Pope Francis has said that he would be willing to baptise aliens if they came to the Vatican, asking “who are we to close doors” to anyone - even Martians.

In a homily yesterday dedicated to the concepts of acceptance and inclusion, Francis recalled a Bible story about the conversion of the first pagans to Christianity, according to reports on Vatican Radio.

He said Catholicism was a church of “open doors”, and that it was up to Christians to accept the Holy Spirit however “unthinkable” and “unimaginable” it appeared.

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Describing how, according to the Bible, Peter was criticised by the Christians of Jerusalem for making contact with a community of “unclean” pagans, Francis said that at the time that too was “unthinkable”.

“If, for example, tomorrow an expedition of Martians came to us here and one said ‘I want to be baptised!’, what would happen?”

Clarifying that he really was talking about aliens, the Pope said: “Martians, right? Green, with long noses and big ears, like in children’s drawings.”

Shape Created with Sketch. In pictures: 'The many popes of Pope Francis' Show all 12 left Created with Sketch. right Created with Sketch. Shape Created with Sketch. In pictures: 'The many popes of Pope Francis' 1/12 The Pro-Gay Pope In just a year, Pope Francis has managed to change the public perception of the Catholic Church, and the stance it takes on civil issues, like gay rights. Despite originally protesting the legalisation of gay marriage in his native Argentina some years ago, he told reporters this year: “If someone is gay and seeks the Lord with good will, who am I to judge?” Getty Images 2/12 The Rebel Pope No other Pope has urged a shake-up of the Catholic Church quite like Pope Francis, a true rebel of the dioceses. Who, incidentally, used to be a night club bouncer. Getty Images 3/12 The Graffiti Pope Pope Francis become... SUPER POPE in this Vatican-approved street art. But was he happy with the reference to the fictional DC comic character?"To depict the pope as a sort of superman, a sort of star, seems offensive to me. The pope is a man who laughs, cries, sleeps tranquilly and has friends like everyone else, a normal person," he said. So, that's a no, then. 4/12 The Biker Pope Yes, the Pope used to own a Harley Davidson. And yes, he auctioned it off this year and donated the proceeds to a charity that feeds the hungry in Rome. Very Papal. 5/12 The ‘Blue’ Pope Dropping the 'F' bomb during Sunday service? Classic Pope Francis. Sadly, down to a Spanish-speaking slip of the Italian language rather than pure bad-assery. 6/12 The ‘Because I’m Worth It’ Pope That awkward moment when your Papal hat blows off, forcing your barnet into Sesame Street-like spikes. Pope Francis has been there. 7/12 The Chocolate Pope Imagine the Pope's delight (horror?) when he was presented with a giant chocolate replica of himself outside the Vatican by by students on a chocolatier course at the Accademia of Maestri Cioccolatieri, near Venice. EPA/Osservatore Romano 8/12 The Rock Star pope The one and only religious leader ever to grace the cover of Rolling Stone magazine? Introducing... Pope Francis. 9/12 The People’s Pope His U-turn attitude towards sexuality won him Time magazine's coveted Person of the Year accolade, and the cover of gay rights magazine The Advocate. Time 10/12 The Merchandise Pope Thongs, mugs, onesies, earrings and even a baby mobile adorned with decapitated Pope heads, the 'Francis Effect' has seen sales of Papal merchandise soar by 200% over the last year. 11/12 The Fashion Pope The only Pope, as far as we're aware, to be compared to fashion royalty (Karl Lagerfeld. Yes way.) and win Esquire's Most Stylish Man of 2013 award, too. EPA 12/12 The Modern Pope Let it be said, Pope Francis knows a thing or two about social media. He might be a way off 'doing a Dalai' and opting for Instagram, but he's not above posing for the odd 'Selfie' on Twitter. 1/12 The Pro-Gay Pope In just a year, Pope Francis has managed to change the public perception of the Catholic Church, and the stance it takes on civil issues, like gay rights. Despite originally protesting the legalisation of gay marriage in his native Argentina some years ago, he told reporters this year: “If someone is gay and seeks the Lord with good will, who am I to judge?” Getty Images 2/12 The Rebel Pope No other Pope has urged a shake-up of the Catholic Church quite like Pope Francis, a true rebel of the dioceses. Who, incidentally, used to be a night club bouncer. Getty Images 3/12 The Graffiti Pope Pope Francis become... SUPER POPE in this Vatican-approved street art. But was he happy with the reference to the fictional DC comic character?"To depict the pope as a sort of superman, a sort of star, seems offensive to me. The pope is a man who laughs, cries, sleeps tranquilly and has friends like everyone else, a normal person," he said. So, that's a no, then. 4/12 The Biker Pope Yes, the Pope used to own a Harley Davidson. And yes, he auctioned it off this year and donated the proceeds to a charity that feeds the hungry in Rome. Very Papal. 5/12 The ‘Blue’ Pope Dropping the 'F' bomb during Sunday service? Classic Pope Francis. Sadly, down to a Spanish-speaking slip of the Italian language rather than pure bad-assery. 6/12 The ‘Because I’m Worth It’ Pope That awkward moment when your Papal hat blows off, forcing your barnet into Sesame Street-like spikes. Pope Francis has been there. 7/12 The Chocolate Pope Imagine the Pope's delight (horror?) when he was presented with a giant chocolate replica of himself outside the Vatican by by students on a chocolatier course at the Accademia of Maestri Cioccolatieri, near Venice. EPA/Osservatore Romano 8/12 The Rock Star pope The one and only religious leader ever to grace the cover of Rolling Stone magazine? Introducing... Pope Francis. 9/12 The People’s Pope His U-turn attitude towards sexuality won him Time magazine's coveted Person of the Year accolade, and the cover of gay rights magazine The Advocate. Time 10/12 The Merchandise Pope Thongs, mugs, onesies, earrings and even a baby mobile adorned with decapitated Pope heads, the 'Francis Effect' has seen sales of Papal merchandise soar by 200% over the last year. 11/12 The Fashion Pope The only Pope, as far as we're aware, to be compared to fashion royalty (Karl Lagerfeld. Yes way.) and win Esquire's Most Stylish Man of 2013 award, too. EPA 12/12 The Modern Pope Let it be said, Pope Francis knows a thing or two about social media. He might be a way off 'doing a Dalai' and opting for Instagram, but he's not above posing for the odd 'Selfie' on Twitter.

Francis said that Christianity had struggled from its earliest stages with the temptation to reject “the living presence of God” in various forms.

But he added: “When the Lord shows us the way, who are we to say, ‘No, Lord, it is not prudent! No, let's do it this way’. Who are we to close doors?”

While Francis appears to have taken the argument to its logical extreme, this is not the first time that the Vatican has raised the prospect of baptising extra-terrestrial beings.

Speaking at the British Science Festival in 2010, one of then-Pope Benedict XVI’s astronomers said he would baptise an alien “if they asked”. While he accepted that the chances of ever getting such an opportunity were slim, Guy Consolmagno said: “Any entity – no matter how many tentacles it has – has a soul.”