木星光环之下有大量氨气

Astronomers² using the upgraded Karl G. Jansky Very Large Array in New Mexico have produced the most detailed³ radio map yet of the atmosphere of Jupiter, revealing the massive movement of ammonia gas that underlies⁴ the colorful bands, spots and whirling clouds visible to the naked eye. The University of California, Berkeley researchers measured radio emissions⁵ from Jupiter's atmosphere in wavelength⁶ bands where clouds are transparent⁷. The observers were able to see as deep as 100 kilometers (60 miles) below the cloud tops, a largely unexplored region where clouds form.

 

The planet's thermal⁸ radio emissions are partially⁹ absorbed by ammonia gas. Based on the amount of absorption, the researchers could determine how much ammonia is present and at what depth.

 

By studying these regions of the planet's atmosphere, astronomers hope to learn how global circulation and cloud formation are driven by Jupiter's powerful internal heat source. These studies also will shed light on similar processes occuring on other giant planets in our solar system and on newly discovered giant exoplanets around distant stars.

 

"We in essence created a three-dimensional picture of ammonia gas in Jupiter's atmosphere, which reveals upward and downward motions within the turbulent atmosphere," said principal author Imke de Pater, a UC Berkeley professor of astronomy.

 

The map bears a striking resemblance to visible-light images taken by amateur astronomers and the Hubble Space Telescope, she said.

 

The radio map shows ammonia-rich gases rising into and forming the upper cloud layers: an ammonium hydrosulfide cloud at a temperature near 200 Kelvin (minus 100 degrees Fahrenheit) and an ammonia-ice cloud in the approximately 160 Kelvin cold air (minus 170 degrees Fahrenheit). These clouds are easily seen from Earth by optical telescopes.

 

Conversely, the radio maps show ammonia-poor air sinking into the planet, similar to how dry air descends¹⁰ from above the cloud layers on Earth.

 

The map also shows that hotspots -- so-called because they appear bright in radio and thermal infrared¹¹ images -- are ammonia-poor regions that encircle the planet like a belt just north of the equator. Between these hotspots are ammonia-rich upwellings that bring ammonia from deeper in the planet. 

 

"With radio, we can peer through the clouds and see that those hotspots are interleaved with plumes¹² of ammonia rising from deep in the planet, tracing the vertical¹³ undulations of an equatorial wave system," said UC Berkeley research astronomer¹ Michael Wong.

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