Mission to Uranus could be gravitational wave detector

Detecting gravitational waves for the first time is very difficult, but they can be detected using a variety of techniques. The now famous first discovery with LIGO in 2015 was just one of many possibilities scientists were looking for. A new paper by European and US researchers published on the preprint server arXiv suggests a way scientists could find out even more by tracking the exact location of the upcoming Uranus Orbiting Probe (UOP). Originally proposed by NASA’s Decadal Survey of Planetary Science and Astrobiology, UOP would be the first mission to Uranus since Voyager visited the planet in 1986. When it finally arrives in 2044, instead of the launch date of 2031, it will be almost 60 years since humanity last observed the Uranus system up close. But 13 years is a long transit time. Some of that time is needed for Jupiter’s gravitational propulsion, but most of it will be spent between planets. And the authors of the article hope to use this time between planets to conduct non-Uranus science.

Gravitational waves can disrupt the fabric of space-time, causing noticeable distortions, especially over long distances. If the instruments in question were sensitive enough, the very long distance between UOP and Earth would be a viable way to detect them. This is not the first time that the distance between a spacecraft and Earth has been considered for detecting gravitational waves. Pioneer 11, Cassini, Galileo, Ulysses, and the Mars Probe triangulation probe all had suggestions of using it to detect gravitational waves on their way to their final destinations. However, the instruments they were equipped with were not sensitive enough to detect the tiny fluctuations necessary for practical detection. UOP will have the added benefit of decades of improved instruments, especially communication and timing electronics that are essential for gravitational wave detection. It also helps that we at least know what to look for, since gravitational waves have already been formally detected. The underlying mechanism is very simple: consistently track UOP’s exact position throughout its 13-year journey to Uranus, and compare position anomalies with the expected position based on known causes. These include the gravity of several planets and asteroids, as well as solar radiation pressure on the spacecraft itself. As the authors point out, any or all of these factors could affect the probe’s exact position. For calculations to detect gravitational waves to work effectively, they need to better take into account the effects of gravitational waves (if they exist). But there’s another possible scientifically interesting cause for UOP’s slight change in position: ultralight dark matter. In theory, UOP could be used to test for a type of dark matter known as ultralight dark matter, or even directly detect it if it exists in our solar system. Theorists have numerous models showing how it might work if it existed. UOP could also contribute to this scientific research, using the same types of precise position calculations. And the best part is that UOP can do all this without changing its primary functional mission: exploring the Uranus system. All that would need to change about this mission is to update Earth with consistent positioning data approximately every 10 seconds during UOP’s 13-year journey to its final destination. Let’s assume that these frequent check-ins at home could be useful for detecting gravitational waves or dark matter. In this case, it would likely be worthwhile for UOP mission planners to consider it, but it remains to be seen whether it will be included. The authors of this article make a compelling argument for why they should.

source: Lorenz Zwick et al, Bridging the micro-Hz gravitational wave gap via Doppler tracking with the Uranus Orbiter and Probe Mission: Massive black hole binaries, early universe signals and ultra-light dark matter, arXiv (2024). DOI: 10.48550/arxiv.2406.02306