Science

The James Webb Space Telescope released its very first image of an exoplanet – here’s what we can learn from it

This series of four images taken by the James Webb Space Telescope shows the first exoplanet (star) seen by a powerful infrared telescope. (Image credit: NASA/ESA/CSA, A Carter (UCSC), ERS 1386 team and A. Pagan (STScI))

This article was originally published in The Conversation. The publication published an article in Expert Voices: Op-Ed & Insights on Space.com.

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-ever image of just that – a planet orbiting a distant star.

The new images show that the JWST will be a fantastic tool for astronomers looking to improve their knowledge of exoplanets (planets around other stars) – even better than we hoped!

But for those who grew up on a diet of Star Trek, Star Wars, and a host of other science fiction titles, the images may not impress. No wonderful swirling clouds in gorgeous or subdued colors. Instead, we see just a spot – a single luminous dot.

So why are astronomers excited about these observations? And what can we learn in the coming months and years?

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Watching Hidden Worlds

Over the past three decades, we have experienced a great revolution – the dawn of the exoplanetary era. Whereas before we didn’t know about any planets orbiting distant stars and wondered if the solar system was unique, we now know planets are everywhere.

At the time of writing, the number of known exoplanets is 5084. (will open in a new tab)and the number is increasing every week.

But the vast majority of these exoplanets are detected indirectly. They orbit so close to their parent stars that with current technology, we simply can’t see them directly. Instead, we watch their host stars do something unexpected and infer the presence of (will open in a new tab) their invisible planetary satellites.

Of all these alien worlds, only a few have been seen directly. The model for such systems is HR 8799. (will open in a new tab)whose four giant planets have been photographed so often that astronomers have made a film showing them moving in their orbits around their host star.

Enter HIP 65426b

To collect the first direct images of the exoplanet JWST, astronomers aimed the telescope at the star HIP 65426, whose massive planetary companion HIP 65426b was discovered using direct images back in 2017. (will open in a new tab).

HIP 65426b is unusual for several reasons, all of which make it a particularly easy direct imaging target. First, it is far from its parent star, orbiting about 92 times farther away from HIP 65426 than the distance between the Earth and the Sun. This means that it is about 14 billion kilometers from its star. From our point of view, this provides a “reasonable” distance from the star in the sky, making it easier to observe.

Further, HIP 65426b is a giant of the world, believed to be several times the mass of the largest planet in the solar system, Jupiter. In addition, it has previously been found to be very hot, with cloud top temperatures of at least 1,200 degrees Celsius.

This combination of the planet’s size and temperature means that it is inherently bright (for a planet).

The first images of the alien world, HIP 65426b, taken by JWST are shown at the bottom of the larger image showing the planet’s host star. The pictures were taken at different wavelengths of infrared light. (Image credit: NASA/ESA/CSA, A Carter (UCSC), ERS 1386 team and A. Pagan (STScI).)

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How were the pictures taken and what do they show us?

Under normal circumstances, the light from HIP 65426 would completely overwhelm the light from HIP 65426b, despite the distance between them.

To get around this problem, JWST uses several “coronographs”. (will open in a new tab), instruments that allow a telescope to block light from a bright star in order to look for fainter objects near it. It’s a bit like blocking the headlights of a car with your hand to see if your friend got out to say hello.

Using these coronagraphs, JWST took a series of images of HIP 65426b, each taken with a different wavelength of infrared light. The planet is clearly visible in each image, a single bright pixel offset from the location of its obscured stellar host.

The images are far from standard science fiction. But they show that the planet was easily detected, standing out like a sore thumb against the dark backdrop of space.

Researchers who conducted the observations (details on the preprint server arXiv (will open in a new tab)) found that JWST performed about ten times better than expected, a result that has made astronomers around the world see what happens next.

Using their observations, they determined the mass of HIP 65426b (about seven times the mass of Jupiter). In addition, the data shows that the planet is hotter than previously thought (with a cloud top of around 1400 degrees Celsius) and somewhat smaller than expected (with a diameter of around 92% that of Jupiter).

These images paint a picture of a completely alien world, different from everything in the solar system.

Pointer to the future

The observations of HIP 65426b are just the first sign of what JWST can do to visualize planets around other stars.

The incredible accuracy of these images 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, he should be able to see planets comparable or even smaller than Saturn.

It’s really interesting. You see, the basic rule of astronomy is that there are more small things than big things. The fact that JWST should be able to see smaller and dimmer planets than expected would greatly increase the number of possible targets available for astronomers to study.

In addition, the accuracy with which JWST has taken these measurements suggests that we will be able to learn much more about their atmospheres than expected. Repeated telescope observations can even reveal details of how these atmospheres change over time.

As such, expect to see many more JWST images of alien worlds in the coming years. While these images may not look like science fiction, they will still revolutionize our understanding of planets around other stars.

This article is republished from The Conversation (will open in a new tab) under a Creative Commons license. Read original article (will open in a new tab).

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