THE American government views China’s space programme with suspicion. Chinese taikonauts are, for instance, banned from the International Space Station, which despite its name is largely an American venture. Most recently, this frosty attitude was on display at an international space conference that took place in Beijing at the end of September. NASA—the world’s biggest space agency—was notable chiefly by its diminutive presence. Its boss, Charles Bolden, had to seek a special dispensation to talk to his hosts.

The frostiness is beginning to affect research, too. Over the past week or so Chinese scientists, including some who work at American universities, have been told that their nationality means they are not welcome at a conference on exoplanets taking place at NASA’s Ames research centre in California next month. Incensed, several prominent American astronomers, including Geoff Marcy at the University of California, Berkeley, who is one of the pioneers of exoplanet research, and Debra Fischer at Yale, who helped discover the first system other than the sun’s with more than one planet in it, have said that they will boycott the meeting in protest.

The ban seems to be related to a law passed earlier this year at the behest of Frank Wolf, a Republican congressman who chairs the congressional committee with jurisdiction over NASA, and who has a history of worrying about China. It forbids NASA from co-operating with the Chinese state or any Chinese company. It also prohibits hosting official Chinese visitors at any NASA facility.

In theory, the conference organisers could have applied for a special exemption from the law. But after rumours emerged earlier this year of Chinese espionage at NASA Mr Bolden imposed a blanket ban on visitors from China, as well as those from Eritrea, Iran, Myanmar, North Korea, Saudi Arabia, Sudan and Uzbekistan.

It is hard to fathom what secrets any supposed spies would be able to pilfer at a conference devoted to alien planets. It will be discussing data collected by NASA’s Kepler space telescope. These are already freely available to anyone who wants them, Chinese or otherwise.

The organisers say that the meeting was scheduled long before the ban came into effect. One of them, Alan Boss, an exoplanetologist at the Carnegie Institution for Science, in Washington, DC, points out that all of the presentations and meetings will be streamed on the web, so any banned researchers will be able to attend electronically, if not physically.

This is almost certainly true for Chinese researchers in America, though given that the restrictions apply to NASA’s computer networks as well as to its buildings, it is unclear whether scientists living in China and those in the other unwelcome countries will in fact be able to view the webstreams. Mr Boss and his fellow organisers have publicly condemned the new rules. But, they say, they have no choice but to comply with the law.

Yet on October 8th Mr Wolf sent a letter to Mr Bolden saying the organisers had overreacted. He pointed out that his law does not forbid co-operation with individual Chinese scientists, and that, as far as he knew, Mr Bolden’s extra restrictions on visitors had been lifted. With America’s government (including NASA) at home twiddling its collective thumbs, no one was available to comment on this.

One option, says Chris Lintott, an astronomer at Oxford University, might be to short-circuit the whole argument by moving the event to a neutral, non-NASA ground. The organisers have discussed this idea, says Dr Boss. But with less than a month to go, America’s government apparently missing in action, and the high cost of a last-minute switch, it seems unlikely that will happen. If the Chinese are absent, and some of the field’s leading lights do indeed stay away, the chill will be unmistakable.