Talk:681: Gravity Wells

Why is Earth's well's depth listed as 5478km but as 6379km in the inset? Compare with Mars which has 1286 in both places. 87.174.225.131 07:21, 12 April 2013 (UTC)

Best guess is either a goof, or that the lower number is just for Earth itself, while the greater number is for the Earth/Moon system as a whole. Proportionally speaking, we have the largest moon in the solar system, so maybe it wouldn't nicely fit in the Earth well as easily as Mars's and Jupiter's moons do.--Druid816 (talk) 08:28, 12 April 2013 (UTC)

It may be the height needed to go from one gravity well to another. You don't have to get all the way up to escape speed for that.

Adapted from the table in Escape velocity, using h = V_e^2 / 2g:

Location	with respect to	Ve (km/s)	Well depth (km)		Location	with respect to	Ve (km/s)	Solar well (Mm)	Total depth (Mm)
on the Sun,	the Sun's gravity:	617.5	19,435,000						19,435
on Mercury,	Mercury's gravity:	4.3	942		at Mercury,	the Sun's gravity:	67.7	233.6	235
on Venus,	Venus' gravity:	10.3	5,407		at Venus,	the Sun's gravity:	49.5	124.9	130
on Earth,	the Earth's gravity:	11.2	6,393		at the Earth/Moon,	the Sun's gravity:	42.1	90.3	97
on the Moon,	the Moon's gravity:	2.4	294		at the Moon,	the Earth's gravity:	1.4		91
on Mars,	Mars' gravity:	5	1,274		at Mars,	the Sun's gravity:	34.1	59.3	61
on Jupiter,	Jupiter's gravity:	59.5	180,400		at Jupiter,	the Sun's gravity:	18.5	17.4	198
on Ganymede,	Ganymede's gravity:	2.7	372
on Saturn,	Saturn's gravity:	35.6	64,600		at Saturn,	the Sun's gravity:	13.6	9.43	74
on Uranus,	Uranus' gravity:	21.2	22,907		at Uranus,	the Sun's gravity:	9.6	4.7	28
on Neptune,	Neptune's gravity:	23.6	28,400		at Neptune,	the Sun's gravity:	7.7	3.02	31
on Pluto,	Pluto's gravity:	1.2	73
at Solar System galactic radius,	the Milky Way's gravity:	525	14,000

Randall wasn't kidding about the Sun being "very very far down"; its well is 100 times deeper than Jupiter's!

Wwoods (talk) 19:47, 12 April 2013 (UTC)