Are we alone in the Universe?
Or is life closer than we think?
Here are the top 5 local locations where alien life is most likely.
And by local, I mean within the solar system.
I'm Sofie and welcome to the countdown.
Coming in at No.5 is Venus,
which seems to be an unlikely planet to support life.
Daily surface temperature is topped off at 465 degree celsius.
And it's covered with clouds of sulfuric acid.
Even the hardest bacteria from earth
probably couldn't heck it in the hellish planet.
But in the past, Venus was much milder
and may have had liquid oceans.
Simple microbes could have evolved in those waters.
That is until a runaway green house effect
turned Venus into a scorcher and evaporated them all.
Astro-biologist David Grinspoon has suggested that
Venusian microbes might have found refugee
high up in the atmosphere and clouds.
Venus's clouds are pretty extreme themselves,
with temperatures at the base
reach a roasting 97 degrees celsius
and a bone chilling -8 degree C near the top.
But they do have a goldilock zone in the middle,
with the temperature and pressure similar to earth.
Life forms living in clouds, you say? Pretty far fetched.
But a recent study found that our own clouds here on earth
are lased with bacteria and their by-products.
Venus's cloud layer is much thicker than earth,
which will create a more stable home for alien microbes.
Our No.4 is Enceladus, one of Saturn's inner moons.
A mere 500 km wide,
this moon is only about 15% as large as our own.
But even tiny Enceladus may be large enough to hide life.
When the Cassini's space probe flew by Enceladus in 2005,
it caught sight of a geyser spewing water vapor from the icy surface.
This suggests an active ocean is surging below the moon's frozen crust.
Where does it get the heat to remain in liquid form?
From the pool of gravity exerted by Saturn and its five other moons.
The ocean provides a friendly environment,
and chemicals detected in the plume of water are also favorable to microbial life.
But just because Enceladus is capable of hosting microbes,
it doesn't mean life is there.
Still, if any creature is living on the tiny moon,
it will have a front seat view of Enceladus's beautiful ice geysers.
That is, if it can SEE.
Our No.3, Titan, is also a moon of Saturn.
But Titan is the largest moon in that system,
more than 10 times larger than Enceladus.
So does Titan get a spot on our list?
Well, this moon is very similar to earth.
A thick atmosphere of hydrocarbons shields Titan's surface,
which contains organic compounds capable of supporting life.
And the moon even has earth like weather,
with wind and clouds, that rain down into rivers and lakes
Of course these clouds and waterways don't actually contain water.
They are filled with liquid ethane and methane.
If there is water on Titan, it will be frozen solid.
The temperature on the surface hovers around -179 degrees celsius.
Any life on Titan will have to survive the chilly climate
and the occasional dip in the methane lake,
which means it will look completely different from any life form on earth.
Our runner-up for the top spot, Europa,
is such a popular candidate for alien life,
it got its own movie--Europa Report.
In the film, a team of entrapped astronauts travels to the distant moon to gather data and look for alien life.
But they found more than they bargain for.
While Europa Report is fictional, some scientists do think Jupiter's moon, about size of our own,
could contain life.
To start with, it has plenty of liquid water,
even more than on earth.
Most of that fluid is located in oceans that cover Europa's surface.
This environment sounds ideal, but there is a catch.
All that water is hidden beneath a layer of ice more than 16 km thick,
which means the oceans have no light to fuel photosynthesis.
Instead, scientists think microbes might harvest energy from hydrogen peroxide stored in the ice.
The presence of simple life forms will be even more likely,
IF, as scientists suspect, Europa has volcanic activity.
This will allow heat and chemicals to escape through hydro-thermal vents,
providing more comfortable conditions for underwater life.
Will we travel there any time soon?
[Male Voice: We are clear of Jupiter's orbit.]
[Female Voice: prepping for power descent]
[Female Voice: ladies and gentlemen, hold on. Here we go]
Probably not.
Any exploratory mission will be staffed with robots,
rather than humans.
We've already began to explore our No.1 pick, Mars.
The many rovers we've sent to the red planet have invest it with machine life.
But do biological creatures do well there as well?
As we discussed in the previous Countdown episode,
the Curiosity rover has gathered ample evidence that liquid H2O once flowed on Mars.
And other observations have revealed the red planet may still contain water below surface.
Mars is also the most earth-like of our fellow planets.
True is atmosphere is much weaker than ours,
but we share a similar size and temperature range.
Finally, Mars has plenty of methane, a gas producted by living organisms.
As Curiosity continues to dig up data, we'll learn more about the potential for life on ancient Mars.
And soon, NASA wants to send yet another rover to hunt for past Marsian life.
The new robot might even ship samples of Marsian soil back to human scientists on earth.
And that's your Countdown.
Links to all of these stories are in the description below.
Also don't forget to visit the space lab channel on Youtube and subscribe.
For Scientific American, I'm Sophie Bushwick.
And until next time, I will be looking for signs of life.