A judge on Thursday ordered a U.S. space exploration scientist suspected of passing classified information to an FBI agent posing as an Israeli intelligence officer to stay behind bars.

Magistrate Judge Deborah Robinson decided there was too much of a flight risk for Stewart Nozette, 52, to be free while he awaits trial.

Nozette pleaded not guilty to charges of attempted espionage. He is accused of seeking $2 million for selling secrets to an undercover FBI agent posing as an Israeli intelligence officer. The Justice Department could seek the death penalty.

At the hearing, prosecutor Anthony Asuncion said Nozette told the agent he had passed classified information to Israel in the past. Nozette is not charged with doing so.

Nozette, who is credited with helping discover evidence of water on the moon, was arrested by federal authorities nearly two weeks ago.

The complaint against him does not allege that the Israeli government or anyone acting on its behalf violated U.S. law.