Astronomers look into atmosphere of ‘planet that shouldn’t exist’

Rob Waugh
·Contributor
·3 min read
The planet has a surface hot enough to melt platinum (University of Kansas)
The planet has a surface hot enough to melt platinum. (University of Kansas)

Astronomers have used space telescopes to peer into the atmosphere of a planet “that should not exist”, where the surface is hot enough to melt platinum and stainless steel.

The recently found exoplanet LTT 9779b, described as a “hot Neptune”, is a large planet blasted by intense rays from its parent star.

“For the first time, we measured the light coming from this planet that shouldn’t exist,” said Ian Crossfield, assistant professor of physics & astronomy at KU and lead author of the paper.

“This planet is so intensely irradiated by its star that its temperature is over 3,000 degrees Fahrenheit and its atmosphere could have evaporated entirely.”

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The astronomers crunched data from Nasa’s Tess and Spitzer space telescopes to analyse the atmosphere of LTT 9779b.

Crossfield says, “Our Spitzer observations show us its atmosphere via the infrared light the planet emits.”

The planet is an extreme environment – and would be a horrific place for humans, the researchers say.

Crossfield said: “This planet doesn’t have a solid surface, and it’s much hotter even than Mercury in our solar system – not only would lead melt in the atmosphere of this planet, but so would platinum, chromium and stainless steel.”

“A year on this planet is less than 24 hours – that's how quickly it’s whipping around its star.

“It’s a pretty extreme system.”

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The planet LTT 9779b was discovered just last year, becoming one of the first Neptune-sized planets discovered by Nasa’s Tess planet-hunting mission.

Crossfield and his co-authors used a technique called “phase curve” analysis to inspect the exoplanet’s atmospheric makeup.

Crossfield said, “We measure how much infrared light was being emitted by the planet as it rotates 360 degrees on its axis.

“Infrared light tells you the temperature of something and where the hotter and cooler parts of this planet are – on Earth, it’s not hottest at noon; it’s hottest a couple of hours into the afternoon.

“But on this planet, it's actually hottest just about at noon. We see most of the infrared light coming from the part of the planet when its star is straight overhead and a lot less from other parts of the planet.”

Taking readings of the planet’s temperature will help researchers understand its atmosphere, the researchers say.

“The planet is much cooler than we expected, which suggests that it is reflecting away much of the incident starlight that hits it, presumably due to dayside clouds,” said co-author Nicolas Cowan of the Institute for Research on Exoplanets (iREx) and McGill University in Montreal, who helped in the analysis and interpretation of the thermal phase curve measurements.

“The planet also doesn’t transport much heat to its nightside, but we think we understand that: The starlight that is absorbed is likely absorbed high in the atmosphere, from whence the energy is quickly radiated back to space.”

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