Have you ever wanted to see an alien world? A planet orbiting a distant star, light years from the Sun? Well, the James Webb Space Telescope (JWST) just returned its first image of just that: a planet orbiting a distant star.
The new images reveal that JWST will be a fantastic tool for astronomers who want to improve their knowledge of exoplanets (planets around other stars), even better than we expected!
But for those who have grown up on a diet of Star Trek, Star Wars and many other works of science fiction, the visuals can be underwhelming. No wonderful swirling clouds, gloriously colored or dull. Instead, we see only one spot: a single point of light.
So why do these observations get astronomers excited? And what could we learn in the coming months and years?
Observing hidden worlds
During the last three decades, we have experienced a great revolution: the dawn of the age of exoplanets. Where before we didn’t know there were no planets orbiting distant stars and wondered if the Solar System was unique, now we know there are planets everywhere.
At the time of this writing, the number of known exoplanets is 5,084, and the number is growing every week.
But the vast majority of these exoplanets are detected indirectly. They orbit so close to their host stars that, with current technology, we simply cannot see them directly. Instead, we observe their host stars doing something unexpected, and deduce from this the presence of their unseen planetary companions.
Of all these alien worlds, only a handful have been seen directly. The poster child for these systems is HR 8799, whose four giant planets have been photographed so often that astronomers have produced a movie showing them moving in their orbits around their host star.
Enter HIP 65426b
To collect JWST’s first direct images of an exoplanet, astronomers turned the telescope toward the star HIP 65426, whose large planetary companion HIP 65426b was discovered by direct imaging in 2017.
HIP 65426b is unusual in several ways, all of which act to make it a particularly “easy” target for direct imaging. First, it is very far from its host star, orbiting approximately 92 times farther from HIP 65426 than the distance between Earth and the Sun. This puts it about 14 billion kilometers from its star. From our point of view, this makes it a “reasonable” distance from the star in the sky, making it easier to observe.
Next, HIP 65426b is a one-world behemoth, thought to be several times the mass of the Solar System’s largest planet, Jupiter. In addition to this, it was also previously found to be remarkably hot, with a cloud-top temperature measuring at least 1,200℃.
This combination of the planet’s size and temperature means that it is intrinsically bright (for a planet).
How were the images made and what do they show us?
Under normal circumstances, the light from HIP 65426 would completely overwhelm that of HIP 65426b, despite the distance between them.
To avoid this problem, JWST carries several “coronographs,” instruments that allow the telescope to block the light of a bright star to look for fainter objects next to it. This is a bit like blocking the headlights of a car with your hand to see if your friend has come out to say hello.
Using these coronagraphs, JWST took a series of images of HIP 65426b, each taken at a different wavelength of infrared light. In each image, the planet can be clearly seen: a single bright pixel displaced from the location of its dim host star.
The visuals are far from your standard sci-fi fare. But they show that the planet was easily spotted, standing out like a sore thumb against the dark background of space.
The researchers who conducted the observations (detailed on the arXiv preprint server) found that JWST is performing about ten times better than expected, a result that has astronomers around the world excited to see what comes next. .
Using their observations, they determined the mass of HIP 65426b (about seven times that of Jupiter). Beyond that, the data reveals that the planet is hotter than previously thought (with cloud tops near 1,400℃) and slightly smaller than expected (with a diameter of about 92% of Jupiter).
These images paint a picture of a completely alien world, unlike anything in the Solar System.
An indicator of the future
The observations of HIP 65426b are just the first sign of what JWST can do in imaging planets around other stars.
The incredible precision of the imaging data suggests that JWST will be able to obtain direct observations of smaller planets than previously expected. Instead of being limited to planets more massive than Jupiter, it should be able to see planets comparable to or even smaller than Saturn.
This is really exciting. You see, a basic rule of astronomy is that there are many more small things than big things. The fact that JWST should be able to see smaller and fainter planets than expected will greatly increase the number of potential targets available for astronomers to study.
Beyond that, the precision with which JWST carried out these measurements suggests that we will be able to learn much more about their atmospheres than expected. Repeated telescope observations could even reveal details of how these atmospheres vary over time.
In the coming years, then, expect to see many more images of alien worlds, taken by JWST. While these images may not look like something out of science fiction, they will still revolutionize our understanding of planets around other stars.
Jonti Horner does not work for, consult with, own stock in, or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond his academic appointment.
/Courtesy of The Conversation. This material from the original organization/author(s) may be ad hoc in nature, edited for clarity, style and length. The views and opinions expressed are those of the author(s).