NASA's James Webb Space Telescope is currently poised to launch and become the most powerful telescope in space. But how will its photos compare to Hubble's?
The Hubble Space Telescope launched into low Earth orbit in April 1990. Over the three decades since, the famous observatory has expanded our view of the cosmos and held our attention with the stunning images it collects. What once was a faint and mysterious abyss became a detailed and colorful universe, and we could see stars and galaxies as they'd never been seen before.
But the James Webb Space Telescope, which is scheduled to launch on Dec. 24, will do things a bit differently. With its giant gold mirror and infrared light observation tools, Webb is designed to "see" objects 10 to 100 times fainter than what Hubble can see, according to a NASA fact sheet. So, how will Webb's view compare to Hubble's?
One thing's for sure: The images Webb will capture "will be detailed and spectacular," according to the sheet.
Live updates: NASA's James Webb Space Telescope launch
Not a replacement telescope
Webb is often described as Hubble's replacement or successor. But despite a handful of glitches over the years, Hubble's science instruments are still going strong, and the two big scopes are set to observe together (albeit far apart from one another) in space.
Hubble is pretty close to us in low Earth orbit, but Webb will travel out much farther, to a gravitationally stable spot 930,000 miles (1.5 million kilometers) from Earth known as the Sun-Earth Lagrange point 2 (L2).
Additionally, while both Hubble and Webb are large space telescopes (though Webb is considerably bigger), the two actually "see" the universe very differently.
"It will take amazing images; they will be better than what Hubble did," Klaus Pontoppidan, Webb project scientist at the Space Telescope Science Institute in Baltimore, said during a news conference in May. But, while better in ways, Webb's images will also be fundamentally "different, because it's different wavelengths," Pontoppidan said.
Beauty in infrared
By observing in infrared, Webb will capture uniquely beautiful images.
"I think it'll be fantastic," Pontoppidan said, "but it's very difficult to predict what it will look like," as this will be the first space telescope mission of its kind.
"It will look very, very different than Hubble," Pontoppidan said. "The stars themselves fade away they get fainter and fainter [when you] go to [a] longer wavelength, but interstellar clouds go brighter and brighter and brighter."
Some gas and dust features become a bit wispy as you start to edge into the infrared light part of the spectrum, Pontoppidan explained. But that's not necessarily a bad thing.
"I think maybe there was some concern that, you know, you don't want images that end up looking wispy," Pontoppidan said. "But as it turns out, actually, if you just go a little bit further out into infrared … the dust itself lights up in thermal light. You get a nebula that shines."
Differences in infrared
Hubble can see light that in a wavelength range from about 200 nanometers (nm) to 2.4 microns, whereas Webb's range will go from about 600 nm to 28 microns, according to the fact sheet, which added that visible light ranges from about 700 to 400 nm.
Even though Webb primarily observes infrared light, it will still be able to see the red/orange portion of the visible light spectrum. The gold coating of its mirrors absorbs blue light from the visible spectrum, but it does reflect yellow and red visible light that will be detected.
Although it is not its primary observation function, Hubble has the ability to observe some infrared as well, so this type of observation is not a complete departure. In fact, in 2013, the Hubble team released a stunning infrared image of the Horsehead Nebula that the space telescope captured to celebrate the 22nd anniversary of its launch.
The power of infrared
Hubble has provided the world with stunning images for decades and has similar sharpness to Webb. "Webb's angular resolution, or sharpness of vision, will be the same as Hubble's," according to the fact sheet. "Webb images will appear just as sharp as Hubble's do," the sheet reads. According to NASA, Webb's resolution would allow it to see the details of an object the size of a U.S. penny 24 miles (40 km) away.
Despite this similarity, Webb has a much larger mirror — 21.3 feet (6.5 m) wide, compared to 7.8 feet (2.4 m) — cutting-edge detectors and is designed to see deeper into the infrared spectrum than Hubble.
By observing in infrared, Webb will allow scientists to see much farther out into the universe, NASA has explained. Its larger mirror also gives it more surface area to collect light, enabling the scope to peer even farther out into space, which essentially allows scientists to look "back in time," at the universe billions of years in the past.
Webb was designed to be able to "see" the first stars and galaxies that ever formed in the early universe. It can detect objects 10 billion times fainter than the faintest stars visible with no telescope, or 10 to100 times fainter than what Hubble can observe.
Webb is equipped with four scientific instruments to help it make its observations. These include the Near Infrared Camera (NIRCam), the Near-Infrared Spectrograph (NIRSpec), the Mid-Infrared Instrument (MIRI) and the Fine Guidance Sensor/Near Infrared Imager and Slitless Spectrograph (FGS-NIRISS).
With these tools, Webb "can do what we call imaging spectroscopy," Pontoppidan said, "where it can take an image, but it will take a spectrum and every pixel of the image as well." In imaging spectroscopy, there is information on the spectrum of wavelengths present in each tiny piece of the image. This can help clue scientists in as to what elements or chemicals might have created that spectrum.
Pontoppidan added that Webb's unique suite of imaging tools will allow it to do all sorts of other scientific work, such as observing exoplanets transiting in front of stars or determining the composition of a cloud in a star-forming region; he pointed to studies that may look for ice, water and complex organics in the atmospheres of exoplanets.
The James Webb Space Telescope is a joint effort involving NASA, the European Space Agency and the Canadian Space Agency.
After an additional delay, Webb is still on track to launch on Dec. 24, 2021, atop an Arianespace Ariane 5 rocket from Europe's Spaceport in Kourou, French Guiana.