Sunsets and sunspots in the Fox

Astronomers have used the Hubble space telescope to make the first ever study of sunset on a planet orbiting another star.

They observed that the sky turns red and hazy – just as it does here on Earth – when dusk falls on the faraway world of HD 189733b.

The remarkable result came by watching tiny changes in light from the planet’s own sun, which lies 63 light-years away in the constellation of Vulpecula, the Fox.

Hubble’s Advanced Camera for Surveys revealed not only the presence of the Jupiter-like planet, but also its atmosphere. As the planet began to move in front of the star, on each orbit, a team from Geneva University Observatory were able to identify the gases around its limb.

A previous team of researchers has picked out clouds in the planet’s atmosphere – but the giant world cannot be home to life as we know it. It is so close to its star that a year lasts just 2.2 days and temperatures reach several hundred degrees Celsius.

Discovery team leader Frédéric Pont said: “One of the long-term goals of studying extrasolar planets is to measure the atmosphere of an Earth- like planet, this present result is a step in this direction.

“HD 189733b is the first extrasolar planet for which we are piecing together a complete idea of what it really looks like.”

Impressively, the astronomers also found that the star HD 189733 also suffers sunspots – a kind of cosmic acne that shows as dark blotches on our own sun.

Their presence was deduced from changing levels of the star’s brightness as the planet travelled in front of its disk. One starspot was measured to be 50,000 miles (80,000 km across).

Paul Sutherland

Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.
Paul Sutherland

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Paul Sutherland

I have been a professional journalist for nearly 40 years. I write regularly for science magazines including BBC Sky at Night magazine, BBC Focus, Astronomy Now and Popular Astronomy. I have also authored three books on astronomy and contributed to others.

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