It's a question that has fascinated many great minds for decades.
Are we alone in the universe?
Everyone and their mother probably has an opinion on this question, with numerous philosophers and scientists weighing in with their thoughts over the years.
Advert
Usually the conclusion reached is 'Who knows?' Perhaps it is unknowable.
But according to one NASA scientist, alien life 'absolutely' exists.
Speaking at an exhibition in New York, Dr Michelle Tanner reflected on the chances of extraterrestrial life existing.
Advert
And in her opinion, it's closer to home than we think.
Dr Tanner said: "I definitely think we'll find life on another planet.
"I think that in our own solar system, we’re quite close to it, but once again we don’t have that 100 per cent thing."
And which of our galactic neighbours does she think is the most likely candidate?
Advert
"On Mars, we see chemistry that on Earth if it were here we would say is due to life," Dr Tanner explained.
"But the question is, how well do we understand Mars and are we being fooled by something?"
However, that doesn't mean we should rule out other planets within our galaxy.
Venus stands a fighting chance in an unexpected way.
Advert
The planet itself is shrouded in an intense atmosphere that has crushed all landers sent to explore.
However, the clouds may be a different story altogether.
Dr Thaller, a scientist at NASA's Goddard Space Flight Center, said: "I never expected Venus.
"[But] Venus is now one where we see something in the atmosphere that looks very much like it could be produced by bacteria."
Elsewhere, missions are being launched in 2030 to look for signs of life on Jupiter.
Advert
"We see possible signs of life in the atmosphere of Venus, and possibly underneath the ice in the icy moons of Jupiter and Saturn," Dr Thaller explained.
"The solar system may be teeming with simple life, microbial life.
"We just have to get that 100 per cent certainty to say that we found it and we don’t have that yet."
Earlier this year, one of Saturn's moons was found to contain elements that were needed for life.
However, the scientists are still being cautious before they make any statements.
"That’s the thing, we’re waiting until there’s nothing else it could possibly be because can you imagine the kind of trouble we’d get in," said Dr Thaller.
Fair enough, it wouldn't be right to get everyone worked up into a frenzy over a false alarm.
"We don’t have absolute proof yet. Do I think there’s life out there? Absolutely."
Dr Thaller was speaking at Beyond the Light, an exhibition that offered an 'immersive deep space experience'.