is one of the most intriguing quests of our time.

From UFOs and little green aliens

to the possibility of life in the underground aquifers of Mars,

there's no end to speculation as to what form this life could take

and how it could have developed.

There's even a raft of videos on the internet

speculating that aliens must have visited

ancient civilisations on Earth,

because otherwise, how else could the Mayans have built

their incredible temples.

Spoiler - there is no evidence at all for this.

Frankly, if I was a Mayan stoneworker from 250AD,

I would find it deeply insulting.

But a more interesting theory, and one which has more credibility,

is that of panspermia.

That life exists throughout the Universe

and can be transported through space from one location to another.

Although it's certainly not proven,

a team of prominent scientists from MIT and Harvard

have been working on a theory that some form of life

was actually delivered to Mars in this way.

Here's what we know.

Life is incredibly adaptable, just look at the way our own species

has managed to thrive across the globe,

and microorganisms, such as archaea and bacteria,

over the course of millions of years of evolution

have been able to modify themselves

in order to adapt to a vast range of conditions.

This means that today there are microbes that can survive

on a variety of diets - sulphur, ammonia, the metal manganese,

and in the presence or absence of oxygen.

Some even survive in the most extreme conditions Earth has to offer.

Pyrococcus furiosus (don't you love that name?)

thrives in hydrothermal vents on the seafloor.

It's optimal growing temperature is 100 degrees Celsius.

Whereas the Antarctic psychrobacter frigidicola

prefers things decidedly chillier.

You can also find these extremophiles hanging out in hot acid,

or surviving desiccation in salt-crusted deserts.

And some of these microbes can even deal with several extremes at once.

Deinococcus radiodurans can be found in both hot springs

and Antarctic soil,

survive desiccation, and is one of the most radiation-resistant

organisms we know.

So these extremophiles are probably the most oven-ready organisms

to survive and, potentially, colonise the hostile environments

of other planets and moons,

as long as there's liquid water at least some of the time.

How would these tiny microbes

even make the journey to these other places?

Well, the easiest way is to hitch a ride with us

as we explore our solar system and beyond.

Tersicoccus phoenicis is a becterium

discovered in Nasa spacecraft cleaning facilities.

Could we have already accidentally introduced bacteria from Earth

to the Moon and Mars?

Another possible way

for these microbes to get around the solar system

is by hitchhiking on meteoroids.

When these crash on a planet,

rocks and debris are shot into space, generating more meteoroids.

So far, 313 Martian meteorites have been found on Earth,

and an Earth rock was also found on the Moon,

therefore we know there has been interplanetary transfer of rocks.

Once in space, the cold and lack of oxygen

are easily dealt with

by our hardy voyagers,

and even regular bacteria can enter a state of dormancy

under extreme conditions,

creating thick-walled internal safe rooms for their DNA called spores.

Heat, cold, acid, drought and UV-resistant packets

of bacterial DNA voyaging through space.

Another big problem is that space is brimming with ionising radiation

that rips DNA to shreds.

Not a problem for deinococcus. Clumps of this little fellow

have survived three years of exposure to outer space.

Others have survived up to six years in spore form.

Yet another problem is time.

Space is big,

so travelling anywhere takes a long time.

That said, in 2020, Japanese scientists revived bacteria

that had laid dormant at the bottom of the ocean

for 100 million years.

So perhaps the extraordinary distances aren't such a problem

for these tiny space travellers.

The final step is surviving the crash landing onto your new home.

And bacteria have been shown to be able to do just that...

As long as they are in deep fractures in the cosmic rock.

So it's entirely possible that microbial life

has already travelled to somewhere like Mars.

Conditions there were remarkably similar to Earth

3.8 billion years ago.

Could these extremophile microbes

have already colonised the underground aquifers of Mars?

If they're already there,

have they adapted to their new environment?

Or maybe life on Earth actually originated on Mars

then travelled over to our planet?

They may not be little green aliens,

or intelligent life as we understand it,

but the very possibility that life could have transferred

across the solar system and beyond is deeply intriguing.

And as the James T Webb telescope begins its search

for tell-tale signs of distant life on other planets,

could we perhaps find out that life is far more inevitable

than we once thought?