This was discovered by Nathan Cape, an astronomer at the University of Oklahoma. †science progressMarch 30).
Long-period comets take at least hundreds of years to orbit the sun. They spend most of their life at distances thousands of times greater than the distance between the Sun and the Earth. But sometimes they later develop highly elliptical orbits that regularly bring them closer to the sun and the inner planets of our solar system. Due to the intense heat of the Sun, its icy surface begins to evaporate and becomes a characteristic “tail”. Because the ice supply is diminishing, the activity of comets that approach the Earth decreases over time.
Cape determined that this phenomenon also occurs in comets that regularly visit the outer reaches of our solar system, close to Saturn’s orbit. This is surprising, because these comets experience much weaker solar heating than comets approaching Earth. As a result, the water ice on its surface cannot or hardly evaporate.
Using computer simulations, Kip showed that the gravity of the giant planets rapidly shrinks the orbits of these comets, so that they do not venture too far from the Sun between visits to the giant planet’s sphere. This should result in a much larger number of comets with “shrinking” orbits in the outer solar system than comets with longer orbits. But instead, astronomers see the opposite: distant comets with deflated orbits are almost completely missing. According to Cape, this paradox can only be explained by assuming that comets in the outer region of our solar system also quickly become inactive, making them invisible to astronomers.
Due to the difficulty of detecting comets at great distances, the current understanding of comets relies mainly on studies of approaching comets. However, Cape’s discovery suggests that the physical properties of many nearby comets may have changed before their discovery.
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