Washington DC: NASA's James Webb Space Telescope will examine the atmospheres of gas giant exoplanets before searching for potentially habitable worlds, the US space agency said.
The telescope, a scientific successor to Hubble Space Telescope, is expected to launch in March 2021.
Ultimately, 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, NASA said in a statement.
Red dwarfs are also the most common stars in our galaxy.
The transiting exoplanet project team at Webb's science operations centre 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 catalyse exoplanet research and make the best use of Webb in the limited time we have available," said Natalie Batalha of NASA Ames Research Center, the project's principal investigator.
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 colours, 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.
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, NASA said. 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