NASA prepares to close one of its Great Observatories

Artistic concept of the NASA Spitzer Space Telescope, as a backdrop an image of the infrared sky. Credit: NASA / JPL-Caltech

NASA will say goodbye to the Spitzer space telescope this week after more than 16 years observing the most distant galaxies ever detected, the planets that orbit other stars and the clouds of dust and gas that form stars.

Spitzer, one of NASA's four Great Observatories, was a workhorse for astrophysicists, bringing new insights into exoplanets and galaxies, while serving as an anchor for the space agency's fleet of space observatories along with the Hubble Space Telescope and the Chanda X-ray Observatory.

Orbiting the sun about 160 million miles (260 million kilometers) from Earth, Spitzer is in the last days of a mission that began on August 25, 2003, with a mid-night launch aboard a Delta 2 rocket from Cape Canaveral. .



Having survived its minimum mission life of two and a half years, Spitzer will be in hibernation on Thursday after the telescope returns its final scientific data on Wednesday. The latest scientific observations of the mission were scheduled to be completed on Tuesday.

NASA is finalizing observations with Spitzer after a review by senior scientists in 2016 ranked the mission at the bottom of a list of six astrophysics missions reviewed by an independent panel. NASA uses high-level review reports to prioritize spending on extended missions, in balance with expenses to design, develop and build new astrophysics probes and telescopes.

“In 2016, we looked to the future and saw the next launch of the James Webb Space Telescope, the next great NASA observatory, which is also an infrared observatory, and the decision was made that the Spitzer mission should end when the mission began James Webb, "said Paul Hertz, director of the astrophysics division at NASA.

"At that time, we extended the Spitzer mission until the launch of James Webb in 2018," Hertz told reporters last week. "When the launch of James Webb was delayed until 2021, we extended Spitzer until now, in 2020, but the time has come to end Spitzer's mission as we move towards the launch of James Webb next year."



NASA announced last year its intention to end the Spitzer mission in early 2020, after searches for private funding sources to continue Spitzer operations were empty.

Thomas Zurbuchen, head of NASA's science division, said last May that NASA followed the main review guide to decide when to close Spitzer.

"From time to time, that means we put out a mission because the return of science no longer guarantees that it will continue in the context of the other missions," Zurbuchen said last year. "It is not that there is no return of science, but there is less."

Spitzer cost $ 11 million to operate in fiscal year 2018, a budget reduction of $ 17 million from Spitzer in 2014. Spitzer escaped the cancellation in 2014 after project managers found ways to reduce mission operating costs .



NASA's Spitzer space telescope is seen before launching from Cape Canaveral on a Delta 2 rocket in 2003. Credit: NASA
The mission that became the Spitzer Space Telescope began to develop in the 1980s. NASA asked scientists in 1983 to propose instruments for an infrared telescope to fly on the space shuttle, a project then known as the Infrared Space Installation of the ferry.

But the success of the first space-based infrared observatory, the infrared astronomical satellite, galvanized support for a larger free-flight infrared mission. In 1984, NASA selected astronomers to develop plans and build instruments for an independent mission called Space Infrared Telescope Installation, or SIRTF.

The SIRTF mission was the last of NASA's four "Great Observatories" to launch, after Hubble, the Compton and Chandra Gamma Ray Observatory. But Spitzer was the only one of the four that did not launch on the space shuttle, and NASA reduced the mission due to funding limitations.

After its launch in 2003, NASA named the telescopes



Built by Lockheed Martin, Spitzer weighed almost a ton when it was launched in 2003, and the spacecraft is 14.6 feet (4.45 meters) long and 6.9 feet (2.1 meters) in diameter. Spitzer measures approximately one third of the length of the largest Hubble space telescope, and an eleventh of the width, allowing it to launch on a Delta 2 rocket instead of the space shuttle, which took Hubble into orbit.

The primary mirror of the Spitzer telescope measures approximately 33.5 inches (85 centimeters) in diameter, reflecting starlight on a series of thousands of individual detectors tuned to be sensitive to infrared radiation.

Ball Aerospace supplied the instruments and structure of the telescope for Spitzer.

Spitzer launched with a supply of super cold liquid helium to cool its most sensitive infrared detectors, which were designed to obtain images of some of the coldest confines in the universe. Since 2009, when Spitzer ran out of cryogenic helium, the telescope has only been able to use two of its shorter bands of wavelength images in one of the three instruments of the observatory. Detectors in the near infrared bands do not need to cool down to do their job.

Infrared telescopes are sensitive to thermal energy or heat, rather than visible light. That means telescopes like Spitzer can see through veils of dust and gas, and look deep into the cosmos to detect some of the coldest and most distant objects in the universe.



"The Spitzer space telescope has presented the infrared universe," said Farisa Morales, an astrophysicist at NASA's Jet Propulsion Laboratory. It has allowed us to see what our human eyes could not see ... These huge molecular clouds in our galaxy, which are stellar nurseries, become transparent when you observe infrared radiation, and allow us to see how these baby stars form. "

And (in) the process of forming a star, some of the debris is left to form planetary systems, ”Morales said. "Spitzer has been a pioneer in allowing us to discover which ones are being formed now for future exploration."


The magnificent spiral arms of the nearby Messier 81 galaxy are highlighted in this image of NASA's Spitzer space telescope. Located in the northern constellation of the Big Dipper, this galaxy is about 12 million light years from Earth. Credit: NASA / JPL-Caltech
The astronomers used Spitzer to determine the chemical composition of the dust and the material around other stars.

"When you analyze through spectroscopy, you can get the chemical composition of the dust in orbit around another star," Morales said. “And you can also get information about the structure of, for example, other planetary systems that are being formed. Therefore, it is surprising how the data can be studied and how much information it gives us. "

Spitzer and Hubble observed the farthest galaxy ever seen in the universe, a collection of ancient stars located some 13.4 billion light years away. Spitzer and Hubble saw the galaxy as only 400 million years after the Big Bang, when the universe was about 5 percent of its current age.



Other emblematic findings of Spitzer include the discovery of a ring never before seen around Saturn, and the analysis of a cloud of dust ejected from comet Tempel 1 in 2005, when NASA's Deep Impact spacecraft intentionally drove the comet to shed light on its frozen interior.

Spitzer discovered five of the seven known planets the size of Earth in the TRAPPIST-1 planetary system around a star 40 light years, or about 235 billion miles (378 billion kilometers), of Earth. The TRAPPIST-1 system has the record of most Earth-sized planets around a single star outside our solar system.

Spitzer's mission cost about $ 1.36 billion from the start of large-scale development until the end of the observatory's operations phase, according to Hertz.

Michael Werner, a Spitzer project scientist at JPL, said astronomers will continue to use Spitzer's data file long after the mission ends.

"An important scientific area that is well represented in that archive is the study of the very distant universe," Werner said. “Spitzer, particularly working with Hubble, has seen galaxies as they were when the universe was only a small percentage of its current age. And they, like the exoplanets, will be well studied by the James Webb space telescope. "

Spitzer was expected to transmit scientific data in his last days.

On Thursday, ground teams will transmit commands for Spitzer to enter safe mode, according to Joseph Hunt.

"James Webb's mirror is 50 times larger than Spitzer's mirror, so we can observe even more deeply in the universe," said Hertz. “In fact, James Webb is designed to detect the first light after the Big Bang, the first stars and the first galaxies. And even beyond that, we began building the Wide Field Infrared Prospecting Telescope, WFIRST, which will be the great observatory to follow Webb.

"WFIRST has the sensitivity of Hubble but 100 times the field of vision," said Hertz. "Then, with each image of WFIRST we will make 100 Hubble Deep fields. So we are well positioned to continue studying the universe in infrared, and the gap of a year or so is not a concern.

Thankyou.