Webb telescope opening a world of possibilities

Did you ever want to see an alien world? A planet orbiting a distant star, light years from the sun?

Well, the James Webb Space Telescope has returned its first picture of just that – a planet orbiting a distant star. The images reveal JWST will be a fantastic tool for astronomers aiming to improve their knowledge of exoplanets (planets around other stars).

Why do the observations have astronomers buzzing with excitement? And what might we learn come? Observing hidden worlds Over the past three decades, we have lived through a great revolution – the dawn of the Exoplanet Era. Where we once knew of no planets orbiting distant stars, and wondered whether the Solar System was unique, we now know planets are everywhere. The number of known exoplanets stands at 5 084, and the count grows larger every week.

But most are detected indirectly. They orbit so close to their host stars that we cannot see them. Instead, we observe their host stars doing something unexpected, and infer from that the presence of their unseen planetary companions. Of all those alien worlds,

only a handful have been seen directly. The poster child for such systems is HR 8799, whose four giant planets have been imaged so frequently that astronomers have produced a movie showing them moving in their orbits around their host star.

Enter HIP 65426b

To gather JWST’s first direct images of an exoplanet, astronomers turned

the telescope towards the star HIP 65426, whose massive planetary companion HIP 65426b was discovered using direct imaging back in 2017.

HIP 65426b is unusual in several ways – all of which act to make it an “easy” target for direct imaging. First, it is a long way from its host star, orbiting roughly 92 times farther from HIP 65426 than the distance between

Earth and the Sun. That puts it around 14 billion kilometres from its star.

Next, HIP 65426b is a behemoth of a world – thought to be several times the mass of the Solar System’s biggest planet, Jupiter.

It was also found to be remarkably hot, with temperature at its cloud tops measuring at least 1 200.

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

How were the images taken, and what do they show us?

Under normal circumstances, the light from HIP 65426 would overwhelm that from HIP 65426b. To get around this problem, JWST carries “coronagraphs”, instruments that let the telescope block the light from a bright star to look for fainter objects beside it. Using the coronagraphs, JWST took images of HIP 65426b, each taken at a different wavelength of infrared light.

In each, the planet can be clearly seen – a single bright pixel offset from the location of its obscured stellar host. The images show that the planet stands out like a sore thumb against the dark background of space.

The researchers who led the observations found that JWST is performing around 10 times better than expected.

They determined the mass of HIP to be 65426b (roughly seven times that of Jupiter). Beyond that, the data reveal the planet is hotter than thought (with cloud tops close to 1 400), and somewhat smaller than expected (with a diameter about 92% that of Jupiter).

A signpost to the future

The incredible precision of the imaging data suggests JWST will be able to obtain direct observations of planets smaller than expected.

This is a exciting. The fact JWST should be able to see smaller and fainter planets than expected will increase the number of possible targets available for astronomers to study.

Beyond that, the precision with which JWST carried out the measurements suggests we will be able to learn far more about their atmospheres than expected. In the coming years, then, expect to see many more images of alien worlds, taken by JWST.