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The Solar System Exploration Telescope (SSET)

by Alan Tokunaga

One of the hottest subjects in astronomy today is searching for planets around other stars. Recent discoveries of planetary systems around nearby stars have, for the first time, given us unequivocal evidence that solar systems are common in the Universe. A new field of astronomical research has developed to answer these questions:

  • How many solar systems have Earth-like planets?
  • How do solar systems, including our own, form?
  • What is the likelihood of life in other solar systems?

These questions are not new, but we now have the technology to obtain definitive answers.

An overexposed image of a star taken with a conventional on-axis telescope. This scattered light will largely go away with an off-axis telescope, enabling us to detect faint planets near bright stars, and faint nebulosity surrounding young stars, where planets may be forming.

A faint companion (TWA 5B) next to a bright star. The estimated mass of the companion is 20 times the mass of Jupiter. These objects are nearby-about 150 light-years from Earth. With a low scattered light telescope, we will be able to observe planets as small as Jupiter, but closer to a bright star. This will provide the means to discover entirely new solar systems and measure their properties.

The proposed Solar Systems Exploration Telescope  will enable us to study the origin of our solar system by measuring the size and composition of objects beyond the orbit of Pluto, and by observing asteroids that come close to Earth. It will also be used to study existing solar systems around nearby stars and solar systems now forming around very young stars.

During the last twenty years, there has been great progress in the field of adaptive optics, which eliminates blurring by Earth's atmosphere. These advances, as well as those in infrared detector technology, enable us to develop the SSET. The SSET will be designed for maximum performance in the infrared portion of the spectrum to take advantage of the high transmission, excellent seeing, minimal water vapor, and low thermal background that characterize the atmosphere above Mauna Kea.

In a conventional telescope (left), the optics are "on-axis." In the alternative design we are considering (right), the light comes to a focus off axis. This significantly reduces the scattered light and heat emission from the telescope itself.

Infrared radiation is especially useful in measuring the temperature and composition of astronomical bodies, particularly those obscured by dust and gas in interstellar space. The infrared region is also the best place to search for new planets, since they are cool and radiate nearly all their energy in the infrared (as heat), rather than at optical wavelengths (as light). Fundamental information about an object's luminosity, composition, and temperature can be best obtained at infrared wavelengths.

Another exciting area of inquiry is the search for nebulae out of which solar systems are likely to have formed or are in the process of forming. To detect planets around these stars, we will need the low scattered light and large aperture of the SSET. It is essential that the design reduce scattered light in the telescope.

Jupiter as seen in the infrared
The bright areas in this infrared image of Jupiter are regions where heat is escaping through gaps in the clouds. Jupiter has an internal heat source, and it emits twice as much heat as it receives from the Sun. With the Solar Systems Exploration Telescope, we will be able to obtain very high resolution images of Jupiter and its satellites, and to acquire information about its composition as well. Massive planets ten to twenty times the mass of Jupiter have been observed near our solar system and around nearby stars.