Spitzer Spots Swirling Planetary Material

...Say that phrase ten times fast. Anyway, the astronomers working with NASA's Spitzer Space Telescope have observed some rather odd behavior around a young star. Something, maybe another star or a planet, appears to be pushing a clump of planet-forming material around. The observations may provide a rare look into the early stages of planet formation.

Our current understanding of planet formation says that planets form out of swirling disks of gas and dust. And over a period of five months, Spitzer observed infrared light coming from one such disk around a young star called LRLL 31, located in the open star cluster IC 348, a star-forming region about 1,000 light years away, in the direction of the constellation Perseus. While observing LRLL 31, the astronomers were surprised to see that the light varied in unexpected ways over a period of just one week. Since we understand planets to take millions of years form, it is rare to see any change over a human lifetime, let alone over one week.

One explanation they offer is that a close companion to the star—either a star or a developing planet—could be shoving planet-forming material together, causing its thickness to vary as it spins around the star.

One theory of planet formation suggests that planets start out as clouds of gas and dust grains swirling around a star in a disk. Over time, the grains slowly clump and gradually increase in size to that of planets. As the planets get bigger and bigger, they carve out gaps in the dust, until a so-called transitional disk takes shape with a large doughnut-like hole at its center. This disk fades very gradually over time, and a new type of disk emerges, made up of debris from collisions between planets, asteroids and comets. Ultimately, a more settled, mature solar system like our own forms.

The observing team suggests that a companion to the star, circling in a gap in the system's disk, could explain the data. The companion would have to be close in order to move the material around this fast—about one-tenth the distance between Earth and the sun.

More information is needed to confirm the presence of a companion. The latest information came from five months of observing LRLL 31, and more observations are planned using Spitzer as well as ground-based telescopes. The next observations may be more of a challenge as Spitzer slowly comes to the end of its operational life. You see, Spitzer needs coolant to keep its temperature low enough to make the necessary infrared observations. Spitzer has already exceeded its 5+ years lifespan estimate, and finally ran out of coolant in May of this year. Spitzer is still operating, but now in a “warmer” state which may influence how much infrared “light” the observatory will be able to detect.

NASA's Spitzer Space Telescope was originally developed as the Space Infrared Telescope Facility (SIRTF), but NASA later renamed the program in honor of renowned American astrophysicist Lyman Spitzer, Jr. (1914-1997). Spitzer is an infrared space telescope—it detects bodies in space by their infrared energy, or heat, which radiates between the wavelengths of 3 and 180 microns (1 micron is one-millionth of a meter). Most of this infrared radiation is blocked by the Earth's atmosphere and cannot be observed from the ground, but can be observed from outside our atmosphere.

Spitzer was launched aboard a Delta rocket from Cape Canaveral, Florida on August 25, 2003. Consisting of a 0.85-meter telescope and three cryogenically-cooled science instruments, Spitzer is the largest infrared telescope ever launched into space. Its highly sensitive instruments give us a unique view of the Universe and allow us to peer into regions of space which are hidden from optical telescopes. Many areas of space are filled with vast, dense clouds of gas and dust which block our view. But infrared light can penetrate these clouds, allowing us to peer into regions of star formation, the centers of galaxies, and into newly forming planetary systems. Infrared also brings us information about the cooler objects in space, such as smaller stars which are too dim to be detected by their visible light, extrasolar planets, and giant molecular clouds. Also, many molecules in space, including organic molecules, have their unique signatures in the infrared.

Because infrared is primarily heat radiation, Spitzer must be cooled to near absolute zero (-459°F or -273°C) so that it can observe infrared signals from space without interference from the telescope's own heat. Also, the Spitzer must be protected from the heat of the Sun and the infrared radiation put out by the Earth. To do this, Spitzer carries a solar shield and was launched into an Earth-trailing solar orbit. This unique orbit places Spitzer far enough away from the Earth to allow the telescope to cool rapidly without having to carry large amounts of cryogen (coolant). Spitzer is the final mission launched in NASA's Great Observatories Program—a family of four orbiting observatories, each observing the Universe in a different kind of light (visible, gamma rays, X-rays, and infrared). Other missions in this program include the Hubble Space Telescope (HST), Compton Gamma-Ray Observatory (CGRO), and the Chandra X-Ray Observatory (CXO). Spitzer is also a part of NASA's Astronomical Search for Origins Program, designed to provide information which will help us understand our cosmic roots, and how galaxies, stars and planets develop and form.

To learn more about Spitzer and this latest discovery, check out the mission home page:

Spitzer Space Telescope Mission Home Page
www.spitzer.caltech.edu/

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