Mysterious Signal Detected from Long-Dead Source Stuns Scientists

A fleeting yet powerful radio burst was recently traced to an unexpected source: a NASA satellite inactive for nearly six decades. On June 13, 2025, Australia’s ASKAP radio telescope detected an ultra-short radio pulse just 30 nanoseconds long, reaching a peak intensity of over 300,000 janskys—outshining entire galaxies momentarily. Initial uncertainty regarding its origin—possibly a distant cosmic phenomenon—led astronomers to focus on a nearby object instead.

Further analysis localized the signal to Relay 2, an experimental communications satellite NASA launched in 1964 and officially deactivated by 1967. Positioned about 4,300–4,500 kilometres above Earth, the satellite had been dormant for nearly 60 years. Data from the ASKAP array confirmed that the pulse emerged precisely as Relay 2 passed overhead, making it the first known radio burst detected from a long-defunct spacecraft.

What Triggered the Signal and Wider Implications

Researchers suggest the burst was not the result of intentional transmission, but rather a sudden natural discharge. Two leading hypotheses emerged: an electrostatic arc caused by accumulated charge, or a micrometeoroid striking the satellite. The rapid pulse profile matched neither typical spacecraft emissions nor known fast radio bursts (FRBs) from deep space. Instead, it resembled a plasma discharge: either from charge buildup across metal components or from vaporized material following a high-speed impact.

This finding highlights a new type of space anomaly with practical implications. Electrostatic discharges and micrometeoroid impacts pose serious risks to spacecraft integrity. Detecting such events via radio telescopes offers a novel method for monitoring satellite health and space debris activity. In the context of growing orbital congestion and escalating debris levels, passive radio-based sensing could help track unplanned satellite failures or hazardous impacts.

Background of Relay 2 and Broader Context

Relay 2 belonged to NASA’s Relay satellite program, whose primary mission involved experimental communications and mapping Earth’s radiation belts. Following its launch in January 1964, the satellite functioned for roughly three years before ceasing operations in 1967. It operated in an elliptical medium Earth orbit, equipped with transponders and instruments for studying charged particles.

Although spacecraft charging and micrometeoroid penetration are well-known orbital hazards—particularly at hypervelocity speeds near 10 km/s—this represents the first time a single, ultra-fast radio flash from such an event has been observed from a decommissioned spacecraft. Previous radio detections of electrostatic arcs were orders of magnitude longer in duration and much weaker in intensity.

Significance and Outlook for Future Research

The detection of a nanosecond-scale burst from Relay 2 opens pathways for improved space situational awareness. By passively monitoring radio transients, telescopes like ASKAP could help identify real-time anomalies—such as debris collisions, satellite component degradation, or electrical arcing—across the growing population of inactive spacecraft.

The research team has published their findings in a peer-reviewed paper, detailing the methods used to isolate the signal and evaluate its origin. Their work demonstrates how astronomical instruments, repurposed for near-Earth tracking, can reveal unanticipated activity in Earth orbit. As space becomes ever more crowded, such capabilities may prove critical for understanding environmental risks and protecting active satellites.