On Monday evening, Microsoft co-founder Paul Allen died of non-Hodgkin's lymphoma at the age of 65. At the time of his death, Allen was the 47th richest person in the world, with a net worth of $26 billion. For the last few decades of his life, Allen used his wealth for a staggering variety of business and philanthropic interests. In addition to owning the Seattle Seahawks and the Portland Trail Blazers, Allen founded a brain science institute, an AI institute, and Stratolaunch Systems, which was exploring private spaceflight.

Yet one of the research areas where Allen made the biggest impact was also the one he spoke about the least: the Search for Extraterrestrial Intelligence (SETI). Indeed, Allen almost single-handedly rescued American SETI by donating over $30 million to scientists scanning the cosmos for intelligent radio signals.

SETI’s early years in the United States was mostly defined by intermittent searches bankrolled with public funds, such as the National Science Foundation-funded program at Ohio State University which discovered the Wow! signal, or university endowments, such as Harvard’s Project Sentinel. By the early 90s, however, many of the early SETI programs had ended. The best hope for detecting extraterrestrial intelligence seemed to be NASA’s first foray into SETI, the Microwave Observing Program, which began observations in 1992. Less than a year after the start of NASA’s SETI program, it was killed by members of Congress who didn’t want to waste money on the “great Martian chase.” The SETI Institute, a nonprofit founded in 1984 by the radio astronomer Jill Tarter, wasn’t going to let SETI die at the hands of a few cynical congressmen, but it also realized that the only hope for the future was privately funded searches.

Fortunately, one of the earliest SETI Institute supporters was Barney Oliver, who founded and directed Hewlett Packard laboratories. So in 1993 Oliver called Bill Hewlett and David Packard of Hewlett Packard, Intel founder Gordon Moore, and Paul Allen to ask for their support.

“It probably only took Barney a few hours on the phone to get each of them to commit $1 million every year for the next five years,” Seth Shostak, the senior astronomer at the SETI Institute, told me on the phone. “I’m not sure any of them were particularly interested in SETI, but they were interested in whatever Barney thought was a good idea.”

This $20 million commitment bankrolled Project Phoenix, a SETI program that ran from 1995 to 1998. Over the course of three years, Project Phoenix rented time on the Parkes radio telescope in Australia and the Green Bank Telescope in West Virginia to scan for signals from 800 stars within 200-light years of Earth.

"There’s no doubt that Paul saved American SETI."

Project Phoenix was better than nothing, but SETI astronomers realized that if the search had any chance of success, it would need its own dedicated SETI radio telescope. Or better yet, an entire array of small telescopes, which together produce a wide view of the sky and can target hundreds of stars at a time. This was the topic of a series of meetings organized by the SETI Institute between 1998 and 2000 that were meant to plot the next two decades of SETI research.

Led by Tarter, the meetings attendees cobbled together a telescope array design that consisted of 350 20-foot radio telescopes. There was just one question: Who would foot the $25-million bill? Knowing that Allen helped revive SETI with Project Phoenix a few years earlier, Tarter reached out to him and asked if he could summon a monetary life raft once again. By 2000, Allen had committed $25 million out of his own pocket to building a telescope array in northern California, the first facility specifically built for SETI in the US.

“We were very excited at the institute,” Shostak said. “Prior to the telescope array, we had to piggyback on other equipment. That’s like being a doctor and everytime you need to do research you need to borrow someone else’s microscope. There’s no doubt that Paul saved American SETI.”

The cost of building a 350-telescope array ended up being far more expensive than anyone at the SETI Institute had anticipated, however. By the time the Allen Telescope Array came online in 2007, only 42 telescopes had been built and Allen’s donation had largely been consumed.

Aerial view of the Allen Telescope Array. Image: Seth Shostak/SETI Institute

Shostak told me he was there for the dedication ceremony where Allen “pushed the button” to turn the system on. He said he briefly had a chance to speak with Allen about what fueled his interest in SETI. According to Shostak, Allen told him that it was because he was interested in finding new ways to use technology.

“I thought it was just a talking point, but Allen’s whole career backs that up,” Shostak said. “The array was in line with that philosophy.”

Over the past ten years, the Allen Telescope Array has had as many successes as setbacks. It has analyzed 200 million signals from thousands of stars, studied unusual high-energy radio emissions, and even scanned the “spliff-shaped” Oumuamua asteroid for signs of intelligent life. The radio telescope experienced a major setback in 2011, however, when it had to shutdown due to lack of funding. It was brought back online the following year with a donation from Qualcomm’s cofounder Franklin Antonio.

Shostak said Allen never returned to the SETI Institute or the radio telescope that bears his name in the decade leading up to his death. Despite this, however, Allen never lost interest in the project or the prospect of communicating with extraterrestrials.