The Enduring Mysteries of the Outer Solar System
The farthest reaches of our solar system remain the most mysterious areas around the sun. Solving the mysteries of the outer solar system could shed light on how the whole thing emerged — as well as how life on Earth was born.
For instance, the Kuiper belt past Neptune is currently the suspected home of comets that only take a few decades or at most centuries to complete their solar orbits — so-called "short-period comets." Surprisingly, Kuiper belt objects "show a wide range of colors — neutral or even slightly blue all the way to very red," said University of Hawaii astrophysicist David Jewitt.
The color of an object helps reveal details about its surface composition. It remains a mystery why Kuiper belt objects show a much wider range of color — and thus surface composition — than other planetoids, such as the asteroids.
What is ultra-red matter?
There appears to be a material dubbed "ultra-red matter" that exists only on about half of all Kuiper belt objects and their immediate progeny, known as centaurs — icy planetoids orbiting between Jupiter and Neptune that very recently escaped from the Kuiper belt.
This ultra-red matter does not exist in the inner solar system, "not even on the comets which come from the Kuiper belt. This suggests that the ultra-red matter is somehow unstable at the higher temperatures close to the sun," Jewitt explained.
Secrets in the Oort cloud?
A distant reservoir of trillions of comets known as the Oort cloud theoretically lies up to 100,000 astronomical units from the sun — an astronomical unit or AU being about 93 million miles (150 million kilometers). This means the Oort cloud is a fifth of the way to the nearest star, so far away that objects within it have never been seen directly, only inferred — but it must exist, given all the comets seen over the years.
The Oort cloud is the conjectured source of comets that require centuries or millennia to complete their long journeys around the sun. Since these "long-period comets" come from all directions, the Oort cloud is often thought to be spherical. However, while comets such as Halley's do not come from the Kuiper belt, their orbits also do not jibe with a spherical Oort cloud, Jewitt explained. This suggests there may be an "inner Oort cloud" shaped kind of like a doughnut.
Astrophysicists think the Oort cloud is a remnant of the protoplanetary disk that formed around the sun roughly 4.6 billion years ago. Learning more about the Oort cloud could shed light on how our solar system — and Earth — were born, Jewitt said.
Are there more dwarf planets?
So far, three dwarf planets are recognized — Ceres, Pluto and Eris. The Kuiper belt, which lies about 50 AU from the sun, could hold some 200 more. Beyond that there could be scores of dwarf-planet-sized bodies beyond roughly 100 AU from the sun "that nobody had seen before due to their faintness and slow motion," said astronomer Chad Trujillo at Gemini Observatory in Hawaii. "Even a body as big as Mars could be missed in our current surveys if it were moved beyond a couple hundred AU."
Trujillo noted projects such as Pan-STARRS (Panoramic Survey Telescope And Rapid Response System) and the LSST (Large Synoptic Survey Telescope) "should fill this gap in our knowledge in the coming decade."
Kemo D. (a.k.a. no.7)