Webb and Exoplanets

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The Webb telescope will help expose telling details about exoplanets, which are often quite different than the planets in our own solar system.
When the Hubble Space Telescope was launched in 1990, the only planets we knew of in the entire universe were the ones in our own solar system. Now we know of thousands of "exoplanets" orbiting other stars.

Yet, we still have much to learn about these alien worlds — and they have much to teach us.

The first exoplanets astronomers discovered were quite puzzling. Some orbited a pulsar — a highly magnetized stellar corpse that expels lethal amounts of radiation into space. Other exoplanets were the size of Jupiter — or larger — orbiting extremely close to their host stars.

In the years since, astronomers have found other types of planets that don't exist in our solar system. There are "super-Earths" and "mini-Neptunes" that are bigger than our home planet, but smaller than the next-largest member of our solar system, Neptune. And there are "super-Jupiters" that are much more massive than the largest planet in our solar system, Jupiter.

Astronomers have also found planets that orbit pairs of stars rather than single stars, and other planets orbiting "failed" stars called brown dwarfs that aren't mighty enough to produce light and energy (or carry out fusion) like normal stars do.

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Planets form around young stars in dusty disks that are difficult to see into with visible light. But Webb's infrared vision will be able to probe the details of these disks and help us understand how planets are born. Credit: NASA/JPL-Caltech
These peculiar planets made astronomers wonder how such planetary systems form. And is our solar system, with its orderly suite of planets orbiting around an average star, not normal, but rather unusual?

Infrared Clues

The Webb telescope could find answers within the disks of dust and gas that surround many young stars in our galaxy. Such disks are where planets are born. However, the secrets of these disks are mostly hidden away from telescopes that observe only visible light. Whereas dust and gas block visible light, infrared light given off by objects veiled in gas and dust can be detected. Webb's infrared vision will detect objects in these disks, observing how minuscule bits of ice and rock grow into larger bodies, and perhaps revealing how and where embryonic planets take shape.

And because planets tend to glow brighter in infrared light than in visible light, Webb will help astronomers discover even more exoplanets than we know of today. Webb will be able to find planets that remain unnoticed by visible-light telescopes. It could even provide images of young, Jupiter-like planets orbiting other stars.

Plus, Webb will take us a step further — not only finding exoplanets, but helping to reveal what these worlds are like. When a planet passes in front of its parent star, Webb will be able to determine the planet's size by measuring how much starlight the planet blocks. By examining starlight that passes through a planet's atmosphere, Webb will be able to learn what the atmosphere is made of by recording the unique chemical "signatures" imprinted on the starlight by different elements and molecules in the atmosphere. If Webb is unable to find evidence of certain constituents that astronomers expect to find in a planet's atmosphere, it could reveal that the planet has clouds blocking Webb's view. Brightness variations that Webb detects in a planet's atmosphere could give us details about the kind of weather the planet experiences.

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When an exoplanet passes in front of its host star, starlight passes through the planet's atmosphere. Elements and molecules absorb some of the light, leaving their marks on the starlight and allowing Webb to "see" what the atmosphere is made of. Credit: NASA/Goddard Space Flight Center
Hubble has helped pioneer such atmospheric explorations for some exoplanets, but only large, Jupiter-like planets in inhospitable environments where life — at least as we know it — is unlikely to exist. Webb will be able to explore a greater variety of planetary atmospheres, perhaps even the atmospheres of "super-Earths" or Earth-sized planets. Webb's search for the chemicals of life on planets that could be friendly for alien organisms will lead us toward an answer to one of humanity's most fundamental and profound questions: "Are we alone?"

Updated: May 10, 2016