WASHINGTON — NASA’s 10 field centers remained closed to all but essential personnel Wednesday as the U.S. space agency maintained a heightened state of alert following Tuesday’s terrorist attacks on the World Trade Center in New York and the Pentagon.

NASA headquarters here, however, was reopened for business Wednesday morning, but employees could elect to stay home at their own discretion, according to NASA News Chief Bob Jacobs.

Jacobs said NASA personnel would meet throughout the day to assess the agency’s security situation and decide when to reopen the 10 field centers.

Despite the center closings, Mission Control Center personnel at Johnson Space Center in Houston remain in place and in contact with the crew of the international space station.