A Beta Probe is a generic UNSC term referring to one of the Slipstream Space probes used by Remote Scanning Outposts. It sends out radio pings and analyzes the spectrum from radio to X-ray. The Beta Probe, like all probes used by the RSOs, is designed to be able to survive the transition from Slipspace to normal space in order to collect data.
The Beta Probe of the Archimedes, at the edge of the Sigma Octanus system, reported the same findings as the Alpha Probe. Both probes gave the mysterious object a mass of 20,000 tons. The mysterious object was a Covenant Fleet en route to the system. William Lovell, stationed aboard the Archimedes at the time, collected the relevant data and logged the anomaly, which had been described by Fhajad-084 in an astrophysics paper published in 2540. This allowed Captain Jacob Keyes to properly alert the other ships in the system of the impending attack.