The planets of the Solar System can be a curious subject. In fact, although they look similar, they can also be very different. And this occurs since their formation, which follows the history of the Sun itself. The formation process of a star, like ours, passes first through an interstellar cloud of gas. This is called molecular cloud, due to the greater presence of molecular hydrogen (in addition toAnd it is the formation of stars that makes these objects more than ordinary nebulae of ionized gas. After all, it is in denser regions of the cloud that gravitational collapse, which forms a protostar, can take place.

If the protostar reaches enough pressure in its core to start nuclear fusion, the star is formed. The rest of the molecular cloud, however, is still there. More than that, the rotation of the gas tends to flatten into a disk-like structure, which we call a protoplanetary disk. In it, just as occurred in the star formation, regions with higher gas density may collapse and form newThis is what happened with the gas planets, like Jupiter and Saturn. And in this, they are quite different from the rocky planets, where stellar winds pushed the gas away from the Sun. Soon, in the region, rocks and dust began to gather until they reached enough gravity for equilibrium.

There are even more planets in our Solar System, however, in the more distant regions. There, smaller gas clusters than in the case of Jupiter and Saturn attract less gas to themselves. And unlike these two, which have a large presence of hydrogen and helium, what there is most in the planets formed in these regions is ice composed of other elements, such as oxygen, nitrogen and sulfur. They are calledice giants, Uranus and Neptune.

Planets (almost) equal

The similarities of Uranus and Neptune go beyond their common origin. In fact, the two planets have similar masses and sizes and even their rotational speeds are similar. And that's not to mention their structures and chemical composition. That is, both are formed by a small rocky core surrounded by a mantle of water, ammonia and methane. Further up, come the planets' atmospheres, composedby hydrogen, helium and methane. In other words, you would expect that, when you look at the two sister planets, they would be very similar in appearance. But that's not the case.

In fact, the two share the bluish color, but in considerably different ways. While Neptune exhibits a vibrant blue, with visible storms in its atmosphere, Uranus has a softer, more delicate color, without many striking features. If we visualize just the atmosphere of the planets in the observations, why, then, do they look so different? The question may have beenfinally resolved in a recent study, available on arXiv.

Planetary haze

The answer, according to the team of scientists led by Patrick Irwin of Oxford University, could involve haze. By analyzing data in visible and near-infrared light, the astronomers produced new atmospheric models aimed at replicating the observed information. The modeling process included a photochemical haze layer, called Aerosol-2, caused by the breakdown ofThis layer seems to be responsible for the condensation of methane ice into clouds in the lower atmosphere, which eventually generate snow. What's more, at Uranus, it would be twice as opaque as Neptune.

It is known that Uranus reflects less ultraviolet radiation back to the Solar System than Neptune. The information matches the tendency of aerosols to absorb this type of radiation. In addition, these particles have greater reflectivity in white, which would cause the less intense color presented by Uranus. The denser layer of aerosols on the planet would also explain the greater ease of observing...spots in Neptune's atmosphere than on Neptune itself.

The discoveries do not stop there. The simulations also point to the existence of a lower layer, called Aerosol-1, where methane re-evaporates and redeposits the particles of the fog. The latter then condenses into hydrogen sulfide. And it is in this region of the atmosphere that the dark spots observed in certain points of Neptune would appear. Moreover, it is not known why one of the planets is somore opaque than the other, but this may have to do with Neptune's atmosphere turning methane more easily into snow than at Uranus, helping to clear up the haze. More observations are needed for stronger conclusions, but it is certain that many avenues have opened up for the study of the Solar System's ice giants.