The relationship between the literary and speculative fiction genres is like the episode of original Star Trek where Captain Kirk is teleported in to an evil, parallel dimension. Both genres have their own star authors, publishers, and of course literary accolades. (Which genre requires that you assassinate your rivals to advance is for you to decide.) Granta's lists of 20 novelists under 40 – American, Spanish-language, Brazilian and most famously the British contingent – being renewed for 2013 this week – have become an institution in literary fiction. SF has no direct equivalent, but if it did, who might be on it?

Two things connect the 20 writers on this list. The first is a fascination with the weird and fantastic. The second is their love and affection for the pulp roots of SF. One or two may be just a smidgeon over 40, but will no doubt be among the writers shaping speculative fiction for decades to come. And I have looked beyond Britain where I can to find the most interesting voices in what is increasingly an international SF genre.

Lauren Beukes is a South African author of "cyberpunk" science fiction whose novel Zoo City brought her very widespread acclaim, and a major publishing deal for upcoming novel The Shining Girls. James Smythe's The Explorer and The Machine are the kind of breathtaking conceptual SF long absent from the genre. Hannu Rajeniemi's soaring space opera The Quantum Thief and Madeleine Ashby's vN series both reawaken the slumbering body of "Hard SF" rooted in real science. French writer Aliette De Boddard fuses many ideas from SF and fantasy in both her novels and short fiction. And with indie publishing phenomenon Wool reaching more than a quarter of a million sales, Hugh Howey has become overnight one of SFs bestsellers.

Joe Abercrombie is the self-proclaimed Lord of "grimdark" epic fantasy, whose writing displays a wit and style beyond the battle sequences and torture scenes that dominate the gritty world of grimdark. NK Jemsin brings an immense storytelling talent to the tradition of epic fantasy, with a series of beautiful stories that have garnered Hugo, Nebula and World Fantasy award nominations. The Throne of the Crescent Moon by Saladin Ahmed is notable for its middle-eastern fantasy setting, but the work's real strengths are its deep sense of irony and dark humour. And of course British author China Miéville has re-worked the fantasy genre into many and varied weird forms from Perdido Street Station to Embassytown, though he is technically ineligible, as he turned 40 last year.

Joe Hill is arguably the most significant horror author of the last decade, with 20th Century Ghosts, Heart Shaped Box and the upcoming NOS4A2 setting the bar for the entire genre. Chuck Wendig's Blackbirds series fulfils the promise of an author who is a firm favourite among fans for his characterful online presence. Seanan McGuire scooped five Hugo nominations this year alone and as Mira Grant writes one of the most acclaimed and accomplished entries among a spate of recent zombie apocalypse novels. Robert Jackson Bennet's debut novel Mr Shivers drew acclaim by crafting an alternative fantasy from the milieu of the Great Depression. And any survey of the contemporary horror genre would not be complete without the bizarro masterpieces of Carlton Mellick III. If Mellick had written only Warrior Wolf Women of the Wasteland he would be on this list, but with dozens of other equally grotesque creations tearing up the world his name is set for sci-fi immortality.

Catherynne Valente's novels and stories range widely across the fantastic, but it is her dark urban fantasies such as Palimpsest that best showcase her baroque prose style. Tom Pollock's debut The City's Son marked the appearance of a powerful new imagination in SF, and hopes are high for the upcoming sequel. As they are for the debut novel of Elizabeth May, with The Falconer among the most anticipated fantasy novels of 2013. The young adult stories of Francis Hardinge follow in the footsteps of the great Diana Wynne Jones by being equally enchanting for children and adults. And Who Fears Death by Nnedi Okorafor scooped its author a prestigious World Fantasy award in 2011, which we can only hope is the first of many.

Who have I missed from my top 20? It's almost a cliche to call the literary world elitist, but it's hard to escape the idea with lists like Granta's defining the best of the best. In contrast the SF genre is open and communal, driven by the passions of fans and the creativity of authors. The top writers in the field choose themselves by writing great books and engaging with the community. The door is open to any writer who wants to make their mark in the SF genre. All we ask is that you tell great stories.