MADISON — Baruch S. Blumberg, the first-ever director of the National Aeronautics and Space Administration (NASA) Astrobiology Institute, told The Scientist yesterday that he would be stepping down in five months. Blumberg, who has held the post since 1999, said he will remain at NASA until the agency appoints a new director.

Under Blumberg's tenure, the Institute — which focuses on how life interacts with planets and other objects in the solar system — grew from nothing at its founding in 1998 to a $20 million-a-year organization with 15 research teams spread out between NASA centers, universities, and research institutes. Based at NASA's Ames Research Center at Moffett Field, California, the Institute, among other ongoing studies, has investigated whether life exists elsewhere in the Universe.

Blumberg, who serves on the editorial advisory board of The Scientist, declined to say why he was leaving the position, but said he had other things he hoped to do and that he was stepping down "with regret." NASA officials, he said, have asked him to stay.

There was no word on a replacement for Blumberg, although the Institute is already advertising for the post. Don Savage, a NASA spokesperson, said a search committee had been formed.

Blumberg received his MD from Columbia University and a PhD in biochemistry from Oxford University. The 1976 Physiology or Medicine Nobel Prize winner — he won for finding a serum marker for hepatitis B and for developing vaccine for the ailment — said he plans to write books. A book on his hepatitis research will be published in May.

Blumberg, 76, said he also plans to devote more time to research. "There's incomplete work I left behind at Fox Chase Cancer Center," he said, referring to the research center in Philadelphia where he spent the bulk of his career.

Michael Meyer, senior scientist for astrobiology at NASA, said the field had "been moving forward" during Blumberg's tenure, and that it was no real surprise that Blumberg was stepping down. "When he was brought on it was with the understanding that he would be here a few years, help establish astrobiology, and that's what's happened," Meyer said.

Blumberg said he will continue to work as a consultant "or in some capacity for NASA."