Next Generation Planetary Missions Hunt for Gravitational Waves

[veraamorim]

TL;DR Summary

Next-generation planetary missions could hunt for gravitational waves, say astronomers

Spacecraft heading to Uranus and Neptune in the next decade could be used to investigate gravitational waves as they venture into the outer Solar System. That is according to a new study by a team of Swiss and Danish researchers, who say that examination of the radio signals from far-flung probes might reveal the signature of these subtle ripples in the fabric of space-time as they roll across our planetary neighbourhood (arXiv: 2101.11975). https://physicsworld.com/a/next-generation-planetary-missions-could-hunt-for-gravitational-waves-say-astronomers/10.02.2021.
If you were one of the crew on this mission, how would you explain in your report what a gravitational wave is and what measuring instrument is available on your ship to track that wave?

 

[Ibix]

Gravitational waves passing through a region can cause the distance between free-floating objects to change. The Earth is a free-floating object, and so would be a space probe. As far as I can see at a fairly quick glance, they're proposing using Doppler in the telemetry signal from a probe to detect changes in distance (or changes in the rate of change of distance, more precisely, since the probe wouldn't be at rest) to detect such changes.

This isn't in principle different from what the LIGO sensor does. That hangs a couple of objects in an evacuated tube and uses interferometry to detect changes in the distance between the objects. In this case, the distance from one object to the other would be much, much larger, so it it potentially more sensitive to lower energy waves. However, it also means that it could only detect very low frequency waves because of the length of time it takes a radio signal to traverse the distance from here to a probe. It'll only detect waves that have periods comparable to the travel time of the light - a lot lower than the tenth-of-a-second period waves LIGO detects.

Just to be clear, there are not going to be crews on these missions. They're talking about unmanned probes.