NASA’s chief scientist is resigning, the space agency announced last month in a blog post.

“After more than three years as chief scientist, Ellen Stofan is departing for new adventures,” the agency wrote on its official Tumblr account Dec. 21.

The chief scientist is the head adviser to the NASA administrator on science issues.

In a statement emailed to The Christian Science Monitor on Thursday, Dr. Stofan added she is stepping down to let the new NASA administrator choose their own adviser, since they typically serve for two years.

"I am looking forward to finding my next challenge!" she said.

Stofan’s resignation comes amid other administrative shakeups within the agency, including calls by other top officials not to worry about the incoming presidential administration.

While details of the exact reason for Stofan’s departure are not known, she leaves behind a legacy as a female trailblazer within the agency, as well as optimism about humankind’s future in space and on the Red Planet.

“People have long wondered if we are alone, and we are now actually going to answer that question in the next few decades,” Stofan told NASA in the Tumblr post, a Q&A about her experiences and thoughts.

“We are exploring Mars, where it is very likely that life evolved at around the same time life evolved here on Earth. Conditions on Mars deteriorated after about a billion years, so life either went underground, or became extinct. It will likely take future Mars astronauts to find the best evidence of Mars life,” she said.

She also mentioned the exploration of ocean worlds in the outer solar system, including Europa, one of the moons that orbits Jupiter, where she said we might find life in subsurface oceans.

And NASA is not limiting its reach to our solar system, she added.

“Beyond our solar system,” she said, “the thousands of planets discovered by the Kepler Space Telescope have made me very optimistic that we are close to finding an Earth 2.0 – though that will take us a little longer.”

Stofan served as NASA’s chief scientist in August 2013. SpaceNews reported she left NASA last month, after hinting about her plans at the start of December.

“I am leaving in two weeks, so I guess that falling sign is some indication of that,” she quipped at an astrobiology symposium in Irvine, Calif., on Dec. 5, when a placard with her name on it fell off the podium during her speech, according to SpaceNews.

Stofan was the principal adviser to NASA Administrator Charles Bolden. She advised him on science issues, including strategic planning of NASA science space programs and coordination with other government agencies and the scientific community, according to SpaceNews.

The shakeup comes as the agency wonders how it will fare during the next presidential administration.

President-elect Donald Trump's transition team has not announced who the new NASA administrator and the director of the White House Office of Science and Technology Policy will be. But scientists have been uneasy about how the incoming administration could affect their work, according to SpaceNews’s Debra Warner. The administration will likely include cabinet nominees skeptical of climate change and a space policy adviser and former chair of the House Science Committee, Robert Walker, who has publicly questioned the value of NASA’s Earth science work.

But top NASA officials have urged other scientists to not contribute to the worry they characterized as “noise.”

"You are leaders in your community, please be a source of signal, not a source of noise," Thomas Zurbuchen, leader of NASA's Science Mission Directorate, said Dec. 12 during the American Geophysical Union conference in San Francisco.

Stofan’s announced resignation also coincides with the naming of another new official. A memo circulated internally within NASA last month announced Dennis Andrucyk was named the new deputy associate administrator of science starting Jan. 17. He is currently the deputy associate administrator for NASA’s Space Technology Mission Directorate and acting chief technologist.

While it’s unclear who will succeed Stofan, she will leave behind an impressive example for other female scientists.

“A lot of times, especially early in my career, when I wasn't self-confident, I would feel like, 'I have to work twice as hard just to be taken half as seriously,' ” she told female high school students at a NASA event held in partnership with the White House Council on Women and Girls, part of Women’s History Month. “But as I got more confident, I realized, 'They actually need me here,' ” Stofan said.

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She noted that for inspiration she thought about people like Katherine Johnson, an African-American woman who started to work for the National Advisory Committee for Aeronautics (NASA's predecessor) in 1953, and who was the inspiration for the 2016 film "Hidden Figures."

[Editor's note: This article has been updated to include a statement from Stofan.]