Webb telescope wows with first image of an exoplanet

The James Webb Space Telescope has taken its first picture of a planet beyond the Solar System — opening a window to understanding other worlds and underscoring the telescope’s immense capabilities.

The image is of a planet called HIP 65426 b, an object similar to Jupiter, but younger and hotter, that lies 107 parsecs from Earth in the constellation Centaurus. It is the first exoplanet image ever taken at deep infrared wavelengths, which allow astronomers to study the full range of a planet’s brightness and what it is made of.

“It gives us wavelengths we’ve never seen planets at before,” says Beth Biller, an astronomer at the University of Edinburgh and a member of the discovery team. The report appeared on 31 August on the arXiv preprint server¹; it has not yet been peer reviewed.

The finding confirms how powerful Webb will be at studying exoplanets. Launched in December as a collaboration between NASA and the European and Canadian space agencies, the telescope began doing science in June, using its 6.5-metre-wide primary mirror to observe the Universe from a spot around 1.5 million kilometres from Earth. The fact that it was able to take such a sharp picture of HIP 65426 b suggests it will be able to photograph even smaller planets, the size of Saturn or even Neptune, around other stars. That would dramatically improve scientific understanding of far-away planetary systems.

Astronomers know of more than 5,000 exoplanets, but they have taken pictures of only around 20 of them. Directly imaging exoplanets is difficult because they are often lost in the glare of the star around which they orbit.

But observing in infrared wavelengths, as Webb does, helps boost the contrast between star and planet. “You’re in the regime where planets are brightest and stars are dimmest,” says Aarynn Carter, an astronomer at the University of California Santa Cruz and lead author on the preprint.

‘Baby Jupiter’

Carter and his colleagues chose to study HIP 65426 b after other astronomers discovered it in 2017², using the European Southern Observatory’s Very Large Telescope in Chile. In July of this year, Carter’s team used instruments on Webb that physically blocked the light from the star, allowing the planet to pop into view. It orbits its star at roughly twice the distance that Pluto orbits the Sun.

Unlocking the additional infrared wavelengths allowed the astronomers to better understand how much energy the planet’s atmosphere radiates. That, in turn, allowed them to use models of stellar evolution to pin down its mass as 7 times, and its radius as 1.45 times, that of Jupiter.

HIP 65426 b is probably around 14 million years old, making it “a baby Jupiter”, Biller says. It’s “like Jupiter, but right after it formed”. Our Solar System is around 4.5 billion years old.

Future studies will probably probe how HIP 65426 b formed and evolved over time. Meanwhile, other astronomers are planning to use Webb to study many other exoplanets, especially big ones that lie relatively far from their host star and can thus be directly imaged.

Such work complements other exoplanet observations that Webb can do, such as analysing the starlight passing through a planet’s atmosphere to see what chemical compounds it contains. Astronomers can’t use that technique on HIP 65426 b, because it lies too far away from its star. But Carter’s team is applying spectral analysis to a different planet, one quite a bit larger than Jupiter that is known as VHS 1256 b. It lies 22 parsecs away from Earth in the constellation Corvus.

That finding, to be reported tonight on arXiv, includes signs of silicate grains — essentially, hot sand — in the atmosphere of that planet. “That’s a hugely exciting result,” Carter says. It is the first time sandy grains have been spotted in the atmosphere of a planet beyond the Solar System.

Such sand clouds can form when temperatures on the planet are hot enough to vapourize rock-forming minerals.