James Webb Unveils His First Exoplanet, An Unusual Image of a Distant World

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One of the main uses of the James Webb Space Telescope is to study the atmospheres of exoplanets, looking for the building blocks of life elsewhere in the universe. Astronomers recently captured a direct image of an exoplanet for the first time with their instruments. Although this observation is yet to be reviewed, it hints at future possibilities for studying distant worlds.

The main methods for detecting exoplanets are based on the residual effects of the planet on its parent star, such as the planet’s gravitational pull on the star (measurement of radial velocity) or the amount of starlight the planet blocks as it passes. front (way observations). While these methods have been very successful in finding exoplanets, they are still limited in terms of the types of planets they can detect and the amount of information they can get from them.

Indeed, measuring a planet’s light allows one to directly estimate the planet’s surface temperature, atmospheric composition, and rotation rate. These data are necessary to determine the habitability of the planet. Unfortunately, direct imaging must overcome many challenges, not least because stars are often much brighter than their moons and most planets are very difficult to see.

Recently, astronomers at the University of California, Santa Cruz (UCSC), with a broad international collaboration, analyzed data provided by NASA’s James Webb Space Telescope, which was used to directly image a planet outside our solar system, exoplanet HIP 65426 b. This image has not yet been peer reviewed and will be published soon.

Coronagraph in action

As mentioned earlier, taking direct pictures of exoplanets is difficult because stars are much brighter than planets. The planet HIP 65426 b is more than 10,000 times fainter than its parent star in the near infrared, and several thousand times fainter in the mid-infrared.

This is where the 5 Corona masks by James Webb, installed on NIRCam, come in. These are three round masks and two “cylindrical” masks that suppress starlight under different conditions of contrast and separation between the star and its satellites. In other words, they work by blocking light from a brighter object (a star) while allowing a nearby dimmer object (a planet) to be seen – just like during an eclipse.

Also, because HIP 65426 b is about 100 times farther from its parent star than the Earth is from the Sun, the James Webb Space Telescope can easily distinguish the planet from the star in the image.

Exoplanet HIP 65426 b in different infrared bands as seen by James Webb: purple and blue for NIRCam at 3.00 and 4.44 micrometers respectively; yellow and red for the MIRI instrument at 11.4 and 15.5 µm, respectively. A small white star in each image marks the location of the parent star HIP 65426. The fringes in the NIRCam images are artifacts of the telescope’s optics. © NASA/ESA/CSA, A Carter (UCSC), ERS 1386 team and A. Pagan (STScI).

Sasha Hinckley, Associate Professor of Physics and Astronomy at the University of Exeter in the UK, who led the observations, said in a statement: “It was really impressive to see how well the Webb coronographs did at suppressing the light from the host star. This is a transformative moment not only for Webb, but for astronomy as a whole.”

You should know that NASA plans to launch the Nancy-Grace-Roman Space Telescope in 2026, equipped with an even more advanced coronagraph. This space-based observatory is about the size of Hubble, but with a panoramic field of view 200 times greater than the infrared field of view of the latter. It is designed to unlock the secrets of dark energy and dark matter, and to search for and image exoplanets, building on the scientific discoveries and technological advances of the Hubble and James Webb space telescopes.

Exoplanet already known as James Webb’s target

The exoplanet HIP 65426 b was an ideal target for James Webb, as it has been known since 2017. Indeed, astronomers discovered the planet using the SPHERE instrument of the European Southern Observatory’s Very Large Telescope in Chile and photographed it using short wavelength infrared light. Webb’s longer infrared view reveals new details that ground-based telescopes could not detect due to the Earth’s own atmospheric infrared glow.

So HIP 65426 b in the Webb image has a mass of about 6 to 12 times that of Jupiter, and these observations could help reduce that mass even further. It is quite young, between 15 and 20 million years old, compared to the Earth, which is 4.5 billion years old. This is a gas giant exoplanet, which means that it does not have a rocky surface and cannot be habitable. It orbits an A-type star in 630.7 years.

While not the first direct image of an exoplanet taken from space — the Hubble Space Telescope has already taken direct images of exoplanets — HIP 65426 b points the way forward for Webb’s exoplanet exploration, “easily” capturing worlds outside our solar system.

Aarinn Carter, UC Santa Cruz postdoctoral researcher who led the image analysis, concludes: “I think the most interesting thing is that we’ve only just begun. There are many more images of exoplanets ahead that will shape our overall understanding of their physics, chemistry, and formation. We may even discover previously unknown planets.”


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