Mercury's surprising core and landscape curiosities

Mar 21, 2012
Mercury's surprising core and landscape curiosities

(PhysOrg.com) -- On March 17, the tiny MESSENGER spacecraft completed its primary mission to orbit and observe the planet Mercury for one Earth-year. The bounty of surprises from the mission has completely altered our understanding of the solar system's innermost planet. As reported in one of two papers published today on Science Express, scientists have found that Mercury's core, already suspected to occupy a greater fraction of the planet's interior than do the cores of Earth, Venus, or Mars, is even larger than anticipated. The companion paper shows that the elevation ranges on Mercury are much smaller than on Mars or the Moon and documents evidence that there have been large-scale changes to Mercury's topography since the earliest phases of the planet's geological history.

The mission's many successes have allowed it to be extended for another year. "The first year of MESSENGER orbital observations has yielded a wonderful harvest of results," says MESSENGER Principal Investigator Sean Solomon, of the Carnegie Institution and a coauthor of the two papers. "From Mercury's extraordinarily dynamic magnetosphere and to the unexpectedly volatile-rich composition of its surface and interior, our inner planetary neighbor is now seen to be very different from what we imagined just a few years ago. The number and diversity of new findings being presented this week to the scientific community in these papers and in presentations at this week's Lunar and Planetary Science Conference provide a striking measure of how much we have learned to date."

This is the planet Mercury, as taken from the spacecraft MESSENGER. Credit: UCSB

A Surprising Core

MESSENGER's radio tracking has allowed the scientific team to develop the first precise model of Mercury's which, when combined with topographic data and the planet's , sheds light on the planet's internal structure, the thickness of its crust, the size and state of its core, and its tectonic and thermal history.

Mercury's core occupies a large fraction of the planet, about 85% of the planetary radius, even larger than previous estimates. Because of the planet's small size, at one time many scientists thought the interior should have cooled to the point that the core would be solid. However, subtle dynamical motions measured from Earth-based radar, combined with MESSENGER's newly measured parameters of the gravity field and the characteristics of Mercury's internal magnetic field that signify an active core dynamo, indicate that the planet's core is at least partially liquid.

Mercury's core is different from any other planetary core in the Solar System. Earth has a metallic, liquid outer core sitting above a solid inner core. Mercury appears to have a solid silicate crust and mantle overlying a solid, iron sulfide outer core layer, a deeper liquid core layer, and possibly a solid inner . These results have implications for how Mercury's magnetic field is generated and for understanding how the planet evolved thermally.

Landscape Curiosities

A planet's topography can reveal fundamental information about its internal structure and its geological and thermal evolution. Ranging observations from MESSENGER's Mercury Laser Altimeter (MLA) have provided the first-ever precise topographic model of the planet's northern hemisphere and characterized slopes and surface roughness over a range of spatial scales. From MESSENGER's eccentric, near-polar orbit, the MLA illuminates surface areas as wide as 15 to 100 meters (50 -325 feet), spaced about 400 meters apart (1,300 feet).

The spread in elevations is considerably smaller than those of Mars or the Moon. The most prominent feature is an extensive area of lowlands at high northern latitudes that hosts the volcanic northern plains. Within this lowland region is a broad topographic rise that formed after the volcanic plains were emplaced.

At mid-latitudes, the interior plains of the Caloris impact basin — 1,550 kilometers (960 miles) in diameter — have been modified so that part of the basin floor now stands higher than the rim. The elevated portion appears to be part of a quasi-linear rise that extends for approximately half the planetary circumference at mid-latitudes. These features imply that large-scale changes to Mercury's topography occurred after the era of impact basin formation and large-scale emplacement of volcanic plains had ended.

These and other latest findings from MESSENGER will be featured in 57 papers presented this week at the 43rd Lunar and Planetary Science Conference in The Woodlands, Texas.

Explore further: NASA team lays plans to observe new worlds

Provided by Carnegie Institution

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baudrunner
2.3 / 5 (8) Mar 21, 2012
Being so close to the sun means that it burns to be on Mercury. Mercury burns alright, but well beyond combustion and into outright elemental disruption from the intense radiation. Mercury might have 'evaporated' to its present volume from a much larger size over time. That still begs the question, "..why is it so spherical?". I haven't figured that one out yet.
Sonhouse
3.3 / 5 (4) Mar 21, 2012
Most likely because it is rotating so slowly and has such a dense core. It may have been a planet as large as Earth at one time with an atmosphere and all that then drifting so close to the sun, about 1/3 of our distance at 1 amu, means it gets about 10 times the energy from the sun as we do, Earth gets about 1300 watts per meter squared on top of the atmosphere so Mercury clocks in around and average of roughly 12,000 watts per meter squared. You would definitely get a sunburn there! If you had solar cells there that could take the heat, 100 square miles would have over 3 tW of power, at 30% efficiency, 1 tW of usable energy.
El_Nose
4.3 / 5 (3) Mar 21, 2012
we keep our atmosphere beacuse of our size and because of our relatively strong magnetosphere in relation to local solar wind strength ---
antialias_physorg
3 / 5 (5) Mar 21, 2012
I'm not sure the magnetosphere has much to do with it. There have been many north-south reversals (which would mean that there have been times in between where the magnetosphere has been next to non-existent) - yet we still do have an atmosphere.
kevinrtrs
1.4 / 5 (10) Mar 21, 2012
These results have implications for how Mercury's magnetic field is generated and for understanding how the planet evolved thermally.

It would have been very interesting if the researchers or the author of the article actually spelled out what the implications were. My take on it is that the normal dynamo theory will be shown to have taken a severe beating - as shown by some recent simulation attempts to explain why the magnetic field strength is so weak.
It will also take a very superbly creative answer to explain why the core is liquid [ hence the reference to the thermal evolution] with regard to the nebular theory.

From what we know already the field strength has decreased by 27% since the last measurement/estimate ( please don't fry me - go and check the official research papers ) and that in itself has big implications which I will not bore you with since I've already written them 3 times already.
Like I said previously - interesting times ahead on this little plane
Osiris1
1 / 5 (9) Mar 21, 2012
Maybe it is spherical because it is largely molten, and once rotated faster. Maybe a good scan would be for transuranic elements, especial stable ones in the area of unumpentium on the table. This planet would be an excellent place to look. Planetary density seems to indicate propensity of heavy elements; and the closer to the central star, the denser they get, and this is logical. Not saying we will find 'naquadda', the fictional element from the TV/Sat series 'StarGateSG-1, but maybe we will get a pleasant surprise gift from God here. HE DID say this was our place to manage for Him...and maybe create a few more Mansions in our system as well, and not all of them in planetary gravity wells.
barakn
5 / 5 (5) Mar 21, 2012
From what we know already the field strength has decreased by 27% since the last measurement/estimate ( please don't fry me - go and check the official research papers ) and that in itself has big implications which I will not bore you with since I've already written them 3 times already.
Still pulling that little turd of an argument out of the fridge and giving it a good sniff every once in a while, eh? Here is the original article http://www.physor...ped.html where I showed why your argument is full of crap.
Baseline
5 / 5 (4) Mar 21, 2012
Maybe it is spherical because it is largely molten, and once rotated faster. Maybe a good scan would be for transuranic elements, especial stable ones in the area of unumpentium on the table. This planet would be an excellent place to look. Planetary density seems to indicate propensity of heavy elements; and the closer to the central star, the denser they get, and this is logical. Not saying we will find 'naquadda', the fictional element from the TV/Sat series 'StarGateSG-1, but maybe we will get a pleasant surprise gift from God here. HE DID say this was our place to manage for Him...and maybe create a few more Mansions in our system as well, and not all of them in planetary gravity wells.


God said that did he? and you spoke to him recently?

Kirk Cameron called and said he left his sweater over at your place when you, Ray Comfort and he were discussing the absence of the Croc-o-duck from the fossil record.
Graeme
not rated yet Mar 21, 2012
It would be intersting if there are denser minerals incompatible with liquid iron, these would have sellted to the innermost parts of the planet at an earlier time when the core was completely molten. The interior of Mercury may actually be more accessible than that of earth due to lower gravity and pressures. It would be interesting to attach several seismic sensors to Mercury to study the interior.
GeoGeo
5 / 5 (1) Mar 21, 2012
Being so close to the sun means that it burns to be on Mercury. Mercury burns alright, but well beyond combustion and into outright elemental disruption from the intense radiation. Mercury might have 'evaporated' to its present volume from a much larger size over time. That still begs the question, "..why is it so spherical?". I haven't figured that one out yet.


Mercury's volatile content (5200) relative to its refractory elements (K/Th) is comparable to the other terrestrial planets (2000-7000). If Mercury was depleted in volatiles it would have values similar to the moon (K/Th of 360).
Given the above - 'mantle stripping hypothesis' cannot be correct.
Ebel and Alexander have a much better hypothesis. Have a read through, "Equilibrium condensation from chondritic porous IDP enriched vapor: Implications for Mercury and enstatite chondrite origins"
baudrunner
1 / 5 (1) Mar 22, 2012
Mercury's volatile content (5200) relative to its refractory elements (K/Th) is comparable to the other terrestrial planets (2000-7000).
That says nothing about the way things were three billion years ago. There is a reason that Mercury is closest to the sun. And that is because it is decidedly *not* like the other terrestrial planets.
GeoGeo
4 / 5 (1) Mar 22, 2012
That says nothing about the way things were three billion years ago. There is a reason that Mercury is closest to the sun. And that is because it is decidedly *not* like the other terrestrial planets.


Actually it tells us a lot about what the early solar system was like (4.5 billion years ago by the way, not 3). In fact, it tells us about what is possible and what is not possible with regards to formation models for Mercury. It's proximity to the sun does not excuse it from the same physical laws that extend to every other terrestrial planet in our solar system and their likely formation path.
Obviously you don't understand the importance of such data. Those values were published to show that Asphaug's, 2011 'mantle stripping', collision / hit-and-run formation model (in an attempt to explain the size of Mercuy's core) could not be correct.
Please educate yourself so you can make an intelligent comment before you embarrass yourself next time.
roboferret
not rated yet Mar 23, 2012

From what we know already the field strength has decreased by 27% since the last measurement/estimate ( please don't fry me - go and check the official research papers ) and that in itself has big implications which I will not bore you with since I've already written them 3 times already.

Would you prefer to be fried in batter or breadcrumbs?
Given Mercury's weak magnetic field and exposure to charged particles, the big surprise would be if it didn't change hugely with solar activity. In addition, the mariner reading was based on a single flyby, and Messenger made it's readings over multiple orbits, means we have to consider the Messenger readings as far more reliable.

http://www.spaced...999.html