The absence of air in the interplanetary spaces
(to a very high degree of exhaustion) was appreciated
by Newton: he may have been the first. His demonstrations
in the Principia are heavily bound up with the combined
effects of gravitation and atmospheric resistance on the
motion of bodies, a subject that attracted his interest
and study, from the earliest 'De Motu..' of 1684, through
Book 2 of the 'Principia'.
In book 2 of the Principia, Newton made it a point
to study at what rate the combination of gravitational
and (de)compressive effects should cause the density of
the earth's atmosphere to decrease with distance above the earth's surface (esp. Book 3 Prop. 10,
(applying Book 2 Prop.22 Scholium)
[https://books.google.com/books?id=6EqxPav3vIsC&pg=PA73 up to PA76]).
He calculated that at an altitude of even 200 miles up, the air should be 'rarer' than at the earth's surface in a ratio of roughly 75 x 10^12 to 1.
This is practically a vacuum. In Book 3 Prop.10 Newton went on to conclude that there should be at most no appreciable atmospheric-type drag on the motion of Jupiter.
In the General Scholium Newton afterwards wrote:
(translation slightly amended here, closer to the Latin original):
"Bodies, projected in our air, suffer no resistance but from the air.
Withdraw the air, as is done in Mr. Boyle's vacuum, and the resistance
ceases. For in this void a bit of fine down and a piece of solid gold
descend with equal velocity. And the same reasoning applies to the
celestial spaces which are above the Earth's atmosphere".
Near-contemporaries saw the interplanetary void as a feature
of Newton's theories (and sometimes as an attackable one, even
absurd). Voltaire, with characterstic dry humour, included it in his contrasts between Newton and Descartes (1733): "A Frenchman arriving
in London finds things quite changed in philosophy as in everything else:
he left the world full, he finds it empty. In Paris one sees that the
universe is composed of vortices of subtle matter: in London one sees
nothing of that." &c. (Voltaire, 'Lettres Philosophiques', 1733,
Lettre XIV. 'Sur Descartes et Newton'.)