NASA's Webb Space Telescope to Inspect Atmospheres of Gas Giant Exoplanet

This is an artist's impression of the Jupiter-size extrasolar planet, HD 189733b, being eclipsed by its parent star. Astronomers using the Hubble Space Telescope have measured carbon dioxide and carbon monoxide in the planet's atmosphere. The planet is a "hot Jupiter," which is so close to its star that it completes an orbit in only 2.2 days. The planet is too hot for life as we know it. But under the right conditions, on a more Earth-like world, carbon dioxide can indicate the presence of extraterrestrial life. This observation demonstrates that chemical biotracers can be detected by space telescope observations. Credits: ESA, NASA, M. Kornmesser (ESA/Hubble), and STScI

In April 2018, NASA launched the Transiting Exoplanet Survey Satellite (TESS). Its main goal is to locate Earth-sized planets and larger “super-Earths” orbiting nearby stars for further study. One of the most powerful tools that will examine the atmospheres of some planets that TESS discovers will be NASA’s James Webb Space Telescope. Since observing small exoplanets with thin atmospheres like Earth will be challenging for Webb, astronomers will target easier, gas giant exoplanets first.

Some of Webb’s first observations of gas giant exoplanets will be conducted through the Director’s Discretionary Early Release Science program. The transiting exoplanet project team at Webb’s science operations center is planning to conduct three different types of observations that will provide both new scientific knowledge and a better understanding of the performance of Webb’s science instruments.

“We have two main goals. The first is to get transiting exoplanet datasets from Webb to the astronomical community as soon as possible. The second is to do some great science so that astronomers and the public can see how powerful this observatory is,” said Jacob Bean of the University of Chicago, a co-principal investigator on the transiting exoplanet project.

“Our team’s goal is to provide critical knowledge and insights to the astronomical community that will help to catalyze exoplanet research and make the best use of Webb in the limited time we have available,” added Natalie Batalha of NASA Ames Research Center, the project’s principal investigator.

Transit – An atmospheric spectrum

When a planet crosses in front of, or transits, its host star, the star’s light is filtered through the planet’s atmosphere. Molecules within the atmosphere absorb certain wavelengths, or colors, of light. By splitting the star’s light into a rainbow spectrum, astronomers can detect those sections of missing light and determine what molecules are in the planet’s atmosphere.

For these observations, the project team selected WASP-79b, a Jupiter-sized planet located about 780 light-years from Earth. The team expects to detect and measure the abundances of water, carbon monoxide, and carbon dioxide in WASP-79b. Webb also might detect new molecules not yet seen in exoplanet atmospheres.

Phase curve – A weather map

Planets that orbit very close to their stars tend to become tidally locked. One side of the planet permanently faces the star while the other side faces away, just as one side of the Moon always faces the Earth. When the planet is in front of the star, we see its cooler backside. But as it orbits the star, more and more of the hot day-side comes into view. By observing an entire orbit, astronomers can observe those variations (called a phase curve) and use the data to map the planet’s temperature, clouds, and chemistry as a function of longitude.

The team will observe a phase curve of the “hot Jupiter” known as WASP-43b, which orbits its star in less than 20 hours. By looking at different wavelengths of light, they can sample the atmosphere to different depths and obtain a more complete picture of its structure. “We have already seen dramatic and unexpected variations for this planet with Hubble and Spitzer. With Webb we will reveal these variations in significantly greater detail to understand the physical processes that are responsible,” said Bean.

Eclipse – A planet’s glow

The greatest challenge when observing an exoplanet is that the star’s light is much brighter, swamping the faint light of the planet. To get around this problem, one method is to observe a transiting planet when it disappears behind the star, not when it crosses in front of the star. By comparing the two measurements, one taken when both star and planet are visible, and the other when only the star is in view, astronomers can calculate how much light is coming from the planet alone.

This technique works best for very hot planets that glow brightly in infrared light. The team plans to study WASP-18b, a planet that is baked to a temperature of almost 4,800 degrees Fahrenheit (2,900 K). Among other questions, they hope to determine whether the planet’s stratosphere exists due to the presence of titanium oxide, vanadium oxide, or some other molecule.

Habitable planets

Ultimately, astronomers want to use Webb to study potentially habitable planets. In particular, Webb will target planets orbiting red dwarf stars since those stars are smaller and dimmer, making it easier to tease out the signal from an orbiting planet. Red dwarfs are also the most common stars in our galaxy.

“TESS should locate more than a dozen planets orbiting in the habitable zones of red dwarfs, a few of which might actually be habitable. We want to learn whether those planets have atmospheres and Webb will be the one to tell us,” said Kevin Stevenson of the Space Telescope Science Institute, a co-principal investigator on the project. “The results will go a long way towards answering the question of whether conditions favorable to life are common in our galaxy.”

The James Webb Space Telescope is the world’s premier infrared space observatory of the next decade. Webb will solve mysteries of our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, the European Space Agency (ESA) and the Canadian Space Agency (CSA).

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Contact:

Christine Pulliam
Space Telescope Science Institute, Baltimore, Maryland
410-338-4366
cpulliam@stsci.edu

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Source: HubbleSite/News

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Hubble Maps the Temperature and Water Vapor on an Extreme Exoplanet

Global Temperature Map of WASP-43b

This is a temperature map of exoplanet WASP-43b. The gas giant planet orbits very close to its parent star with a period of 19.5 hours. Because the planet keeps one side facing its star, there are huge temperature extremes between the day and night sides. The white-colored region on the daytime side is 2,800 degrees Fahrenheit. The nighttime-side temperatures drop below 1,000 degrees Fahrenheit. This steep gradient is in stark contrast to the predominantly uniform temperatures of the solar system's giant planets. Infrared observations with the Hubble Space Telescope measured how temperatures change with both altitude and longitude on the planet.  Credit: NASA, ESA, and K. Stevenson, L. Kreidberg, and J. Bean (University of Chicago)

Artist's Illustration of WASP-43b (Annotated)

Credit: NASA, ESA, K. Stevenson, L. Kreidberg, and J. Bean (University of Chicago), and Z. Levay (STScI)

A team of scientists using NASA's Hubble Space Telescope have made the most detailed global map yet of the glow from a planet orbiting another star, revealing secrets of air temperatures and water.

The map provides information about temperatures at different layers of the world's atmosphere and traces the amount and distribution of water vapor on the planet. The findings have ramifications for the understanding of atmospheric dynamics and the formation of giant planets like Jupiter.

"These measurements have opened the door for a new kind of comparative planetology," said team leader Jacob Bean of the University of Chicago.

"Our observations are the first of their kind in terms of providing a two-dimensional map of the planet's thermal structure that can be used to constrain atmospheric circulation and dynamical models for hot exoplanets," said team member Kevin Stevenson of the University of Chicago.

The Hubble observations show that the planet, called WASP-43b, is no place to call home. It's a world of extremes, where seething winds howl at the speed of sound from a 3,000-degree-Fahrenheit day side that is hot enough to melt steel to a pitch-black night side that sees temperatures plunge below a relatively cool 1,000 degrees Fahrenheit.

As a hot ball of predominantly hydrogen gas, there are no surface features on the planet, such as oceans or continents that can be used to track its rotation. Only the severe temperature difference between the day and night sides can be used by a remote observer to mark the passage of a day on this world.

WASP-43b is located 260 light-years away and was first discovered in 2011. WASP-43b is too distant to be photographed, but because its orbit is observed edge-on to Earth, astronomers detected it by observing regular dips in the light of its parent star as the planet passes in front of it.

The planet is about the same size as Jupiter, but is nearly twice as massive. The planet is so close to its orange dwarf host star that it completes an orbit in just 19 hours. The planet is also gravitationally locked so that it keeps one hemisphere facing the star, just as our moon keeps one face toward Earth.

The scientists combined two previous methods of analyzing exoplanets and put them together in one for the first time to study the atmosphere of WASP-43b. Spectroscopy allowed them to determine the water abundance and temperature structure of the atmosphere. By observing the planet's rotation, the astronomers were also able to measure the water abundances and temperatures at different longitudes.

Because there's no planet with these tortured conditions in our solar system, characterizing the atmosphere of such a bizarre world provides a unique laboratory for better understanding planet formation and planetary physics. "The planet is so hot that all the water in its atmosphere is vaporized, rather than condensed into icy clouds like on Jupiter," said team member Laura Kreidberg of the University of Chicago.

"Water is thought to play an important role in the formation of giant planets, since comet-like bodies bombard young planets, delivering most of the water and other molecules that we can observe," said Jonathan Fortney, a member of the team from the University of California, Santa Cruz.

However, the water abundances in the giant planets of our solar system are poorly known because water is locked away as ice that has precipitated out of their upper atmospheres. But on "hot Jupiters" — that is, large planets like Jupiter that have high surface temperatures because they orbit very close to their stars — water is in a vapor that can be readily traced. Kreidberg also emphasized that the team didn't simply detect water in the atmosphere of WASP-43b, but also precisely measured how much of it there is and how it is distributed with longitude.

In order to understand how giant planets form, astronomers want to know how enriched they are in different elements. The team found that WASP-43b has about the same amount of water as we would expect for an object with the same chemical composition as the Sun. Kreidberg said that this tells something fundamental about how the planet formed.

For the first time astronomers were able to observe three complete rotations of a planet, which occurred during a span of four days. This was essential to making such a precise measurement according to Jean-Michel Désert of the University of Colorado, Boulder.

The team next aims to make water-abundance measurements for different planets to explore their chemical abundances. Hubble's planned successor, the James Webb Space Telescope, will be able to not only measure water abundances, but also the abundances of carbon monoxide, carbon dioxide, ammonia, and methane, depending on the planet's temperature.

The results are presented in two new papers, one published online in Science Express on Oct. 9, and the other published in The Astrophysical Journal Letters on Sept. 12.

Contact:

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu

Source: HubbleSite