Rubin Planetarium Video - Comets
A comet is a small Solar System body that orbits the Sun. Comets are made largely of ice. When close to the Sun the ice will outgas, producing a halo around the comet. In some cases the solar wind can cause a comet to have a tail.
Comets usually have highly eccentric orbits, which means that their distance from the Sun can change dramatically. Their orbital periods range from decades to millions of years. Short-period comets originate from the Kuiper Belt and have orbits that extend into the outer Solar System. Long-period comets originate much farther away, in the Oort Cloud.
LSST will discover an estimated 10,000 comets. Currently only about 6000 are known, and of these roughly half were cometary fragments discovered by the SOHO spacecraft shortly before they were evaporated by the Sun. Comets are hard to detect at large distances because there is little Sunlight to reflect and because they have not yet warmed up enough to start outgassing (which increases their reflectivity). Because of its ability to see faint objects, LSST will detect and track comets over much of their orbits, recording them at large distances from the Sun, to the onset of outgassing, and then back to inactivity as they return to the outer Solar System.
This animation moves around and into a comet within the Solar System, showing off its large-scale features (coma, tail) as well as small-scale features (nucleus, jets). Presenting the comet in one continuous sequence helps to establish the dramatic differences in scale between the core and the outer dust and gas features. The overall look of the comet is loosely modeled after Comet Hyakutake:
As our viewpoint sweeps underneath the comet and its slowly-changing tail, the back-swept geometry of its tail is clearly shown to be in the opposite direction of the Sun.
We now start moving inwards towards the head of the comet.
To refocus attention on the core of the comet, we undergo a shift in exposure to compensate for the burned-in view of the nucleus and establish that its brightness profile is sharply peaked at the center, and not a featureless blob (as commonly seen in photos).
At this point the undifferentiated glow of the nucleus is resolved into an extended jet structure as we continue moving closer. The jets are seen only in the sunward direction.
The rubble-pile shape of the comet nucleus is now visible. Its color is dark because comets typically have a low albedo. Jets emanating from many discrete points on the surface can be seen coming to life as they rotate into the Sunʼs illumination and warmth, and fading out as they rotate into darkness.
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