APOD: Gravitational Anomalies of Mercury (2015 May 05)

Comments and questions about the APOD on the main view screen.
User avatar
APOD Robot
Otto Posterman
Posts: 3543
Joined: Fri Dec 04, 2009 3:27 am

APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by APOD Robot » Tue May 05, 2015 4:11 am

Image Gravitational Anomalies of Mercury

Explanation: What's that under the surface of Mercury? The robotic MESSENGER spacecraft that had been orbiting planet Mercury for the past four years had been transmitting its data back to Earth with radio waves of very precise energy. The planet's gravity, however, slightly changed this energy when measured on Earth, which enabled the reconstruction of a gravity map of unprecedented precision. Here gravitational anomalies are shown in false-color, superposed on an image of the planet's cratered surface. Red hues indicate areas of slightly higher gravity, which in turn indicates areas that must have unusually dense matter under the surface. The central area is Caloris Basin, a huge impact feature measuring about 1,500 kilometers across. Last week, after completing its mission and running low on fuel, MESSENGER was purposely crashed onto Mercury's surface.

<< Previous APOD This Day in APOD Next APOD >>
[/b]

User avatar
neufer
Vacationer at Tralfamadore
Posts: 15946
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by neufer » Tue May 05, 2015 12:34 pm

APOD Robot wrote:Image Gravitational Anomalies of Mercury

Explanation: What's that under the surface of Mercury? The robotic MESSENGER spacecraft that had been orbiting planet Mercury for the past four years had been transmitting its data back to Earth with radio waves of very precise energy. The planet's gravity, however, slightly changed this energy when measured on Earth, which enabled the reconstruction of a gravity map of unprecedented precision.
The implication here is that an energy change in frequency (i.e., something second order in v/c) is somehow being measured.

Certainly it is primarily the velocity Doppler shift in frequency (i.e., something first order in v/c) that is being monitored.

The MESSENGER spacecraft reaches maximum velocity as it passes directly over mascons; this results in a local maximum Doppler shift vis-a-vis the Earth.
Art Neuendorffer

FloridaMike
Science Officer
Posts: 413
Joined: Fri Nov 04, 2011 2:21 pm
Location: Florida, USA

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by FloridaMike » Tue May 05, 2015 12:49 pm

So Arthur C. Clarke was wrong, it's not on the moon.
Certainty is an emotion. So follow your spindle neurons.

User avatar
neufer
Vacationer at Tralfamadore
Posts: 15946
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by neufer » Tue May 05, 2015 2:44 pm

FloridaMike wrote:
So Arthur C. Clarke was wrong, it's not on the moon.
http://www.nasa.gov/mission_pages/messenger/multimedia/messenger_news20110616_image3.html wrote: <<As a result of the north-south asymmetry in Mercury's internal magnetic field, the geometry of magnetic field lines is different in Mercury's north and south polar regions. In particular, the magnetic "polar cap" where field lines are open to the interplanetary medium is much larger near the south pole. This geometry implies that the south polar region is much more exposed than in the north to charged particles heated and accelerated by solar wind–magnetosphere interactions. The impact of those charged particles onto Mercury's surface contributes both to the generation of the planet's tenuous atmosphere and to the "space weathering" of surface materials, both of which should have a north-south asymmetry given the different magnetic field configurations at the two poles.
http://en.wikipedia.org/wiki/Monolith_%28Space_Odyssey%29 wrote:
<<The name Tycho Magnetic Anomaly-1 (also known as the TMA-1) refers to the strong magnetic field found somewhere in the lunar Crater Tycho by an American scientific satellite. Astronauts find that this magnetic anomaly is caused by an alien monolith buried about 15 meters below the surface. When the monolith is excavated and examined, it is found to be a black parallelepiped whose sides extend in the precise ratio of 1 : 4 : 9 (1² : 2² : 3²). The TMA-1 was dug up during the lunar night, but after sunrise and its exposure to direct sunlight, TMA-1 emits a single powerful burst of radio waves – aimed at Iapetus (Saturn) in the novel, and aimed at Jupiter in the motion picture. Its powerful magnetic field disappears immediately. In the novel, some scientists speculate that its magnetic field came from large electric current, circulating in a system of superconductors for millions of years as an energy-storage mechanism. All of that electric power was expended in the one radio signal.>>
Art Neuendorffer

Boomer12k
:---[===] *
Posts: 2481
Joined: Sun Apr 22, 2007 12:07 am

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by Boomer12k » Tue May 05, 2015 4:12 pm

More dense matter????
Gold is dense....um.... Nooooooooo... Er.....LEAD!!!!!! Yeah, that is it!!!! LEAD!!!!!

Well....um.... Got to go..... Seeeeeeee you later.....just, um, going to step out for awhile......

Actually, since it is a basin.... Where a large object struck... There may be a deposit of iron....

:---(===) *

ke0cgu

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by ke0cgu » Tue May 05, 2015 4:41 pm

Looks like pac man to me.

User avatar
BMAONE23
Commentator Model 1.23
Posts: 4076
Joined: Wed Feb 23, 2005 6:55 pm
Location: California

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by BMAONE23 » Tue May 05, 2015 5:00 pm

ke0cgu wrote:Looks like pac man to me.
The first thing that came to mind for me was Guess I am showing my age
Last edited by BMAONE23 on Tue May 05, 2015 5:06 pm, edited 1 time in total.

User avatar
BMAONE23
Commentator Model 1.23
Posts: 4076
Joined: Wed Feb 23, 2005 6:55 pm
Location: California

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by BMAONE23 » Tue May 05, 2015 5:05 pm

Boomer12k wrote:More dense matter????
Gold is dense....um.... Nooooooooo... Er.....LEAD!!!!!! Yeah, that is it!!!! LEAD!!!!!

Well....um.... Got to go..... Seeeeeeee you later.....just, um, going to step out for awhile......

Actually, since it is a basin.... Where a large object struck... There may be a deposit of iron....

:---(===) *
Although a liquid at room temperature Mercury (Hg) has an atomic wt. of 80 vs. Gold (Au) at 79

Markus Schwarz
Science Officer
Posts: 217
Joined: Wed Apr 29, 2009 11:55 am
Location: Germany

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by Markus Schwarz » Tue May 05, 2015 7:51 pm

BMAONE23 wrote:Although a liquid at room temperature Mercury (Hg) has an atomic wt. of 80 vs. Gold (Au) at 79
The atomic numbers of gold and mercury are 79 and 80, respectively, and are the number of protons inside the nucleus. The atomic weights are ~197u and ~201u, respectively, with 1 u being 1/12 of the mass of a carbon-12 atom.

User avatar
neufer
Vacationer at Tralfamadore
Posts: 15946
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by neufer » Tue May 05, 2015 8:16 pm

http://en.wikipedia.org/wiki/Felix_the_Cat#Legacy wrote:
<<In 1929 when television was in the experimental stages, the very first image to ever be seen was an illustration of Felix the Cat.
It remained on there for hours while engineers used it as a test pattern.>>
http://en.wikipedia.org/wiki/Mass_concentration_%28astronomy%29 wrote: <<In astronomy and astrophysics, a mass concentration (or mascon) is a region of a planet or moon's crust that contains a large positive gravitational anomaly. In general, the word "mascon" can be used as a noun to describe an excess distribution of mass on or beneath the surface of a planet (with respect to some suitable average), such as Hawaii. However, this term is most often used to describe a geologic structure that has a positive gravitational anomaly associated with a feature (e.g. depressed basin) that might otherwise have been expected to have a negative anomaly, such as the "mascon basins" on the Moon.

Typical examples of mascon basins on the Moon are the Imbrium, Serenitatis, Crisium and Orientale impact basins, all of which possess prominent topographic lows and positive gravitational anomalies. Examples of mascon basins on Mars include the Argyre, Isidis, and Utopia basins. Theoretical considerations imply that a topographic low in isostatic equilibrium would exhibit a slight negative gravitational anomaly. Thus, the positive gravitational anomalies associated with these impact basins indicate that some form of positive density anomaly must exist within the crust or upper mantle that is currently supported by the lithosphere. One possibility is that these anomalies are due to dense mare basaltic lavas, which might reach up to 6 kilometers in thickness for the Moon. However, while these lavas certainly contribute to the observed gravitational anomaly, uplift of the crust-mantle interface is also required to account for its magnitude. Indeed, some mascon basins on the Moon do not appear to be associated with any signs of volcanic activity. [And] the huge expanse of mare basaltic volcanism associated with Oceanus Procellarum does not possess a positive gravitational anomaly.>>
Art Neuendorffer

User avatar
Nitpicker
Inverse Square
Posts: 2685
Joined: Fri Sep 20, 2013 2:39 am
Location: S27 E153

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by Nitpicker » Tue May 05, 2015 10:47 pm

I wasn't able to find any quantitative results on the variation of gravity on Mercury, resulting from this study (without looking up the actual paper). If the variation is slight, I don't suppose the variation in density is so "unusual".

Boomer12k
:---[===] *
Posts: 2481
Joined: Sun Apr 22, 2007 12:07 am

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by Boomer12k » Wed May 06, 2015 2:14 am

BMAONE23 wrote:
Boomer12k wrote:More dense matter????
Gold is dense....um.... Nooooooooo... Er.....LEAD!!!!!! Yeah, that is it!!!! LEAD!!!!!

Well....um.... Got to go..... Seeeeeeee you later.....just, um, going to step out for awhile......

Actually, since it is a basin.... Where a large object struck... There may be a deposit of iron....

:---(===) *
Although a liquid at room temperature Mercury (Hg) has an atomic wt. of 80 vs. Gold (Au) at 79
I distinctly said...NOT GOLD....right? Yup...no gold there....probably from an Iron Meteor, or Asteroid, or something...but NOT GOLD....

Now, where is my toothbrush, oh, and Oxygen.....

:---[===] *

User avatar
DavidLeodis
Perceptatron
Posts: 1169
Joined: Mon May 01, 2006 1:00 pm

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by DavidLeodis » Wed May 06, 2015 1:36 pm

In the information brought up through the 'radio waves' link it states "Radio waves have the longest wavelengths in the electromagnetic spectrum. They range from the length of a football to larger than our planet". Wow, that last bit in particular staggered me! :-o. I'm amazed that such long wavelengths can even be detected. Is there a maximum wavelength or could there be such as for example galaxy-sized wavelengths :?:.

User avatar
Chris Peterson
Abominable Snowman
Posts: 14338
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by Chris Peterson » Wed May 06, 2015 2:15 pm

Boomer12k wrote:Actually, since it is a basin.... Where a large object struck... There may be a deposit of iron....
An iron impactor wouldn't leave much material. What remained would be scattered out a great distance. A thick basalt layer is much more likely.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
Chris Peterson
Abominable Snowman
Posts: 14338
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by Chris Peterson » Wed May 06, 2015 2:18 pm

DavidLeodis wrote:In the information brought up through the 'radio waves' link it states "Radio waves have the longest wavelengths in the electromagnetic spectrum. They range from the length of a football to larger than our planet". Wow, that last bit in particular staggered me! :-o. I'm amazed that such long wavelengths can even be detected. Is there a maximum wavelength or could there be such as for example galaxy-sized wavelengths :?:.
There's no upper limit on the wavelength of an electromagnetic wave. There may be a longest wave that is produced by known natural phenomena, not sure about that. Of course, the only reason that radio waves are the longest waves is because we haven't chosen a name for longer ones. We tend to name regions of the electromagnetic spectrum based on the methods we use for detection and production. So if we encountered a practical use for extremely long wavelengths, it's possible we'd give them a new name to distinguish them from "radio".
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
DavidLeodis
Perceptatron
Posts: 1169
Joined: Mon May 01, 2006 1:00 pm

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by DavidLeodis » Wed May 06, 2015 4:50 pm

Thanks Chris for answering my query. You take the time (and possible trouble) to answer many of those that I ask, for which I am very grateful. :)

I do search for many things I don't ask about but I do ask questions when I think they may also be of interest to others, such as the statement that radio wavelengths can be larger than planet size. Perhaps planet-sized wavelengths can be used to play planet/galaxy snooker (would that be Pool in the United States). :wink:

Interociter Operator

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by Interociter Operator » Wed May 06, 2015 4:56 pm

Why was MESSENGER crashed on the opposite side of Mercury where it would not be visible from Earth?

Were they trying to avoid filing a Mercurean Environment Impact Statement?

User avatar
Chris Peterson
Abominable Snowman
Posts: 14338
Joined: Wed Jan 31, 2007 11:13 pm
Location: Guffey, Colorado, USA

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by Chris Peterson » Wed May 06, 2015 4:58 pm

Interociter Operator wrote:Why was MESSENGER crashed on the opposite side of Mercury where it would not be visible from Earth?
I don't think they really had much control over where it crashed. To have a planned crash, they would have needed to expend fuel for that purpose, which would have shortened the science phase of the mission.
Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

User avatar
neufer
Vacationer at Tralfamadore
Posts: 15946
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by neufer » Wed May 06, 2015 5:44 pm

Chris Peterson wrote:
<<There's no upper limit on the wavelength of an electromagnetic wave. There may be a longest wave that is produced by known natural phenomena, not sure about that. Of course, the only reason that radio waves are the longest waves is because we haven't chosen a name for longer ones. We tend to name regions of the electromagnetic spectrum based on the methods we use for detection and production. So if we encountered a practical use for extremely long wavelengths, it's possible we'd give them a new name to distinguish them from "radio".>>
  • It is difficult to produce, receive, or propagate (even in interstellar space for more than a few wavelengths)
    Extremely Low Frequency (ELF) waves but they do exist:
http://en.wikipedia.org/wiki/Extremely_low_frequency wrote:
<<Extremely low frequency (ELF) is the ITU designation for electromagnetic radiation (radio waves) with frequencies from 3 to 30 Hz, and corresponding wavelengths from 100,000 to 10,000 kilometers. ELF radio waves are generated by lightning and natural disturbances in Earth's magnetic field, so they are a subject of research by atmospheric scientists. Because of the difficulty of building antennas that can radiate such long waves, ELF frequencies have been used in only a very few human-made communication systems. The frequency of alternating current flowing in electric power grids, 50 or 60 Hz, also falls within the ELF band, making power grids an unintentional source of ELF radiation.

Because of its electrical conductivity, seawater shields submarines from most higher frequency radio waves, making radio communication with submerged submarines at ordinary frequencies impossible. Signals in the ELF frequency range, however, can penetrate much deeper. Two factors limit the usefulness of ELF communications channels: the low data transmission rate of a few characters per minute and, to a lesser extent, the one-way nature due to the impracticality of installing an antenna of the required size on a submarine (the antenna needs to be of an exceptional size in order to achieve successful communication). Generally, ELF signals were used to order a submarine to rise to a shallow depth where it could receive some other form of communication. The US maintained two sites, in the Chequamegon-Nicolet National Forest, Wisconsin and in the Escanaba River State Forest, Michigan (originally named Project Sanguine, then downsized and rechristened Project ELF prior to construction), until they were dismantled, beginning in late September 2004. Both sites used long power lines, so-called ground dipoles, as leads. These leads were in multiple strands ranging from 22.5 to 45 kilometres long. Because of the inefficiency of this method, considerable amounts of electrical power were required to operate the system.

Transmitters in the 20 Hz range are also found in pipeline inspection gauges, also known as "PIGs". Some radio hams record ELF (or even lower) signals from very large homemade antennas, and play them back at higher speeds to catch natural fluctuations in the Earth's electromagnetic field. Increasing the playback speed increases the pitch, so that it can be brought into the audio frequency range.

Naturally occurring ELF waves are present on Earth, resonating in the region between ionosphere and surface. They are initiated by lightning strikes that make electrons in the atmosphere oscillate. Though VLF signals were predominantly generated from lightning discharges, it was found that an observable ELF component (slow tail) followed the VLF component in almost all cases. The fundamental mode of the Earth-ionosphere cavity has the wavelength equal to the circumference of the Earth, which gives a resonance frequency of 7.8 Hz. This frequency, and higher resonance modes of 14, 20, 26 and 32 Hz appear as peaks in the ELF spectrum and are called Schumann resonance.

ELF waves have also been tentatively identified on Saturn's moon Titan. Titan's surface is thought to be a poor reflector of ELF waves, so the waves may instead be reflecting off the liquid-ice boundary of a subsurface ocean of water and ammonia, the existence of which is predicted by some theoretical models. Titan's ionosphere is also more complex than Earth's, with the main ionosphere at an altitude of 1,200 km but with an additional layer of charged particles at 63 km. This splits Titan's atmosphere into two separate resonating chambers. The source of natural ELF waves on Titan is unclear as there does not appear to be extensive lightning activity.

Huge ELF radiation power outputs of 100,000 times the Sun's output in visible light may be radiated by magnetars. The pulsar in the Crab nebula radiates powers of this order at the frequency 30 hertz. Radiation of this frequency is below the plasma frequency of the interstellar medium, thus this medium is opaque to it, and it cannot be observed from Earth. The solar 22-year magnetic cycle is thought to emit ELF photons with 22 light-year long wavelengths.
>>
Art Neuendorffer

Confusedagain

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by Confusedagain » Thu May 07, 2015 11:16 pm

Just when I had been almost persuaded that gravity is a mere depression in the fabric of space time as pictured in countless illustrations that idea goes out the window? Mercury makes a spacetime dip, right or wrong? Different blobs of Mercury make different spacetime dips? How many spacetime dips does Mercury make? I think the experts, really now, are as confused as I am. Or did we go back to the idea of gravity being magnetic? What's the new story?

User avatar
neufer
Vacationer at Tralfamadore
Posts: 15946
Joined: Mon Jan 21, 2008 1:57 pm
Location: Alexandria, Virginia

Re: APOD: Gravitational Anomalies of Mercury (2015 May 05)

Post by neufer » Fri May 08, 2015 2:26 am

Confusedagain wrote:
Just when I had been almost persuaded that gravity is a mere depression in the fabric of space time as pictured in countless illustrations that idea goes out the window? Mercury makes a spacetime dip, right or wrong? Different blobs of Mercury make different spacetime dips? How many spacetime dips does Mercury make? I think the experts, really now, are as confused as I am. Or did we go back to the idea of gravity being magnetic? What's the new story?
There is no need, whatever, to have to think about Einsteinian "spacetime dips."

The APOD is simply about observed Newtonian gravitational strength anomalies that vary over Mercury's surface (and which are probably indicative of dense underground basaltic lava extrusions).

FloridaMike's aside reference to the fictitious Tycho Magnetic Anomaly-1 in 2001 A Space Odyssey made me think of the strong magnetic lines observed to be coming out of Mercury's North Pole. But none of this magnetic stuff has anything to do with the gravitational APOD.
Art Neuendorffer