What if Earth had a small close satellite?

Earth now has just 1 satellite. Moon.

Yet Mars has 2. Jupiter, Saturn and Uranus each have many.

If Earth had an asteroid-type satellite, what would happen next?

Its orbit would be perturbed, among other things, by Sun, Moon,
Earth's oblacy, Earth's relief and the tidal wave it raises on Earth.

We know that perturbations by Sun do not rule out existence of
satellites for many planets, and perturbations by quite large
satellites do not rule out existence of others.

What orbits could a natural satellite of Earth naturally have,
assuming that Moon has orbit as in OTL?

Mars has a satellite whose orbital period is less than 8 hours.

What would happen if a satellite of Earth crossed the Roche limit?

If it is weak, it could break immediately into a ring. But when the
fragments of the satellite spread out along the orbit, the tidal force
on them would vanish and tidal braking would stop. What would the ring
do next?

If it is strong and small, it would first break into a few large
pieces. These would then orbit for some time on closeby orbits and
undergo collisions at sloew speed. What else can be said about this
process?

Small and strong satellites might ultimately reach atmosphere. If a
large hard rock moves in upper atmosphere at 8 km/s, what are the
effects on ground? What will happen with the smoke in atmosphere? It
is likely that the orbit may be close to equator.

If a large body eventually reaches ground, its speed cannot be over 8
km/s, but probably nor can it be much less. What will the explosion be
like? Will it produce distinctive results that cannot happen if a body
hits Earth on hyperbolic orbit? Will the results be distinctive even
if the final splashdown is in an ocean?

At which geological - or historical - times could the Earth have had
rings or satellites without us knowing about it now?

Wasn't it Jaak Suurpere who wrote:

If it is weak, it could break immediately into a ring. But when the
fragments of the satellite spread out along the orbit, the tidal force
on them would vanish and tidal braking would stop. What would the ring
do next?

The tidal force on the fragments is unchanged by the break up of the
object. If the fragments are weak, they continue to break up.

The tidal forces of the ring particles on the Earth effectively vanish
(because the pulls from fragments in different parts of the ring are in
different directions), so there's no longer any tidal braking. Tidal
braking would have previously applied a force on the object tending to
cause it to move away from the Earth.

(You did mean "tidal braking", not "tidal breaking" didn't you?)

--
Mike Williams
Gentleman of Leisure

Jaak Suurpere wrote:

Earth now has just 1 satellite. Moon.

Yet many of the simulations of the Moon-forming impact result in
two moons, of which only one sticks around for long (which hints at
what the long-term outcome might be).

We know that perturbations by Sun do not rule out existence of
satellites for many planets,...

Although I should add there's a very good reason (solar
perturbations) that Mercury & Venus do not have moons. It doesn't
(yet) apply to Earth, but it could for a different solar system

What orbits could a natural satellite of Earth naturally have,
assuming that Moon has orbit as in OTL?

The basic tidal evolution is simple, for a moon in a circular
orbit. If it is below synchronous orbit, tidal effect will collapse
the moons orbit, ending up with the moon spiraling inside the Roche
limit (or even impacting the surface intact - the fate of Phobos).
Outside sychronous orbit, tidal interactions slow the planet's
rotation, expand the moons orbit, until either the system enters tidal
lock (as with Pluto-Charon) or the moon escapes (as would likely
happen with our own Moon, given enough time). Finally, if the moon is
in a retrograde orbit, it will spin down the planet, collapse the
moons orbit, resulting in the moon again entering the Roche limit or
impacting the hapeless planet below (a'la Triton).
As to the effect of the Moon on this system, moons (for reasons I
honestly don't understand fully) can become locked in stable
mean-motion resonances. If, for instance, you had a small moonlet in a
closer orbit (but outside synchronous),it would expand its orbit,
until it entered into a 2:1 resonance (or, perhaps, 3:1? Not sure)
with the Moon, at which point it would (I *suspect*!) become locked
into resonance.

What would the ring do next?

Sit there, for a long period of time. Charging by radiation, and
interactions with the Earth's B-field, might lead to some interesting
"spokes". The inclined Moon orbit might be *very* interesting, perhaps
warping the rings, but here again there could be some funny resonance
issues (not gaps; gaps too are resonant issues, but I'm thinking
beyond that).

[fragments] would then orbit for some time on closeby orbits and
undergo collisions at slow speed. What else can be said about this
process?

Define "slow". The relative speed for two objects formed from tidal
disruption of a single parent would not be "slow enough".

At which geological - or historical - times could the Earth have had
rings or satellites without us knowing about it now?

Geologically-speaking, it could have - but it's very very unlikely
within the last 3 billion years or so.

--
Brian Davis

Brian Davis wrote:

Sit there, for a long period of time. Charging by radiation, and
interactions with the Earth's B-field, might lead to some interesting
"spokes". The inclined Moon orbit might be *very* interesting, perhaps
warping the rings, but here again there could be some funny resonance
issues (not gaps; gaps too are resonant issues, but I'm thinking
beyond that).

Isn't it pretty well accepted that for long-term stability ring systems
require shepherding satellites? The creation of an Earth ring by the
tidal disruption of a satellite, it seems to me, would dissipate on
pretty short astronomical timescales, especially what with the Moon out
there. It would start as a ring arc, then become a ring with a lump in
it, then a defuse ring, then just debris contaminating Earth orbit.

--
Erik Max Francis && && http://www.alcyone.com/max/
__ San Jose, CA, USA && 37 20 N 121 53 W && &tSftDotIotE
/ \ It's a man's world, and you men can have it.
\__/ Katherine Anne Porter

Erik Max Francis wrote:

Isn't it pretty well accepted that for long-term stability
ring systems require shepherding satellites?

Hmm... AFAIK, sheperding satellites are really nice to maintain
sharp edges on rings, but not needed absolutely to *have* rings. You
also have a great source of such sheperding satellites - the tidal
breakup itself. Some chunks would be larger than others.
Even maintaining the sharp edge to the rings does not require
sheperds - look at Saturn. the outer edge of the ring system is right
at the 2:3 resonance with Mimas (Cassini's division being at the 1:2
resonance).

The creation of an Earth ring by the tidal disruption of a
satellite, it seems to me, would dissipate on pretty short
astronomical timescales, especially what with the Moon out
there.

As usual, you hit it on the head. I would suspect such a riung
would be stable for at least 10 Ma or so, but I've got no calculation
to back it up as yet. Could Earth maintain a Saturn-class ring system
for a few billion years? No - but I'm not at all sure where to draw
the line in the lifetime issue. Let's face it, *only* Saturn's rings
appear stable for billions of years. Jupiter, Uranus, Neptune - all
present evidence that they are in a state of evolution, and not stable
over billion of years.

--
Brian Davis

On 8 Oct 2003 20:33:15 -0700, (Brian Davis) wrote:

As usual, you hit it on the head. I would suspect such a riung
would be stable for at least 10 Ma or so, but I've got no calculation
to back it up as yet. Could Earth maintain a Saturn-class ring system
for a few billion years? No - but I'm not at all sure where to draw
the line in the lifetime issue. Let's face it, *only* Saturn's rings
appear stable for billions of years.

I was given to understand Saturn's rings will only persist for ~100 Ma
or so?

--
"Sore wa himitsu desu."
To reply by email, remove
the small snack from address.
http://www.esatclear.ie/~rwallace

(Jaak Suurpere) wrote in message . com...
Earth now has just 1 satellite. Moon.

Yet Mars has 2. Jupiter, Saturn and Uranus each have many.

If Earth had an asteroid-type satellite, what would happen next?

Its orbit would be perturbed, among other things, by Sun, Moon,
Earth's oblacy, Earth's relief and the tidal wave it raises on Earth.

We know that perturbations by Sun do not rule out existence of
satellites for many planets, and perturbations by quite large
satellites do not rule out existence of others.

What orbits could a natural satellite of Earth naturally have,
assuming that Moon has orbit as in OTL?

Mars has a satellite whose orbital period is less than 8 hours.

What would happen if a satellite of Earth crossed the Roche limit?

If it is weak, it could break immediately into a ring. But when the
fragments of the satellite spread out along the orbit, the tidal force
on them would vanish and tidal braking would stop. What would the ring
do next?

If it is strong and small, it would first break into a few large
pieces. These would then orbit for some time on closeby orbits and
undergo collisions at sloew speed. What else can be said about this
process?

Small and strong satellites might ultimately reach atmosphere. If a
large hard rock moves in upper atmosphere at 8 km/s, what are the
effects on ground? What will happen with the smoke in atmosphere? It
is likely that the orbit may be close to equator.

If a large body eventually reaches ground, its speed cannot be over 8
km/s, but probably nor can it be much less. What will the explosion be
like? Will it produce distinctive results that cannot happen if a body
hits Earth on hyperbolic orbit? Will the results be distinctive even
if the final splashdown is in an ocean?

At which geological - or historical - times could the Earth have had
rings or satellites without us knowing about it now?


Depending on what you classify as "close", one word

Cruithne

http://www.google.com/search?sourcei...ent&q=Cruithne