gaseous atmospheres of such extrasolar planets and have made the first detection of water in the atmosphere of the Jupiter-mass planet orbiting the nearby star Tau Boötis. With further development and more sensitive instruments, this technique could help researchers learn about how many planets with water — like Earth — exist within our galaxy.

Scientists have previously detected water vapor on a handful of other planets, but these detections could only take place under very specific circumstances, says graduate student Alexandra Lockwood, the first author of the study. “When a planet transits — or passes in orbit in front of its host star — we can use information from this event to detect water vapor and other atmospheric compounds,” she says. “Alternatively, if the planet is sufficiently far away from its host star, we can also learn about a planet’s atmosphere by imaging it.”

No Real Yardstick

However, significant portions of the population of extrasolar planets do not fit either of these criteria, and there was not really a way to find information about the atmospheres of these planets. Looking to resolve this problem, Lockwood and her adviser Geoffrey Blake, professor of cosmochemistry and planetary sciences and professor of chemistry, applied a novel technique for finding water in a planetary atmosphere. Other researchers had used similar approaches previously to detect carbon monoxide in Tau Boötis b.

The method utilized the radial velocity (RV) technique — a technique commonly used in the visible region of the spectrum to which our eyes are sensitive — for discovering non-transiting exoplanets. Using the Doppler effect, RV detection traditionally determines the motion of a star due to the gravitational pull of a companion planet; the star moves opposite that of the orbital motion of the planet, and the stellar features shift in wavelength. A large planet or a planet closer to its host star provides a larger shift.

Looking Deeper

Lockwood, Blake, and their colleagues expanded the RV technique into the infrared to determine the orbit of Tau Boötis b around its star, and added further analysis of the light shifts via spectroscopy — an analysis of the light’s spectrum. Since every compound emits a different wavelength of light, this unique light signature allows the researchers to analyze molecules that make up the planet’s atmosphere. Using data of Tau Boötis b from the Near Infrared Echelle Spectrograph (NIRSPEC) at the W. M. Keck Observatory in Hawaii, the researchers were able to compare the molecular signature of water to the light spectrum emitted by the planet, confirming that the atmosphere did indeed include water vapor.

http://www.howitworksdaily.com/wp-content/uploads/2014/02/hot-jupiter.jpg

Although water is an essential ingredient to life as we know it, wet hot Jupiters are not likely to harbor any creatures.

“The information we get from the spectrograph is like listening to an orchestra performance; you hear all of the music together, but if you listen carefully, you can pick out a trumpet or a violin or a cello, and you know that those instruments are present,” she says. “With the telescope, you see all of the light together, but the spectrograph allows you to pick out different pieces; like this wavelength of light means that there is sodium, or this one means that there’s water.”

In addition to using the spectrographic technique to study the planet’s atmospheric composition, the method also provides a way for researchers to analyze the mass of planets. “They’re actually two separate findings, but they’re both very exciting,” says Lockwood. “When you’re doing calculations to look for the atmospheric signature — which tells you that there’s water present — you also determine the 3-D motion of the star and the planet in the system. With this information, if you also know the mass of the star, you can determine the mass of the planet,” she says.

 ‘Massive’ Is Important

Previous RV methods for measuring a planet’s mass could only determine the planet’s indicative mass — an estimation of its minimum mass, which might be much less than its actual mass. This new technique provides a way to measure the true mass of a planet since both light from the star and the planet are detected, which is critical for understanding how planets and planetary systems form and evolve.

Although the technique promises to augment how planetary scientists analyze the properties of extrasolar planets, it has limitations, the researchers say. For example, the technique is presently limited to so-called “hot Jupiter” gas giant planets like Tau Boötis b — those that are large and orbit very close to their host star.

Limited Vision

“The technique is limited by the light-collecting power and wavelength range of the telescope, and even with the incredible collecting area of the Keck mirror on the high, dry summit of Mauna Kea we can basically only analyze hot planets that are orbiting bright stars, but that could be expanded in the future as telescopes and infrared spectrographs improve,” Lockwood says. In the future, in addition to analyzing cooler planets and dimmer stars, the researchers plan to continue looking for and analyzing the abundance of other molecules that might be present in the atmosphere of Tau Boötis b.

“While the current state of the technique cannot detect Earth-like planets around stars like the Sun, with Keck it should soon be possible to study the atmospheres of the so-called ‘super-Earth’ planets being discovered around nearby low-mass stars, many of which do not transit,” Blake says. “Future telescopes such as the James Webb Space Telescope and the Thirty Meter Telescope (TMT) will enable us to examine much cooler planets that are more distant from their host stars and where liquid water is more likely to exist.”

Characterizing the Atmosphere on Alien World: Q&A with Laura Kreidberg

Laura Kreidberg, a third-year graduate student in the Department of Astronomy and Astrophysics at the University of Chicago. Credit: astro.uchicago.edu

 Laura Kreidberg, a third-year graduate student in the Department of Astronomy and Astrophysics at theUniversity of Chicago, recently led a team of astronomers that characterized the atmosphere of a super-Earth class planet orbiting another star for the first time. The exoplanet called GJ 1214b, a rocky world located 40 light-years from Earth is classified as a super-Earth type planet because its mass is intermediate between those of Earth and Neptune. The researchers described their work as an important milestone on the road to characterizing potentially habitable, Earth-like worlds beyond the solar system. In an email interview with astrowatch.net, Kreidberg talks about the recent findings.

 Astrowatch.net: Do we know exactly what does the GJ 1214b atmosphere consist of? Is it possible that it’s potassium chloride or zinc sulfide?
 
Laura Kreidberg: We don’t yet know what the atmosphere of GJ 1214b is made of. At the temperature and pressure we expect on the planet, it’s possible that clouds made of potassium chloride or zinc sulfide could form, but the only thing we’re definitively sure of is that there are clouds in the atmosphere.
 
Astrowatch.net: Is the atmosphere there as thick as on Titan, for example?
 
Kreidberg: Most work on exoplanet atmospheres has been focused on Jupiter-size planets (gas giants). For those planets, astronomers have detected a number of different molecules, including water, carbon monoxide, methane. Gas giants must have hydrogen/helium in the atmospheres to explain their large size. GJ 1214b is the only planet that’s been studied so far that might not have any hydrogen or helium in its atmosphere. It’s possible that the planet’s atmosphere is made mostly of heavier molecules, like nitrogen, as is the case for the atmospheres of the Earth and Titan.
 
Astrowatch.net: Are we sure that this is a rocky planet?
 
Kreidberg: We’re sure that GJ 1214b isn’t entirely rocky. Based on the observed mass and radius of the planet, several scenarios for its composition are possible. It could have a rocky core and a thick, extended atmosphere made of light molecules, like hydrogen. Alternatively, it could have a larger, icy core, and a denser atmosphere made mostly of water, nitrogen, or some other heavy molecule. Our discovery of clouds in the atmosphere doesn’t rule out either of these possibilities.
 
Astrowatch.net: Do we know any other exoplanets with so thick atmosphere?
 
Kreidberg: So far, GJ 1214b is the only planetary atmosphere we’ve been able to study that might not have any hydrogen/helium.
 
Astrowatch.net: Could you reveal something about your current research?
 
Kreidberg: I’m working now on Hubble Space Telescope observations of a few other exoplanets, to try to learn how much oxygen and carbon they have in their atmospheres. The amount of O and C traces the process by which the planet formed.
 
Astrowatch.net: Do you plan more observations of GJ 1214b or similar exoplanets?
 
Kreidberg: We still have a few tricks up our sleeve for GJ 1214b. In particular, we’re looking at the planet in a different color of light (bluer than before) to see if we can detect scattering of light off the clouds in the atmosphere.
 
Astrowatch.net: What new information about those planets could be provided using James Webb Space Telescope (JWST) in the future?
 
Kreidberg: JWST will transform what we can learn about exoplanets. The telescope is bigger than Hubble, which will allow us to make more sensitive measurements and push to smaller, more Earth-like planets. It may also help us see through the clouds on planets like GJ 1214b by providing broader wavelength coverage. We hope to use it to learn about the atmospheric composition and temperature on Earth-size exoplanets, to test whether they might be hospitable for life.
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