![]() ![]() ![]() Increased solar activity since August of 2021 has heated up the upper atmosphere of the Earth, causing the atmosphere to expand. Since the LightSail 2 was initially placed in Low Earth Orbit (LEO) by a Falcon Heavy rocket, the spacecraft experiences a steady drag force caused by the high atmospheric density of LEO altitude air molecules. Even though the thrust generated by solar photons is very tiny, it is continuous, with the spacecraft experiencing constant acceleration. This momentum exchange generates a force (thrust) that propels the spacecraft into a higher orbit. When the photons of sunlight reflect off the Mylar sail of the LightSail 2, they exchange momentum with the spacecraft. Even though photons have no mass, they have momentum due to their energy content. Light is made up of particles called photons that are made up of energy according to Einstein’s famous equation E = mc 2. Solar Sail propulsion is based on the physics of light. LightSail 2 uses the technique called laser ranging to determine the increase in spacecraft orbital altitude by measuring how long it takes a ground-based laser beam to reflect off a small array of mirrors located at the bottom of the CubeSat. The spacecraft is powered by 4 solar arrays with 8 rechargeable lithium-ion batteries that keep the CubeSat functioning during ecliptic periods. The LightSail 2 is a 78 cm length CubeSat that is attached to a 32 square meter solar sail. The LightSail 2 made history by becoming the first spacecraft to change its orbital altitude by thrust generated by the pressure of sunlight. Journal reference: Nature, DOI: 10.On July 22, 2022, the Planetary Society held a Webinar event celebrating the three year anniversary of the solar sail deployment of the Society-built LightSail 2 spacecraft. “The question is, what does this discrepancy tell us? And, especially, what can we learn about the proton structure by understanding these things?” “Other measurements will elucidate whether or not this has an experimental origin, but it seems to be a genuine discrepancy between theory and experiment,” says Juan Rojo at Vrije University Amsterdam in the Netherlands. However, if the anomaly remains, there will have to be a revision to our understanding of the proton’s structure. “We have to eliminate any possibility that this is due to an experimental parameter or artefact, so we do plan to go back and perform more measurements,” he says. Sparveris and his team intend to do further experiments. ![]() ![]() Protons inside some types of hydrogen and helium are behaving weirdlyĭifferent future experiments, like using a beam of positrons – the antimatter counterpart to the electron – could shed light on whether this anomaly is really there or not, says McGovern. “I don’t think most people took really seriously, I think they assumed that it would go away, and, if I’m quite honest, I think most people will still assume that it will go away.” It is very difficult in general to measure the proton’s polarisabilities at low energies with high precision, she says, and there is no obvious explanation from current theories for why it should spike as it does in Sparveris’s result. While the anomalous result appears similar to the 2000 work, the size of the effect has more than halved, says Judith McGovern at the University of Manchester, UK. By measuring how the electrons and protons scatter away from each other, the team can calculate how much each proton is distorted by each photon. In their set-up, when an electron moves past a proton within the hydrogen, it produces a photon, effectively an electromagnetic field, which distorts the proton. To measure the proton’s stretch, Sparveris and his team fired a beam of low-energy electrons at a liquid-hydrogen target. In 2000, one of the first measurements of these found that as you examine ever smaller sections of the proton, it gets briefly stretchier in response to magnetic and electric fields, before becoming stiffer, or harder to deform. These two quantities, which have been measured many times, tell us about the proton’s internal structure. The extent to which the proton can be stretched in this way is determined by its electric and magnetic polarisabilities. When a proton is exposed to electric and magnetic fields, these internal constituents move about according to their charge, causing the proton to deform, or stretch. Protons contain three smaller particles called quarks, which are held together by other particles called gluons, as well as very short-lived “virtual” particles. But physicists are divided on whether this anomaly will persist in future measurements or if our fundamental understanding of the proton’s structure will need to change. The proton is stretchier than we thought, according to new measurements. ![]()
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