Contrasting the Doyens: A Look at the Hubble & James Webb Space Telescopes

All eyes are on the James Webb Space Telescope (JWST) capabilities, which promise to herald a new era in space exploration. And with new technology come comparisons. Everyone wants to know more about the space telescope comparisons or how the JWST is superior to its predecessor, the Hubble Telescope. But while the crowd is keen on making this a clash of the titans, like the Google Pixel surpassing the iPhone, it really isn’t the same. Rather, it is more akin to an upgrade of an iPhone model. The Hubble continues to serve the space community but there will no longer be any Hubble telescope upgrades to its apparatus. The Hubble and JWST with their varying capabilities, as we shall learn below, are a formidable pair that will work together to reveal the mysteries of the cosmos.

Origins

The Hubble was born from the scientific need to observe the universe without the Earth’s cloudy and misty atmosphere getting in the way. The idea of a 3-metre space telescope was conceptualised by NASA and the European Space Agency in 1970, and completed by 1985. Due to issues with the Challenger Shuttle the launch of the Hubble, named after astronomer Edwin Powell Hubble, was delayed till April 1990, when the Discovery carried this 2.4 metre telescope to be placed in the earth’s orbit.

Work on the JWST formally began in 2014 but the idea had been floating since the mid-1990s when scientists proposed an infrared telescope with a mirror larger than four metres. Christened the Next Generation Space Telescope, it was named after James Webb- the leader who supervised the Apollo program. It was launched in Dec 2021, on an Ariane 5 rocket to enable space exploration with telescopes. The Webb orbits the Sun and is placed around the second Lagrange or L2 point.

Learnings: The Hubble was humankind’s first eyes into space and was primarily designed as a general observatory for scrutinising celestial entities. Accordingly, its optimisation is geared towards studying the visible and UV spectrum wavelengths. The JWST, on the other hand, is more ambitious and focused, with a mission to explore the first galaxies formed after the Big Bang and witness stars forming planetary systems. It works most proficiently in the infrared spectrum which is the wavelength that reaches Earth from faraway galaxies.

Technology

The Hubble carries three types of instruments, namely, cameras, spectrographs and interferometers.

• Camera: The Advanced Camera for Surveys (ACS) and the Wide Field Camera 3 (WFC3) are the two primary cameras on the Hubble. The former provides wide-field imagery in visible wavelengths while the latter is for capturing images in ultraviolet, visible and infrared light.
• Spectrographs: A spectrograph studies light emitted by an object by breaking it down into its components. This information is then studied to learn details like temperature, density, chemical composition and velocity of the light-emitting object. The Cosmic Origins Spectrograph (COS) and the Space Telescope Imaging Spectrograph (STIS) are the main spectrographs aboard the Hubble. STIS is the bright light measurer, while COS is capable of emitting extremely faint lights from far away.
• Interferometers: Called the Fine Guidance Sensors, Hubble’s three interferometers are sensitive instruments that seek a source of light and then gather information about it like the relative positions and brightness of stars.

The JWST comprises three major elements- Integrated Science Instrument Module (ISIM), the Optical Telescope Element (OTE) and the Spacecraft Element (Spacecraft Bus and Sunshield). Of these, it is the ISIM which contains the instruments of the telescope, including-

• NIRCam: Provided by the University of Arizona, the Near Infrared Camera or NIRcam is Webb’s primary camera capable of detecting light from the earliest stars and galaxies. Being equipped with coronagraphs that shield the camera from light, it can also view the dimmer bodies around a central bright star.
• NIRSpec: Operating over a wavelength range of 0.6 to 5 microns, the Near InfraRed Spectrograph (NIRSpec) was a contribution of the European Space Agency and is amongst the James Webb Telescope Innovations. Since the Webb is tasked with collecting information from the first formed galaxies after the Big Bang, the NIRSpec is capable of observing 100 objects simultaneously!
• MIRI:  The Mid-Infrared Instrument (MIRI), a camera-cum-spectrograph, is one of the technologies that differentiates the Hubble from the JWST. The only instrument capable of operating at mid-infrared wavelengths, MIRI will play a pivotal role in exploring the earliest formed faraway galaxies.
• FGS/NIRISS: With a wavelength range of 0.8 to 5.0 microns, the Fine Guidance Sensor on the JWST operates on a wide spectrum. This guider is what aids the telescope in pointing at objects with accuracy and precision to obtain high-quality imagery.

Mirrors

Mirrors are an integral part of all reflecting telescopes and enable the viewing of distant objects clearly. The Hubble is based on a variation of the Cassegrain design, called the Ritchey-Chrétien variation, which utilises two mirrors. Its primary mirror has a diameter of 2.4 metres, while the secondary is 12 inches wide. The Hubble’s mirror is crafted from one large piece of Ultra-Low Expansion Glass®

The mirror on the JWST is a massive 6.5 metre hexagon that was sent to space in a folded structure to fit into the launch vehicle. Based on the three mirror anastigmat telescope design, the Webb consists of three curved mirrors of which the primary is concave and the secondary is a concave mirror. The Webb’s mirrors are made from beryllium to keep them strong yet light.

Learnings: Webb’s super wide mirror is designed to serve its mission of exploring faraway galaxies that are constantly expanding. Since expanding galaxies emit very dim light, primarily in the infrared spectrum, the Webb needs a wide mirror to execute its task meticulously. The Hubble, on the other hand, is meant for space exploration in the visible and UV wavelengths and thus does not need a large mirror to produce accurate images.  Despite Webb’s large mirror size, the resolution of photographs from both telescopes remains the same.

 Summing Up

Hope the above discussion puts an end to the “Hubble v/s James Webb: Which is Better” debate! Thanks to Hubble and James Webb science missions, the scientific community is poised to unravel more space secrets far and beyond our realm. With the two’s ability to cover a broad spectrum of wavelengths, we are now in a position to amplify our learnings and discover more of the cosmos.