Where does the edge of space start? (Credits: Getty Images)
Richard Branson will have spent the last few days celebrating his historic journey to the outer reaches of Earth’s atmosphere on Sunday.
Aspiring astronaut and fellow billionaire Jeff Bezos seems to think Branson’s rocket didn’t reach the edge of the great expanse.
A few days before Branson’s flight, his Blue Origin company seemed to suggest Virgin Galactic’s passengers would have ‘an asterisk next to their name’ because their vessel doesn’t travel far enough from Earth.
So where is the boundary between our planet and space? It turns out the answer is far from straightforward.
Where does space start – what is the Kármán line?
Caption: Jeff Bezos questioned whether Richard Branson had really reached space on Twitter
Blue Origin claims that the so-called ‘Kármán line’ — 100km above Earth — is the ‘internationally recognized’ start of space.
The Virgin Galactic craft reached approximately 86km, some 14km short of this boundary on Sunday.
Named after engineer and physicist Theodore von Kármán, the 100km line was established in the 1960s by an organisation called the Fédération Aéronautique Internationale.
Kármán wanted to define the point where aeronautics became astronautics.
Earth’s atmosphere becomes progressively thinner the higher an altitude you reach.
Air helps carry a plane as it flies through the air in a phenomenon known as ‘aerodynamic lift.’
The thinner the air becomes, the faster a craft must travel to generate enough lift to stay in the sky.
Kármán thought that at a certain point, the air would become so thin that it would stop contributing to lift. This, he suggested, would occur at the physical boundary of space.
The Virgin Galactic space plane in space – or, at least – very near it (Getty Images)
He thought defining this point could help governments decide on airspace boundaries.
He wrote in his autobiography: ‘Below this line, space belongs to each country. Above this level there would be free space.’
In reality, however, the 100km Kármán line is arbitrary, and no legal international definition of the boundary of space exists.
In fact, Kármán himself suggested the line should sit at 84km.
In recent years, astronomers such as Harvard University’s Jonathan McDowell have argued in favour of this lower limit, citing the fact that objects can stay in orbit without disintegrating even if they drop to altitudes of around 80km to 90km.
What are Jeff Bezos and Richard Branson saying?
Virgin Galactic founder Richard Branson, left, receives his astronaut wings from Canadian astronaut Chris Hadfield after his flight to space (Credits: AP)
‘From the beginning, New Shepard was designed to fly above the Kármán line so none of our astronauts have an asterisk next to their name,’ Blue Origin wrote in a tweet.
‘For 96 per cent of the world’s population, space begins 100 km up at the internationally recognized Kármán line.
‘Only 4 per cent of the world recognizes a lower limit of 80 km or 50 miles as the beginning of space. New Shepard flies above both boundaries. One of the many benefits of flying with Blue Origin.’
And, just to twist the knife a bit further, Blue Origin said that Virgin Galactic only has ‘airplane-sized windows’.
Meanwhile, Branson has previously pointed out that the experience for those aboard Blue Origin and Virgin Galactic will be almost identical.
During an interview with National Public Radio (NPR), Branson pointed out Nasa recoginses the 50-mile boundary as the start of space.
In addition, ‘the actual difference in experience is going to be almost non-existent,’ Branson said, explaining that passengers will get roughly equal amounts of weightless time on Unity and New Shepard.
Following his successful flight, Branson said he was able to evaluate the astronaut experience for future passengers.
‘I have dreamt about this moment since I was a child, but nothing could have prepared me for the view of Earth from space,’ Sir Richard said after returning to Earth.
For what it’s worth, Nasa, the Federal Aviation Administration and the US Air Force count anyone as astronaut so long as they’ve travelled to a height of at least 50 miles (80km).
And for passengers on the Virgin Galactic flight, who experienced zero gravity for a few seconds and got a birds-eye view of the entire planet, it will certainly have felt like they flew to space.