On Thursday, space comes to the inner city as the Barbican opens its new exhibition, The Martian Museum of Terrestrial Art. The (somewhat daft) premise of the show, which contains work by contemporary artists from Joseph Beuys and Bruce Nauman to Andy Warhol and Damien Hirst, is that it is a museum collection of Earth art, curated by a Martian, for Martian visitors.

But what if aliens really did exist? How would Earth art help them to understand us? We asked experts to choose the artworks they would blast off into space to give extraterrestrials a sense of our humanity.

The collector: Anita Zabludowicz

There is only one work that could communicate the entire human existence to an alien; from teenage gangs to the FTSE 100, and that is Keith Tyson's epic Large Field Array (2007, above). The work's title comes from the Very Large Array (VLA), the massive field of radio telescopes in New Mexico, which focuses on one location in space from multiple viewpoints in order to give us as clear a picture of the universe; so we can watch the aliens in their natural habitat. Tyson's sculptural installation focuses our attention on our life on Earth rather than the possibilities of it out there in the Universe. It is made up of 300 60cm (23in) cubes arranged at 1m intervals in a roughly cubic layout on the floor and walls of the gallery. Each cube is different; they range from hyper- real representations (suburban doorstep with cat, milk and newspaper) to experiments in process (a handmade cyclone in a box). Each cube links to the next, making the possibilities of interpretation enormous.

Zabludowicz's 176 gallery is currently showing Living London by Gerry Fox (www.projectspace176.com)

The critic: Rachel Campbell-Johnston, the Times chief art critic

The Crucifixion panel from Matthias Grünewald's Isenheim altarpiece is the most terrifying painting in Christian art. His grisly image of a pierced and putrifying Christ, hung up as a sign of salvation for the sufferers in a leper hospital, speaks of the hopes and horrors of our life. It highlights a mystery at the core of the human condition - the tortured disjunction between faith and flesh.

Théodore Géricault's vast The Raft of the Medusa packs an incredible emotional punch. And who knows, we might need it to. As our own planet's resources are drained, the last survivors might require something to wave that will attract the attention of a passing spaceship. Finally, Walter de Maria's Lightning Field. This sublime work evokes the fundamental powers of creation - and destruction.

The artist: Mark Wallinger, Turner prizewinner 2007

If we presume that life would eventually evolve to such a degree that it produces similarly unfortunate creatures, aware of their own mortality but possessed of complex systems of ethical and aesthetic values, among other unnecessary appendices, this also presumes the inevitability of the development of eyes in the process of alien natural selection. Are there any universal indicators in art? Would abstract art be more able to transcend the normal difficulties involved in reaching accord with aliens or would they have a rather limited nuts-and-bolts approach to mimetic representation?

For these pieces, we have to presume that it is possible to identify something that is quite literally universally popular for all time, as it will be a good few light years before the work is discovered.

This might be a long way round of picking three of my favourite artworks but hoping that our alien friend is curious about what we might look like and that we spend a lot of time wondering how we got here, I would choose three self-portraits. Velázquez's

Las Meninas, the 1669 Rembrandt self-portrait in the National Gallery and Caravaggio's David and Goliath. We can teach those aliens about alienation.

The auctioneer: Jussi Pylkkänen, President, Christie's Europe

We, the viewing public, often behave like Martians when confronted with artworks we do not understand and sometimes seek intentionally to misunderstand.

I would like to send Brancusi's sublime Bird in Space since he was the victim of public derision when he executed the most significant sculptures of the 20th century. In 1926, when his works were sent for exhibition in America, they were seized by customs officials who accused the shipping agents of attempting to import factory machine parts in the guise of works of art to avoid expensive import duties. How ironic that 80 years later we regard these sculptures as visionary.

I also wonder what the Martians would make of our attitude to the artists who create the works on which the market relies. In an industry worth billions of dollars, the truth is that we all stand on the shoulders of the giants who produce the work. The true geniuses knew and know exactly who they are. To stand before their self-portraits is immediately to recognise it: Dürer, Caravaggio, Rembrandt, Picasso, Bacon and Freud all executed remarkable self-portraits, but the work I would send above all others is Sir Joshua Reynolds's self-portrait, which hangs in the National Portrait Gallery. Here the artist sees himself as a visionary, a man looking into the soul of the viewer. This portrait, painted at the age of 25, depicts a man who would certainly be more interested in capturing a world beyond our own than the colourless world around him.

It would also be important to send a Picasso. The artist possessed such self-belief and intellect that he dominated much of the 20th century. That, coupled with an ability to turn his hand to every medium, led to 70 years of brilliance. He was the Mozart of the 20th century.

The Martian Museum of Terrestrial Art, Barbican,

Silk Street, London EC2 (www.barbican.org.uk 020-7638 4141), Thur-May 18

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