7 ms·

Giant 'Gravity Hole' in the Ocean May Be the Ghost of an Ancient Sea

128 points by _Microft 3y ago

pangolinja 3y ago
why is the sea level lower where the gravity is lower? surely more gravity would create more "pull"? confused by how this works...
- rob74 3y ago
  Maybe more gravity in other places creates more pull there and pulls the water away from places with less gravity? Similar to how the gravity of the moon pulls at the water, creating high tide? But that's just my guess, I'm not an expert either...
- wumms 3y ago
  (From the article) "As a result of the low pull of gravity there, combined with the higher gravitational pull from the surrounding areas, the sea level of the Indian Ocean over the hole is a whopping 106 meters lower than the global average"
- netsharc 3y ago
  Probably like iron filings and magnets, the stronger magnet would have a bigger pile of iron filings on it. Water isn't compressible, so the distribution would always give the stronger region more water.
  - a1o 3y ago
    Water is dense and gravity is proportional to mass, I wonder if there's any chance that water itself is also a contributor to the perceived gravity at that region.
    - kibwen 3y ago
      I don't think the mass of the water would have a very noticeable effect on the perceived gravity. The average depth of the ocean is about 4 km, whereas the radius of the Earth is 6,000 km, and stone is denser than water as well.
- pmontra 3y ago
  > more gravity would create more "pull"? Exactly. There is more mass below the ocean in the areas around where the hole developed and less mass below the hole. That mass is pulling water from the hole so it became a hole. By the way, less water in the hole and more around it further contribute to making the hole deep because water also have a mass. It doesn't go on forever up to draining the center of the hole dry, there is an equilibrium. Calculating the sea levels could be an unusual physics problem for students.
- rcxdude 3y ago
  gravity's impact on liquids is much more defined by them being pulled 'sideways' than 'up' or 'down'. For example, the tides are not mostly caused by the water being lighter or heavier due to the tidal forces of the moon and being pulled down by a greater or lesser degree, but by the sideways pull of the water on the 'side' of the earth causing it to bunch up where the sideways pulls converge (which is why you get tides with bodies of water as big as the oceans but not so much with lakes). The same thing happens here: stronger gravity elsewhere pulls the water sideways away from the low-gravity area, causing the depression (in fact, absent dynamic effects and other forces like wind, the surface of a liquid will be an isograv: every point at its surface will have the same gravitational potential).
- PopAlongKid 3y ago
  This is similar to recent discussions here on HN around the effects of melting ice (Antarctica, Greenland) on sea level. Not only does the meltwater itself cause increase, but the gravitational pull of so much ice pulls the water level around it up higher, resulting in lower sea level everywhere else. When the ice melts, that local gravity lessens, letting the surrounding elevated water spread out to the rest of the ocearn.
2-718-281-828 3y ago
> A vast expanse of the Indian Ocean is a staggering 100 meters lower than the global average sea level because of a major dip in Earth’s gravity. who would write such a gibberish in a scientific magazine?
- Etrnl_President 3y ago
  Scientific American mostly ceased being scientific in the latter 90's, and should be more correctly named Political American.
  - 2-718-281-828 3y ago
    i wouldn't mind this gibberish if the article would at least make clear afterwards what this is supposed to mean. but i can't find any explanation of the gravitational dynamics at play or even a description how exactly this is measured. 100m relative to what? i mean isn't sea level always 0m by definition? even on that "dip" sea level is 0m. so there is some assumed distance between sea surface and something else. an ideal circumference around the equator with the same volume (or technically area) of air under it as water over it? like an x-axis going through a sinus curve? one might argue that sth like that shouldn't show up on the hn front page. but maybe the meta message and discussion of the quality of sa journalism is worth the +31 points.
    - SketchySeaBeast 3y ago
      > 100m relative to what? You quoted it yourself: "the sea level of the Indian Ocean over the hole is a whopping 106 meters lower than the global average" We already know that sea level isn't a uniform height. If it were tides wouldn't be a thing. The various ocean's waters are going to be at different levels. > i mean isn't sea level always 0m by definition? You could make the same argument for ground level but we know that's not uniform.
      - misnome 3y ago
        ... Finally, proof of flat-earth! Everywhere on land is 0cm above the land-level! Checkmate, scientists.
AlbertoGP 3y ago
Talking about the Indian Ocean, and the first image in the article shows the Atlantic. This is not the Scientific American of my youth. Further below they show a plain 2D graph with the Indian Ocean dip, but why pick the wrong version of the “Potsdam Potato” (fancy 3D picture at the beginning) when one showing exactly what they are talking about exists in a press release from the European Geosciences Union they link to in their own article? “The Indian Ocean Geoid Low at a plume-slab overpass” https://blogs.egu.eu/divisions/gd/2021/02/24/the-indian-ocean-geoid-low-at-a-plume-slab-overpass/ https://blogs.egu.eu/divisions/gd/2021/02/24/the-indian-ocea...
- waynecochran 3y ago
  Fascinating topic, but it was as if i was reading a high school report on the subject.
  - bell-cot 3y ago
    This, so sadly this. The SciAm I subscribed to in the 70's and 80's is long since dead and gone. Back then, articles were routinely dense, tough long reads, with excellent editing and fact-checking. Now...it's filler fluff, and I'd trust Wikipedia more for facts.
    - acegopher 3y ago
      Unfortunately, no one buys subscriptions any more, and advertisers have moved to Facebook and Google. The ad-based internet has conditioned people to expect free content, and the internet ad model incentivizes click-bait low quality content because it's easy to publish and provides a place to hang ads from.
      - bell-cot 3y ago
        Yeah...though SciAm seemed to be in a long, slow decline for a decade+ before "free with ads on the web" was really a thing. And (that I've found) there is nothing comparable (to the old SciAm) that is free on the web. Did the demographic that was willing to think hard & long enough to enjoy the old SciAm gradually die off? Or did they just replace eating paid-for healthy brain food with eating free junk food. (FWIW - I pretty much dropped all the "premium" subscriptions I once had - all dead-tree editions - between ~2000 and ~2010, as either their quality went to crap, or they ceased publication.)
crystaln 3y ago
Does anyone know how much impact this has on weight at the highest vs lowest gravity point?
- jalk 3y ago
  And would it make economical sense to build rocket launch pads at the lowest points?
  - dredmorbius 3y ago
    Not appreciably (the delta is less than 1%, see my response to OP in this thread), but since lowest gravitational acceleration happen to coincide roughly with areas of maximal rotational tangential velocity, that is, of the Earth's rotation about its axis, of roughly 1,000 mph, the optimal siting of rocket launch facilities tends to be near the Earth's equator, where gravitational acceleration itself tends to be lower, and near where the lowest measured accelerations are found. Other factors would tend to dominate launch location choice, including particularly areas of open water east of the launch pad, useful both for deorbiting stages and in the event of any RUD[1] events in early-boost phase. ________________________________ Notes: 1. See <https://space.stackexchange.com/questions/10022/who-coined-the-phrase-rapid-unscheduled-disassembly https://space.stackexchange.com/questions/10022/who-coined-t...>
- dredmorbius 3y ago
  Interesting question. This article discusses identifying regions of gravitational variance, and the abstract discusses where gravitational pull at Earth's surface is highest (near the North Pole) and lowest ("at the top of the Huascaran mountain in the South American Andes"), but not by how much ... The project measures local gravitational acceleration across the surface of the Earth at 200m resolution. <https://www.sciencedaily.com/releases/2013/09/130904105345.htm https://www.sciencedaily.com/releases/2013/09/130904105345.h...> And the linked field map doesn't give specific measurements either. (Archive as original is 404): <https://web.archive.org/web/20160309210505/http://geodesy.curtin.edu.au/research/models/GGMplus/gallery.cfm https://web.archive.org/web/20160309210505/http://geodesy.cu...> The linked PDF article however does give values, on page 5: <https://web.archive.org/web/20160307144931/http://ddfe.curtin.edu.au/gravitymodels/GGMplus/hirt2013_ultrahighres_gravity.pdf https://web.archive.org/web/20160307144931/http://ddfe.curti...> Minimum: 9.76392 m * s^-2 Maximum: 9.83366 m * s^-2 Given a 100 kg human (somewhat heavier than typical, but simpler to compute), the difference would amount to a difference of 6.974 newton, or 1.567 pound-force. Or a delta of about 0.712%.
chiefalchemist 3y ago
> As a result of the low pull of gravity there, combined with the higher gravitational pull from the surrounding areas, the sea level of the Indian Ocean over the hole is a whopping 106 meters lower than the global average" This feels highly suspect. So any area below the average is because of this same condition? That doesn't seem likely. And if so, then check other area now that there's a theory. The world is a (fairly) big place. Using average as a guide feels cherry pick-y or at the very least random.
- rcxdude 3y ago
  Absent any other external forces, liquids (even non-uniform ones like the ocean) will form an isograv, where every part of their surface is at an equal gravitational potential. This is a natural consequence of how pressure works. So you expect this kind of deviation from gravitational anomaly. And while other forces can have a significant impact, there's not a lot else which can cause a persistent change in the average of this size. Dynamic effects will just to make things oscillate around the average but not chang the average much if at all, and even an extremely heavy prevailing wind (rare at the surface) won't be enough to cause much of a change in sea level. (ok, there is one really big thing left off of this which is important with respect to what 'average sea level' means: the largest other persistent effect is the centrifugal effects from the spinning of the earth, which results in the bulging at the equator (both for the rock itself, which at planet scales and timelines is approximately liquid, and for the oceans). This is way larger: the oceans are actually about 7km higher near the equator than you would expect if the earth was a sphere. The average they are comparing to here is coming from measuring sea level with respect to the shape it would be if the earth were just a ball of liquid with the same mass and spin. There's a bunch of different approximations which get used here and the details get really messy, but the next step after taking into account the centrifugal effect is basically various levels of approximation of the distribution of gravity: https://en.wikipedia.org/wiki/Geoid https://en.wikipedia.org/wiki/Geoid)
  - chiefalchemist 3y ago
    Ok. Now I get it. Sorry. Thanks for explaining.
defrost 3y ago
Here's a useful "start here" link: https://en.wikipedia.org/wiki/Geoid https://en.wikipedia.org/wiki/Geoid an important concept, the invisible "Geoid" is an equipotential surface of equal gravitational strength .. call it the " 1 G surface ". Where there is a large amount of dense mass ( a giant iron deposit | all other things being equal ) the immediate gravitational field is stronger .. it's the usual surface 1G PLUS the extra gravity from the mass of the iron .. therefore the constant 1G equipotential surface is much higher 'above' the mean ellipsoid surface. There's a lot going on here to get your head around - it generally takes a few WTF?!? iterations to fully grasp the various geophysical surfaces ( the WGS84 ellipsoid (and others), the various 'standard' geoids, the (diurnal flucuating) magnetic topography, etc ).
- axus 3y ago
  " a GPS receiver on a ship may, during the course of a long voyage, indicate height variations, even though the ship will always be at sea level (neglecting the effects of tides). That is because GPS satellites, orbiting about the center of gravity of the Earth, can measure heights only relative to a geocentric reference ellipsoid. To obtain one's orthometric height, a raw GPS reading must be corrected. Conversely, height determined by spirit leveling from a tide gauge, as in traditional land surveying, is closer to orthometric height. Modern GPS receivers have a grid implemented in their software by which they obtain, from the current position, the height of the geoid (e.g. the EGM-96 geoid) over the World Geodetic System (WGS) ellipsoid. They are then able to correct the height above the WGS ellipsoid to the height above the EGM96 geoid. When height is not zero on a ship, the discrepancy is due to other factors such as ocean tides, atmospheric pressure (meteorological effects), local sea surface topography and measurement uncertainties."
  - hinkley 3y ago
    I would think if one needed to measure the altitude of their ship, things have already gone very, very sideways at this point.
    - defrost 3y ago
xrguy 3y ago
interestingly the entire country of Maldives falls inside the marked area, a country with islands 2m above sea level.
deleted 3y ago
[deleted]
wumms 3y ago
According to the image caption this article seems to be based on ESA's GOCE mission (2009-2013)[0]. "Detailed analysis of GOCE's thruster and accelerometer data serendipitously revealed that it had detected the infrasound waves generated by the 2011 Tōhoku earthquake (whereupon it inadvertently became the first seismograph in orbit)." [0][1] There's also NASA's GRACE mission (2002-2017) which has been relaunched (GRACE-FO, 2018) with almost identical hardware [2]: "GRACE measures time variations while GOCE measures the static gravity field." [3] [0] https://en.wikipedia.org/wiki/Gravity_Field_and_Steady-State_Ocean_Circulation_Explorer https://en.wikipedia.org/wiki/Gravity_Field_and_Steady-State... [1] GOCE: the first seismometer in orbit (2013) https://www.esa.int/Applications/Observing_the_Earth/FutureEO/GOCE/GOCE_the_first_seismometer_in_orbit https://www.esa.int/Applications/Observing_the_Earth/FutureE... [2] https://en.wikipedia.org/wiki/GRACE_and_GRACE-FO https://en.wikipedia.org/wiki/GRACE_and_GRACE-FO [3] GRACE & GOCE (2008) https://www.science20.com/planetbye/grace_goce https://www.science20.com/planetbye/grace_goce (Edit: fixed link)

128 points by _Microft 3y ago

why is the sea level lower where the gravity is lower? surely more gravity would create more "pull"? confused by how this works...

rob74 3y ago
Maybe more gravity in other places creates more pull there and pulls the water away from places with less gravity? Similar to how the gravity of the moon pulls at the water, creating high tide? But that's just my guess, I'm not an expert either...
wumms 3y ago
(From the article) "As a result of the low pull of gravity there, combined with the higher gravitational pull from the surrounding areas, the sea level of the Indian Ocean over the hole is a whopping 106 meters lower than the global average"
netsharc 3y ago
Probably like iron filings and magnets, the stronger magnet would have a bigger pile of iron filings on it. Water isn't compressible, so the distribution would always give the stronger region more water.
- a1o 3y ago
  Water is dense and gravity is proportional to mass, I wonder if there's any chance that water itself is also a contributor to the perceived gravity at that region.
  - kibwen 3y ago
    I don't think the mass of the water would have a very noticeable effect on the perceived gravity. The average depth of the ocean is about 4 km, whereas the radius of the Earth is 6,000 km, and stone is denser than water as well.
pmontra 3y ago
> more gravity would create more "pull"? Exactly. There is more mass below the ocean in the areas around where the hole developed and less mass below the hole. That mass is pulling water from the hole so it became a hole. By the way, less water in the hole and more around it further contribute to making the hole deep because water also have a mass. It doesn't go on forever up to draining the center of the hole dry, there is an equilibrium. Calculating the sea levels could be an unusual physics problem for students.
rcxdude 3y ago
gravity's impact on liquids is much more defined by them being pulled 'sideways' than 'up' or 'down'. For example, the tides are not mostly caused by the water being lighter or heavier due to the tidal forces of the moon and being pulled down by a greater or lesser degree, but by the sideways pull of the water on the 'side' of the earth causing it to bunch up where the sideways pulls converge (which is why you get tides with bodies of water as big as the oceans but not so much with lakes). The same thing happens here: stronger gravity elsewhere pulls the water sideways away from the low-gravity area, causing the depression (in fact, absent dynamic effects and other forces like wind, the surface of a liquid will be an isograv: every point at its surface will have the same gravitational potential).
PopAlongKid 3y ago
This is similar to recent discussions here on HN around the effects of melting ice (Antarctica, Greenland) on sea level. Not only does the meltwater itself cause increase, but the gravitational pull of so much ice pulls the water level around it up higher, resulting in lower sea level everywhere else. When the ice melts, that local gravity lessens, letting the surrounding elevated water spread out to the rest of the ocearn.

2-718-281-828 3y ago

> A vast expanse of the Indian Ocean is a staggering 100 meters lower than the global average sea level because of a major dip in Earth’s gravity. who would write such a gibberish in a scientific magazine?

Etrnl_President 3y ago
Scientific American mostly ceased being scientific in the latter 90's, and should be more correctly named Political American.
- 2-718-281-828 3y ago
  i wouldn't mind this gibberish if the article would at least make clear afterwards what this is supposed to mean. but i can't find any explanation of the gravitational dynamics at play or even a description how exactly this is measured. 100m relative to what? i mean isn't sea level always 0m by definition? even on that "dip" sea level is 0m. so there is some assumed distance between sea surface and something else. an ideal circumference around the equator with the same volume (or technically area) of air under it as water over it? like an x-axis going through a sinus curve? one might argue that sth like that shouldn't show up on the hn front page. but maybe the meta message and discussion of the quality of sa journalism is worth the +31 points.
  - SketchySeaBeast 3y ago
    > 100m relative to what? You quoted it yourself: "the sea level of the Indian Ocean over the hole is a whopping 106 meters lower than the global average" We already know that sea level isn't a uniform height. If it were tides wouldn't be a thing. The various ocean's waters are going to be at different levels. > i mean isn't sea level always 0m by definition? You could make the same argument for ground level but we know that's not uniform.
    - misnome 3y ago
      ... Finally, proof of flat-earth! Everywhere on land is 0cm above the land-level! Checkmate, scientists.

AlbertoGP 3y ago

Talking about the Indian Ocean, and the first image in the article shows the Atlantic. This is not the Scientific American of my youth. Further below they show a plain 2D graph with the Indian Ocean dip, but why pick the wrong version of the “Potsdam Potato” (fancy 3D picture at the beginning) when one showing exactly what they are talking about exists in a press release from the European Geosciences Union they link to in their own article? “The Indian Ocean Geoid Low at a plume-slab overpass” https://blogs.egu.eu/divisions/gd/2021/02/24/the-indian-ocean-geoid-low-at-a-plume-slab-overpass/ https://blogs.egu.eu/divisions/gd/2021/02/24/the-indian-ocea...

waynecochran 3y ago
Fascinating topic, but it was as if i was reading a high school report on the subject.
- bell-cot 3y ago
  This, so sadly this. The SciAm I subscribed to in the 70's and 80's is long since dead and gone. Back then, articles were routinely dense, tough long reads, with excellent editing and fact-checking. Now...it's filler fluff, and I'd trust Wikipedia more for facts.
  - acegopher 3y ago
    Unfortunately, no one buys subscriptions any more, and advertisers have moved to Facebook and Google. The ad-based internet has conditioned people to expect free content, and the internet ad model incentivizes click-bait low quality content because it's easy to publish and provides a place to hang ads from.
    - bell-cot 3y ago
      Yeah...though SciAm seemed to be in a long, slow decline for a decade+ before "free with ads on the web" was really a thing. And (that I've found) there is nothing comparable (to the old SciAm) that is free on the web. Did the demographic that was willing to think hard & long enough to enjoy the old SciAm gradually die off? Or did they just replace eating paid-for healthy brain food with eating free junk food. (FWIW - I pretty much dropped all the "premium" subscriptions I once had - all dead-tree editions - between ~2000 and ~2010, as either their quality went to crap, or they ceased publication.)

crystaln 3y ago

Does anyone know how much impact this has on weight at the highest vs lowest gravity point?

jalk 3y ago
And would it make economical sense to build rocket launch pads at the lowest points?
- dredmorbius 3y ago
  Not appreciably (the delta is less than 1%, see my response to OP in this thread), but since lowest gravitational acceleration happen to coincide roughly with areas of maximal rotational tangential velocity, that is, of the Earth's rotation about its axis, of roughly 1,000 mph, the optimal siting of rocket launch facilities tends to be near the Earth's equator, where gravitational acceleration itself tends to be lower, and near where the lowest measured accelerations are found. Other factors would tend to dominate launch location choice, including particularly areas of open water east of the launch pad, useful both for deorbiting stages and in the event of any RUD[1] events in early-boost phase. ________________________________ Notes: 1. See <https://space.stackexchange.com/questions/10022/who-coined-the-phrase-rapid-unscheduled-disassembly https://space.stackexchange.com/questions/10022/who-coined-t...>
dredmorbius 3y ago
Interesting question. This article discusses identifying regions of gravitational variance, and the abstract discusses where gravitational pull at Earth's surface is highest (near the North Pole) and lowest ("at the top of the Huascaran mountain in the South American Andes"), but not by how much ... The project measures local gravitational acceleration across the surface of the Earth at 200m resolution. <https://www.sciencedaily.com/releases/2013/09/130904105345.htm https://www.sciencedaily.com/releases/2013/09/130904105345.h...> And the linked field map doesn't give specific measurements either. (Archive as original is 404): <https://web.archive.org/web/20160309210505/http://geodesy.curtin.edu.au/research/models/GGMplus/gallery.cfm https://web.archive.org/web/20160309210505/http://geodesy.cu...> The linked PDF article however does give values, on page 5: <https://web.archive.org/web/20160307144931/http://ddfe.curtin.edu.au/gravitymodels/GGMplus/hirt2013_ultrahighres_gravity.pdf https://web.archive.org/web/20160307144931/http://ddfe.curti...> Minimum: 9.76392 m * s^-2 Maximum: 9.83366 m * s^-2 Given a 100 kg human (somewhat heavier than typical, but simpler to compute), the difference would amount to a difference of 6.974 newton, or 1.567 pound-force. Or a delta of about 0.712%.

chiefalchemist 3y ago

> As a result of the low pull of gravity there, combined with the higher gravitational pull from the surrounding areas, the sea level of the Indian Ocean over the hole is a whopping 106 meters lower than the global average" This feels highly suspect. So any area below the average is because of this same condition? That doesn't seem likely. And if so, then check other area now that there's a theory. The world is a (fairly) big place. Using average as a guide feels cherry pick-y or at the very least random.

rcxdude 3y ago
Absent any other external forces, liquids (even non-uniform ones like the ocean) will form an isograv, where every part of their surface is at an equal gravitational potential. This is a natural consequence of how pressure works. So you expect this kind of deviation from gravitational anomaly. And while other forces can have a significant impact, there's not a lot else which can cause a persistent change in the average of this size. Dynamic effects will just to make things oscillate around the average but not chang the average much if at all, and even an extremely heavy prevailing wind (rare at the surface) won't be enough to cause much of a change in sea level. (ok, there is one really big thing left off of this which is important with respect to what 'average sea level' means: the largest other persistent effect is the centrifugal effects from the spinning of the earth, which results in the bulging at the equator (both for the rock itself, which at planet scales and timelines is approximately liquid, and for the oceans). This is way larger: the oceans are actually about 7km higher near the equator than you would expect if the earth was a sphere. The average they are comparing to here is coming from measuring sea level with respect to the shape it would be if the earth were just a ball of liquid with the same mass and spin. There's a bunch of different approximations which get used here and the details get really messy, but the next step after taking into account the centrifugal effect is basically various levels of approximation of the distribution of gravity: https://en.wikipedia.org/wiki/Geoid https://en.wikipedia.org/wiki/Geoid)
- chiefalchemist 3y ago
  Ok. Now I get it. Sorry. Thanks for explaining.

defrost 3y ago

Here's a useful "start here" link: https://en.wikipedia.org/wiki/Geoid https://en.wikipedia.org/wiki/Geoid an important concept, the invisible "Geoid" is an equipotential surface of equal gravitational strength .. call it the " 1 G surface ". Where there is a large amount of dense mass ( a giant iron deposit | all other things being equal ) the immediate gravitational field is stronger .. it's the usual surface 1G PLUS the extra gravity from the mass of the iron .. therefore the constant 1G equipotential surface is much higher 'above' the mean ellipsoid surface. There's a lot going on here to get your head around - it generally takes a few WTF?!? iterations to fully grasp the various geophysical surfaces ( the WGS84 ellipsoid (and others), the various 'standard' geoids, the (diurnal flucuating) magnetic topography, etc ).

axus 3y ago
" a GPS receiver on a ship may, during the course of a long voyage, indicate height variations, even though the ship will always be at sea level (neglecting the effects of tides). That is because GPS satellites, orbiting about the center of gravity of the Earth, can measure heights only relative to a geocentric reference ellipsoid. To obtain one's orthometric height, a raw GPS reading must be corrected. Conversely, height determined by spirit leveling from a tide gauge, as in traditional land surveying, is closer to orthometric height. Modern GPS receivers have a grid implemented in their software by which they obtain, from the current position, the height of the geoid (e.g. the EGM-96 geoid) over the World Geodetic System (WGS) ellipsoid. They are then able to correct the height above the WGS ellipsoid to the height above the EGM96 geoid. When height is not zero on a ship, the discrepancy is due to other factors such as ocean tides, atmospheric pressure (meteorological effects), local sea surface topography and measurement uncertainties."
- hinkley 3y ago
  I would think if one needed to measure the altitude of their ship, things have already gone very, very sideways at this point.
  - defrost 3y ago

xrguy 3y ago

interestingly the entire country of Maldives falls inside the marked area, a country with islands 2m above sea level.

deleted 3y ago

[deleted]

wumms 3y ago

According to the image caption this article seems to be based on ESA's GOCE mission (2009-2013)[0]. "Detailed analysis of GOCE's thruster and accelerometer data serendipitously revealed that it had detected the infrasound waves generated by the 2011 Tōhoku earthquake (whereupon it inadvertently became the first seismograph in orbit)." [0][1] There's also NASA's GRACE mission (2002-2017) which has been relaunched (GRACE-FO, 2018) with almost identical hardware [2]: "GRACE measures time variations while GOCE measures the static gravity field." [3] [0] https://en.wikipedia.org/wiki/Gravity_Field_and_Steady-State_Ocean_Circulation_Explorer https://en.wikipedia.org/wiki/Gravity_Field_and_Steady-State... [1] GOCE: the first seismometer in orbit (2013) https://www.esa.int/Applications/Observing_the_Earth/FutureEO/GOCE/GOCE_the_first_seismometer_in_orbit https://www.esa.int/Applications/Observing_the_Earth/FutureE... [2] https://en.wikipedia.org/wiki/GRACE_and_GRACE-FO https://en.wikipedia.org/wiki/GRACE_and_GRACE-FO [3] GRACE & GOCE (2008) https://www.science20.com/planetbye/grace_goce https://www.science20.com/planetbye/grace_goce (Edit: fixed link)