BDanielMayfield wrote:Mercury is toast for sure. But with its elliptical orbit it should put on an interesting show for a relatively short while as it skims the Sun's surface at periastron. Perhaps it will briefly "plunge" beneath the Sun's photosphere several times only to re-emerge on the outward part of its orbit. But it's doomed, as its orbit decays and the Sun swells.
By my calculations when the Sun's corona reaches out to Mercury
it will start to intercept about 50 x 1016 kg of material per 88 day orbit.
Since the mass of Mercury is only 33,000,000 x 1016 kg
it should begin to rapidly dissipate kinetic energy over a period of ~660,000 orbits or ~160,000 years.
Note, however, that Mercury will transition into a circular orbit long before it reaches the chromosphere or photosphere.
Point well made, and accepted. So, no periastron plunges for Mercury. Darn. It seemed like that would have been quite impressive.
BDanielMayfield wrote:
Mercury will come to have a liquid metallic surface, and thus its name will be even more fitting near its end.
It may not. The outer part of a red giant is remarkably tenuous and cool. That combination means that planets may orbit inside the expanded Sun for thousands of years without melting. Of course, it may be a lot rougher ride for Mercury than for Earth or Mars.
The sub-solar point on Mercury is already 700 K
... about half the lava temperature of ~1400 K
The Sun only has to become about 16 times as luminous to turn the sub-solar point on Mercury to ~1400 K lava.
I wonder where the point will be on the Sun's evolutionary tract where Mercury is just skimming the photosphere? At that point the surface of the poor planet would have to have reached the same temp as the photosphere, wouldn't it?
Re: APOD Retrospective: December 11
Posted: Thu Dec 14, 2017 3:08 pm
by Chris Peterson
BDanielMayfield wrote:I wonder where the point will be on the Sun's evolutionary tract where Mercury is just skimming the photosphere? At that point the surface of the poor planet would have to have reached the same temp as the photosphere, wouldn't it?
Again, not necessarily. The ISS flies through the upper atmosphere of Earth, which is at a temperature of 1000°C or more. Does the surface of the ISS reach that temperature? Luckily not! What Mercury is going to encounter as the Sun swells to a red giant is a tenuous atmosphere and a complicated radiative and convective environment. Not something easily analyzed, I think, so I'd be cautious making any assumptions.
Re: APOD Retrospective: December 11
Posted: Thu Dec 14, 2017 3:21 pm
by neufer
BDanielMayfield wrote:
I wonder where the point will be on the Sun's evolutionary tract where Mercury is just skimming the photosphere?
At that point the surface of the poor planet would have to have reached the same temp as the photosphere, wouldn't it?
If Mercury were somehow to retain its (periastron) distance of 46 million kilometers = 66 Solar radii
the Sun would cool have to around 3600 K with a luminosity of ~660 [= 662 x (3600 K / 5772 K)4 ].
At such a time the sub-Solar point of a then tidally locked Mercury
would only see the Sun and would, indeed, have to share its 3600 K temperature.
However, this scenario total ignores the tremendous frictional forces
and thermal heating of the mercurial meteor.
Re: APOD Retrospective: December 11
Posted: Fri Dec 15, 2017 9:03 am
by BDanielMayfield
neufer wrote:
BDanielMayfield wrote:
I wonder where the point will be on the Sun's evolutionary tract where Mercury is just skimming the photosphere?
At that point the surface of the poor planet would have to have reached the same temp as the photosphere, wouldn't it?
If Mercury were somehow to retain its (periastron) distance of 46 million kilometers = 66 Solar radii
the Sun would cool have to around 3600 K with a luminosity of ~660 [= 662 x (3600 K / 5772 K)4 ].
At such a time the sub-Solar point of a then tidally locked Mercury
would only see the Sun and would, indeed, have to share its 3600 K temperature.
However, this scenario total ignores the tremendous frictional forces
and thermal heating of the mercurial meteor.
Ah yes. Fleet footed Mercury's forward hemisphere would have to be heated, and the planet's orbit would shrink as it rips through the Sun's transparent outer atmosphere. Chris, I understand your point here;
Chris Peterson wrote:
BDanielMayfield wrote:I wonder where the point will be on the Sun's evolutionary tract where Mercury is just skimming the photosphere? At that point the surface of the poor planet would have to have reached the same temp as the photosphere, wouldn't it?
Again, not necessarily. The ISS flies through the upper atmosphere of Earth, which is at a temperature of 1000°C or more. Does the surface of the ISS reach that temperature? Luckily not! What Mercury is going to encounter as the Sun swells to a red giant is a tenuous atmosphere and a complicated radiative and convective environment. Not something easily analyzed, I think, so I'd be cautious making any assumptions.
but still I don't think that this assumption:
MarkBour wrote:I suppose Mercury would become an "ocean planet" at the last.
is all that far fetched. The question I think would be, will then tidally locked Mercury's magma ocean grow to encompass the entire planet before it sinks below the Sun's photosphere? Due to Chris's point I would think that perhaps it wouldn't, and Mercury may likely come to have a continental sized landmass centered somewhere in its anti-sunward trailing quadrant.
Bruce
Re: APOD Retrospective: December 11
Posted: Fri Dec 15, 2017 3:08 pm
by Chris Peterson
BDanielMayfield wrote:but still I don't think that this assumption:
MarkBour wrote:I suppose Mercury would become an "ocean planet" at the last.
is all that far fetched.
It's certainly not an unreasonable assumption. Just as long as we don't forget that it is still an assumption until somebody provides a more rigorous analysis. Sometimes we get caught off guard by things. I know how surprised I was when I first came to understand that planets could orbit, unmelted, in stable orbits, for a long time inside a red giant. That was entirely counter to my intuition at the time.
Re: APOD Retrospective: December 11
Posted: Fri Dec 15, 2017 9:02 pm
by MarkBour
Chris Peterson wrote:
BDanielMayfield wrote:
neufer wrote:
... At such a time the sub-Solar point of a then tidally locked Mercury would only see the Sun and would, indeed, have to share its 3600 K temperature.
... However, this scenario total ignores the tremendous frictional forces and thermal heating of the mercurial meteor.
... tidally locked Mercury's magma ocean ...
Bruce
It's certainly not an unreasonable assumption. Just as long as we don't forget that it is still an assumption until somebody provides a more rigorous analysis. Sometimes we get caught off guard by things. I know how surprised I was when I first came to understand that planets could orbit, unmelted, in stable orbits, for a long time inside a red giant. That was entirely counter to my intuition at the time.
A fascinating discussion. Perhaps exoplanet research will give us some answers in the form of an example. I do see in good old Wikipedia that Kepler 70 (https://en.wikipedia.org/wiki/Kepler-70) is an interesting star, apparently it passed through a red giant phase, and is settling into a subdwarf B stage, now having 0.496 M☉ . It has a planet that is orbiting very close to the star (Kepler 70b -- https://en.wikipedia.org/wiki/Kepler-70) and is the hottest planet yet discovered, and is thought to have a composition much like the Earth (and current mass is about 0.440 M⊕). I assume it is quite molten, but it seems to be able to exist in that state. I think astronomers do not expect it had a history such as we're discussing for Earth/Venus/Mercury, but it still may be instructive to us as we observe it.
Re: APOD Retrospective: December 11
Posted: Fri Dec 15, 2017 9:08 pm
by MarkBour
neufer wrote:
... However, this scenario total ignores the tremendous frictional forces
and thermal heating of the mercurial meteor.
Re: APOD: Mercury Visualized from MESSENGER (2017 Dec 11)
Posted: Sun Oct 21, 2018 4:37 am
by Confused
MarkBour wrote: ↑Mon Dec 11, 2017 10:44 pm
I can recall being surprised that instrumental music was included on a JPL or a NASA video once or twice, but I think it is pretty common to do so now, particularly when one is just "looking at landscape", so I no longer think about it.
Yes it is becoming so common to always have music playing that some people are going to think that there must be something wrong if there is no music. People are playing music automatically, without thinking, just because it is the way to do things; at least people are being told that implicitly. Stores and restaurants and many other businesses think that music is a requirement.
I think it is reasonable and probably necessary for some people to make it clear that it is not really necessary to add music.
Re: APOD: Mercury Visualized from MESSENGER (2017 Dec 11)
MarkBour wrote: ↑Mon Dec 11, 2017 10:44 pm
I can recall being surprised that instrumental music was included on a JPL or a NASA video once or twice, but I think it is pretty common to do so now, particularly when one is just "looking at landscape", so I no longer think about it.
Yes it is becoming so common to always have music playing that some people are going to think that there must be something wrong if there is no music. People are playing music automatically, without thinking, just because it is the way to do things; at least people are being told that implicitly. Stores and restaurants and many other businesses think that music is a requirement.
I think it is reasonable and probably necessary for some people to make it clear that it is not really necessary to add music.
<<Musica universalis (literally universal music), also called Music of the spheres or Harmony of the Spheres, is an ancient philosophical concept that regards proportions in the movements of celestial bodies—the Sun, Moon, and planets—as a form of musica (the Medieval Latin term for music). This "music" is not usually thought to be literally audible, but a harmonic, mathematical or religious concept. The idea continued to appeal to thinkers about music until the end of the Renaissance, influencing scholars of many kinds, including humanists. Further scientific exploration has determined specific proportions in some orbital motion, described as orbital resonance.
In a theory known as the Harmony of the Spheres, Pythagoras proposed that the Sun, Moon and planets all emit their own unique hum based on their orbital revolution, and that the quality of life on Earth reflects the tenor of celestial sounds which are physically imperceptible to the human ear. Aristotle criticised the notion that celestial bodies make a sound in moving in the context of his own cosmological model.
According to Max Heindel's Rosicrucian writings, the heavenly "music of the spheres" is heard in the Region of Concrete Thought, the lower region of the mental plane, which is an ocean of harmony.>>
Re: APOD: Mercury Visualized from MESSENGER (2017 Dec 11)
Fascinating example, Art. (Narrated by Michel Nabti, with the Computer Music Group at Princeton.)
I have always benefited much from visualizations to help appreciate data. Very little have I paid attention to the art of sonification, but some inventive examples like this one are indeed very helpful.
