Loeb argues that 3I/ATLAS, discovered on July 1, 2025 and set to make its closest approach to Earth on December 19, displays brightness changes far too dramatic to be explained by its nucleus alone. The object’s light fluctuates every 16.16 hours with amplitudes of several tens of percent, a pattern initially attributed to its shape and rotation. But Loeb says the real cause may be periodic bursts of gas and dust streaming from the coma, pumping outward like “blood” through a cosmic heartbeat.
He points to recent images showing multiple jets, including a striking sunward “anti-tail,” indicating that mass loss may occur only when a volatile-rich patch on the object faces the Sun. Such pulsed outgassing could inflate the coma in regular cycles, a signature that would match the observed brightness pattern far better than rotation alone.
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What do the 3I/ATLAS new images reveal?
Recent observations from Hawaii and Thailand captured multiple prominent jets, including a sunward-pointing anti-tail. The images align with a July 21, 2025 Hubble Space Telescope finding that most of 3I/ATLAS’ light comes from a glowing coma surrounding its unresolved nucleus.
Because the nucleus contributes less than 1% of the total reflected light, based on size limits of about 2.8 km, Loeb says it cannot account for the strong brightness swings that observers recorded.
Why a comet ‘heartbeat’ could explain the variability
According to Loeb, the periodic pulsation is more consistent with jets that switch on and off as the object rotates. If a large patch of ice faces the Sun every 16.16 hours, it could trigger a burst of sublimation, sending out a plume of gas and dust.
“This resembles a heartbeat with a puff of gas and dust serving the role of a stream of “blood” through the coma periodically over the rotation period of 16.16 hours,” he wrote.
He compares this cycle to a heartbeat, with each pulse pushing material outward through the coma. Using a Webb Telescope-reported outflow speed of 440 m/s, Loeb estimates the jets could reach 25,600 km within one rotation.
How could scientists confirm this?
Loeb argues that a clear test exists: a movie-like sequence of well-calibrated images taken over several days. Such a dataset could show whether the brightening of the jets consistently aligns with the Sun, which would support a natural explanation.
If the pulses point in arbitrary directions, he says, it could raise questions about whether the object might be technological in origin.
Ultimately, Loeb says the widely discussed 16.16-hour cycle is not tied to the comet’s shape or nucleus rotation but to collimated jets extending far beyond it. Whether these “heartbeats” are natural or something more unusual will depend on future systematic observations, which have not yet been carried out.
FAQs on 3I/ATLAS
Why is 3I/ATLAS showing a “heartbeat”?
According to Avi Loeb, the object may be releasing periodic jets of gas and dust that brighten its coma every 16.16 hours — creating a pulse-like effect similar to a heartbeat.
Does this mean 3I/ATLAS is alive?
No. The “heartbeat” is a metaphor for rhythmic outgassing. It suggests unusual activity, not biological life or consciousness.
When will 3I/ATLAS be closest to Earth?
The interstellar object will make its closest approach on December 19offering astronomers their best opportunity yet to study the source of its mysterious pulses.