Cosmology Views

Solar System 1km Debris

I doubt whether an object sized at 1km is called debris appropriately. However this 1km threshold occurs in various descriptions in our solar system.

This information is trivia to some but useful to those interested in the evolution of our solar system.

There are several types of asteroids and meteorites. There are multiple classification schemes so these objects are not consistent.
Some of the small moons around the planets are also in these types.

Wikipedia (source of excerpts) has a long description of the classifications for asteroids and meteorites.

There is just too much detail to include here (one comment: some are very dark, assumed to be covered by carbon but perhaps that is electrical scarring like the comets we have visited). This topic is about the distribution of this debris. Their origin is another topic.

Asteroid belt ...

Contrary to popular imagery, the asteroid belt is mostly empty. The asteroids are spread over such a large volume that it would be improbable to reach an asteroid without aiming carefully. Nonetheless, hundreds of thousands of asteroids are currently known, and the total number ranges in the millions or more, depending on the lower size cutoff. Over 200 asteroids are known to be larger than 100 km,and a survey in the infrared wavelengths has shown that the asteroid belt has between 700,000 and 1.7 million asteroids with a diameter of 1 km or more.

my comment: Many at 1km or larger.

Centaurs ...

Centaurs are small Solar System bodies with either a perihelion or a semi-major axis between those of the outer planets. They generally have unstable orbits because they cross or have crossed the orbits of one or more of the giant planets; almost all their orbits have dynamic lifetimes of only a few million years, but there is one Centaur, 514107 KaŹ»epaokaŹ»awela, which may be in a stable (though retrograde) is this a centaur if the Trojans aren't?] Centaurs typically behave with characteristics of both asteroids and comets. They are named after the mythological centaurs that were a mixture of horse and human. Observational bias toward large objects makes determination of the total Centaur population difficult. Estimates for the number of Centaurs in the Solar System more than 1 km in diameter range from as low as 44,000 to more than 10,000,000.

The first Centaur to be discovered, under the definition of the Jet Propulsion Laboratory and the one used here, was 944 Hidalgo in 1920. However, they were not recognized as a distinct population until the discovery of 2060 Chiron in 1977. The largest confirmed Centaur is 10199 Chariklo, which at 260 kilometers in diameter is as big as a mid-sized main-belt asteroid, and is known to have a system of rings. However, the lost Centaur 1995 SN55 may be somewhat larger. The transneptunian object 2018 VG18, which is a Centaur under the broader definition, may be quite a bit larger.

No Centaur has been photographed up close, although there is evidence that Saturn's moon Phoebe, imaged by the Cassini probe in 2004, may be a captured Centaur that originated in the Kuiper belt. In addition, the Hubble Space Telescope has gleaned some information about the surface features of 8405 Asbolus.

1 Ceres may have originated in the region of the outer planets, and if so might be considered an ex-Centaur, but the Centaurs seen today all originated elsewhere.

Of the objects known to occupy Centaur-like orbits, approximately 30 have been found to display comet-like dust comas, with three, 2060 Chiron, 60558 Echeclus, and 29P/Schwassmann-Wachmann 1, having detectable levels of volatile production in orbits entirely beyond Jupiter. Chiron and Echeclus are therefore classified as both asteroids and comets, while Schwassmann-Wachmann 1 has always held a comet designation. Other Centaurs, such as 52872 Okyrhoe, are suspected of having shown comas. Any Centaur that is perturbed close enough to the Sun is expected to become a comet.

my comment:
Interesting admission here: these asteroids can be 'expected to become a comet.'
About 30 have comet-like comas.
The orbit lifetimes are in millions of years, not billions like our planets

2018 VG18 has an average diameter of 656 km. By comparison, Sedna (much further) is about 1000 km

my comment: There are many Centaurs.

Jupiter Trojans ...

. The total number of Jupiter trojans larger than 1 km in diameter is believed to be about 1 million, approximately equal to the number of asteroids larger than 1 km in the asteroid belt. Like main-belt asteroids, Jupiter trojans form families.

my comment:

A similar number of 1km objects is in the main asteroid belt as around Jupiter's belt of its asteroids.
This observation is a big surprise to me, as well as the total number.

Venus asteroids ...

Wikipedia topic:
"ist of Venus-crossing minor planets"

A Venus-crosser is an asteroid whose orbit crosses that of Venus. There are 2,809 Venus-crosser and 98 outer-grazers known. Mercury-crossers or grazers are [in the list also].

Venus also has a quasi-satellite, (524522) 2002 VE68. This asteroid is also a Mercury- and Earth-crosser; it seems to have been a "companion" to Venus for the last 7000 years or so only, and is destined to be ejected from this orbital arrangement about 500 years from now.
my comment:
I clicked on several of these Venus crossers and each was > 1km.

Notable EU-related excerpt:

 2002 VE68 exhibits resonant (or near-resonant) behavior with Mercury, Venus and Earth.It seems to have been co-orbital with Venus for only the last 7,000 years, and is destined to be ejected from this orbital arrangement about 500 years from now. During this time, its distance to Venus has been and will remain larger than about 0.2 AU.

my comment:
This object is assumed to be in its orbit for only 7000 years. This is within human history.

There many Venus asteroids.

Saturn's irregular satellites ...

The remaining 58 [satellites after the main 7], with mean diameters ranging from 4 to 213 km, are irregular satellites, whose orbits are much farther from Saturn, have high inclinations, and are mixed between prograde and retrograde. These moons are probably captured minor planets, or debris from the breakup of such bodies after they were captured, creating collisional families. The irregular satellites have been classified by their orbital characteristics.

Uranus's irregular moons ...

[Uranus] has 27 known moons, Uranus's moons are divided into three groups: thirteen inner moons, five major moons, and nine irregular moons. The inner moons are small dark bodies that share common properties and origins with Uranus's rings. The five major moons are ellipsoidal, indicating that they reached hydrostatic equilibrium at some point in their past (and may still be in equilibrium), and four of them show signs of internally driven processes such as canyon formation and volcanism on their surfaces.The orbits of the regular moons are nearly coplanar with Uranus's equator. Uranus's irregular moons have elliptical and strongly inclined (mostly retrograde) orbits at large distances from the planet.

Neptune's irregular moons ...

Neptune has 14 known moons. By far the largest of them is Triton; over a century passed before the discovery of the second natural satellite, Nereid. Neptune's outermost moon Neso orbits further from its planet than any other moon in the Solar System.

Triton is unique among moons of planetary mass in that its orbit is retrograde to Neptune's rotation and inclined relative to Neptune's equator, which suggests that it did not form in orbit around Neptune but was instead gravitationally captured by it. The capture of Triton, probably occurring some time after Neptune formed a satellite system, was a catastrophic event for Neptune's original satellites, disrupting their orbits so that they collided to form a rubble disc. Triton is massive enough to have achieved hydrostatic equilibrium and to retain a thin atmosphere capable of forming clouds and hazes.

Inward of Triton are seven small regular satellites, all of which have prograde orbits in planes that lie close to Neptune's equatorial plane; some of these orbit among Neptune's rings. The largest of them is Proteus. They were re-accreted from the rubble disc generated after Triton's capture after the Tritonian orbit became circular. Neptune also has six more outer irregular satellites other than Triton, including Nereid, whose orbits are much farther from Neptune and at high inclination: three of these have prograde orbits, while the remainder have retrograde orbits. In particular, Nereid has an unusually close and eccentric orbit for an irregular satellite, suggesting that it may have once been a regular satellite that was significantly perturbed to its current position when Triton was captured. The two outermost Neptunian irregular satellites, Psamathe and Neso, have the largest orbits of any natural satellites discovered in the Solar System to date.

my comment:
interesting explanations involving a 'catastrophic event' and 'a rubble disk' and orbits being perturbed.

Kuiper belt ...

Kuiper belt was named after Dutch-American astronomer Gerard Kuiper. In 1992, Albion was discovered, the first Kuiper belt object (KBO) since Pluto and Charon. Since its discovery, the number of known KBOs has increased to thousands, and more than 100,000 KBOs over 100 km (62 mi) in diameter are thought to exist. The Kuiper belt was initially thought to be the main repository for periodic comets, those with orbits lasting less than 200 years. Studies since the mid-1990s have shown that the belt is dynamically stable and that comets' true place of origin is the scattered disc, a dynamically active zone created by the outward motion of Neptune 4.5 billion years ago.

my comment:

There is a possible conflict: Neptune's outward motion created this 'active zone' but the comets take a path inward toward the planets and the very distant Sun.

The estimate for those > 100 km is substantial so the number > 1km is probably similar.
My conclusion:

I must confess being unaware of the magnitude of large debris in our solar system.

The quantities in this distribution are impressive but with a weak explanation.

This distribution cannot be from just a primordial disk of dust building to create so much debris.

My questions:
Where did the debris come from if not formed in place?

How many catastrophic events involving how many large bodies were required for this distribution of substantial debris?
What is the origin of the forces involved for such solid bodies in motion? This would be a true big bang!

This post can offer only interesting details but no credible explanation.


The following is not is not part of the original post:

My research included compiling the names, sizes,  and orbits of most moons and many asteroids to support future posts; that pdf is available here:

Solar System Data