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Mysterious Shift in Earth's Gravity Suggests Equator is Bulging
space.com ^ | 1 Aug 02 | Robert Roy Britt

Posted on 08/01/2002 3:13:16 PM PDT by RightWhale

Mysterious Shift in Earth's Gravity Suggests Equator is Bulging

By Robert Roy Britt Senior Science Writer

posted: 02:00 pm ET 01 August 2002

Something strange has been going on under our feet for the past four years. Earth's gravity field suddenly shifted gears and began getting flatter, reversing a course of centuries during which the planet and its gravity field grew rounder each year.

The scientists who noticed the change and report it in the Aug. 2 issue of the journal Science suspect Earth itself may be flattening out, with the oceans rising near the equator, but they aren't sure.

What they do know is that Earth has never been round. It has always bulged at the equator and is about 0.3 percent fatter there, partly a result of the planet's rotation.

Getting rounder

Yet ever since the last Ice Age, the planet has been getting rounder as ground beneath the polar regions, relieved of the weight from ice that was miles thick in places, has been rebounding. In some parts of Scandinavia and Canada, the ground rises a quarter-inch (1 centimeter) per year.

Since the late 1970s, satellite measurements have shown that this post-glacial rebound, as it is called, generates a corresponding rounding of Earth's gravity field.

Suddenly the trend has reversed.

"Sometime around 1998, something began to make the Earth's gravity field flatter," says Christopher Cox of Raytheon Information Technology and Scientific Services. "The result is it looks as if post-glacial rebound has reversed itself. But, we do not have any reason to think that post-glacial rebound has in any way stopped or changed."

In effect, Cox said in an interview, while post-glacial rebound continues to make the Earth rounder, some movement of mass on the surface of the Earth must be making the gravity field flatter. It's not a change anyone could notice; it's only revealed by sensitive satellite measurements.

The shift, however, is significant.

"The effect is twice as large as post-glacial rebound in terms of effect on the gravity field, and it's in the opposite direction," Cox said. "Whatever it is, it's big."

Like a rubber ball

Cox, who also works at NASA's Goddard Space Flight Center, described post-glacial rebound as similar to pushing a rubber ball in at the top and bottom with your fingers. "The sides come out, and the top and bottom go in. Take your fingers off that rubber ball, and the sides are going to go in and the top is going to come out again."

What does this have to do with Earth?

"You have material moving inside," Cox explained. The rubber is compressed, but air is also pushed around. Some of the post-glacial rebound is caused by the ground simply decompressing. But scientists have long known that to account for what they've measured, Earth's physical shape must change. Material --ground, water or air -- must be moved around. Though the planet's shape and its gravity field are not directly correlated, they are related.

Cox and his colleague, Benjamin Chao of Goddard, were at first baffled by the sudden reversal and flattening of the gravity field. They considered that ice melting at the poles and raising the overall sea level could be the culprit. Calculations showed, however, that "you would have to drop a 10x10x5 kilometer cube of it into the ocean every year for the past five years." Separate measurements of sea surface height from NASA's TOPEX/Poseidon mission don't support this scenario.

Material in Earth's crust can't be responsible -- it couldn't move so quickly from the poles to the equator. Molten rock oozing around in Earth's core might be to blame, but data do not support such a scenario. Changes in the atmosphere might be involved, but no data supports that being the primary cause, either.

So what is it?

Instead, Cox said, long-term circulation patterns in the ocean seem to be the most likely cause.

Shifts in huge ocean currents -- similar to El Nino but on larger scales and moving in a north-south direction -- might transport enough water toward the equator to account for the flattened gravity field. One such cycle is called the Pacific Decadal Oscillation.

"We have a strong suspicion that it's in the ocean," Cox said.

"Whatever the cause, the results of Cox and Chao emphasize the importance of gravity variations as a barometer of integrated mass changes in the Earth system," write scientists Anny Cazenave and R. Steven Nerem in an analysis of the research for Science. "Monitoring these variations with improved spatial and temporal resolution would provide an important tool for studying Earth system changes."

Since Cox and Chao submitted their paper to the journal, they've continued to look into the mystery and are more confident that the ocean is behind it all. "But we need more data," Cox said.

That data could come from NASA's GRACE (Gravity Recovery and Climate Experiment) satellite mission, which will provide the most precise measurements ever made of Earth's gravity field. GRACE launched in March.


TOPICS: Culture/Society; Extended News
KEYWORDS: flatearth; globalwarming; gravity; isostaticrebound; potsdamgravitypotato
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To: RightWhale
And this will affect us how???
41 posted on 08/01/2002 3:44:08 PM PDT by rwfromkansas
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To: mewzilla
It's from all the fat people.

But most of the fat people are here in the US!

42 posted on 08/01/2002 3:46:20 PM PDT by 6ppc
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To: Centurion2000
Maybe so, but it is data and it shows lumps, irregularities and mass concentrations all over the planet. Same for the moon, same for Mars. Scandinavia is experiencing glacial rebound, there is no doubt about it. Greenland is practically sunken under its icecap. No doubt, straight data.
43 posted on 08/01/2002 3:48:03 PM PDT by RightWhale
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To: RightWhale
"We have a strong suspicion that it's in the ocean," Cox said.

Somewhere off the coast of Japan, tiny twin girls are beginning to sing.

44 posted on 08/01/2002 3:48:27 PM PDT by tet68
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To: rwfromkansas
this will affect us

It affects our space satellites. Apparently it also affects waterlines adjecent to oceans. It's not like the planet is suddenly going to become flat as a pancake, but the changes are measureable.

45 posted on 08/01/2002 3:51:09 PM PDT by RightWhale
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To: Wingsofgold
My Mama says it's cause hell has enlarged itself

How much of that belief is due to her children? :-)

46 posted on 08/01/2002 3:51:31 PM PDT by decimon
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To: tet68
That would be an obscure reference. What are you referring to?
47 posted on 08/01/2002 3:53:27 PM PDT by RightWhale
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To: 6ppc; cmsgop
Not any more.

And is it just me, or does the person in that pic from cmsgop remind anyone else of Janet Reno?

48 posted on 08/01/2002 3:53:58 PM PDT by mewzilla
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To: decimon
HeheheHEE. Have we met? :)
49 posted on 08/01/2002 3:55:40 PM PDT by Wingsofgold
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To: cmsgop
Get a clue, buddy. Kind of cruel to post this poor soul's picture. What are you thinking, that the rest of us will make fun of him or something? Your sense of humor is pathological, and if you think posting a photo of a poor, retarded person is funny, well shame on you.
50 posted on 08/01/2002 3:56:42 PM PDT by ladyrustic
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To: dead
...but not most thinking people.

Ah, the hole in your logic. Heh heh heh... Take it easy.

51 posted on 08/01/2002 3:57:10 PM PDT by DoughtyOne
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To: decimon
When I see someone jump up and not come down, I'll start worrying about it!

Sac

52 posted on 08/01/2002 3:58:14 PM PDT by Sacajaweau
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To: RightWhale
Mothra is coming!
53 posted on 08/01/2002 4:04:20 PM PDT by 11Bush
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To: 11Bush
Mothra flaps it's wings in Tokyo, and there's Global Warming in Central Park...
54 posted on 08/01/2002 4:13:10 PM PDT by Chad Fairbanks
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To: RightWhale
I know what it is. It's that guy Caesar Barber, who suing the fast-food chains -- he must be on vacation somewhere near the equator. He probably took Rosie O'Donnell and Jerrold Nadler with him.
55 posted on 08/01/2002 4:16:22 PM PDT by Schatze
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Comment #56 Removed by Moderator

To: r9etb
Why do you think variations in Earth's gravity are important to GPS. For an example of the important effects on the satellites' orbits, see:

http://www.ngs.noaa.gov/GPS/noaa_acn.html
57 posted on 08/01/2002 4:23:40 PM PDT by RossA
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To: RightWhale
"Mysterious Shift in Earth's Gravity Suggests Equator is Bulging"

Americans must demand that a cabinet level agency be created and funded to counteract any deleterious affects of this global phenomenon. It is imperative that massive studies be funded to see what this change in the gravity field portends for minorities, blacks, hispanics, gays, lesbians, transexuals, the differently gendered, women, low income inner city residents and those on Social Security and fixed incomes, welfare recipients, the elderly, and the differently abled. We must not leave any of these people out. Leave no child behind. After all this for the CHILDREN!

58 posted on 08/01/2002 4:23:40 PM PDT by StormEye
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To: RightWhale
Earth's gravity field suddenly shifted gears and began getting flatter

I knew it. Global Flatulence.

59 posted on 08/01/2002 4:25:32 PM PDT by Nick Danger
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To: ladyrustic
WOW LADY, THATS QUITE A RANT!

Are You Done?

Ya know the Internet is a strange place, Why you ask???

Because College Students Like to Goof Off in front of Camera's and be funny???? and make you think one ran around a Mental Ward with a Minolta taking Pic's of the Patients???

I think your leg has been pulled sweetie........
60 posted on 08/01/2002 4:46:13 PM PDT by cmsgop
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