Measuring the neutron’s lifetime from space could solve an enduring mystery

To really understand neutrons, physicists may have to take to space.

When outside the confines of an atomic nucleus, a neutron decays into other particles in about 15 minutes on average. But exactly how long it lives has been tough to pin down, because two different methods of measuring disagree (SN: 2/1/17).

Now, scientists have made a third type of measurement, using data from NASA’s MESSENGER spacecraft. Although the new measurement isn’t sensitive enough to resolve the discrepancy, a future space mission could help overcome the impasse, physicists report June 11 in Physical Review Research. Determining the neutron’s lifetime is essential to understanding cosmic questions like how certain elements formed after the Big Bang (SN: 5/9/18).

The MESSENGER spacecraft orbited Mercury from 2011 to 2015 and flew by Venus on the way there, taking measurements of neutrons in the vicinity of the two planets. Neutrons are produced in reactions set off by high-energy particles from space slamming into the planets. By measuring how the number of neutrons detected decreased as the spacecraft got farther from each planet, the researchers estimated how quickly those particles were disappearing.

That analysis suggests a shorter lifetime of about 13 minutes, but the large experimental uncertainty on that figure means that it is still consistent with both previous types of measurements.

MESSENGER wasn’t intended to measure the neutron’s lifetime, so a future space mission dedicated to the task could do much better, Jack Wilson of the Johns Hopkins Applied Physics Laboratory in Laurel, Md., and colleagues report.

“Having a third technique to break the tie could be critically important,” Wilson says.