PDA

View Full Version : Phobos on a death spiral?!



Laguna
2004-Nov-12, 01:39 PM
This tiny moon is thought to be in a ‘death spiral’, slowly orbiting toward the surface of Mars. Here, Phobos was found to be about five kilometres ahead of its predicted orbital position. This could be an indication of an increased orbital speed associated with its secular acceleration, causing the moon to spiral in toward Mars.

Eventually Phobos could be torn apart by Martian gravity and become a short-lived ring around Mars, or even impact on the surface. This orbit will be studied in more detail over the lifetime of the Mars Express.
From:
http://www.esa.int/SPECIALS/Mars_Express/SEM21TVJD1E_0.html

pghnative
2004-Nov-12, 01:46 PM
FYI,

The is being discussed here (see Nov 11th postings) (http://www.badastronomy.com/phpBB/viewtopic.php?p=363856#363856).

Tom Mazanec
2004-Nov-12, 07:42 PM
When will Phobos crash/break up (whichever happens first)?
And how about Triton, BTW (which is also in a death spiral)?

Kullat Nunu
2004-Nov-12, 07:51 PM
When will Phobos crash/break up (whichever happens first)?

In about 50 million years according to The Nine Planets (http://www.nineplanets.org/).


And how about Triton, BTW (which is also in a death spiral)?

It'll take billions of years.

AK
2004-Nov-13, 10:17 AM
It'll take billions of years.

Are you sure? I remember reading somewhere that Triton could break up into a ring in as little as 100 million years.

Tom Mazanec
2004-Nov-13, 05:35 PM
I have read both estimates. Wikipedia says 100 million, if that means anything.

Crimson
2004-Nov-13, 09:08 PM
According to the chapter on the Martian moons in Ken Croswell's book Magnificent Mars (http://KenCroswell.com/magnificentmars.html), Phobos' orbital decay was discovered in 1945. Also:

"Phobos hasn't long to live. Modern observations indicate that its distance from the red planet shrinks 1 to 2 inches a year--not because of atmospheric friction but because Mars and Phobos exert tidal forces on each other. Unless human beings intervene to save the moon, it will smash into the Martian surface within 40 million years. How many other Martian moons have already met the same fate? Deimos is safe, however, because it's farther away. Indeed, theory suggests that Deimos is slowly receding from Mars, although this has not yet been observed."
--Magnificent Mars by Ken Croswell, page 183.

Evan
2004-Nov-13, 11:27 PM
Unless human beings intervene to save the moon, it will smash into the Martian surface within 40 million years

SAVE PHOBOS! SAVE PHOBOS! SAVE PHOBOS! Lets march on the UNITED NATIONS and DEMAND ACTION.

Uh, now, where was I?

Makgraf
2004-Nov-13, 11:50 PM
It'll take billions of years.

Are you sure? I remember reading somewhere that Triton could break up into a ring in as little as 100 million years.
That's a great line, I have to put it on the 'understatement thread' :)

Spacewriter
2004-Nov-14, 01:51 AM
Well, in terms of the evolution of the solar system, that's a pretty short time scale.

;)

Makgraf
2004-Nov-14, 02:37 AM
Oh yeah, but to (at least this) layman's ears still sounds pretty funny :)

Like how Isaac Asimov described the small number of atoms of a certain isotype by saying there were "only a trillion" (From the eponymous Only a Trillion).

Edit: Fixed italitics

George
2004-Nov-14, 08:53 PM
Unless human beings intervene to save the moon, it will smash into the Martian surface within 40 million years

SAVE PHOBOS! SAVE PHOBOS! SAVE PHOBOS! Lets march on the UNITED NATIONS and DEMAND ACTION.
I think it might be too late to "turn the tide". :wink:

Evan
2004-Nov-15, 02:53 AM
Oh well, I will have to find another cause to support, DANG...

SSJPabs
2004-Nov-15, 11:49 PM
When will Phobos crash/break up (whichever happens first)?

In about 50 million years according to The Nine Planets (http://www.nineplanets.org/).


And how about Triton, BTW (which is also in a death spiral)?

It'll take billions of years.This always struck me as interesting
There is no completely satisfactory theory as to how Deimos and Phobos came to be in orbit around Mars Really? Hmm.

Anyhow if Phobos is death spiraling, maybe we could hollow it out and make it a colony ship like in Marathon :roll:

Salamandaa
2004-Nov-17, 09:09 AM
But then we'd need to make cyborgs to keep it safe from aliens and crazy A.I.s.

Kullat Nunu
2004-Nov-17, 09:19 AM
There is no completely satisfactory theory as to how Deimos and Phobos came to be in orbit around Mars Really? Hmm.

Yes, it is not known how the moons could have ended up such regular (circular and not inclined) orbits, if they are captured asteroids. Secondly, Mars couldn't capture asteroids unless its atmosphere was much more massive in the past. Still their composition resemble C-type (carbonaceous) asteroids. Instead being captured objects, they may be remains of a larger, shattered moon.

Tom Mazanec
2004-Nov-17, 12:28 PM
If Mars' atmosphere was so thick that it slowed a passing asteroid that much, the asteroid would pass through the atmosphere at the "trajectory correction" point again and crash.
BTW, I actually read someone suggest dismantling Phobos into spaceships and such, since it was "doomed anyway"!

tjm220
2004-Nov-17, 10:28 PM
I read this on the BBC science/nature (http://news.bbc.co.uk/2/hi/science/nature/4004001.stm) site this morning:


But some scientists say there is evidence that Phobos and Deimos are by-products of the break-up of a huge moon that once circled Mars.

I hadn't heard about this theory before, how likely is this?

Toutatis
2004-Nov-17, 11:55 PM
Owing to tidal friction the orbit[s] of satellite[s] of any body will, time permitting, either: (1) Egress and eventually allow escape or (2) decay with ultimate union (i.e. collision) of satellite and 'master' object --- Direction (i.e. egression/decay) - all other factors being equal - dependant upon initial (harmonic) mean distance -- I apologize that I ignore the formulae descriptive of said process... http://www.badastronomy.com/phpBB/images/smiles/icon_redface.gif

Oh! Yea! FYI Luna (Earth's moon) is 'wandering' away -- but *EVER SO SLOWLY* --- Loss of our 'outrigger' will indeed be problematic but compares rather favorably with a 385,000 km (Dia) / 11.3 kmps impactor!!! Of course its 'escape' may, through torturous and convoluted modes, place said object in a 'colliding orbit'... But hey! - Should management of mere physical 'difficulties' remain an issue at such length (billions of years) we won't have 'made the trip' anyway :D

BTW if anyone 'has' the math -- or knows of a link to same -- *please* post it --- I'm feeling a bit like the 'village idiot'! :,(

Best
Sarandon