From Nature‘s Guide to Authors:

Futures is the award-winning science-fiction section of Nature and Nature Physics. Contributions are usually commissioned, but unsolicited articles are welcome. Each Future should be an entirely fictional, self-contained story between 850-950 words in length, and the genre should, broadly speaking, be ’hard’ (that is, ‘scientific’ SF) rather than, say, outright fantasy, slipstream or horror. Each item should be sent as a Word (.doc) attachment to futures@nature.com, including full contact details and a 30-word autobiographical note to be appended to the story if published. (Please do not send presubmission enquiries, but send the whole story.) Unsolicited artwork is not considered. Before submitting, prospective authors are advised to read earlier Futures columns in Nature and Nature Physics; selected examples are available free, and the whole collection of Futures published in Nature is available here (subscription or site licence required).