(ORDO NEWS) — When comets first appear near Earth, their bright tails of ionized gas stun observers, but they grow fainter with each successive return.
Comets are essentially balls of dirty ice. Therefore, astronomers believe that these objects become dimmer on repeated returns to Earth because they released too much ice and gas during previous visits to the inner solar system.
Comets were melting and shrinking due to the heat of the sun, astronomers believed, so when they returned, they had less material to release and, consequently, a dimmer coma.
But a new study by scientists at the University of Oklahoma has shown that even those comets that bypass the inner solar system and remain outside the orbit of Saturn dim over time. It doesn’t make sense, because in these far corners of the solar system, sunlight is so weak that it shouldn’t melt the comet’s ice.
In a statement about the new study, scientists suggest that something must be happening in the depths of space that changes the physical properties of these comets and causes them to fade.
The researchers came to this conclusion when they ran computer simulations of comets traveling through the outer solar system near the giant massive planets Jupiter and Saturn. Models have shown that the powerful gravity of these planets changes the orbits of comets.
Comets could begin their journey in what are called highly eccentric elliptical orbits, approaching from the farthest regions of the solar system far beyond the orbit of Neptune, then rushing towards the Sun and disappearing into the external environment for centuries.
But with each pass near Jupiter and Saturn, the comets’ orbits become more circular, and they don’t recede that far from the Sun, the study says.
“Therefore, it should be expected that there are many more comets in the outer solar system in such reduced orbits compared to comets in large orbits,” said Nathan Kaib, assistant professor of astronomy at the University of Oklahoma and lead author of the new study.
The only problem is that these results do not match what astronomers actually see.
“Instead, astronomers see the opposite,” Kaib said. “Distant comets with reduced orbits are almost completely absent from astronomers’ observations, and comets with large orbits dominate our census of the outer solar system.”
To explain this strange absence, the researchers speculate that the comets must have dimmed, and although they are there, somewhere beyond the orbit of Saturn, they are no longer visible to our telescopes.
“The extinction of distant comets was discovered by combining the results of computer simulations of comet formation with the current catalog of known distant comets,” Kaib said.
“These distant comets are dim and extremely difficult to detect, and comet-watching campaigns have put a lot of effort into creating this catalog over the past 20 years.
But understanding what exactly is happening will require more powerful telescopes than what scientists can use today. Once they appear, Kaib and his colleagues say, astronomers will likely find that the outer solar system is full of faded comets.
Astronomers are aware of comets that orbit between Jupiter and Saturn and regularly flare up with powerful eruptions despite the cold environment, so it is clear that “dirty snowballs” can lose their matter even far from the Sun.
The study based on these findings was published Wednesday (March 30) in the journal Science Advances.
If you’re looking for a telescope or binoculars for observing comets, check out our guide to the best deals on binoculars and telescopes.
Our guides to the best cameras for astrophotography and the best lenses for astrophotography also have tips on how to choose the best shooting equipment.
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