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From Eric Kvaalen, Les Essarts-le-Roi, France

Frédéric Marin and Camille Beluffi find that a crew of 98 might be all that is needed for humanity to reach Proxima Centauri in 6300 years at 700,000 kilometres per hour (23 June, p 4). In , they say this is the speed of the Parker Solar Probe. But it will achieve this only by falling deep into the gravity well of the sun. With current technology, a craft would take many tens of thousands of years to reach Proxima Centauri.

The editor writes:
• The Parker Solar Probe was chosen as broadly representative of current technology. A colony ship would, of course, require new technologies to succeed.