The Solar Systems Exploration Telescope

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:

These questions are not new. They were asked by ancient Greek philosophers. We are now on the verge of obtaining definitive answers.

(left) 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. This will be a tremendous advantage for studies of faint planets near bright stars and faint nebulosity surrounding young stars, where planets may be forming. (right) A Nearby Planet. 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 enable us to discover entirely new solar systems and measure their properties.

A New Type of Telescope. Advances in telescope fabrication techniques and detector arrays now make it possible to consider new ways to design and use telescopes. We have developed a telescope concept, the Solar Systems Exploration Telescope (SSET), that will enable us to begin new scientific investiga-tions and pave the way for a new generation of telescope design.

The SSET will be used 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 older solar systems around nearby stars and the formation of new solar systems around very young stars.

The great advances during the last 20 years in adaptive optics, which eliminate blurring by Earth's atmosphere, and in infrared detectors enable the development of the SSET. These advances make it essential that the design reduce scattered light in the telescope.

The SSET will also 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. 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 the best place to search for new planets, since they are cool and radiate nearly all their energy in the infrared, rather than at optical wavelengths.

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 the thermal emission from the telescope itself.

Why the Infrared Is Important. Any object with a temperature less that 5000 F will radiate most of its energy in the infrared. This is the case for all solar system objects. If we want to know the total amount of energy emitted by an astronomical object, we usually need to observe it in the infrared.
Another reason the infrared wavelength range is important is that many elements and molecules have strong absorption bands at infrared wavelengths. These bands give us information about the composition of planets, comets, asteroids, stars, and galaxies.
Finally, since the infrared is heat radiation, if we want to know the temperature of an object, we generally have to observe it in the infrared. Therefore, fundamental information about an object’s luminosity, composition, and temperature can be best obtained at infrared wavelengths.

Circumstellar disks may contain young solar systems. The unit “AU” (astronomical unit) is the distance from Earth to the Sun (about 93 million miles). For comparison, the distance to Pluto is 40 AU.

Nearby Solar Systems. An exciting area of research is the search for the nebula out of which solar systems are likely to have formed or are in the process of forming. The picture above, which shows three of these “circumstellar disks,” was taken with instruments on the NASA Infrared Telescope Facility by scientists affiliated with the University of Arizona’s Lunar and Planetary Laboratory. The black area in the center is where the bright star has been removed, allowing the very faint dusty material around the star to be seen (red to green color). This dusty material is thought to be the remnants of the material out of which the star formed. It is very possible that a solar system has also formed. To detect the planets around these stars, we will need the low scattered light and larger aperture of the SSET.

 

The Solar Systems Exploration Telescope will have an equatorial mount, which keeps any optical aberrations constant and, therefore, easier to remove. To achieve the necessary sensitivity and spatial resolution, the primary mirror should be at least 6 m in diameter. Although smaller than the largest optical/infrared telescopes, the Solar Systems Exploration Telescope will be designed for low scattered light with a superpolished primary mirror. Optimized in this way, this telescope will provide unsurpassed sensitivity for detecting faint planets next to bright stars.   The bright areas in this infrared image of Jupiter show 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. The Solar Systems Exploration Telescope 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 10–20 times the mass of Jupiter have been observed near our solar system and around nearby stars.