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Planetary Sciences

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Giant Planets
Giant Planets

Research on giant planets consists of studies on planets in our own solar system, such as Jupiter and Saturn, along with efforts to hunt for giant planets in distant galaxies. Many new technologies in both imaging and interferometry have enabled scientists to discover the existence of far-away planets as they search for other earth-like, habitable planets in our universe.


Our solar system contains both distant gas-giant planets (notably Jupiter, Saturn) and much smaller terrestrial (rocky) planets in or close to the Suns habitable zone Venus, Earth, and Mars. Studies of planet-induced velocity "wobbles" of other stars have already found more than 100 giant planets some in near-circular orbits as far from their parent stars as Jupiter is from our Sun. These few are quite reminiscent of our own solar system. Although we cannot with this method detect terrestrial planets in these systems, we can learn a great deal about the degree to which they resemble our own solar system by studying the giant planets themselves. Also, by perfecting new observational tools to study the properties of these giant planets we will take a big step toward developing the more advanced tools that will later be required for finding and studying terrestrial planets.

image of jupiter
Image of Jupiter, the largest planet in our solar system.

A first characterization of the properties of one giant planet has already been achieved, by careful study of the combined light of the planet and its parent star. This would normally be extremely difficult because a planets light is typically between a million and a billion times fainter than its star and the planet is so close to the star that its faint light is lost in the stars glare. This first characterization was possible because the orbit of the planet just happens to be aligned so that the planet passes directly in front of the star during its orbital path. The exact amount of the starlight the planet blocks tells the size of the planet, which, interestingly, is about the same as our own Jupiter. A tiny fraction of the stars light is absorbed by the planets atmosphere while it transits the star; detailed analysis of its spectrum tells us something about the chemical composition of the planets atmosphere, and even about the possible presence of opaque clouds high in the atmosphere. These observations require extraordinary precisionbest attainable only from space by large telescopes such as the Hubble Space Telescope (HST) or the James Webb Space Telescope (JWST), or possibly by giant ground-based telescopes equipped with large spectrographs. Future observations of this sort may even reveal circulation patterns in the giant planets atmosphere, and day/night side variations.

If we are lucky, we may discover more such transiting giant planets passing in front of their stars. However, a more powerful tool for understanding the properties of giant planets requires the development of instruments that can actually make an image of the planetary system, so that the light of planets is separated from that of the parent star. Though difficult, direct imaging of giant planets has powerful diagnostic potential, by enabling the direct observation of orbital motions, measuring planetary rotation and seasonal effects, and undertaking detailed studies of the composition of their atmospheres. Direct imaging of the giant planets in extrasolar planetary systems will mark a major milestone in our search to understand the nature and origins of our own solar system. The techniques developed in the process will lay the foundation for a later generation of instruments with the greater sensitivity necessary to image terrestrial planets and to search for signs of life.

transit method of finding giant planets
astrometric method of finding planets
Left image: The transit method of finding giant planets. This method uses a stars brightness to detect planets.
Right image: Researches use this astrometric method to deduce a planets mass an orbit from its stars motion.

Research aimed toward understanding the physical properties of giant extrasolar planets incorporates two investigations:

  1. Investigation Eleven: Study the properties of giant extrasolar planets using the combined light of the planet and the parent star.

  2. Investigation Twelve: Detect giant planets by direct imaging, and study their properties.


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