When Jill Tarter first began to look for aliens, she drew looks askance from her friends and colleagues. The perception was “What’s a nice girl like you doing in a subject like this?” she recalled in an interview with Ars. Tarter, now 72, would go on to rise above that perception, becoming a leading figure at the SETI Institute. And the astronomer played by Jodie Foster in the movie Contact, which was largely based on Tarter, would further bolster her reputation.

She and her fellow searchers haven’t found E.T. yet, but they have become respected members of the scientific community. These days, when NASA plots future explorations of Mars or ice-covered moons in the outer solar system, they’re driven by the search for microbial life. And with the discovery of billions of planets in the Milky Way, no one snickers any more at the idea of sniffing atmospheres around other worlds for biosignatures.

The search for aliens has become respectable because it no longer is a philosophical or religious matter to ask if we are alone. During Tarter’s lifetime, scientists and engineers have developed the tools and technology to finally probe this question in a meaningful way.

“When I first started in this field, we were coming off the bad science done by Percival Lowell and Martian canals,” Tarter said. “It made the field odoriferous.”

Lowell, an American businessman and astronomer, popularized the idea that the long, somewhat linear features seen on Mars were canals. This influence pervaded the public mind through the middle of the 20th century and featured in science fiction works by both Robert Heinlein and Ray Bradbury. But then NASA probes to Mars, beginning in 1964 with Mariner 4, found a cold, barren, and likely dead world. Many scientists began to dismiss the notion of aliens.

Tarter became intrigued with the search for alien signals from other worlds in the 1970s, while earning a PhD in astronomy from the University of California, Berkeley. She was working on brown dwarfs, objects too large to be planets but too small to be stars. But the work felt remote to her. “I was always wondering why is the taxpayer paying my salary? Once I started working on SETI I no longer had that feeling," she said. "The person on the street I’d talk to understood it. It wasn’t like trying to explain the Large Hadron Collider. It was a topic people have been interested in forever.”

Over time, the alien hunters slowly garnered respect, but during the 1980s and 1990s, SETI remained on the fringes of mainstream science. For example, on Columbus Day in 1992, NASA formally launched a $100 million radio astronomy program called SETI. Yet Congress canceled funding a year later, with some members criticizing the plan as a “search for little green men.” Things began to change soon after that however, aided by two key discoveries which had implications both for life inside the solar system and beyond.

By the 1990s, scientists were finding organisms that survived at very high and very low pressures and temperatures, and sometimes in environments with no oxygen at all. Scientists learned that microbes were a lot more adaptable than previously thought, and they began to consider all of the places in the solar system where life might exist today, such as on ice-covered ocean worlds in the outer solar system like Europa and Enceladus.

Gradually NASA’s plans to explore Mars and these worlds have made finding evidence of present or past life as a key goal. The agency's chief scientist, Ellen Stofan, said in 2015 that NASA is close to achieving that goal. "I think we're going to have strong indications of life beyond Earth within a decade,” she said during a panel discussion last year.

The second key discovery has come far outside solar system. Scientists first began finding exoplanets about 20 years ago, but these were giant, Jupiter-like worlds close to their stars. The launch of the Kepler spacecraft in 2009 changed everything. It has found more than 1,000 confirmed exoplanets, with thousands of more candidate worlds. Moreover, many of the planets it has found are close in size to Earth. Based upon calculations by astronomers working with Kepler’s data, there may be as many as 40 billion Earth-sized worlds in the habitable zones of solar systems in the Milky Way Galaxy.

“Kepler has been a game changer,” Tarter said. “When I first started this work, we didn’t know if there were any planets beyond our solar system. The fact that many of them are Earth-sized and close to Earth mass is also a hopeful outcome because we don’t know what’s required for life.”

For a long time, the SETI Institute’s work was largely an ad hoc affair. But with the Allen Telescope Array and better computation, its ability to search for alien signals has gotten much better. Think of it like this, Tarter says, comparing the area and dimensions of space and time that must be searched to the vastness of Earth’s oceans. During the last 50, years SETI astronomers have looked at about one glass of that water. With new tools, she said, they will perhaps look at an amount the size of Lake Michigan during the next two decades.

And NASA is getting into the game, too. It is contemplating projects such as a giant starshade, which would block the light from distant stars and allow astronomers to image rocky, Earth-like worlds directly. It is proposing projects to study the atmospheres of those worlds as well.

It is perhaps a measure of the SETI Institute’s success that when the Kepler spacecraft found a world with rapidly dimming light, the explanation of an alien megastructure as the cause wasn’t dismissed out of hand. Instead, astronomers have considered aliens as one possible cause of the unique light curve from KIC 8462852.

For Tarter, hunting for aliens has paid dividends. After the movie Contact, she was named one Time’s 100 most influential people in the world and recently became a member of the Creative Class. Respect is nice, she says, but what Tarter is really after is answers. “I think this is our century,” she said. “I would like to be able to stay around long enough to see this play out.”