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Planetary Scientist Alejandro Soto takes a Comparative View of the Solar System

 Alejandro Soto smiling.
Alejandro Soto, Ph.D.

While AAAS Member Alejandro Soto, Ph.D., has degrees in astronomy, astronautics and aerospace engineering, and planetary science, he thinks of himself first and foremost as a planetary scientist.

“My focus isn’t just on one planet,” says Soto, a senior research scientist at the Southwest Research Institute, an independent and global non-profit research organization. “I’m trying to understand how all the planets function, how they came to be, what does it mean for our past, what does it mean for our future. I’m interested in the commonalities of it all.”

He is particularly interested in Mars and Titan, one of Saturn’s moons. He specializes in modeling their atmospheres, using the same tools climate scientists use to study Earth’s climate.

For example, he and collaborators modeled how Mars’ atmosphere interacts with salty water on and near the planet’s surface. Their analysis showed it is very unlikely microbial life as we know it on Earth could survive in brines on Mars’ frigid surface, so there is little cause for concern about contaminating the Martian ecosystem with Earth microbes.

The team published their results in Nature Astronomy in May 2020.

“I’m looking forward to other groups trying to tackle the same question and seeing what kind of results they come up with,” Soto says. In the meantime, his team plans to run analyses on more localized scales, such as craters and the next rover landing site, to see if the results continue to hold.

Soto is also passionate about developing new instruments to study planets. For example, he is working on a new device to measure dust particles in the air at a very high resolution.

“It’s something we’d love to send to Mars,” he says. “Dust dominates everything in the climate system on Mars, so a better understanding of dust will be critical for basic science, and especially if we ever have human operations there.”

He took the new device to Iceland in 2019 for field testing and is now busy working with his colleagues to improve its data analysis. He has found himself running minor systems checks in his backyard in Lafayette, Colorado, while the institute’s labs were closed due to the pandemic.

Science runs in Soto’s Puerto Rican family: his father was an engineer; his sister is a wildlife-biologist-turned-data-analyst. Growing up in Atlanta, Georgia, Soto was immediately fascinated by outer space after watching movies like “2001: A Space Odyssey.” From an early age, he was playing with chemistry sets and devouring space books.

After studying astronomy as an undergraduate at Dartmouth College, he realized the time scale for proving astronomical theories – hundreds of years – was not going to satisfy his desire to know more. A 1997 summer school course at the Vatican Observatory sparked his interest in the solar system. But still not entirely sure what to study, he pursued a master's in astronautics and aerospace engineering at Stanford University. There, he helped build a satellite that was launched into space, and discovered how much he enjoyed engineering.

He spent four years at the NASA Jet Propulsion Laboratory (JPL), where he helped work on several NASA missions, including Deep Impact, which slammed a missile into an asteroid to study its guts, and Mars Reconnaissance Orbiter, which has studied Mars’ atmosphere and terrain from orbit since 2006. As a junior engineer, his role was not a glamorous one; he recalled a midnight shift babysitting a camera as it ran through tests to withstand extreme temperatures. He also helped coordinate between instrument designers and spacecraft engineers to ensure all parts would integrate.

“What brings me the most glee is knowing I worked on something that is now somewhere else in the solar system,” he says.

As much as he liked the hands-on work, Soto realized he was most fascinated by the underlying science. His work at JPL fostered connections with atmospheric scientists at the California Institute of Technology, where he went on to complete a Ph.D. in planetary science.

Now at the Southwest Research Institute, he has the opportunity to pursue diverse topics, from possible habitability on Mars, to the methane clouds of Titan, to asteroid dust particles as part of a NASA-funded project called Project ESPRESSO. Core funds are available for preliminary instrument development, but otherwise, researchers are required to secure 100% of their own research funding.

“I enjoy it,” he says. “With the exception of the time I spend writing proposals, I do research all day.”

A willingness to collaborate and “follow the random threads as they come along” continues to open new doors and research questions. But ultimately, it all ties back into his desire to understand the differences between planets and draw comparisons that inform life on Earth.

“The same set of physics produces a menagerie of wonderful, fascinating, different planets,” he says. “That’s the stuff that drives me forward.”

Many other researchers can now also turn their sights to the sky, even if they hadn’t considered it before. Soto observed that when Mars rovers began sending back data, many Earth geologists began studying Mars geology.

“They suddenly became planetary scientists because the opportunity to study that came along,” Soto says. “A lot of what makes a planetary scientist comes down to: do we have the means to ask these questions? With more support for space-based measurements, the more we can ask and the more we can discover.”