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View Full Version : Could this happen? (Changing Mercury)



Sergio Silva
2013-Nov-05, 11:46 AM
I'm assuming some issues that i don't have complete certain. First, Mercury by the influence of solar wind is losing mass. I say that because the discovery of some hollows that were found by Messenger Mission. The better hypothesis is that holes were formed recently by volatile materials from comets or asteroids that crashed in the planet. The hollows are new features in surface of the planet, so, because Mercury is so massive in relation of his size, this phenomena could be only explained by falling of other celestial bodies. Solar wind eroded this new materials creating the holes. Another assumption is that Mercury is so massive because long ago his most volatile materials were volatilized by the same solar wind. Another aspect to consider is that the orbit of Mercury is the most eccentric of the 8 planets of solar system. So, if the Mercury is progressively loosing mass, his orbit will be falling gradually in direction of the Sun. The velocity is the same but the mass is less, than, only falling and gaining speed again, will put him in new stable orbit. I must say that all this writing is a "shooting in the dark" and could be refuted. For instance, the creation of the hollows could have another origin. The expanding and contraction of the planet might explain the holes, but, i must say, by the shape of this features, this explanation is somehow strange. Another situation is the rate of impacts. Assuming that the proximity of the sun and orbit speed of the planet will increase the impact rate, this planet could not loose mass at all.
So the question is, Mercury is losing mass and in this process is changing his orbit?

Noclevername
2013-Nov-05, 02:00 PM
Since it, like most planets, receives millions of tons of micrometeorites every (Earth) year, it seems more probable IMO that it is gaining mass.

CaptainToonces
2013-Nov-06, 08:53 AM
I'll wager it experiences a net loss of mass when it's more massive, and a net gain of mass when it gets smaller.

Due to the fact it exists.

galacsi
2013-Nov-06, 10:00 AM
The hollows formation don't prove the planet loses mass in space. The contains of these hollows could be distributed on the whole planet. Dust just near them and volatiles ,if they exists , trapped as ices at the poles.

Does this process changes the planet's orbit ? Only in very microscopic ways , completely impossible to measure.

Sergio Silva
2013-Nov-06, 10:15 AM
What i want to know is how you know this. Do you have sources of information that i don't have? About orbit changes, of course i'm thinking in space time scale.

Van Rijn
2013-Nov-06, 10:19 AM
So the question is, Mercury is losing mass and in this process is changing his orbit?

While the sun is on the main sequence (billions of years) there should be no significant change in Mercury's mass, and so that process couldn't affect its orbit. Most of Mercury's volatiles were lost billions of years ago, and even then, it wouldn't have been all that large a fraction of Mercury's mass. And as Noclevername points out, Mercury is gaining mass as well. There would be a net gain, but the amount is negligible.

On the other hand, over billions of years, while on the main sequence, the sun loses a little mass (lost in the mass converted to light, and the solar wind). That should have a small effect on Mercury's orbit. Unfortunately for Mercury, that won't be enough to save it after the sun goes off the main sequence and expands. It's expected that the sun will eventually* expand enough to vaporize Mercury (and Venus, and probably Earth as well).

*this would be five or six billion years from now, so nothing for us to worry about.

Jeff Root
2013-Nov-06, 05:56 PM
I'll wager it experiences a net loss of mass when it's more
massive, and a net gain of mass when it gets smaller.

Due to the fact it exists.
I'm trying to make that make sense, and can't. It appears
to be exactly backwards. If impacting matter or radiation
cause a body to lose mass, that would be a less-massive
body which doesn't have enough gravity to hold on to stuff
that is blown off of it. If impacting matter or radiation
cause a body to gain mass, that would be a more-massive
body which has enough gravity to pull back the stuff that
is blown off of it, and prevent it from escaping. So small
bodies get smaller and large bodies get larger.

A different interpretation of what you said is also backward.
If the matter impacting or thrown off by Mercury is more
massive, it will not have enough speed to escape Mercury's
gravity. If the matter impacting or thrown off by Mercury is
sufficiently low mass, then it may have enough speed to
escape Mercury's gravity. And that's what actually happens.
Lightweight atoms are blown away by solar wind, while
heavier dust particles fall back to the surface.

-- Jeff, in Minneapolis

chornedsnorkack
2013-Nov-06, 09:03 PM
How about Moon?
There are 2 issues.
Mass and orbit.
1) The mass of Moon.
If a meteor of, say, 1 tons hits Moon at a speed of 30 km/s, it explodes with the power of 100 t TNT.
If the explosion moves 100 000 tons of moon (moon is not earth, therefore there is no earth on moon, therefore the explosion cannot move any earth on moon) then most of it is moved only a few metres, from the crater bottom to the crater rampart.
But if 90 000 tons of moon are piled up into the crater rampart, and of the 10 000 tons thrown beyond the rampart, 9990 tons fall back into ejecta sheets and crater chains on Moon, then 10 tons still fly out of moon at speeds from 2,4 to 30 km/s. And since 1 ton meteor fell on Moon, 10 tons of moon were thrown away, Moon is 9 tons lighter.

Does anyone have actual estimates for the effect of craters that actually form on Moon? Is Moon gaining more mass by falling meteors, or losing more by moon thrown from craters past escape speed?
And how does that same comparison go for Mercury?
2) Orbit.
Are meteors giving angular momentum to Mercury, or taking it away?
If meteors come from asteroid belt then they orbit in the same direction as Mercury. Since they are near their perihelion, they are faster than Mercury. Thus they give angular momentum to Mercury and cause it to spiral out.
But if the meteors that hit Mercury are comets then they come at all inclinations - prograde as well as retrograde. They therefore are not conferring momentum on Mercury, and if they are giving mass then they are slowing down Mercury. They therefore cause Mercury to spiral in.
So which is the case? If asteroids and comets both collide with Mercury, what is the relative numbers of these, and are they on the net result causing Mercury to spiral out (if asteroids have most effect) or spiral in (if comets have most effect)?

CaptainToonces
2013-Nov-07, 07:59 AM
I'm trying to make that make sense, and can't. It appears
to be exactly backwards. If impacting matter or radiation
cause a body to lose mass, that would be a less-massive
body which doesn't have enough gravity to hold on to stuff
that is blown off of it. If impacting matter or radiation
cause a body to gain mass, that would be a more-massive
body which has enough gravity to pull back the stuff that
is blown off of it, and prevent it from escaping. So small
bodies get smaller and large bodies get larger.

A different interpretation of what you said is also backward.
If the matter impacting or thrown off by Mercury is more
massive, it will not have enough speed to escape Mercury's
gravity. If the matter impacting or thrown off by Mercury is
sufficiently low mass, then it may have enough speed to
escape Mercury's gravity. And that's what actually happens.
Lightweight atoms are blown away by solar wind, while
heavier dust particles fall back to the surface.


What I said isn't that complicated, Jeff. If Mercury was losing mass at a significant rate, and there was no counter force causing it to gain mass, then it would have evaporated away a long time ago. How long has Mercury been in its current orbit? If it's in the billions of years, can we not assume that its mass experiences a state of equilibrium in which when it gets larger the process causing it to enlarge slows and when it gets smaller the process causing it to shrink slows?

Noclevername
2013-Nov-07, 08:07 AM
What I said isn't that complicated, Jeff. If Mercury was losing mass at a significant rate, and there was no counter force causing it to gain mass, then it would have evaporated away a long time ago. How long has Mercury been in its current orbit? If it's in the billions of years, can we not assume that its mass experiences a state of equilibrium in which when it gets larger the process causing it to enlarge slows and when it gets smaller the process causing it to shrink slows?

We don't know exactly how long Mercury has been in its current orbit, or if minor perturbations have occurred. The amount of mass change caused by addition and subtraction in the last billion years is probably very small compared to the overall mass of the planet.

Jeff Root
2013-Nov-07, 02:02 PM
What I said isn't that complicated, Jeff. If Mercury was
losing mass at a significant rate, and there was no counter
force causing it to gain mass, then it would have evaporated
away a long time ago.
As Noclevername suggested, there are no forces causing
Mercury to either gain or lose mass at a significant rate.
When the Sun was young it had a far stronger solar wind,
which blew away Mercury's atmosphere. That atmosphere
was likely very extensive. Over the last four billion years,
though, Mercury has probably been gaining mass very, very
very slowly (compared to its overall mass) due to meteor
hits, the same as Earth.

A body much smaller than Mercury would instead generally
lose mass due to meteor hits.



How long has Mercury been in its current orbit? If it's in
the billions of years, can we not assume that its mass
experiences a state of equilibrium in which when it gets
larger the process causing it to enlarge slows and when
it gets smaller the process causing it to shrink slows?
No No No No No No No No No! Absolutely the opposite.
The larger the planet, the more tightly it holds on to its
mass, and the faster it adds more mass. Small asteroids
don't have strong enough gravity to hold on to the debris
from high-speed collisions, so they generally lose mass
over time.

-- Jeff, in Minneapolis

CaptainToonces
2013-Nov-08, 12:42 AM
Absolutely the opposite.
The larger the planet, the more tightly it holds on to its
mass, and the faster it adds more mass. Small asteroids
don't have strong enough gravity to hold on to the debris
from high-speed collisions, so they generally lose mass
over time.

Well then, perhaps Mercury is destined to become a hot jupiter rather than remaining as it is now.

Noclevername
2013-Nov-08, 12:49 AM
Well then, perhaps Mercury is destined to become a hot jupiter rather than remaining as it is now.

Not unless real Jupiter crashes into it! As said above, the amount of mass change in the current era is miniscule.