One of Webb’s strong points is its ability to directly image planets around another solar system. The telescope has been in operation for long enough now that a flood of those images are starting, as more and more systems come under the telescope’s gaze. One of those is described in a recent paper and press release from NASA. According to the paper, the planet in a nearby system is about the size of Saturn, which would make it the smallest planet ever found by direct observation.
The planet is located in TWA 7, a system located about 111 light years from Earth, though there has been some debate about that, with some estimates putting it closer to 34 light years away. Either way it is a blink of an eye in galactic terms. Also known as CE Antliae, it is located in the constellation Antlia, hence its name. It garnered some attention in the astronomical community as of late due to its well-defined protoplanetary disk, which happens to be facing us directly, allowing us to see its full extent.
That protoplanetary disk is further divided into three “dust rings”, with what had previously been a very obvious gap in one of them. Astronomers had predicted there could be a planet there, and therefore turned Webb’s Mid-Infrared Imager (MIRI), along with its powerful coronagraph, towards the star.
Fraser discusses Webb's first image of exoplanet.Webb’s coronagraph blocked out most of the star’s light, and with some further image processing to eliminate the rest of it, astronomers led by Anne-Marie Lagrange of France’s CNRS, found a particularly strong infrared light source right where they predicted a planet should be. Further confirmation assured the team the light wasn’t coming from some other object in our solar system that might have been crossing Webb’s observational path at the time.
What they found was what is believed to be a planet about 100 times the size of the Earth - or equivalent to the size of Saturn. It orbits the TWA 7’s star at about 50 times the distance from the Earth to the Sun and has an average temperature of about 47 degrees Celsius - putting it potentially in the habitable zone of its parent star.
TWA 7’s star itself is a red dwarf that is only 6.4 million years old and still in the early stages of planet formation, hence the interesting disk. One feature of the disk that the researchers are hoping to more clearly define is whether there are “trojan” dust rings that precede and follow the planet in its orbit. Importantly, in addition to being the smallest planet ever imaged directly, if confirmed this would also be the first case of an imaged planet directly interacting with the protoplanetary disk it formed from.
Fraser discusses how to use Webb to hunt for exoplanets.As with all exoplanet discoveries, this one will need further confirmation. Properties like its size, composition, temperature, and location all need to be verified using a different source, though it is unlikely any other instrument can directly image the planet the way Webb could. One added benefit - while the Saturn-sized planet, known as TWA 7-b, is the only one known to exist in the system currently, there is a strong case to be made for other planets going through the same formation motions around this relatively young star.
Even if there aren’t, it's worth taking a closer look at the system as it continues to evolve. Webb is the strongest platform we have to do so currently, but, with luck, it won’t be the last powerful telescope turned on the CE Antliae system in the near future.
Learn More:
NASA - Likely Saturn-Mass Planet Imaged by NASA Webb Is Lightest Ever Seen
A.-M. Lagrange et al. - Evidence for a sub-Jovian planet in the young TWA 7 disk
UT - Webb Should Be Able to Detect Exo-Jupiters and Exo-Saturns
