How Long Do Neutrons Live? Space Probe Could Put Debate to Rest

Extensive absent are the days when physicists could validate new theories by dropping objects from the Leaning Tower of Pisa. From the discovery of the Higgs boson to the detection of gravitational waves, new findings in physics have essential a staggering degree of precision. In look for of this precision, experts are significantly turning to house as the final laboratory.

The hottest thriller that physicists hope to unravel further than Earth is the neutron life span. Within atomic nuclei, neutrons are steady. But when they travel freely, they decay into other particles inside minutes. Pinning down the precise length of neutrons’ lifetime has been significantly tougher than expected. For many years experiments have specified conflicting effects. Being aware of the legitimate price would not just settle this long-standing discussion. It would also aid expose the abundance of helium in the early universe and shed light-weight on the formation of the very first stars and galaxies.

Earth-certain neutron experiments have relied on two approaches to measure the particles’ length. The “bottle” strategy, which involves trapping neutrons in a container and counting how quite a few stay as time passes, offers a life span of 879 seconds. But in accordance to the “beam” strategy, in which experiments detect the protons designed when neutrons decay, the latter particles dwell for 888 seconds. This 9-2nd distinction is enormous, compared with the calculated uncertainty in both measurement. So one particular of them should be wrong—but experts do not know which.

Enter MESSENGER, a NASA spacecraft introduced to examine Mercury in 2004. The probe carried a neutron spectrometer—an instrument that detected no cost neutrons escaping the earth to aid map the minerals on its floor. Using the instrument to measure a fundamental physical continuous was in no way on MESSENGER’s agenda.

Massive Bottle Trap

Just lately, experts understood that they may possibly be able to reanalyze the mission’s facts to measure the neutron life span. In a way, neutrons trapped by the gravity of a earth kind an huge bottle experiment—albeit one particular with a fully distinct set of systematic uncertainties than those related with that strategy (or the beam strategy) on Earth. Moreover, the house location presents benefits these types of as a absence of sounds from vibrations, says Nan Yu, who researches house-primarily based precision measurements at NASA’s Jet Propulsion Laboratory.

A staff led by Jack Wilson, a planetary scientist at the Johns Hopkins College Utilized Physics Laboratory, very first attempted to use facts from MESSENGER’s 2008 flyby of Mercury. But the intricate floor composition of the earth designed as well significantly uncertainty in the calculations. Venus, on the other hand, hosts a properly-comprehended environment of carbon dioxide and nitrogen, so experts realized how neutrons escaping from it would behave. The staff turned its consideration to MESSENGER’s 2007 flyby of Venus, which was created on the spacecraft’s way to Mercury—and produced a scant forty five minutes of facts. “The only reason that the MESSENGER devices had been actually switched on during the Venus flyby was to check that they worked,” Wilson says. “It was not attempting to do any science there.”

For the duration of the Venus flyby, the craft arrived inside 340 kilometers of the earth, making it possible for the staff to count the neutrons current at a huge assortment of altitudes. “Altitude is essentially a proxy for time,” Wilson describes. “The farther you are from the earth, the extended neutrons travel, the a lot more probable they decay.”

In the long run, he and his colleagues at Johns Hopkins and Durham College in England wanted facts from both flybys to finish their product. They calculated the neutron life span to be 780 seconds, moreover or minus ninety seconds—a significant uncertainty assortment steady with both the beam and bottle strategies. The effects had been published on June 11 in Bodily Assessment Analysis. Even though the measurement was not precise adequate to split the measurement impasse nonetheless, the strategy retains assure, experts say.

Hope for a Resolution

“I believe it is a definitely neat concept. I was amazed that [the researchers] had been able to do it,” says Shannon Hoogerheide, who runs ongoing beam experiments at the Nationwide Institute of Expectations and Know-how. Peter Geltenbort, who conducts bottle experiments at the Laue-Langevin Institute in France, also welcomes the “amazing and exciting” consequence. Neither researcher was concerned with the new examine. Long term measurements in house “could have a important effects on the resolution of the neutron life span puzzle,” Geltenbort says. But he cautions that there is a long road in advance.

The actuality that the MESSENGER calculations included facts from flybys of both Mercury and Venus designed a significant systematic uncertainty. In a potential mission, traveling by Venus many times would reduce the need to have for facts from Mercury and considerably lower the uncertainty. Even so, Hoogerheide says, reducing the error bars from ninety seconds to a lot less than 9 seconds will be challenging. “The devil’s in the systematics,” she says. And specified the price and complexities of a mission to Venus, it will be yrs before particle physicists get the prospect to accumulate new facts.

In the meantime, Wilson’s staff is examining outdated facts from Lunar Prospector, a NASA probe that orbited the moon from 1998 to 1999. Like MESSENGER, the probe carried a neutron spectrometer that may possibly generate an estimate of the particle’s life span. In this scenario, systematic uncertainties will crop up from the modest sizing of the moon and its absence of a thick environment. Inspite of the issues in advance, Wilson is optimistic. “I believe getting some radically distinct answer is thrilling,” he says, “because it indicates that there is actual prospective below to make important development.”