Summary/Reader Response Draft #4

 The webpage “Why stars look spiky in images from the James Webb Space Telescope” from Griggs (2022) tells us the reason why the stars look spiky. The features from the James Webb Space Telescope (JWST) contribute to why the star looks spiky in images from JWST are the mirror on the space telescope, the near-infrared cameras (NIRCam) and sunshields (NASA, n.d.d). The shape of the primary will affect how the light is reflected onto the secondary mirror. Hence, a hexagonal mirror results in an image with six diffraction spikes from Griggs (2022). The near-infrared camera (NIRCam) is JWST’s primary imager capable of covering a “wavelength range 0.6 to 5 microns” (NASA, n.d.b). NIRCam can detect light from the earliest stars and galaxies in the process of formation. The near-infrared spectrograph (NIRSpec) is an instrument that analysis the wavelength that is captured by the NIRCam (Instrument NIRCam, n.d). JWST has a 5-layer, tennis court-size sunshield that acts like a parasol providing shade (NASA, n.d.c). With the enhanced features, including the mirror, the NIRCam and the sunshield, JWST is not a replacement but a successor to Hubble Space Telescope as its capabilities are not identical. 

One enhanced feature of the JWST is the size and shape of the primary mirrors. According to Erickson (2022), “the bigger the mirror, the more details the telescope can see”. A huge, weighty mirror is incredibly challenging to send into space. Therefore, engineers created 18 smaller mirrors that fit together like a puzzle for the Webb telescope. Inside the rocket, the mirror is folded, and once in orbit, they unfurl to form a single, enormous mirror. Gianopoulos (2021) states that Webb’s 21.3-foot (6.5-meter) primary mirror is substantially bigger than Hubble's 7.9-foot (2.4-meter) primary mirror, providing Webb with a light-collection surface that is more than six times that of Hubble. The shape of the mirror will affect how the is reflected. According to (NASA, n.d.e) a nearly round, segmented mirror with a "high filling factor and six-fold symmetry" is made possible by the hexagonal shape. A high filling factor indicates that there are no gaps between the segments. The segments would have gaps between them if they were circular. Hubble Space Telescope, in contrast, “the mirror was round, so it didn’t add to the spikiness” (Griggs, 2022).

Another feature of the JWST that shows it is not a replacement but a successor is a near-infrared camera (NIRCam). According to Scientific instruments (2021), one of the four scientific tools onboard the Webb spacecraft is the Near-Infrared Camera (NIRCam). The main near-infrared imager aboard Webb, NIRCam, offers high-resolution imaging and spectroscopy for a variety of research projects. NIRCam is essential for many planetary research since it is the only near-infrared instrument with coronagraphic and time-series imaging capabilities. NIRCam is a component of Webb’s wavefront sensing and control system, which in addition to imaging and spectroscopy also detects and corrects for minute imperfections in the primary mirror’s shape and misalignment between mirror segments, enabling the telescope to focus clearly on both nearby and distant objects. In contrast, Hubble Space Telescope has two primary camera systems the Advanced Camera for survey (ACS) and the Wide Field Camera 3 (WFC3) to capture the cosmos. Garner (2017) states that ACS was primarily made to survey enormous “areas of the sky at a visible and red wavelength with times” more efficient compared to the previous top Hubble camera, the Wide Field Planetary Camera 2 (WFPC2). Garner (2017) states that WFC3 investigates a wide variety of objects and processes, including exoplanets, young, very distant galaxies, much closer stellar systems and items in our own solar system. Its capacity to cover the entire electromagnetic spectrum, from ultraviolet (UV) to visible, is its important characteristic from light to near-infrared (NIR). In addition to allowing Hubble to view father into the cosmos, WFC3 also allows for the provision of images in the UV, visible and near-infrared (NIR) spectrums.

The last feature of the JWST is the sunshield. NASA (n.d.c) states that the infrared light emitted by dim and extremely far-off objects will be predominantly seen by the JWST. The telescope itself must be maintained at a very low temperature in order to be able to detect those little heat signals. Webb includes a 5-layer, tennis court-size sunshield that acts like a parasol to provide shade in order to shield the telescope from heat and light coming from the observatory itself as well as from other sources (such as the Sun, Earth, and Moon). According to NASA (n.d.c), by passively releasing its heat into space, the sunshield will enable the telescope to drop to a temperature below 50 Kelvin (-370°F or -223°C). Through a passive cooling system, the near-infrared instruments (NIRCam, NIRSpec, FGS/NIRISS) will operate at roughly 39 K (-389°F, -234°C).

One advantage that the Hubble Space Telescope has over the James Webb Space Telescope would be the accessibility to be serviced. NASA (n.d.a) states that the Hubble Space Telescope “orbits around the Earth at an altitude of~570 km. Instead of orbiting the Earth, JWST will orbit the sun 1.5million kilometers away from the Earth L2 Lagrange point.” (NASA, n.d.a). Hubble Space telescope orbit at around 570 km from earth, this allows NASA to conduct service missions to maintain or install new instruments for Hubble Space Telescope. Hubble was built to support routine maintenance and equipment updates while in orbit. As replacement units for orbital debris, instruments and limited-life things were created. NASA Space Shuttle carried out five service missions (SM 1, 2, 3A, 3B and 4), the first in December 1993 and the last in May 2009 (“Hubble Space Telescope,” 2022).

In conclusion, although Webb is frequently referred to as Hubble's replacement, we prefer to use the term "successor." Since Webb is the scientific successor to Hubble, the results of Hubble served as the basis for its scientific objectives. The science behind Hubble compelled us to "go beyond" what Hubble has previously accomplished by turning to longer wavelengths. Particularly, objects are more strongly redshifted farther away, pushing their light out of the UV and optical spectrum and into the near-infrared. An infrared telescope is thus necessary for views of these far-off objects, such as the first galaxies that the universe's beginnings produced (NASA, n.d.a).

References

Erickson, K. (2022, September 26). What is the James Webb Space Telescope? Space Place https://spaceplace.nasa.gov/james-webb-space-telescope/en/ 

Garner, R. (2017, December 5). Observatory - instruments. The National Aeronautics Space Agency (NASA). https://www.nasa.gov/content/goddard/hubble-space-telescope-science-instruments

Gianopoulos, A. (2021, December 13). Observatory - Hubble vs. Webb. The National Aeronautics Space Agency (NASA). https://www.nasa.gov/content/goddard/hubble-vs-webb-on-the-shoulders-of-a-giant

Griggs, M. B. (2022, July 15). Why stars look spiky in images from the James Webb Space Telescope. The Verge. https://www.theverge.com/23220109/james-webb-space-telescope-stars-diffraction-spike

Hubble Space Telescope. (2022, September 7). In Wikipedia. https://en.wikipedia.org/wiki/Hubble_Space_Telescope#Servicing_overview

National Aeronautics and Space Administration (NASA), James Webb Space Telescope (JWST). (n.d.a). About Webb vs Hubble Telescope. https://www.jwst.nasa.gov/content/about/comparisonWebbVsHubble.html

National Aeronautics and Space Administration (NASA). (n.d.b). Instrument: NIRCam. https://webb.nasa.gov/content/observatory/instruments/nircam.html

National Aeronautics and Space Administration (NASA). (n.d.c). Observatory the Sunshield. https://webb.nasa.gov/content/observatory/sunshield.html 

National Aeronautics and Space Administration (NASA). (n.d.d). Observatory the Webb Observatory. https://webb.nasa.gov/content/observatory/index.html

National Aeronautics and Space Administration (NASA). (n.d.e). Observatory Webb’s Mirror. https://webb.nasa.gov/content/observatory/ote/mirrors/index.html

Scientific instruments on the James Webb Space Telescope: Near-Infrared Camera (NIRCam). (2021, July 15). Webb Space Telescope. https://webbtelescope.org/contents/media/images/01FA0SZSEW1TZ51BHG0EGW2EZP