<p>Quantities in the fact sheets are explained <a href="https://nssdc.gsfc.nasa.gov/planetary/factsheet/fact_notes.html" rel="nofollow noreferrer">here</a>.   The surface acceleration is slightly lower than the surface gravity because the former also includes the effects of rotation, which slightly offsets the gravitational force.</p>

CC BY-SA 4.0
2020-09-06T16:59:20.300Z
Unfortunately, the explanation is incorrect. The centrifugal acceleration at the Earth's equator at sea level is 0.0339 m/s^2. The acceleration due to the Earth's mass (not including centrifugal acceleration) at sea level at the equator is about 9.814 m/s^2.. They should not have added the 0 after 9.8. 9.8 would have been fine. 9.80 was not.
David Hammen
CC BY-SA 4.0
2020-09-06T17:11:26.617Z
The numbers for Earth may be slightly off at the 0.01 m/s^2 (0.1%) level as you note, but it’s clear what NASA’s definition of the two quantities is - one with gravitational acceleration from mass alone, and one including the effects of rotation.
Eric Jensen
CC BY-SA 4.0
2020-09-06T18:45:55.740Z
It's not 0.1%. It is a 75% error as far as I'm concerned.
David Hammen
CC BY-SA 4.0
2020-09-06T16:44:10.810Z
2020-09-06T16:44:10.810Z
Eric Jensen
<p>The technical content of NASA's web pages have sadly declined over the years. The planet fact sheets are exemplary of that decline. The <a href="https://web.archive.org/web/20021208181213/http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html" rel="nofollow noreferrer">December 8, 2002</a> version of that page provides only one value instead of two, titled &quot;surface gravity&quot;. The values are 3.69 m/s<sup>2</sup> for Mars and 9.78 m/s<sup>2</sup> for Earth.</p>
<p>The gravitational acceleration at the surface of the Earth (or Mars) is not constant. It varies with latitude and altitude. The value of 9.78 m/s<sup>2</sup> for the Earth represents the gravitational acceleration, including centrifugal acceleration, at Earth sea level at the Earth's equator. The gravitational acceleration at the Earth's North Pole is a bit greater than this, about 9.834 m/s<sup>2</sup>. There is no centrifugal acceleration at the Earth's poles, and the Earth's poles are a bit closer to the center of the Earth than is the equator thanks to the Earth's rotation. The same concepts apply to Mars.</p>
<p>The value of 9.80 m/s<sup>2</sup> added to the cited page a bit later is arguably erroneous; it should be 9.81 m/s<sup>2</sup> (or even better, 9.80665 m/s<sup>2</sup>) rather than 9.80 m/s<sup>2</sup>. As I've said elsewhere regarding Wikipedia, &quot;that's Wikipedia for you.&quot; Unfortunately, the same applies to NASA web pages, in spades.</p>

CC BY-SA 4.0
2020-09-12T03:52:59.827Z
See also "[@DavidHammen's cool table](https://physics.stackexchange.com/a/141981/83380)" (as referenced [here](https://astronomy.stackexchange.com/a/31825/7982))
uhoh
CC BY-SA 4.0
2020-09-06T16:43:56.003Z
2020-09-06T16:43:56.003Z
David Hammen
<p>The <a href="https://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html" rel="nofollow noreferrer">Mars Fact Sheet at NASA</a> (their NSSDC or NSSDCA section, whatever that means) lists a value for 'surface acceleration' just below one for 'surface gravity'.  They also have the values for Earth, for comparison.  The values for surface acceleration are very similar to those for gravity, just slightly smaller...</p>

<gravity><mars><planetary-science>
What is 'surface acceleration' of a planet or other body? As opposed to its 'g' (gravity)?
Kurt Hikes
# What is 'surface acceleration' of a planet or other body? As opposed to its 'g' (gravity)?

(Asked by: username_0 on 2020-09-06)

The [Mars Fact Sheet at NASA](https://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html) (their NSSDC or NSSDCA section, whatever that means) lists a value for 'surface acceleration' just below one for 'surface gravity'. They also have the values for Earth, for comparison. The values for surface acceleration are very similar to those for gravity, just slightly smaller...

**Tags:** gravity, mars, planetary-science


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## 2 answers

### Answer by username_1 on 2020-09-06. Score: 3

Quantities in the fact sheets are explained [here](https://nssdc.gsfc.nasa.gov/planetary/factsheet/fact_notes.html). The surface acceleration is slightly lower than the surface gravity because the former also includes the effects of rotation, which slightly offsets the gravitational force.

> **Comments:**
> **username_2**: Unfortunately, the explanation is incorrect. The centrifugal acceleration at the Earth's equator at sea level is 0.0339 m/s^2. The acceleration due to the Earth's mass (not including centrifugal acceleration) at sea level at the equator is about 9.814 m/s^2.. They should not have added the 0 after 9.8. 9.8 would have been fine. 9.80 was not.  
> **username_1**: The numbers for Earth may be slightly off at the 0.01 m/s^2 (0.1%) level as you note, but it’s clear what NASA’s definition of the two quantities is - one with gravitational acceleration from mass alone, and one including the effects of rotation.  
> **username_2**: It's not 0.1%. It is a 75% error as far as I'm concerned.  

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### Answer by username_2 on 2020-09-06. Score: 3

The technical content of NASA's web pages have sadly declined over the years. The planet fact sheets are exemplary of that decline. The [December 8, 2002](https://web.archive.org/web/20021208181213/http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html) version of that page provides only one value instead of two, titled "surface gravity". The values are 3.69 m/s2 for Mars and 9.78 m/s2 for Earth.

The gravitational acceleration at the surface of the Earth (or Mars) is not constant. It varies with latitude and altitude. The value of 9.78 m/s2 for the Earth represents the gravitational acceleration, including centrifugal acceleration, at Earth sea level at the Earth's equator. The gravitational acceleration at the Earth's North Pole is a bit greater than this, about 9.834 m/s2. There is no centrifugal acceleration at the Earth's poles, and the Earth's poles are a bit closer to the center of the Earth than is the equator thanks to the Earth's rotation. The same concepts apply to Mars.

The value of 9.80 m/s2 added to the cited page a bit later is arguably erroneous; it should be 9.81 m/s2 (or even better, 9.80665 m/s2) rather than 9.80 m/s2. As I've said elsewhere regarding Wikipedia, "that's Wikipedia for you." Unfortunately, the same applies to NASA web pages, in spades.

> **Comments:**
> **username_3**: See also "[@username_2's cool table](https://physics.stackexchange.com/a/141981/83380)" (as referenced [here](https://astronomy.stackexchange.com/a/31825/7982))  

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