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 even to be there.
The frostiness is beginning to affect scientific research, too. Over the past few days Chinese researchers, including some who work at American universities, have been told that their nationality means they are not welcome at a conference on exoplanets due to be hosted at NASA's Ames research centre in California next month. Incensed, several prominent American astronomers have said that they will boycott the meeting in protest.

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

The language of the law is so broad that it extends to Chinese researchers affiliated to American universities. In theory, the conference organizers could have applied for a special exemption from the law. But after rumours emerged earlier this year of Chinese espionage at NASA Dr Bolden imposed a blanket ban on visitors from China, as well as from Burma, Eritrea, Iran, North Korea, Saudi Arabia, Sudan and Uzbekistan.

It is hard to fathom what secrets any supposed Chinese spies would have been able to pilfer at a conference devoted to alien planets. (The Economist tried to speak to both NASA and Mr Wolf's office, but the government shutdown in America means there was no one to talk to.) The conference will be discussing data from NASA's Kepler telescope, all of which is freely available to anyone, Chinese or otherwise, already.
Dismayed by the ban, several big names in exoplanet research—including Debra Fischer, who leads a research group at Yale University, and Geoff Marcy, an exoplanet pioneer from the University of California, Berkeley—have announced that they will not be attending. "I understand people from certain other countries are being excluded from attending," writes Dr Marcy in an e-mail to the organisers.  "In good conscience, I cannot attend a meeting that discriminates in this way. The meeting is about planets located trillions of miles away, with no national security implications." 

The organizers say that the meeting was scheduled long before the ban came into effect. They have no choice but to comply with the law. 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 its buildings, it is unclear whether scientists in China and other unwelcome countries will in fact be able to view the streams.)

One option, says Chris Lintott, an astronomer from the University of Oxford, might be to move the event to a neutral, non-NASA ground. The organizers have discussed the idea, says Dr Boss. But with only a month to go and much of the American government on involuntary leave (not to mention the costs of a last-minute switch), it seems unlikely that will happen. With the Chinese absent and some of the field's leading lights planning to stay away, the chill will be unmistakable.