The Time Traveler: James Webb Space Telescope

James Webb Space Telescope

Humans have been curious and wondered about infinite space for centuries. Their insatiable curiosity drove them to observe & explore space by inventing various technical devices over time to time. With the advancement of science & technology in the 21st-century space exploration has gone beyond its old limits. As a result of the experiments, observations, and endless sacrifices made by all the scientists, astronomers, & designers, the James Webb Space Telescope (JWST) has been produced as a great scientific leap in space science.

The James Webb Space Telescope is intended to answer the universe’s greatest mysteries and step forward in a new era of astronomical discovery. It is known as the most potent, unique, complex, and technologically advanced space telescope ever launched by man. It was lifted off on Ariane 5 rocket from Europe’s Spaceport in French Guiana, at 12.20 GMT/ 13.20 CED on 25 December 2021. Webb is a large-scale international collaboration between the National Aeronautics and Space Administration (NASA), European Space Agency (ESA), and Canadian Space Agency (CSA).

JWST primarily looks at the universe in the infrared. With a wider wavelength range and significantly increased sensitivity, the orbiting infrared observatory Webb will expand upon the findings of the Hubble Space Telescope.

Mission Goals Of James Webb Space Telescope

  • Search for the first galaxies or luminous objects formed after the Big Bang.

Webb is a powerful time machine that can look back 13.5 billion years to observe the first stars & galaxies emerging from the darkness of the early universe by making ultra-deep near-infrared surveys of the universe. This darkness was because of that there were neither galaxies nor stars at the beginning of the universe.

  • Determine how galaxies evolved from their formation until now.

When compared to the very distant galaxies, the galaxies we see today have evolved and developed their structure over time. Webb can peer far closer to the beginning of time and search for the undetected development of the first galaxies due to the longer wavelengths it uses.

  • Observe the formation of stars from the first stage to the formation of planetary systems.

In order to understand the origin and early evolution of stars and planets, need to observe the centres of thick and dusty clouds where star formation starts. These regions must be studied at infrared wavelengths because visible light waves cannot observe due to the dust that would make them opaque.

  • Measure the physical & chemical properties of the planetary systems, including our own solar system, and investigate the potential for life in those systems.

The James Webb Space Telescope will examine exoplanet atmospheres in order to look for the elements necessary for life elsewhere in the universe. It will use the transit method (looking for dimming of the light from a star to detect the presence of one or more exoplanets orbit around it) and carry coronagraphs (to enable direct imaging of exoplanets near bright stars).

Webb Orbit & The Sunshield

Webb is currently at its observatory spot L2 (second Lagrange point). It doesn’t orbit around the earth like the Hubble Space Telescope, it actually orbits around the sun, 1.5 million kilometres from the earth in the direction away from the sun.

Webb's orbit at L2
Image 1: Webb’s orbit at L2

What actually happens at the Lagrange point?

At Lagrange points, the centripetal force needed to cause a smaller object to move with two large masses precisely equals the gravitational pull of two large masses. Webb is orbiting around the sun, the combined gravitational pull of the sun and the earth holds the telescope at this L2 point. Since its direction is away from the earth, the time it takes for this object to go around the Sun is the same as the time it takes the earth to go around the sun. That is, this object is always in the line connecting the earth and the sun.

Telescope has to be kept extremely cold in order to detect heat signals. Due to this position, Webb’s Sunshield can always block light and heat from both the sun & the earth. It is one of Webb’s unique features that reduces the temperature between the warm (maximum temperature of the outermost layer 383 K / approximately 370°F) and cold (minimum temperature 36 K/ approximately -394°F) sides of the observatory by ~570°F and allows the telescope to functions at its operating temperature which is under 50 K (-370°F).

It is a five-layered, roughly tennis court-sized structure (Actual dimensions: 21.197 m x 14.162 m (69.5 ft x 46.5 ft)) made of Kapton and coated with Aluminium. Sun-facing side of the hottest layers (layers 1 & 2) have doped (treated with) Silicon additionally. The speciality here is each successive layer is cooler than the other below and the vacuum between the layers radiates out heat. 

The sunshield protects the telescope from external sources of heat & light
Image 2: The sunshield protects the telescope from external sources of heat & light
Webb's five layered Sunshield
Image 3: Webb’s five layered Sunshield

The observatory consists of major 4 instruments.

  • Near Infrared Camera (NIRCam)
  • Near Infrared Spectrograph (NIRSpec)
  • Mid Infrared Instrument (MIRI)
  • Fine Guidance Sensor / Near Infrared Imager & Slitless Spectrograph (FGS/NIRISS)

Through a passive cooling system, the near-infrared instruments (NIRCam, NIRSpec, FGS/NIRISS) will operate at about 39 K (-389°F, -234°C). The mid-infrared instrument (MIRI) will operate utilizing a helium refrigerator, or cryocooler system at a temperature of 7 K (-447°F, -266°C).

The Golden Mirrors

Webb is a three-mirror anastigmat telescope. The quantity of detail that a telescope can observe is directly correlated with the size of the mirror area that collects light from the objects. The primary mirror is a segmented one, 6.5 meters (21 feet 4 inches) broad, made from beryllium which is light, strong, and not magnetic. 18 hexagonal-shaped mirror segments which are 1.32 meters in diameter & they fit together without gaps due to their hexagonal, honeycomb shape. The secondary mirror is round in shape and is 0.74 meters in diameter. The surfaces of the mirrors are covered with a tiny layer of gold to improve their reflection of infrared light.

Webb's gold coated mirrors
Image 4: Webb’s gold coated mirrors

Six actuators are mounted to the back of each mirror segment and are used to move the primary mirror segments and secondary mirror. There’s an extra actuator that controls the primary mirror segments’ curvature located in the middle of each segment. The tertiary mirror of the telescope doesn’t move.

James Webb Space Telescope First Images of Unseen Universe

Carina Nebula (emerging stellar nurseries & individual stars in the Carina Nebula)
Image 5: Carina Nebula (emerging stellar nurseries & individual stars in the Carina Nebula)
Stephan's Quintet (a visual grouping of 5 galaxies gives information about galaxy evolution & Black holes)
Image 6: Stephan’s Quintet (a visual grouping of 5 galaxies gives information about galaxy evolution & Black holes)
Southern ring nebula (dying star’s final performance)
Image 7: Southern ring nebula (dying star’s final performance)
SMACS 0723 (the deepest and sharpest IR image of distant universe)
Image 8: SMACS 0723 (the deepest and sharpest IR image of distant universe)
WASP-96b (steamy atmosphere of distant planet in detail)
Image 9: WASP-96b (steamy atmosphere of distant planet in detail)

How was life originated on the earth? Are we alone in this universe? Does life exist anywhere in the universe other than the earth? What will the thousands of millions of stars in the far away mysterious universe tell us? All are yet to be answered…

James Webb can see backwards in time to just after the Big Bang by looking for galaxies that are so far away that the light has taken many billions of years to get from these galaxies to our telescope.

Jonathan Gardner (Webb’s Deputy Project Scientist)


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