"Initially, you think whoever is doing that is crazy," said Pérez, 19, an international relations major and president of Penn's junior class. "But now, looking back, I think anything is possible. That's sort of the motto we have - anything can be done if you put hard work and effort and passion into it."
Pérez made his ambitious run in late May as part of an expedition sponsored by the nonprofit impossible2Possible, which pushes youth to reach beyond their limits and educate others through adventure. Its founder, Ray Zahab, a Canadian former pack-a-day smoker turned extreme athlete, ran 4,300 miles through the Sahara over 111 days in 2006, raising awareness of clean-water initiatives in Africa. His story was featured in the documentary Running the Sahara, narrated by Matt Damon.
In addition to running, Pérez and his four companions taught astronomy lessons via video conferencing to students at dozens of schools around the world. With its high altitude, virtually no cloud cover, and terrain resembling Mars, the Atacama Desert is generally considered one of the best places in the world for astronomical observation.
The program, funded by sponsors and the founders, is free to participants and schools. Each expedition costs in excess of $100,000, Zahab said.
"It's life-altering for these kids," Zahab said. Reflecting on his Saharan journey, Zahab, 45, a college dropout, said: "It was the greatest learning experience of my life."
Pérez is the first student from Pennsylvania or New Jersey to run in one of the nonprofit's expeditions, program officials said. He was the only U.S. runner on the Chile trip; two were from Canada, one from New Zealand, and one from Italy.
Born in Puerto Rico, Pérez moved to Louisiana six years ago knowing little English. He graduated from high school in New Orleans and earned a spot at Penn. He nurtured his grit by wrestling, swimming, and practicing judo.
He heard of impossible2Possible while in high school. A friend boasted on Facebook of taking part in an expedition in Bolivia. With a love of travel and adventure, Pérez applied for the next trip, to Botswana. He was turned down but didn't give up.
Optimistic that he would be chosen for the Chile trip, he started training in December, a month before he was selected. He ran along the beach near his parents' home, now in Galveston, Texas, and later along the Schuylkill. The program provided him with a nutritionist and three coaches, who also helped him get ready via regular Skype calls.
"It became a passion for me to train and really be prepared," Pérez said.
On the trip, Pérez and his running mates rose at 6 a.m. daily. They cleaned up with baby wipes - they had no running water - tended to blisters, and had breakfast. At 7:30 a.m., they filmed their introductory video of the day, then began running. They continued until about noon, then broke for lunch and a video conference lesson, which allowed children to ask questions from their classrooms.
A support vehicle stayed out in front of the runners, and other support staff followed. Runners traversed sand, asphalt, stones, dried lava, even salt flats. They finished each day about 6 p.m., then filmed another segment.
"It was a pretty intense schedule," Pérez said.
As hot as it was - temperatures reached into the 90s - it was late-fall cool by desert standards.
Pérez at first didn't know how much to eat and drink, which led to dehydration the first day. His teammates huddled around him when he stopped and clasped his leg, and a team doctor rendered assistance before clearing him to run again.
"It's so dry. You don't realize it," he said.
Pérez covered his head with a water-soaked hat to cool down. He drank several gallons of water daily. Runners also gulped a nutritious formula every four minutes - set to a timer - to avoid dehydration.
He ate undercooked salted potatoes for lunch. They gave him needed carbs but didn't weigh him down.
The runners became like family, supporting one another.
"You get really, really close," Pérez said. "There's no bathrooms in the desert. No trees in the desert. You go figure."
Pérez, who is interning this summer with the White House Initiative on Educational Excellence for Hispanics, said the adventure taught him resilience.
"When you're in the middle of the desert," he said, "nothing in front of you, nothing behind you, it really makes you appreciate the beauty of life, the beauty of nature, the beauty of what you're doing it for - the students, who are following you."