# Earth's mass

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#### the_id

##### Guest
Would anyone tell me what Earth’s mass is (preferably in kilograms)? I’m trying to calculate a variety of orbital & escape velocities and can’t believe the difficulty locating that figure (accurately) online.<br /><br />Actually, if anyone had a link to such things, I’d love that.<br /><br />Thanks<br />

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#### the_id

##### Guest
<i>Outstanding!</i> Thank you very much. That appears to be exactly what I needed.

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#### spacester

##### Guest
The most authoritative source AFAIK is JPL's Horizons system.<br /><br />Using the telnet link and entering 399 for Earth, I see they have the mass of the Earth at 5.9736 x 10^24 kg<br /><br />Note that for your calculations to be 100% correct you may or may not need to use the mass of the Earth-Moon system, not just the Earth itself. <div class="Discussion_UserSignature"> </div>

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Welcome.

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#### the_id

##### Guest
Thanks also spacester. <br /><br />Hmm. Figure in the moon, too, 'eh? I'll give that shot. At least one of these orbits would be at 5,000 km above Earth's suface; certainly far enough out for the moon to be a factor.

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#### tony873004

##### Guest
At 5,000 km altitude, the Moon is still a very insignificant player. It doesn't even seriously perturb geosynchronous satellites over 40,000 km up. It could affect escape velocities if the trajectory took it near the Moon. The Moon could slow the craft enough to keep it bound to Earth, or it could boost a craft that didn't quite have escape velocity onto an escape trajectory.

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#### the_id

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Yeah, what I’ve seen so far, the moon is a non-issue unless you just get too close to it.

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#### spacester

##### Guest
I agree that the moon is unlikely to be a factor. I'm sorry for the red herring. My bad, sorry.<br /><br />I mean, it's possible for the moon to matter in calculations, but you can ignore it for all practical purposes. I was thinking about such a possible scenario at the time, and posted too quickly. <div class="Discussion_UserSignature"> </div>

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#### newtonian

##### Guest
Thalion - Thank you for the fact sheet.<br /><br />I have a question, though, concerning the atmospheric figures:<br /><br />They seem to add up to about 101% if you include water vapor average composition of 1%.<br /><br />I assume that does not change the mass, but simply the position of the mass.<br /><br />Is there a degree of accuracy for the mass estimate, say +- 1%? <br /><br />Both spacestar and thallion come up with the same mass, as both have 24 zeros which clearly would not be exactly zero.<br /><br />What I mean to ask is can we with any degree of certainty assign more numbers to those 24 zero digits?

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#### arobie

##### Guest
<font color="yellow">Note that for your calculations to be 100% correct you may or may not need to use the mass of the Earth-Moon system, not just the Earth itself.</font><br /><br />Like for example, a mission to Mars?<br /><br />It's funny, I did a google to find the Earth's mass for some of my own calculations...and I ended up back here at the forums. <br /><br />Thanks The_Id for starting this topic, and thanks Thalion and Spacester for those links.

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