Space controllers have begun powering up the four state-of-the-art instruments on the James Webb Space Telescope NASA in preparation for the observatory's first look at a target star.
That star, HD 84406, is 241 light-years from Earth and belongs to the constellation Ursa Major, the Great Bear. The images will not be used for scientific purposes, but will help ground teams align the 18 golden segments of Webb's 6.5-meter (21-foot) wide primary mirror.
The images will be taken by Webb's near-infrared camera (NIRCam), which must first cool to its operating temperature of minus 244 degrees Fahrenheit (minus 153 degrees Celsius).
"In the beginning, we will have 18 separate blurry images," Mark McCaughrean, a JWST Science Working Group scientist and senior advisor at the European Space Agency (ESA) who is familiar with the process, told Space.com. "In the end, we will have a nice, sharp image.
NIRCam will continue to stare at HD 84406 while Webb's optics experts move the mirror segments in nanometer increments to create a perfectly smooth surface. This work is expected to take until the end of April. Only then will the individual science instruments begin to train their sights on objects in the near and far universe. The first real images are expected to be released to the public in late June or early July.
McCaughrean said none of the other three instruments can do NIRCam's job in aligning the mirror. The telescope's success depends on NIRCam, and it simply cannot fail.
"If NIRCam were to fail, we would not be able to align the mirror," McCaughrean said. "That's why it's basically two cameras in one. There's complete redundancy. If one fails, we still have the other."
Of the remaining three instruments, the Mid-Infrared Instrument (MIRI) was already partially turned on during the telescope's month-long journey to its destination. For the other two instruments - the Near Infrared Spectrograph (NIRSPec) and the Fine Guidance Sensor/Near Infrared Imager and Slitless Spectrograph (FGS/NIRiss) - the control teams have now turned off the heaters that kept them warm during the travel phase.
These heaters allowed the instruments to gradually release the air trapped inside them and prevent condensation and ice from forming.
It will take weeks for the instruments to reach their operating temperature. For MIRI, that temperature is only 10 degrees Fahrenheit (5.5 degrees Celsius) above absolute zero (minus 460 degrees F or minus 273 degrees C), the coldest temperature at which the motion of atoms (which are the source of heat in the universe) ceases. Spectrographs can operate at slightly warmer temperatures of minus 393 degrees F (minus 236 degrees C).
These extremely low temperatures are critical to Webb's ability to perform its scientific tasks. The telescope is designed to image the oldest stars and galaxies that formed in the universe in the first hundreds of millions of years after the Big Bang. However, due to the expansion of the universe, the light emitted by these galaxies is only visible in infrared wavelengths (a consequence of the so-called redshift). Since infrared light is essentially heat, the faint signal would not be noticeable if the telescope itself were radiating heat.
While the cameras, such as NIRCam and MIRI, will produce stunning images of stars and galaxies, the spectrographs will provide detailed information about the chemical composition of these distant objects, McCaughrean explained.
The James Webb Space Telescope arrived at its destination, Lagrange Point 2 (L2), on Jan. 24. L2 is a point on the Sun-Earth axis located 930,000 miles (1.5 million kilometers) from Earth from the Sun. The interaction of the gravity of the two bodies provides stable conditions on L2, making it a popular location for astronomical missions. A spacecraft located at this site orbits the Sun in synchrony with the Earth (in practice, the James Webb Space Telescope is not located directly at L2, but orbits it as it accompanies the Earth around the Sun).
The James Webb Space Telescope launched Dec. 25 after a decade of delays. The $10 billion mission, conceived by astronomers in the early 1990s, was pushing the limits of what was technically feasible. Once the mirrors are aligned and the instruments calibrated, Webb is expected to revolutionize many areas of astronomy. In addition to the first stars and galaxies, Webb will contribute to the study of exoplanets, star formation, dark matter, and even the solar system and its asteroids.