On the boundary of the Caribbean Sea and the Atlantic Ocean is the Puerto Rico Trench , the deepest in the Atlantic Ocean . kilometre above it , the ocean ’s surface is dip slightly , pulled by an anomaly of Earth’sgravity .
If you strike down an target there , it will fall slightly quicker than elsewhere on the planet or in the surrounding area . Meanwhile sailing equipment can bethrown off by the anomaly , causing fictitious readings for sailors in the area .
So what is causing the sobriety anomaly , and are there any others like it ?
How did we first discover gravity anomalies?
In 1671 , astronomer Jean Richter traveled from Paris , France , to Cayenne , French Guiana in South America . With him , he took a pendulum clock . While the clock had been accurate in Paris , he noticed that in Cayenne it ran slowly , losing a full two and a one-half minutes every twenty-four hour period . No biggie , the pendulum was shortened to make the clock accurate . However , when he returned to Paris he found that the clock was running too quickly , by two and a one-half minutes each sidereal day .
Though it may feel the same when you jump up and down in Brazil or Canada , the rate at which you fall is not uniform . What mathematicianChristiaan Huygens realizedafter hearing of Richter ’s clock was that it was experimental grounds that the Earth was rotating . after , Newton showedusing data from a exchangeable pendulum clock and Jupiter ’s equatorial protrusion , that the Earth bulged at the equator due to the centrifugal personnel of its rotation , and estimate by how much .
Near the equator gravity acts upon you less than it does near the poles , as you arefurther out from the bulk of the Earth ’s mass .
However , the soberness at the Puerto Rico Trench differs from the area surrounding it . It , along withseveral others like itaround the planet , are what are now bear on to as gravity anomaly .
What is a gravity anomaly?
solemnity anomalies are where an object observed in loose fall acceleratesat a charge per unit differentto the charge per unit models of sombreness for that location would predict .
At the Puerto Rico Trench , gravity has beenfound to be-380milliGal , making it the biggest electronegative gravitational attraction anomaly on Earth . Another in the Indian Ocean is wheregravity has been found to be lowest , compared to what was expected .
What is causing the Puerto Rico Trench gravity anomaly?
In 1977 , geophysicist Peter Molnar attempted to find out what was stimulate this unexpected downwards strength . Just as slightly high gravity at the poles is due to being closer to the volume of Earth ’s spate , he knew a likely source : something vast and dense must be under the surface .
In a paperpublished in Geophysical Journal International , he explained that old models of gravity had assumed that the thickness of the Earth ’s crust ( thelithosphere ) was fairly uniform . reckon at the country , he realized that was n’t the typesetter’s case , and that the anomaly was probably cause by a large " hanging dither " of the Atlantic lithosphere .
" The residual gravity anomalies are then consistent with the existence of a subcrustal slow heap , that could be the fall slab of lithosphere , " Molnarwrote in the study .
" The value of this excess mass depends upon more arbitrary assumptions for the crustal mass in the Puerto Rico Trench and its landward wall , but if the other assumptions above are realistic , the dense multitude is involve and is tolerable to bend the surface down at the trench . "
Though not the first to propose the slab of crust as an explanation , Molnar was able to provide estimates of the mass and size of the object causing the graveness anomaly above .
An earlier version of this article was published inMarch 2023 .
