The James Webb Space Telescope is in the final stages of commissioning as it prepares for science observations. The team said they will deploy about two hundred of the more than 1.000 stages that need to be reached for the observatory to be fully operational since launch.
"I call it home tension," Webb observatory project scientist Michael McElwain said at a May 9 media briefing. "We have 17 scientific steps we need to bring online in the next two months, and we need to demonstrate the telescope's operational capabilities before we're ready to unleash the science tools in the Universe."
The team said they are currently investigating the details of the science instruments to complete the commissioning of each. Over the next two months, they will conduct detailed measurements of the performance of their instruments before routine science operations begin in the summer.
Webb project scientist Klaus Pontoppidan of the Space Telescope Science Institute said that the first official images, called early broadcast observations (ERO), will be made public in mid-July, predicting a more precise date will come later.
“Early release observations will be a suite of gorgeous color images and spectra to show that Webb is fully operational,” Pontoppidan said. “It will be an opportunity to celebrate the beginning of Webb science and showcase all of Webb's talents.”
Pontoppidan added that although JWST is an infrared observatory, the ERO images will be color images where infrared colors will be translated into visible colors that humans can see.
The mirrors are now fully aligned and the observatory is near its final cryogenic temperatures.
The four observation instruments on it are in the open position.
- Near-Infrared Camera (NIRCam)
- Near-Infrared Spectrometer (NIRSpec)
- Near-Infrared Imager and Slitless Spectrometer (NIRISS)
- Mid-Infrared Instrument (MIRI)
The final set of commissioning activities includes items for each instrument as well as mechanisms for the entire observatory, wrote Webb's chief commissioning scientist, Scott Friedman, in a blog post.
“We ran [each device's] mechanisms and detectors, including filter wheels, grid wheels, and the NIRSpec microcutter assembly,” Friedman said.
“The Webb optics team used images of isolated stars taken with each of the instruments to align the observatory's primary and secondary mirrors. But we still have more work to do before Webb is fully ready to embark on ambitious science observations that will unlock the secrets of the universe.”
This requires using a wide variety of astronomical resources to test the capabilities and strengths of each instrument. This includes extensive calibrations and characterizations of instruments.
“We will measure the efficiency of the instruments and how much of the light entering the telescope reaches the detectors and is recorded,” Friedman said.
“In instruments inside the mirrors of the telescope, there is always some loss in each reflection. No detector can record every incoming photon.
We will measure this efficiency at multiple wavelengths of light by observing known standard stars with light emission obtained from data obtained by other observatories, along with theoretical calculations.”
We will also observe a small patch of sky in a nearby galaxy, the Large Magellanic Cloud, and compare the images with previous observations from other observatories, including the Hubble Space Telescope. It will perform the astrometric calibration of each instrument.
The team will also test their ability to make "time-series observations," in which "a very long series of exposures are made to track what's going on during an exoplanet transit," said Marcia Rieke, principal investigator of Webb's Near Infrared Camera, at Webb's May 9 briefing.
This is where an exoplanet passes in front of its host star, and JWST can measure the dimming of the star's light when the planet moves forward. “We have already proven that we can load the right command and time sequence to capture these transitions,” Reike said.
They also need to test JWST's moving target tracking. This is for observing objects in our own solar system objects such as moons, asteroids, and ice-covered Kuiper Belt Objects around other planets.
“Since these objects are always moving, we must adjust the marking of the JWST to keep the object centered in the field of view,” Reike said. “This requires coordination between the device, the fine guidance system, and the controls pointing at the telescope. There is more to come, but we are learning how to do all these elegant and complex data retrieval techniques. We are learning what the telescope can do.”
And so far, the telescope exceeds even the most optimistic estimates of what jwst can see and do. The sharper visions they're seeing now point to even greater possibilities for the kinds of science the new observatory can perform, the scientists said.