Balloon launches to search for particles coming from outer space

May 12, 2023

Update May 14, 2023

After a successful launch and more than a day in flight, our second super pressure balloon (SPB) carrying EUSO-2 developed a leak, and flight controllers safely terminated the flight over the Pacific Ocean. 

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On May 12, NASA launched an experiment built by an international team led by the University of Chicago to send a scientific balloon to 110,000 feet above the Earth. 

The project, termed Extreme Universe Space Observatory on a Super Pressure Balloon or EUSO-SPB2, is searching for messengers from outer space: tiny, highly energetic particles that hit the Earth on their way from elsewhere in the universe.

EUSO-SPB2 will travel at an altitude about 20 miles above the Earth’s surface—just above the atmosphere. It will ride wind currents around the southern hemisphere, gathering data and searching for tracks produced by two types of rare incoming particles. 

“These extreme particles arrive on Earth with the highest energies ever observed, and we have very few clues of their origins. We are looking forward to finally identifying their deep space sources,” said Angela Olinto, the University of Chicago Albert A. Michelson Distinguished Service Professor of Astronomy and Astrophysics and Dean of the Physical Sciences Division, who heads the experiment. “EUSO-SPB2 will conclude the development of space detectors for the highest energy cosmic rays and begin a new development phase for space neutrino detectors.”

The mission, which involves 280 researchers from 13 countries and 77 institutions, consists of two telescopes attached to a high-altitude balloon launched by NASA.

The instrument moves outside for final confirmation checks before launch.
The instrument moves outside for final confirmation checks before launch. Photo by NASA/Bill Rodman

One telescope searches for particles called ultra-high-energy cosmic rays. These are charged particles that have been accelerated to extremely high energies elsewhere in the universe, and they occasionally slam into the Earth’s atmosphere. They are extremely powerful; they are the highest-energy particles we know of in the universe. 

The other telescope is searching for particles called neutrinos, which can carry information from far away in the universe without being perturbed like other particles do. 

Scientists would love to track these particles back to their origins, because this could tell us how the particles were made: by supermassive black holes, or two massive neutron stars slamming into one another, or even a gigantic shock between clusters of galaxies. The particles would carry information about that event to us, billions of light-years away.

EUSO-SPB2 looks for telltale signs of cosmic neutrinos and cosmic rays as they collide with the molecules inside the Earth or in the atmosphere. Both telescopes look for the light produced by the shower of particles generated by these collisions. 

One telescope detects ultra-high-energy cosmic rays, by looking for the UV light produced when the cosmic rays hit particles in the atmosphere. 

The other telescope looks for a special kind of blue light called Cherenkov radiation that is produced when neutrinos interact with the Earth. These neutrinos generate a very energetic particle which in turn produces particle showers and the telltale Cherenkov light.

Most previous experiments to find these particles have sat on the ground looking up at the atmosphere. EUSO-SPB2 instead sits just above the atmosphere looking down. This gives the instruments a much wider potential view of the traces of these collisions.

EUSO-SPB2 is intended to prove that space-based detection for these particles is possible. Olinto hopes it can provide proof-of-concept for follow-up missions, including one that will sit aboard a satellite orbiting Earth, picking up particle tracks to determine their cosmic origin. 

“The extreme energies involved in the creation of these particles challenge our imagination for how they are produced,” said Olinto. “Understanding which objects can accelerate such extreme particles can lead us to probing the energetic limits of our universe.”

Prof. Angela Olinto, leader of the EUSO-SPB2 project, visits the instrument during pre-flight
checks in Wanaka, New Zealand
Prof. Angela Olinto, leader of the EUSO-SPB2 project, visits the instrument during pre-flight checks in Wanaka, New Zealand Photo courtesy Angela Olinto

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