Gas planet here, no gas planet there

Gas planet here, no gas planet there

Artist’s impression of HD 189733b, a giant gas planet orbiting its star at close range. In its atmosphere 7000 kilometers per hour fast winds could drive a glass rain before itself.

The Hubble telescope has for the first time determined the color of an exoplanet by direct observation. Researchers, meanwhile, show why sometimes there’s nothing where you thought there was a planet

The epithet "blue planet" The Earth rightly wears. But it is by far not the only celestial body that looks blue from a distance. Already in our solar system Uranus and even more Neptune are clearly blue colored. While on Earth the reflection of the oceans is responsible for the coloration, the substance that gives Neptune its intense blue is not yet known.

In the case of HD 189733b, it’s a different story, as the Hubble team reports in the August ie of Astrophysical Journal Letters: The exoplanet, a ball of gas orbiting its star at a close distance, gets its deep blue from silicates in the upper atmospheric layers.

The color itself has now been determined by Hubble for the first time in direct observation. To do this, the researchers compared the spectrum of the planet when it was in front of, to the side of and behind its parent star. From the changes made in the process, they were able to derive the color itself. However, a sunset for inhabitants of HD 189733b was made to look powerfully red – this is due to the reflective properties of the silicates in the atmosphere.

Such a sunset would not be likely, because the planet receives so much energy from its mother star that winds with 7000 km/h speed drive the silicates (vulgo: glass) in small pieces through the atmosphere.

While the existence of HD 189733b is clearly confirmed, the astronomers were not successful in other systems, in which they suspected rough planets on the basis of rough circumstances. In the scientific journal Nature they are now investigating the causes of this phenomenon. Visible gaps in dust disks around young planets, for which the existence of planets still to be confirmed was regularly held responsible, can also arise in another way. This is shown by two astrophysicists on the basis of various hydrodynamic models of such dust disks.

The decisive factor for this effect is the gas content of these dust disks. The dust generally concentrates where the concentration of the gas (and thus the prere) is highest. However, when the disk around the star is not yet highly concentrated and thus permeable to light, the medium heats up most where the most dust is present.

Because the dust heats up, the prere increases there, too, which in turn increases the dust concentration. So concentric dust rings with gaps are formed around the star, which can be observed from a distance – without a planet being responsible for keeping the gaps clean (as it is the case with the rings of Saturn).

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