Spitzer Space Telescope

Spitzer Space Telescope

Artist rendering of the Spitzer Space Telescope
Names Space Infrared Telescope Facility
Mission type Infrared telescope
Operator NASA / JPL / Caltech
COSPAR ID 2003-038A
SATCAT № 27871
Website http://www.spitzer.caltech.edu/
Mission duration Planned: 2.5 to 5+ years[1]
Primary: 5 years, 8 months and 20 days
Elapsed: 13 years, 3 months and 17 days
Spacecraft properties
Manufacturer Lockheed
Ball Aerospace
Launch mass 950 kg (2,094 lb)[1]
Dry mass 884 kg (1,949 lb)
Payload mass 851.5 kg (1,877 lb)[1]
Start of mission
Launch date 25 August 2003 05:35:00 (2003-08-25UTC05:35Z) UTC[2]
Rocket Delta II 7920H[2]
Launch site Cape Canaveral SLC-17B
Entered service 18 December 2003
Orbital parameters
Reference system Heliocentric[1]
Regime Earth-trailing[1]
Eccentricity 0.02[2]
Perihelion 0.98 AU[2]
Apohelion 1.02 AU[2]
Period 363 days[2]
Epoch 25 August 2003 04:35:00
Main telescope
Type Ritchey–Chrétien[3]
Diameter 0.85 m (2.8 ft)[1]
Focal length 10.2 m (33 ft)
Wavelengths infrared, 3.6–160 µm[4]

Great Observatories program
This was the 300th Delta rocket launch, sending what was still called SIRTF into orbit around the Sun (not Earth orbit). Liftoff on August 25, 2003 from Cape Canaveral

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

The planned 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.[5] Without liquid helium to cool the telescope to the very low temperatures needed to operate, most of the 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.[6] All Spitzer data, from both the primary and warm phases, are archived at the Infrared Science Archive (IRSA).

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

The contest led to the telescope being named in honor of astronomer Lyman Spitzer, who had promoted the concept of space telescopes in the 1940s.[7] Spitzer wrote a 1946 report for RAND Corporation describing the advantages of an extraterrestrial 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."[7]

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 heliocentric instead of geocentric orbit, 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 centimeters (33 in) in diameter, f/12, made of beryllium and was cooled to 5.5 K (−267.65 °C; −449.77 °F). The satellite contains three instruments that allow it to perform astronomical imaging and photometry from 3.6 to 160 micrometers, spectroscopy from 5.2 to 38 micrometers, and spectrophotometry from 5 to 100 micrometers.[4]


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 report from the National Research Council of the National Academy of Sciences, A Strategy for Space Astronomy and Astrophysics for the 1980s, identified a Space Infrared Telescope Facility (SIRTF) as "one of two major astrophysics facilities [to be developed] for Spacelab", a Shuttle-borne platform. Anticipating the major 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.

Spitzer in a Kennedy Space Center clean room

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 LH2LOX 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 that could use the smaller Delta II expendable launch vehicle.

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 shorter-wavelength infrared detectors were developed by Raytheon in Goleta, California. Raytheon used indium antimonide and a doped silicon detector in the creation of the infrared detectors. It is stated that these detectors are 100 times more sensitive than what was once available in the beginning of the project during the 1980s.[13] The Far-IR detectors (70 - 160 micrometers) were developed jointly by the University of Arizona and Lawrence Berkeley National Laboratory using Gallium-doped Germanium. The spacecraft was built by Lockheed Martin. The mission is operated and managed by the Jet Propulsion Laboratory and the Spitzer Science Center,[14] located on the Caltech campus in Pasadena, California.

Spitzer ran out of liquid helium coolant on 15 May 2009, which stopped far-IR observations. Only the IRAC instrument remains in use, and only at the two shorter wavelength bands (3.6 µm and 4.5 µm). The telescope equilibrium temperature is now around 30 K (−243 °C; −406 °F), and IRAC continues to produce valuable images at those wavelengths as the "Spitzer Warm Mission".[15]


Spitzer carries three instruments on-board:[16][17][18][19]

As an example of data from the different instruments, the nebula Henize 206 was imaged in 2004, allowing comparison of images from each device.

Nebula Henize 206 viewed by different camera devices on the Spitzer Space Telescope (March 2004). The separate IRAC and MIPS camera images are at right (click image to enlarge).


SST images 12th Anniversary (20 August 2015)

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

Spitzer's first light image of IC 1396.

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-1b (although it did not resolve that light into actual images).[23] 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.

The Helix Nebula. Blue shows infrared light of 3.6 to 4.5 micrometers; green shows infrared light of 5.8 to 8 micrometers; and red shows infrared light of 24 micrometers.

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.

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.

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.[24]

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 16 March 2006.

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

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 21 September 2006 through 27 September. 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.

The Andromeda Galaxy taken by MIPS at 24 micrometers

Scientists have long wondered how tiny silicate crystals, which need high temperatures to form, have found their way into frozen comets, born in the very cold environment of the Solar System's outer edges. The crystals would have begun as non-crystallized, amorphous silicate particles, part of the mix of gas and dust from which the Solar System developed. This mystery has deepened with the results of the Stardust sample return mission, which captured particles from Comet Wild 2. Many of the Stardust particles were found to have formed at temperatures in excess of 1000 K.

In May 2009, Spitzer researchers from Germany, Hungary and the Netherlands found that amorphous silicate appears to have been transformed into crystalline form by an outburst from a star. They detected the infrared signature of forsterite silicate crystals on the disk of dust and gas surrounding the star EX Lupi during one of its frequent flare-ups, or outbursts, seen by Spitzer in April 2008. These crystals were not present in Spitzer's previous observations of the star's disk during one of its quiet periods. These crystals appear to have formed by radiative heating of the dust within 0.5 AU of EX Lupi.[25][26]

In August 2009, the telescope found evidence of a high-speed collision between two burgeoning planets orbiting a young star.[27]

In October 2009, astronomers Anne J. Verbiscer, Michael F. Skrutskie, and Douglas P. Hamilton 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.[28]


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 four separate wavelengths using the Infrared Array Camera.[29]

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

On 3 June 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.[30][31] This composite survey is now viewable with the GLIMPSE/MIPSGAL Viewer.[32]


An arrow points to the embryonic star HOPS-68, where scientists believe forsterite crystals are raining down onto the central dust disk.
Asteroid 2011 MD seen by IRAC, 2014

Spitzer observations, announced in May 2011, indicate that tiny forsterite crystals might be falling down like rain on to the protostar HOPS-68. The discovery of the forsterite crystals in the outer collapsing cloud of the protostar is surprising, because the crystals form at lava-like high temperatures, yet they are found in the molecular cloud where the temperatures are about minus 170 degrees Celsius. This led the team of astronomers to speculate that the bipolar outflow from the young star may be transporting the forsterite crystals from near the star's surface to the chilly outer cloud.[33][34]

In January 2012, it was reported that further analysis of the Spitzer observations of Ex Lupi can be understood if the forsterite crystalline dust was moving away from the protostar at a remarkable average speed of 38 kilometres per second. It would appear that such high speeds can only arise if the dust grains had been ejected by a bipolar outflow close to the star.[35] Such observations are consistent with an astrophysical theory, developed in the early 1990s, where it was suggested that bipolar outflows garden or transform the disks of gas and dust that surround protostars by continually ejecting reprocessed, highly heated material from the inner disk, adjacent to the protostar, to regions of the accretion disk further away from the protostar.[36]

In April 2015 Spitzer has co-discovered one of the most distant planets ever identified: a gas giant about 13,000 light-years away from Earth.[37]

In October 2016, Spitzer began its 2 and half year Beyond extended mission.[38] One of the goals is to prepare for the coming of the James Webb Space Telescope, and to push the hardware and limits of exploration even further.[38]

Planet hunter

Artist concept of HD219134b, synthesizing data collected about this exoplanet by Spitzer, its rocky nature and orbit, into a speculative view of what it might look like based on that data

Spitzer has been put to work studying exoplanets thanks to creatively tweaking its hardware.[39] This included doubling its stability by modifying its heating cycle, finding a new use for the "peak-up" camera, and analyzing the sensor at a sub-pixel level.[39] Although in its "warm" mission, the spacecraft's passive cooling system keeps the sensors at 29 K (−244 °C; −407 °F).[39] Spitzer has used the transit method and microlensing techniques to study exoplanets.[38] Spitzer worked with the ground based OGLE program to discover one of the most distant exoplanets found up to that time.[38]

"We never even considered using Spitzer for studying exoplanets when it launched, ... It would have seemed ludicrous back then, but now it's an important part of what Spitzer does."
NASA's Spitzer Science Center[38]

(Spitzer was launched in 2003, at time when just over 100 exoplanets had been discovered)[40] (Space Interferometry Mission and Terrestrial Planet Finder were two big exoplanet missions. See also Kepler (spacecraft))

"Spitzer has many qualities that make it a valuable asset in exoplanet science, including an extremely accurate star-targeting system and the ability to control unwanted changes in temperature. Its stable environment and ability to observe stars for long periods of time led to the first detection of light from known exoplanets in 2005. More recently, Spitzer's Infrared Array Camera (IRAC) has been used for finding exoplanets using the "transit" method -- looking for a dip in a star's brightness that corresponds to a planet passing in front of it. This brightness change needs to be measured with exquisite accuracy to detect exoplanets. IRAC scientists have created a special type of observation to make such measurements, using single pixels within the camera."

An example of the telescope is when it discovered HD 219134b transits in front its star in 2015.[41] This showed that it was rocky planet about one and half times as big as Earth, in a 3-day orbit.[41]

Spitzer Beyond

On October 1, 2016, Spitzer program began its extended mission called "Beyond" or Spitzer Beyond extended mission.[38] In this 2.5 year extended mission Spitzer will help prepare for the James Webb Space Telescope, also an infrared telescope, by observing a multitude of targets with a variety of techniques developed over its lifetime.[38] Spitzer helped discover the most distant known galaxy as of 2016, GN-z11(about 13.4 billion year light travel distance away, see List of the most distant astronomical objects) by working in conjunction with the Hubble Space Telescope (In addition to UV and Visible light cameras, Hubble has a powerful near-infrared instrument, the infrared channel of the Wide Field Camera 3, but it cannot see as deep into the infrared as Sptizer IRAC) [38] Sptizer, which launched in 2003, and concluded its extra-cold phase in 2009, is now it whats called Observation cycle 13 for its Beyond mission.[38] Rather than give up on the telescope, NASA has pushed it farther then it was envisioned, and thus produced new discoveries and developed new techniques for using the hardware.[38] NASA has found it especially handy for supporting other projects, with its capabilities filling in where other instruments could not.[38]

See also


  1. 1 2 3 4 5 6 "About Spitzer: Fast Facts". Caltech. 2008. Archived from the original on 2 February 2007. Retrieved 22 April 2007.
  2. 1 2 3 4 5 6 7 "Spitzer Space Telescope: Launch/Orbital Information". National Space Science Data Center. Retrieved 26 April 2015.
  3. "About Spitzer: Spitzer's Telescope". Caltech. Archived from the original on 24 February 2007. Retrieved 22 April 2007.
  4. 1 2 Van Dyk, Schuyler; Werner, Michael; Silbermann, Nancy (March 2013) [2010]. "3.2: Observatory Description". Spitzer Telescope Handbook. Infrared Science Archive. Retrieved 18 October 2015.
  5. Clavin, Whitney (15 May 2009). "NASA's Spitzer Begins Warm Mission". NASA/Caltech. ssc2009-12, jpl2009-086. Retrieved 26 April 2015.
  6. Spitzer Science Center. "Cycle-6 Warm Mission". NASA / JPL. Retrieved 16 September 2009.
  7. 1 2 "Who was Lyman Spitzer?". Nasa: For Educators. California Institute of Technology and the Jet Propulsion Laboratory. 11 March 2004. Retrieved 6 January 2009.
  8. Carolyn Collins Petersen; John C. Brandt (1998). Hubble vision: further adventures with the Hubble Space Telescope. CUP Archive. p. 193. ISBN 0-521-59291-7.
  9. Zimmerman, Robert (2008). The universe in a mirror: the saga of the Hubble Telescope and the visionaries who built it. Princeton University Press. p. 10. ISBN 0-691-13297-6.
  10. William Harwood (18 December 2003). "First images from Spitzer Space Telescope unveiled". Spaceflight Now. Retrieved 23 August 2008.
  11. Watanabe, Susan (22 November 2007). "Studying the Universe in Infrared". NASA. Retrieved 8 December 2007.
  12. Kwok, Johnny (Fall 2006). "Finding a Way: The Spitzer Space Telescope Story". Academy Sharing Knowledge. NASA. Archived from the original on 8 September 2007. Retrieved 9 December 2007.
  13. Raytheon Company : Investor Relations : News Release. Investor.raytheon.com (8 January 2004). Retrieved on 21 July 2013.
  14. Spitzer Science Center Home Page -- Public information.
  15. Clavin, Whitney B.; Harrington, J. D. (5 August 2009). "NASA's Spitzer Sees the Cosmos Through 'Warm' Infrared Eyes". NASA. Retrieved 30 January 2016.
  16. SSC Observatory general information page, 4 October 2009.
  17. SSC Observatory Overview, 4 October 2009.
  18. SSC Science Information home page, 4 October 2009.
  19. Spitzer Observers' Manual, reference for technical instrument information, Ver 8, 15 August 2008.
  20. SSC IRAC (Mid IR camera) science users information page, 4 October 2009.
  21. SSC IRS (spectrometer) science users' information page, 4 October 2009.
  22. SSC MIPS (long wavelength 24um, 70um, & 160um) imaging photometer and spectrometer science users' information page, 4 October 2009.
  23. Press Release: NASA's Spitzer Marks Beginning of New Age of Planetary Science.
  24. Infrared Glow of First Stars Found: Scientific American.
  25. JPL News | Spitzer Catches Star Cooking Up Comet Crystals
  26. Ábrahám, P.; et al. (14 May 2009). "Episodic formation of cometary material in the outburst of a young Sun-like star". Nature. 459 (7244): 224–226. arXiv:0906.3161Freely accessible. Bibcode:2009Natur.459..224A. doi:10.1038/nature08004.
  27. BBC NEWS | Science & Environment | Traces of planet collision found
  28. Verbiscer, Anne; Michael Skrutskie; Douglas Hamilton (7 October 2009). "Saturn's largest ring" (PDF). Nature. 461 (7267): 1098–100. Bibcode:2009Natur.461.1098V. doi:10.1038/nature08515. PMID 19812546.
  29. Galactic Legacy Infrared Mid-Plane Survey Extraordinaire, University of Wisconsin–Madison Department of Astronomy
  30. Press Release: Spitzer Captures Stellar Coming of Age in Our Galaxy
  31. Released Images and Videos of Milky Way Mosaic
  33. NASA Mission News | Spitzer Sees Crystal Rain in Infant Star Outer Clouds
  34. Poteet, C. A.; et al. (June 2011). "A Spitzer Infrared Spectrograph Detection of Crystalline Silicates in a Protostellar Envelope". The Astrophysical Journal Letters. 733 (2): L32. arXiv:1104.4498Freely accessible. Bibcode:2011ApJ...733L..32P. doi:10.1088/2041-8205/733/2/L32.
  35. Juhász, A.; et al. (January 2012). "The 2008 Outburst of EX Lup—Silicate Crystals in Motion". The Astrophysical Journal. 744 (2): 118. arXiv:1110.3754Freely accessible. Bibcode:2012ApJ...744..118J. doi:10.1088/0004-637X/744/2/118.
  36. Liffman, K.; Brown, M. (October 1995). "The motion and size sorting of particles ejected from a protostellar accretion disk". Icarus. 116 (2): 275–290. Bibcode:1995Icar..116..275L. doi:10.1006/icar.1995.1126.
  37. Newfound Alien Planet Is One of the Farthest Ever Detected
  38. 1 2 3 4 5 6 7 8 9 10 11 12
  39. 1 2 3 NASA - How Engineers Revamped Spitzer to Probe Exoplanets (Sept 24, 2013)
  40. 1 2
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