This week in astronomy news: A star-forming cloud reveals its structure through vibrations and researchers discover the first completely cloud-free exoplanet.

A 3D View of Star Formation

A dense, gaseous filament, called Musca after its namesake constellation, is shaped more like a a edge-on pancake than a needle, find Aris Tritsis (University of Crete, Greece and Australian National University) and Konstantinos Tassis (University of Crete, Greece). They published their conclusions in the May 11th Science.

The Herschel satellite had imaged far-infrared radiation (250 microns) from the cloud years ago as part of its Gould Belt Survey. Now, Tritsis and Tassis have examined hair-thin stripes that appear at the edge of the cloud in these observations, where molecular hydrogen had piled due to vibrations passing through the structure. Other observations had shown that these stripes are aligned with magnetic field lines that cross the cloud. The duo measured the distance between the stripes of denser gas, and then modeled those separations using a computer simulation. But to reproduce the observations, the simulation required a cloud that was not needle-shaped at all; instead it had to be flatter, like a piece of futomaki.

3D View of Musca star-forming cloud
3D model of Musca molecular cloud.
Aris Tritsis / ANU

“This is a cloud in space that is singing to us – all we had to do was listen,” says Tritsis.

Musca has long been a prototypical filament used to study the early stages of star formation. Now that researchers know it's not actually a filament, they can more accurately test their ideas of how gas comes together to make stars.

Read more about Musca in Australian National University's press release and watch a video of Musca's 3D shape here:

WASP-96b: A Cloud-Free "Hot Saturn" Exoplanet

An artist imagines the appearance of the "hot Saturn" WASP-96b. A distant observer would see WASP-96b blueish in color, because sodium would absorb the yellow-orange light from the planet’s full spectrum.
Engine House

Researchers appear to have found the first cloud-free exoplanet: WASP-96b, a Saturn-mass, Jupiter-size gas giant in a close, 3.5-day orbit around its Sun-like star.

Nikolay Nikolov (University of Exeter, UK) led a team that measured the spectrum of starlight passing through the planet's atmosphere as it passed in front of its star. In the May 7th Nature, the team report the chemical fingerprint of neutral sodium, which indicates that the hot Saturn is free of clouds. In fact, it's the only completely cloud-free exoplanet of more than 20 that the team has been studying using the Very Large Telescope in Chile. Indeed, most other investigations of exoplanet atmospheres have been hindered by clouds and/or haze.

Unsurprisingly, the abundance of sodium in WASP-96b is roughly the same as in the solar system; now, with a cloud-free atmosphere to study in-depth, researchers will be able to investigate the abundance of other molecules, such as water, carbon monoxide, and carbon dioxide.

Read more about WASP-96b in the University of Exeter's press release.


Image of Jim-Baughman


May 19, 2018 at 1:56 pm

Can you explain the “why” behind this conclusion, quoted from the Nature paper in your fine article:

“…the team report the chemical fingerprint of neutral sodium, which indicates that the hot Saturn is free of clouds.”

Not being an astronomer, chemist or physicist I don’t know the chain of reasoning whereby the detection of sodium indicates no cloud cover on this planet.

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Image of Monica Young

Monica Young

May 21, 2018 at 11:04 am

Great question, Jim! Definitely a point that deserves more explanation. If you plot the brightness of a spectral line versus wavelength, it looks like a narrow bell curve. Astronomers have previously only seen the "cores" of sodium spectral lines (the peak of the bell curve), rather than the "wings," in exoplanet atmospheres. Based on atmospheric models, they've concluded that the wings of the sodium line are produced at different heights than the core, and so clouds or haze could be hiding the wings. In this case, the astronomers observed the full sodium line, core and wings, so they figured that there are no clouds/haze present. I hope that helps clear things up (pun intended)!

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