Planetary Systems and the Origins of Life - JWST will tell us more about the atmospheres of extrasolar planets, and perhaps even find the building blocks of life elsewhere in the universe. In addition to other planetary systems, JWST will also study objects within our own Solar System.
The First Exoplanet Discoveries?
The first solar system found outside our own did not involve a main sequence star like our own, but a pulsar. Unexpected to say the least.
An artist's conception of PSR B1257+12's system of planets
Credit: NASA/JPL-Caltech/R. Hurt (SSC)
Since then we have found thousands of exoplanets (and in every sort of star system imaginable), and we continue to narrow in on smaller and more earth-like planets. (See JPL's Planetquest website for the latest discoveries.)
One of the main uses of the James Webb Space Telescope will be to study the atmospheres of exoplanets, to search for the building blocks of life elsewhere in the universe. But JWST is an infrared telescope. How is this good for studying exoplanets?
JWST and Exoplanets
One method JWST will use for studying exoplanets is the transit method, which means it will look for dimming of the light from a star as its planet passes between us and the star. (Astronomers call this a "transit".) Collaboration with ground-based telescopes can help us measure the mass of the planets, via the radial velocity technique (i.e., measuring the stellar wobble produced by the gravitational tug of a planet), and then JWST will do spectroscopy of the planet’s atmosphere.
JWST will also carry coronagraphs to enable direct imaging of exoplanets near bright stars. The image of an exoplanet would just be a spot, not a grand panorama, but by studying that spot, we can learn a great deal about it.Â That includes its color, differences between winter and summer, vegetation, rotation, weather...Â How is this done? The answer again is spectroscopy.
Spectroscopy is simply the science of measuring the intensity of light at different wavelengths. The graphical representations of these measurements are called spectra, and they are the key to unlocking the composition of exoplanet atmospheres.
When a planet passes in front of a star, the starlight passes through the planet’s atmosphere. If, for example, the planet has sodium in its atmosphere, the spectra of the star, added to that of the planet, will have what we call an "absorption line" in the place in the spectra where would expect to see sodium (see graphic below). This is because different elements and molecules absorb light at characteristic energies; and this is how we know where in a spectrum we might expect to see the signature of sodium (or methane or water) if it is present.
Sodium in the atmosphere of the Hot Jupiter exoplanet of HD 209458, a 7th magnitude star, 150 light years away in the constellation Pegasus. Sodium filters out light from its parent star, and is detected using by analyzing absorption spectrum. Credit: A. Field, STScI
Why is an infrared telescope key to characterizing the atmospheres of these exoplanets? The benefit of making infrared observations is that it is at infrared wavelengths that molecules in the atmospheres of exoplanets have the largest number of spectral features. The ultimate goal, of course, is to find a planet with a similar atmosphere to that of Earth.
The Solar System
In addition to studying planets outside our solar system, scientists want to learn more about our own home. JWST actually complements NASA's other solar system missions, including those observatories on the ground, orbiting Earth, and in deep space. Data of different wavelengths and from different sources can help us build a broader, fuller picture of the objects in our solar system especially with the help of JWSTâ€™s unprecedented improvements in sensitivity and resolution. JWST will observe Mars and the giant planets, minor planets like Pluto and Eris - and even the small bodies in our solar system: asteroids, comets, and Kuiper Belt Objects.
JWST will help us to understand the trace organics in Mars' atmosphere, and be used to do studies that verify the findings of the Mars rovers and landers. In the outer solar system, JWST's observations of the outer solar system will be used with Cassini's Saturn observations to give us a better picture of the seasonal weather on our giant gas planets. As for asteroids and other small bodies in our solar system - there are some features in the spectra of these objects that Earth-based observatories are blind to, but that JWST will be able to see. JWST will help us learn more about the mineralogy of these rocky objects.