In reality the equator isn’t a nice line as one finds one a globe, and similarly there isn’t an altitude where the atmosphere conveniently stops and space begins.
So how does one define that demarcation?
Theodore von Kármán calculated an altitude of 83.6 kilometres (51.9 miles) as a measure at which the atmosphere is so thin that a vehicle would have to travel faster than orbital velocity to derive sufficient aerodynamic lift to support itself.
In practical terms, the Fédération aéronautique internationale (FAI), the go-to body for aeronautics and space record keeping, demarked 100 km (62 mi) as the boundary to space, while NASA and US Air Force defined 80.5 km (50 mi) as their limit by which to measure and attribute astronaut status. There is currently no international law either way.
In a recent paper surveying historical satellite orbit data of the last 50 years (PDF) J. C. McDowell proposed a redefinition of the Kármán Line down to 80 km, close to the 50 mi boundary NASA uses. One of his arguments are the historical precedents set by satellites dipping below the 100 km boundary multiple times before ultimately deorbiting.
The FAI holds annual meetings for their various commissions, among them astronautics, and a general conference, during which members can vote on a number of issues. On 30 Nov the FIA announced they’d be holding a joint FAI/IAF workshop in 2019 to explore possible alterations to the definition of the boundary of space.
Will the Kármán Line be changed before 2023?
This will resolve positive if the FAI changes their definition in regards to altitude requirements (in particular Sporting Code Section 8, at 2.18 and others), negative if not, and ambiguous if the FAI or a similarly placed and recognised international body ceases to exist by the resolution date. Note that the altitude has to be explicitly changed, and indirect changes from amendments to measurement methods, definitions of longitude and latitude, and permitted errors do not count toward positive resolution.