Scientists Capture Rare Evidence of Two Planets Colliding

Approximately 11,000 light-years away from Earth, in the constellation Pupis, a rather common star has been acting in an almost theatrical manner. For stars like this one, astronomers typically anticipate steady, steady light. Rather, this star, identified as Gaia20ehk, started to flicker in peculiar and unpredictable ways. Researchers were initially perplexed by the pattern. Then a more dramatic possibility started to emerge: it’s possible that two planets crashed into each other there, sending glowing debris flying throughout the system.

Quietly, the discovery started. Anastasios “Andy” Tzanidakis, a doctoral researcher at the University of Washington, was going through telescope data that had been archived around 2020. This is the kind of laborious, slow work that rarely yields spectacular results. However, this specific star persisted in bothering him. For years, its brightness record appeared flat, consistent, and dependable. Then something altered. The light dipped a few times around 2016; these were minor disruptions that could have been easily ignored. However, the star’s actions had become erratic by 2021.

Generally speaking, stars like our sun don’t behave that way. Suspicion was aroused by that fact alone. Astronomers started to suspect that something big had moved between Earth and the star, partially obstructing its glow, based on their observations of the light intensity graphs.

They now think that a catastrophic planetary collision is the most likely explanation.

That may sound dramatic, but it is. However, such collisions were once frequent in young solar systems. The formation of planets is a messy process. A newborn star is surrounded by gas, rock, ice, and dust. These materials are drawn together by gravity, gradually creating bodies the size of planets. And occasionally those bodies collide with one another. Tens of millions of years may pass before the system stabilizes. However, it is incredibly uncommon to see such an event from Earth.

Astronomers did not witness the planets colliding in the vicinity of Gaia20ehk because it would have been too far away and too fleeting to do so. Instead, enormous clouds of debris drifting through the system and obstructing the star’s visible light in erratic bursts were captured by telescopes.

Then another hint appeared. The narrative changed once more when scientists looked at infrared data—light that is invisible to the human eye but can be detected by specialized equipment. The infrared signal increased as the star’s visible brightness decreased. There was a glowing, hot thing. Dust is hot. Maybe newly made.

That is an important detail. Massive heat could be produced by a violent collision between two planetary bodies, easily producing glowing debris that could be seen at infrared wavelengths. The actual collision might have been the result of a gradual build-up, with two planets spiraling closer to one another and possibly brushing against one another multiple times before colliding catastrophically.

Imagining it has a strangely cinematic quality. For millions of years, two worlds drifted through darkness, gradually tightening their orbits until gravity and momentum finally brought them together. Not a sound. Just a rock and molten debris explosion that spreads across space.

There’s a feeling that astronomers might be seeing something akin to an event that shaped our own planet as the data develops.

Scientists estimate that Earth and another planetary body about the size of Mars collided violently some 4.5 billion years ago. The debris from that impact eventually formed the Moon. Earth’s tides, climate stability, and possibly even the conditions that allowed life to emerge were all influenced by that ancient disaster.

The debris cloud surrounding Gaia20ehk seems to orbit about one astronomical unit from its star, which is about the same distance Earth does from the Sun. The wreckage may eventually condense into new planetary bodies, though this is far from certain. Perhaps even a pair of planets and moons.

Whether that will occur is still up in the air. The material may gradually come together over millions of years, or the dust cloud may disperse. Human schedules do not govern the passage of cosmic time.

It’s remarkable that patience, not ostentatious new technology, led to this discovery. A narrative that developed gradually was revealed by piecing together decades’ worth of telescope observations. Many astronomers have a tendency to look for abrupt events, such as dramatic flares, fast radio bursts, and supernova explosions. Slowly, like a long mystery written in dim starlight, this event unfolded. That contains a subtle lesson.

Sometimes the universe shows itself in subtle patterns rather than spectacular flashes, which can only be found by carefully examining historical data.

Such discoveries might be made in the future. Over the course of the next ten years, the Vera C. Rubin Observatory in Chile is getting ready to start a massive sky survey. According to some researchers, it might be able to identify dozens or even a hundred planetary collisions like the one that is thought to have occurred near Gaia20ehk.

The discovery made public this week may be just the beginning if that prediction comes to pass.

For the time being, however, astronomers are left to reconstruct a cosmic accident that occurred thousands of years ago while gazing at flickering starlight from the far side of the galaxy.

It’s also difficult to avoid experiencing an odd sense of perspective. There once was a violent collision between two worlds that scattered molten rock into space. After eleven thousand years of traveling across the galaxy, the light from that catastrophe finally made it to Earth in time for someone looking through old telescope data to notice that something seemed a little off.