Spitzer Space Telescope

Spitzer Space Telescope

The Spitzer Space Telescope prior to launch
General information
NSSDC ID	2003-038A
Organization	NASA / JPL / Caltech
Major contractors	Lockheed Martin Ball Aerospace
Launch date	25 August 2003 [1]
Launched from	Cape Canaveral, Florida [1]
Launch vehicle	Delta II 7920H ELV [1]
Mission length	2.5 to 5+ years [1] (7 years, 5 months, and 20 days elapsed)
Mass	950 kilograms (2,100 lb)[1]
Type of orbit	Heliocentric [1]
Orbit period	1 year
Location	Orbiting the Sun
Telescope style	Ritchey-Chrétien [2]
Wavelength	3 to 180 micrometers [1]
Diameter	0.85 m[1]
Focal length	10.2 m
Instruments
IRAC	infrared camera
IRS	infrared spectrometer
MIPS	far infrared detector arrays
Website	www.spitzer.caltech.edu/

The Spitzer Space Telescope (formerly the Space Infrared Telescope Facility, SIRTF) is an infrared space observatory launched in 2003. It is the fourth and final of NASA's Great Observatories.

The planned phenominal mission period was to be 2.5 years with a pre-launch expectation that the mission could extend to five or slightly more years until the onboard liquid helium supply was exhausted. This occurred on 15 May 2009.^[3] Without liquid helium to cool the telescope to the very cold temperatures needed to operate, most instruments are no longer usable. However, the two shortest wavelength modules of the IRAC camera are still operable with the same sensitivity as before the cryogen was exhausted, and will continue to be used in the Spitzer Warm Mission.^[4]

In keeping with NASA tradition, the telescope was renamed after successful demonstration of operation, on December 18, 2003. Unlike most telescopes which are named after famous deceased astronomers by a board of scientists, the name for SIRTF was obtained from a contest open to the general public.

The contest led to the scope being named in honor of Lyman Spitzer, one of the 20th century's great scientists.^[5] Though he was not the first to propose the idea of the space telescope (Hermann Oberth being the first, in Wege zur Raumschiffahrt, 1929,^[6] and also in Die Rakete zu den Planetenräumen, 1923^[7]), Spitzer wrote a 1946 report for RAND describing the advantages of an extra-terrestrial observatory and how it could be realized with available (or upcoming) technology.^[8][9] He has been cited for his pioneering contributions to rocketry and astronomy, as well as "his vision and leadership in articulating the advantages and benefits to be realized from the Space Telescope Program."^[5]

The US$800 million Spitzer was launched from Cape Canaveral Air Force Station, on a Delta II 7920H ELV rocket, Monday, 25 August 2003 at 13:35:39 UTC-5 (EDT).^[10] It follows a rather unusual orbit, heliocentric instead of geocentric, trailing and drifting away from Earth's orbit at approximately 0.1 astronomical unit per year (a so-called "earth-trailing" orbit). The primary mirror is 85 cm in diameter, f/12 and made of beryllium and was cooled to 5.5 K. The satellite contains three instruments that allowed it to perform imaging and photometry from 3 to 180 micrometers, spectroscopy from 5 to 40 micrometers, and spectrophotometry from 5 to 100 micrometers.

History

By the early 1970s, astronomers began to consider the possibility of placing an infrared telescope above the obscuring effects of Earth's atmosphere. In 1979, a National Research Council of the National Academy of Sciences report, A Strategy for Space Astronomy and Astrophysics for the 1980s, identified a Shuttle Infrared Telescope Facility (SIRTF) as "one of two major astrophysics facilities [to be developed] for Spacelab", a Shuttle-borne platform. Anticipating the exciting results from an upcoming Explorer satellite and from the Shuttle mission, the report also favored the "study and development of ... long-duration spaceflights of infrared telescopes cooled to cryogenic temperatures." The launch in January 1983 of the Infrared Astronomical Satellite, jointly developed by the United States, the Netherlands, and the United Kingdom, to conduct the first infrared survey of the sky, whetted the appetites of scientists worldwide for follow-up space missions capitalizing on the rapid improvements in infrared detector technology.

Earlier infrared observations had been made by both space-based and ground-based observatories. Ground-based observatories have the drawback that at infrared wavelengths or frequencies, both the Earth's atmosphere and the telescope itself will radiate (glow) strongly. Additionally, the atmosphere is opaque at most infrared wavelengths. This necessitates lengthy exposure times and greatly decreases the ability to detect faint objects. It could be compared to trying to observe the stars at noon. Previous space-based satellites (such as IRAS, the Infrared Astronomical Satellite, and ISO, the Infrared Space Observatory) were operational during the 1980s and 1990s and great advances in astronomical technology have been made since then.

Most of the early concepts envisioned repeated flights aboard the NASA Space Shuttle. This approach was developed in an era when the Shuttle program was expected to support weekly flights of up to 30 days duration. A May 1983 NASA proposal described SIRTF as a Shuttle-attached mission, with an evolving scientific instrument payload. Several flights were anticipated with a probable transition into a more extended mode of operation, possibly in association with a future space platform or space station. SIRTF would be a 1-meter class, cryogenically cooled, multi-user facility consisting of a telescope and associated focal plane instruments. It would be launched on the Space Shuttle and remain attached to the Shuttle as a Spacelab payload during astronomical observations, after which it would be returned to Earth for refurbishment prior to re-flight. The first flight was expected to occur about 1990, with the succeeding flights anticipated beginning approximately one year later. However, the Spacelab-2 flight aboard STS-51-F showed that the Shuttle environment was poorly suited to an onboard infrared telescope due to contamination from the relatively "dirty" vacuum associated with the orbiters. By September 1983 NASA was considering the "possibility of a long duration [free-flyer] SIRTF mission".^[11][12]

Spitzer is the only one of the Great Observatories not launched by the Space Shuttle, which had been originally intended. However after the 1986 Challenger disaster, the Centaur LH2/LOX upper stage, which would have been required to place it in its final orbit, was banned from Shuttle use. The mission underwent a series of redesigns during the 1990s, primarily due to budget considerations. This resulted in a much smaller but still fully capable mission which could use the smaller Delta II expendable launch vehicle.

Logo

One of the most important advances of this redesign was an Earth-trailing orbit. Cryogenic satellites that require liquid helium (LHe, T ≈ 4 K) temperatures in near-Earth orbit are typically exposed to a large heat load from the Earth, and consequently entail large usage of LHe coolant, which then tends to dominate the total payload mass and limits mission life. Placing the satellite in solar orbit far from Earth allowed innovative passive cooling (such as the sun shield, against the single remaining major heat source) to drastically reduce the total mass of helium needed, resulting in an overall smaller lighter payload, with major cost savings. This orbit also simplifies telescope pointing, but does require the Deep Space Network for communications.

The primary instrument package (telescope and cryogenic chamber) was developed by Ball Aerospace & Technologies Corp., in Boulder, CO. The individual instruments were developed jointly by industrial, academic, and government institutions, the principals being Cornell, the University of Arizona, the Smithsonian Astrophysical Observatory, Ball Aerospace, and Goddard Spaceflight Center. The spacecraft was built by Lockheed Martin. The mission is operated and managed by the Jet Propulsion Laboratory and the Spitzer Science Center^[13], located on the Caltech campus in Pasadena, California.

Instruments

Spitzer^[14][15][16] has three instruments^[17] on-board:

• IRAC (Infrared Array Camera), an infrared camera which operates simultaneously on four wavelengths (3.6 µm, 4.5 µm, 5.8 µm and 8 µm). Each module uses a 256 × 256 pixel detector—the short wavelength pair use indium antimonide technology, the long wavelength pair use arsenic-doped silicon impurity band conduction technology^[18]. The two shorter wavelength bands (3.6 um & 4.5 um) for this instrument remain productive after LHe depletion in the spring of 2009, at the telescope equilibrium temperature of around 30 K, so IRAC continues to operate as the "Spitzer Warm Mission".

• IRS (Infrared Spectrograph), an infrared spectrometer with four sub-modules which operate at the wavelengths 5.3-14 µm (low resolution), 10-19.5 µm (high resolution), 14-40 µm (low resolution), and 19-37 µm (high resolution). Each module uses a 128x128 pixel detector—the short wavelength pair use arsenic-doped silicon blocked impurity band technology, the long wavelength pair use antimony-doped silicon blocked impurity band technology^[19].

• MIPS (Multiband Imaging Photometer for Spitzer), three detector arrays in the far infrared (128 × 128 pixels at 24 µm, 32 × 32 pixels at 70 µm, 2 × 20 pixels at 160 µm). The 24 µm detector is identical to one of the IRS short wavelength modules. The 70 µm detector uses gallium-doped germanium technology, and the 160 µm detector also uses gallium-doped germanium, but with mechanical stress added to each pixel to lower the bandgap and extend sensitivity to this long wavelength^[20].

Results

A popular Spitzer photo of the Helix Nebula. Blue shows infrared light of 3.6 to 4.5 microns; green shows infrared light of 5.8 to 8 microns; and red shows infrared light of 24 microns.

The first images taken by SST were designed to show off the abilities of the telescope and showed a glowing stellar nursery; a swirling, dusty galaxy; a disc of planet-forming debris; and organic material in the distant universe. Since then, monthly press releases have shown off Spitzer's capabilities, as the NASA and ESA images do for the Hubble Space Telescope.

Image of Andromeda Galaxy (M31) taken by Spitzer in infrared, MIPS, 24 micrometers (Credit:NASA/JPL-Caltech/K. Gordon (University of Arizona).

As one of its most noteworthy observations, in 2005, SST became the first telescope to directly capture the light from extrasolar planets, namely the "hot Jupiters" HD 209458b and TrES-1. (It did not resolve that light into actual images though.)^[21] This was the first time extrasolar planets had actually been visually seen; earlier observations had been indirectly made by drawing conclusions from behaviors of the stars the planets were orbiting. The telescope also discovered in April 2005 that Cohen-kuhi Tau/4 had a planetary disk that was vastly younger and contained less mass than previously theorized, leading to new understandings of how planets are formed.

Clockwise from the upper-left: Infrared views of spiral galaxy Messier 81; Embedded outflows from Herbig-Haro 46/47 protostar; Protostars uncovered in multiple views of dark globule in IC1396; and Comet Schwassmann-Wachmann 1.

While some time on the telescope is reserved for participating institutions and crucial projects, astronomers around the world also have the opportunity to submit proposals for observing time. Important targets include forming stars (young stellar objects, or YSOs), planets, and other galaxies. Images are freely available for educational and journalistic purposes.

In 2004, it was reported that Spitzer had spotted a faintly glowing body that may be the youngest star ever seen. The telescope was trained on a core of gas and dust known as L1014 which had previously appeared completely dark to ground-based observatories and to ISO (Infrared Space Observatory), a predecessor to Spitzer. The advanced technology of Spitzer revealed a bright red hot spot in the middle of L1014.

Scientists from the University of Texas at Austin who discovered the object believe the hot spot to be an example of early star development, with the young star collecting gas and dust from the cloud around it. Early speculation about the hot spot was that it might have been the faint light of another core that lies 10 times further from Earth but along the same line of sight as L1014. Follow-up observation from ground-based near-infrared observatories detected a faint fan-shaped glow in the same location as the object found by Spitzer. That glow is too feeble to have come from the more distant core, leading to the conclusion that the object is located within L1014. (Young et al., 2004)

In 2005, astronomers from the University of Wisconsin at Madison and Whitewater determined, on the basis of 400 hours of observation on the Spitzer Space Telescope, that the Milky Way Galaxy has a more substantial bar structure across its core than previously recognized.

Also in 2005, astronomers Alexander Kashlinsky and John Mather of NASA's Goddard Space Flight Center reported that one of Spitzer's earliest images may have captured the light of the first stars in the universe. An image of a quasar in the Draco constellation, intended only to help calibrate the telescope, was found to contain an infrared glow after the light of known objects was removed. Kashlinsky and Mather are convinced that the numerous blobs in this glow are the light of stars that formed as early as 100 million years after the big bang, red shifted by cosmic expansion.^[22]

Artificial color image of the Double Helix Nebula, thought to be generated at the galactic center by magnetic torsion 1000 times greater than the sun's.

In March 2006, astronomers reported an 80 light year-long nebula near the center of the Milky Way Galaxy, the Double Helix Nebula, which is, as the name implies, twisted into a double spiral shape. This is thought to be evidence of massive magnetic fields generated by the gas disc orbiting the supermassive black hole at the galaxy's center, 300 light years from the nebula and 25,000 light years from Earth. This nebula was discovered by the Spitzer Space Telescope, and published in the magazine Nature on March 16, 2006.

In May 2007, astronomers successfully mapped HD 189733 b atmospheric temperature, thus obtaining the first map of some kind of an extrasolar planet.

A cluster of new stars forming in the Serpens South cloud

Since September 2006 the telescope participates in a series of surveys called the Gould Belt Survey, observing the Gould’s Belt region in multiple wavelengths. The first set of observations by the Spitzer Space Telescope were completed from September 21, 2006 through September 27. Resulting from these observations, the team of astronomers led by Dr. Robert Gutermuth, of the Harvard-Smithsonian Center for Astrophysics reported the discovery of Serpens South, a cluster of 50 young stars in the Serpens constellation.

In August 2009, the telescope found evidence of a high-speed collision between two burgeoning planets orbiting a young star.^[23]

In October 2009, astronomers published findings of the "Phoebe ring" of Saturn, which was found with the telescope; the ring is a huge, tenuous disc of material extending from 128 to 207 times the radius of Saturn.^[24]

GLIMPSE and MIPSGAL surveys

GLIMPSE, the Galactic Legacy Infrared Mid-Plane Survey Extraordinaire, is a survey spanning 300° of the inner Milky Way galaxy. It consists of approximately 444,000 images taken at 4 separate wavelengths using the Infrared Array Camera.^[25]

MIPSGAL is a similar survey covering 278° of the galactic disk at longer wavelengths.

On June 3, 2008, scientists unveiled the largest, most detailed infra-red portrait of the Milky Way, created by stitching together more than 800,000 snapshots, at the 212th meeting of the American Astronomical Society in St.Louis, Missouri.^[26][27]

See also

• COBE
• DIRBE
• Great Observatories program
• James Webb Space Telescope
• Herschel
• Infrared astronomy
• IRAS
• Infrared Space Observatory
• List of space telescopes
• Space telescope

References

External links

• Spitzer official site
• Spitzer Space Telescope Profile by NASA's Solar System Exploration
• Spitzer images
• Spitzer newsroom
• Spitzer podcasts
• Spitzer video podcasts
• Simulation of Spitzer's orbit
• Zoomable version of the GLIMPSE/MIPSGAL surveys