Astronomers have used NASA’s James Webb Space Telescope for the first time to take a direct image of a planet outside our solar system. An exoplanet is a gas giant, which means it does not have a rocky surface and cannot be habitable. Seen through four different light filters, the image shows how Webb’s powerful infrared view can easily pick up worlds outside our solar system, pointing the way to future observations that will reveal more information than ever about exoplanets.
“This is a transformative moment not just for Webb, but for astronomy in general,” said Sasha Hinkley, associate professor of physics and astronomy at the University of Exeter in the United Kingdom, who led the observations in a major international collaboration. Webb is an international mission led by NASA in collaboration with its partners ESA (European Space Agency) and CSA (Canadian Space Agency). The exoplanet in Webb’s image, called HIP 65426 b, is about six to 12 times the mass of Jupiter, and these observations could narrow it down even further. It is as young as the planets – about 15 to 20 million years old compared to our 4.5 billion year old Earth.
Astronomers discovered the planet in 2017 using the SPHERE instrument on the European Southern Observatory’s Very Large Telescope in Chile, taking images using short infrared wavelengths of light. Webb’s view at longer infrared wavelengths reveals new details that ground-based telescopes would not be able to detect due to the inner infrared glow of Earth’s atmosphere. The researchers analyzed the data from these observations and are preparing a paper to submit to journals for peer review. But Webb’s first capture of an exoplanet already hints at future possibilities for studying distant worlds.
Since HIP 65426 b is about 100 times farther from its host star than Earth is from the Sun, it is far enough from the star that Webb can easily separate the planet from the star in the image. Webb’s Near-Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) are both equipped with coronagraphs, which are sets of small masks that block starlight, allowing Webb to take direct images of certain exoplanets like this one. NASA’s Nancy Grace Rome Space Telescope, scheduled for launch later this decade, will demonstrate an even more advanced coronagraph.
“It was really impressive how well Webb’s coronagraphs worked to suppress the light of the host star,” Hinkley said. Taking direct images of exoplanets is challenging because stars are much brighter than planets. The planet HIP 65426 b is more than 10,000 times fainter than its host star in the near-infrared region and several thousand times fainter in the mid-infrared region.
In each image of the filter, the planet appears as a slightly differently shaped drop of light. This is due to the peculiarities of Webb’s optical system and how it translates light through different optics.”Getting this image felt like a cosmic treasure hunt,” said Aarynn Carter, a postdoctoral fellow at the University of California, Santa Cruz, who led the analysis of the images. “At first I only saw light from the star, but with careful image processing I was able to remove this light and reveal the planet.”
While this is not the first direct image of an exoplanet taken from space the Hubble Space Telescope has taken direct images of exoplanets before HIP 65426 b points the way forward for Webb’s exoplanet exploration.”I think the most exciting thing is that we’ve only just begun,” Carter said. “There are many more images of exoplanets coming that will shape our overall understanding of their physics, chemistry and formation. We may even discover previously unknown planets.”