We pick apart some of the most com­mon mis­con­cep­tions in the cos­mos

How It Works - - SPACE MYTHS -


Blame Star Wars for this one. In The Em­pire Strikes Back, Han and co weave their way through an as­ter­oid belt in the Mil­len­nium Fal­con, dodg­ing fly­ing rocks all over the place, against the odds. It was a great scene, sure, but the sci­ence was lack­ing. The prob­lem is that as­ter­oids just aren’t that close to­gether. They’re re­ally, re­ally far apart, and fly­ing be­tween them would be a breeze. In the as­ter­oid belt be­tween the or­bits of Mars and Jupiter, you’d be hard-pressed to even see one as­ter­oid from the sur­face of another.

Sci­en­tists es­ti­mate the main as­ter­oid belt con­tains be­tween 1.1 and 1.9 mil­lion as­ter­oids larger than one kilo­me­tre in di­am­e­ter, and mil­lions of smaller ones. Most known as­ter­oids or­bit in this main re­gion, and on av­er­age each size­able as­ter­oid is at least sev­eral mil­lion kilo­me­tres away from another, with the chances of a col­li­sion be­ing about one in 1 bil­lion. Could we as­sume that in a galaxy far, far away, they’ve found an as­ter­oid belt that’s much more tightly packed? Ab­so­lutely. But in ours, this scene would have been a lot less ex­cit­ing.


Per­haps the most com­mon mis­con­cep­tion about space con­cerns what space ac­tu­ally is. A lot of peo­ple seem to think that when you launch a rocket straight up­wards, you even­tu­ally reach a point where you start float­ing. That’s why the as­tro­nauts on the In­ter­na­tional Space Sta­tion (ISS) ap­pear weight­less, right?

Well, we’re afraid that’s just not true. The rea­son as­tro­nauts on the ISS ap­pear to be float­ing is be­cause they’re in con­stant free fall towards Earth. In the late 17th cen­tury, Isaac Newton first pub­lished his thought ex­per­i­ment to demon­strate his con­cept. He sug­gested that if you fired a can­non­ball hor­i­zon­tally from the sur­face of Earth — at greater and greater speeds — the ball would not hit the Earth but in­stead or­bit the planet. That’s ba­si­cally what’s hap­pen­ing on the ISS. They’re mov­ing so fast (over 28,000 kilo­me­tres per hour) that they con­stantly fall towards the Earth. As a re­sult, they’re in con­stant free fall and ap­pear to ex­pe­ri­ence weight­less­ness.

In fact, at an alti­tude rang­ing be­tween 370–460 kilo­me­tres above the Earth’s sur­face, the ISS still ex­pe­ri­ences 90 per cent of Earth’s grav­ity. Ev­ery­thing in or­bit ex­pe­ri­ences the pull of our planet, it’s just that they move so fast side­ways that it seems like they are weight­less. So, the next time you see footage of as­tro­nauts float­ing around, just remember they’re not in zero grav­ity. They’re ac­tu­ally con­stantly fall­ing, but thanks to the ex­tremely low fric­tion of the up­per at­mos­phere, their space­craft never slows down, so they never fall to Earth.


Con­trary to pop­u­lar be­lief, black holes are not cos­mic vac­uum clean­ers that suck up ev­ery­thing in their vicin­ity. In fact, they be­have not that dif­fer­ently from a star at first. It’s when you get close that things start to get weird.

First, let’s back up. A black hole forms when the cen­tre of a mas­sive star goes su­per­nova, leav­ing be­hind a dense core that col­lapses in on it­self. These are known as stel­lar mass black holes and, as their name sug­gests, they’re ac­tu­ally quite sim­i­lar in mass to a star. If the Sun was sub­sti­tuted by a black hole of equal mass, all the plan­ets cur­rently or­bit­ing the Sun would con­tinue on their or­bits as they are now and would not in­stantly be pulled in. But the Sun is not mas­sive enough to ever evolve into a black hole.

At the heart of our galaxy is a su­per­mas­sive black hole, known as Sagit­tar­ius A*, and we see these at the cen­tre of al­most ev­ery mas­sive galaxy. Again, these black holes clearly don’t suck ev­ery­thing in. Some, in more dis­tant gal­ax­ies, are sur­rounded by a quasar — a su­per­heated ac­cre­tion disc of gas and dust — and some can fire jets.

But there is a point be­yond which black holes be­have quite strangely. At the edge of its in­ner core, which can be just a few kilo­me­tres across, you’ll find the event hori­zon. This is where the grav­i­ta­tional pull is so in­tense that noth­ing — not even light — can es­cape. At this point, you could prob­a­bly say that the black hole was suck­ing you in. What hap­pens next is any­one’s guess, how­ever, be­cause what goes in never comes out.


Con­trary to what some films might have you be­lieve, tak­ing your suit off in space won’t cause you to im­me­di­ately ex­plode. Yes, your out­look isn’t great, but it might not be as dra­matic as some think. The first thing that would hap­pen is you’d lose con­scious­ness after about 15 sec­onds due to a lack of oxy­gen after your body has used up the oxy­gen in your blood. Be­fore this hap­pens, you would have needed to breathe out as much air from your lungs as pos­si­ble, oth­er­wise that oxy­gen will rup­ture your lung tis­sue.

Next up you’ve got ebullism, where the drop in pres­sure (space­suits are like mini space­craft, remember) causes gas bub­bles to form in­side your body flu­ids. A test sub­ject ac­ci­den­tally ex­posed to a vac­uum in 1965 re­ported that he also started to feel saliva on his tongue boil­ing due to the drop in pres­sure. So after a few min­utes you’d be in pretty se­ri­ous trou­ble, and while you might not ex­plode, you prob­a­bly don’t want to stay out­side for too long.

“Black holes are not cos­mic vac­uum clean­ers”

Mer­cury is the clos­est planet to the Sun, so surely it should be the hottest planet, right? Well, not quite, and the rea­son why is rather in­ter­est­ing. The hottest planet in the

So­lar Sys­tem is ac­tu­ally Venus, with an av­er­age sur­face tem­per­a­ture of 462 de­grees

Cel­sius. But, Mer­cury reaches highs of ‘only’ 427 de­grees Cel­sius.

The rea­son for this dif­fer­ence is that Venus, un­like Mer­cury, has a thick at­mos­phere. In­stead,

Mer­cury pos­sesses a thin ex­o­sphere made up of atoms blasted off its sur­face by so­lar wind and mi­crom­e­te­oroids. While Mer­cury heats up in di­rect sun­light, things get hot­ter on Venus, where the mainly car­bon diox­ide at­mos­phere traps the Sun’s heat in a run­away green­house ef­fect. Sci­en­tists think that Venus may once have ac­tu­ally had shal­low-liq­uid wa­ter oceans and hab­it­able sur­face tem­per­a­tures, but ex­po­sure to sun­light caused the ocean to evap­o­rate, and with no wa­ter vapour re­main­ing, the planet’s at­mos­phere has thick­ened and its tem­per­a­tures have risen.

Trav­el­ling through the as­ter­oid belt would not be as ex­cit­ing as you might think As­ter­oids very rarely col­lide in space, but it’s prob­a­bly spec­tac­u­lar when they do The sen­sa­tion of be­ing in space can make it feel like there’s no grav­ity As­tro­nauts on the ISS can have a great time in the mi­cro­grav­ity en­vi­ron­ment

Su­per­mas­sive black holes are thought to be at the cen­tre of nearly ev­ery large galaxy Try and stay in­side your space­suit if you can Black holes aren’t as dan­ger­ous and deadly as is com­monly thought

Mer­cury might be the clos­est planet to the Sun, but it’s not the hottest Venus is the hottest planet in our So­lar Sys­tem thanks to its thick at­mos­phere

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