Episode for August 16th, 2023 Download

The launch and deployment of the James Webb Space Telescope in July 2022, marked the beginning of a new era in exoplanet science. Never before had humanity launched a more powerful and technologically advanced instrument into orbit that had the capabilities that JWST does.

It was designed to satisfy many science requirements, among them: to measure the properties of exoplanet atmospheres and even resolve their planetary disks. As you can imagine, imaging exoplanets directly is not easy. JWST does it by masking out the bright light of the host star using a one-of-a-kind coronagraph. Coronagraphs are easy to visualize, they are just masks that block light from some part of the camera sensor. Some solar telescopes for example use a little metal disk to block out the sun, but in true JWST style, the coronagraphs on Webb take things beyond.

JWST has 248,000 microshutters that can open and close individually and when used in unison, create a mask that can cover the disk of a star. There are five masks on the infrared camera and four on the infrared spectrograph. When the light from the bright host star is blocked by these masks, the reflected light from the planet can be seen.

So, how well does it work? Has JWST imaged a planet yet? Yep. Sure has. Just a few months after deployment, astronomers have used NASA’s James Webb Space Telescope to take a direct image of a planet outside our solar system. The exoplanet is a gas giant, meaning it has no rocky surface and could not be habitable.

This was a transformative moment, not only for Webb but also for exoplanet astronomy generally.

The exoplanet in Webb’s image, called HIP 65426 b, is about six to 12 times the mass of Jupiter, and these observations could help narrow that down even further. It is young as planets go — about 15 to 20 million years old, compared to our 4.5-billion-year-old Earth.

Since HIP 65426 b is about 100 times farther from its host star than Earth is from the Sun, it is sufficiently distant that Webb can easily separate the planet from the star in the image.

Taking direct images of exoplanets is challenging because stars are so much brighter than planets. The HIP 65426 b planet is more than 10,000 times fainter than its host star in the near-infrared, and a few thousand times fainter than that in the mid-infrared. Obtaining this image is like digging for space treasure and finding it.

And the Webb Space Telescope managed to do it, just as designed.

What’s most exciting is that we’ve only just begun. There are many more images of exoplanets to come that will shape our overall understanding of their physics, chemistry, and planet formation. We may even discover previously unknown planets.