Spacecraft controllers started powering up the four cutting-edge instruments
on NASA's James Webb Space Telescope as they prepare for the observatory's
first glimpses of a target star.
That star, called HD 84406, is located 241 light-years from Earth and part
of the constellation Ursa Major, the Great Bear. The images will not be used
for science, but will help the ground teams align the 18 golden segments of
Webb's 21-foot-wide (6.5 meters) main mirror.
The images will be taken by Webb's Near Infrared Camera (NIRCam), which
first has to cool down to its operational temperature of minus 244 degrees
Fahrenheit (minus 153 degrees Celsius).
"At the beginning, we will have 18 individual blurry images," Mark
McCaughrean, a scientist at the JWST Science Working Group and senior
advisor at the European Space Agency (ESA), who is familiar with the
process, told Space.com. "At the end, we will have one nice sharp image."
NIRCam will keep staring at HD 84406 while Webb's optics experts move the
mirror segments in nanometer-scale steps to create a perfectly smooth
surface. This work is expected to last until late April. Only after that
will the individual science instruments start fully training their eyes on
objects in the near and distant universe. The first proper images are
expected to be revealed to the public in late June or early July.
McCaughrean said that none of the other three instruments could take over
NIRCam's job in helping to align the mirror. The telescope's success depends
on NIRCam and it simply isn't allowed to fail.
"If NIRCam failed, we wouldn't be able to align the mirror," said
McCaughrean. "That's why it's essentially two cameras in one. There is full
redundancy. If one fails, we still have the other."
Of the remaining three instruments, the Mid-Infrared Instrument (MIRI) has
already been partially turned on during the telescope's month-long cruise to
its destination. In case of the other two — 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 cruise phase.
These heaters allowed the instruments to gradually release the air trapped
inside them and prevent water condensation and ice build-up.
It will take weeks for the instruments to reach their operational
temperatures. For MIRI, this temperature is only 10 degrees Fahrenheit (5.5
degrees Celsius ) above absolute zero (minus 460 degrees F or minus 273
degrees C), the coldest possible temperature at which the motion of atoms
(which are the source of heat in the universe) stops. The spectrographs can
operate at slightly warmer temperatures of minus 393 degrees F (minus 236
degrees C).
These extremely low temperatures are key for Webb to be able to perform its
scientific tasks. The telescope was 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. But because of the expansion of the universe, the
light emitted by these galaxies is only visible in infrared wavelengths (a
result of the so-called redshift). Since infrared light is essentially heat,
the dim signal wouldn't be noticeable if the telescope itself radiated any
warmth.
While the cameras, like NIRCam and MIRI, will produce stunning images of
stars and galaxies, the spectrographs will provide detailed information
about the chemical composition of those distant objects, McCaughrean
explained.
The James Webb Space Telescope arrived at its destination, the Lagrangian
Point 2 (L2), on Jan. 24. L2 is a point on the sun-Earth axis located at a
distance of 930,000 miles (1.5 million kilometers) from Earth away from the
sun. The gravitational interplay of the two bodies creates stable conditions
at L2, which makes it a popular spot for astronomy missions. A spacecraft in
this spot orbits the sun in sync with Earth (in practice the James Webb
Space Telescope doesn't sit directly at L2 but makes circles around it as it
accompanies Earth around the sun).
The James Webb Space Telescope launched on Dec. 25 after a decade of delays.
The $10 billion mission, dreamed up by astronomers in the early 1990s,
pushed the limits of what's technically possible. Once its mirrors are
aligned and 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.