Scientists use cosmic trick to peek inside Uranus

If you shine a light through something and measure how that light changes, you can learn a lot about the material it passed through.

That’s exactly what NASA scientists did in April to uncover new details about the atmosphere of Uranus. But since they couldn’t exactly send a torch two billion miles into deep space to beam light back through the planet, they used a star instead.

Stellar occultation reveals Uranus’ secrets

“Uranus passed in front of a star about 400 light years from Earth,” said William Saunders, a planetary scientist at NASA’s Langley Research Center in Hampton, Virginia. “As Uranus began to occult the star, the planet’s atmosphere refracted the starlight, causing the star to appear to gradually dim before being blocked completely. The reverse happened at the end of the occultation, creating what we call a light curve. By observing this curve from many large telescopes, we’re able to determine the atmospheric properties at various altitudes.”

The technique is known as stellar occultation, and it’s one of the best tools scientists have for studying distant planetary atmospheres without sending a spacecraft. (Video showing stellar occultation)

In this case, measuring the starlight gave NASA and its collaborators valuable new data on the temperature, pressure, and chemical composition of the atmosphere of Uranus.

The event lasted about an hour and was visible only from parts of western North America. In total, 30 astronomers at 18 professional observatories worked with NASA Langley scientists to record it.

“This was the first time we’ve collaborated on this scale for an occultation,” Saunders said. “I’m extremely grateful to each member of the team and each observatory for taking part in this extraordinary event.”

Ice giant Uranus

Uranus is often called the “ice giant” due to its cold, methane-rich atmosphere. Despite temperatures that plunge to –224°C, its upper atmosphere is mysteriously hotter than expected, a mystery this observation could help solve. Scientists also plan to use the data to study the planet’s faint rings, its atmospheric turbulence, and refine its orbital path around the Sun.

This rare opportunity offered a new window into one of the solar system’s least-explored planets. The last spacecraft to visit Uranus was Voyager 2, in 1986.

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