# Local atmospheric pressure and local surface gravity in Jezero crater?

Did Perseverance and/or Ingenuity measure the local atmospheric pressure and local gravity where they are? Ingenuity had been tested in a 0.006 atm chamber on Earth, therefore I guess the local atmospheric pressure is about the same as the global average on Mars (and Ingenuity eventually did well on its maiden flight), but was such pressure measured by the probes on Mars, to make it safe? Did they also measure the local surface gravity, or their own weight on Mars perhaps?

• There seems to be some confusion over the role of atmospheric pressure. Remarkably, this confusion also appears to extend to the Ingenuity project manager MiMi Aung, who said of the Martian atmosphere: "It has significantly less gravity, but less than 1% the pressure of our atmosphere at its surface" (link); this obviously implying that it was a problem for Ingenuity. But the pressure is irrelevant; what matters for Ingenuity is the atmospheric density, which is about 1.6% of earth's Apr 19 at 23:38
• @TonyK Right, carbon dioxide has a 67% higher density than the Earth's atmospheric composition. However, density varies with temperature. Apr 20 at 5:01

Perseverance has been making pressure measurements daily it seems for a while: https://mars.nasa.gov/mars2020/weather/

750 Pa / 101325 Pa = ~0.007 atm

I believe most surface probes include an 'weather' station to monitor temperatures and pressures for science and engineering purposes.

As for the gravity part of your question, gravitational anomalies are really really small in most cases. Consider these kind of maps from the GRACE and GRACE-FO missions (Earth orbit):

https://en.wikipedia.org/wiki/GRACE_and_GRACE-FO

Notice the units here are milligals, gals are an acceleration unit named after Galileo, 1cm/s^2 or 0.01m/s^2. Using g = 9.81m/s^2 means the local gravity field variations are about +/- 0.005%, not very significant.

On Mars these variations are larger, but still at most +0.27% difference from the nominal 3.721m/s^2: https://pgda.gsfc.nasa.gov/products/57

That being said, there was some more nuanced gravity field modelling for Perseverance's entry, descent, and landing. As I recall from one of the JPL webcasts (I don't remember which one, but it was pre landing with Al Chen talking about it) they noticed a slight drift (sideways motion) when Curiosity was touching down on Mars in 2012 and attributed that to a lower fidelity gravity model. They upgraded to a more accurate model for Perseverance using a "a local gravity correction to the to the onboard J2 gravity model", probably using the data from the second image above.

The EDL parameter update ground command provides a predicted bank command (pre-bank), ground derived navigation states to seed the navigation filter and a local gravity correction to the to the onboard J2 gravity model. The local gravity correction is new for Mars 2020. This parameter was added to mitigate the MSL touchdown velocity anomaly

• These gravity maps neglect the gravitational differences due to rotation, between equator and poles. They only show mascons. Apr 19 at 16:11
• @Giovanni are you asking if they measured those differences due to rotation? Apr 19 at 16:36
• I ask on whether they measured the local gravity, which includes all factors. The rover Curiosity did that: i.stack.imgur.com/2TwLB.png Apr 19 at 16:40
• +1 Very nice answer! I added a bit from your linked source, there was no title or other way to reconstruct the link if/when it breaks/rots. Are meaningless link titles like “Source” sub-optimal, leaving the answer unrepairable if a link rots/breaks?