Asteroid 2025 SC79 captured during twilight observations after remaining hidden near the Sun.
Credit : Scott S. Sheppard /carnegiescience.edu/
It sounds almost unreal, but it happens more often than people imagine. A massive asteroid, around 700 metres wide, was quietly travelling through the inner Solar System – and no one saw it coming.
Not because scientists weren’t looking. Not because the technology failed. But because the object was hiding in the one place telescopes struggle most: the glare of the Sun.
The asteroid, now officially named 2025 SC79, was only detected recently, after slipping through a long-known observational blind spot. Its discovery is already raising uncomfortable questions about how much of the space around Earth remains effectively invisible.
Spotted by chance, at the edge of daylight
Most asteroid discoveries happen at night. That is when telescopes work best, scanning dark skies for faint moving dots. But 2025 SC79 did not follow the rules.
It was identified by Scott S. Sheppard, an astronomer at the Carnegie Institution for Science, using the Dark Energy Camera attached to the Blanco 4-metre telescope in Chile. This instrument is normally used for deep-space surveys, but it also has the rare ability to work under difficult light conditions.
On September 27 2025, Sheppard was observing during a narrow window around twilight – that awkward moment when the Sun has just dipped below the horizon but its light still floods the sky. In that brief interval, two images revealed something unusual: a fast-moving object racing across the field of view.
It was not a reflection, not an artefact, not a mistake.
Follow-up observations from the Gemini Observatory and the Magellan telescopes confirmed the finding. A new asteroid had been spotted – one that had managed to stay hidden simply because it spends most of its time too close to the Sun to be seen.
As Sheppard himself has noted on several occasions, the most dangerous asteroids are not always the biggest ones – but the hardest to detect.
An extreme orbit, closer to the Sun than Venus
What immediately set 2025 SC79 apart was its orbit. This is not a typical near-Earth asteroid drifting between Mars and Jupiter.
Instead, it belongs to an exceptionally rare group known as Atira asteroids – objects whose entire orbit lies inside Earth’s, and in this case, inside the orbit of Venus.
Only 39 Atira asteroids are known so far. Among them, 2025 SC79 is especially unusual: it is only the second asteroid ever discovered that remains completely within Venus’s orbit.
Its speed is equally remarkable. The asteroid completes a full lap around the Sun in just 128 days, making it one of the fastest-orbiting asteroids ever recorded. Only one object, 2021 PH27 – also discovered by Sheppard – moves faster, completing its orbit in 113 days.
For comparison, Mercury, the closest planet to the Sun, takes 88 days to orbit it once. That gives an idea of just how extreme the environment is where 2025 SC79 spends its time.
The asteroid’s path also crosses Mercury’s orbit, creating complex gravitational interactions that make its long-term trajectory difficult to model. These forces, combined with intense solar heat and radiation, turn continuous observation into a challenge.
In simple terms: it is fast, it is hot, and it is hard to keep track of.
Should we be worried? Not right now – but the warning is real
At around 700 metres in diameter, 2025 SC79 is not a planet-killer. It is nowhere near the size of the asteroid that wiped out the dinosaurs, which measured roughly 10 kilometres across.
But it is still large enough to cause catastrophic regional damage if it were ever to hit Earth. An impact of that scale could devastate an entire region and have serious climate effects.
The good news is that there is no immediate risk. Current calculations show no collision threat with Earth.
The uncomfortable part is what the discovery reveals.
An asteroid of this size existed, moved rapidly through the inner Solar System, and remained completely undetected – not for days or weeks, but potentially for decades – simply because it stayed close to the Sun’s glare.
This is not a failure of astronomy. It is a limitation of physics and observation.
Most telescopes cannot safely or effectively look too close to the Sun. As a result, dawn and dusk remain some of the least explored regions of near-Earth space.
NASA-supported detection programmes, including those using the Dark Energy Camera, are now placing increasing emphasis on these overlooked zones. The discovery of 2025 SC79 strengthens the case for doing so.
More than a threat: a scientific goldmine
Beyond planetary defence, 2025 SC79 is a fascinating scientific object.
Its composition remains unknown, but researchers are eager to study how an asteroid of this size survives such extreme conditions. Temperatures near its orbit can exceed 400°C, raising questions about how its surface and internal structure have evolved over time.
Scientists suspect it may have originated in the main asteroid belt, later pushed inward by gravitational interactions – possibly involving one of the giant planets. Over millions of years, prolonged exposure to solar radiation may have altered its surface chemistry and physical properties.
Studying objects like this helps researchers better understand how material migrates through the Solar System, how rocky bodies age, and how orbital paths change over time.
It also helps refine impact prediction models – a crucial step in assessing future risks.
A reminder hiding in plain sight
The discovery of 2025 SC79 does not mean Earth narrowly avoided disaster. But it does serve as a quiet warning.
Even with modern technology, some of the biggest objects near our planet remain hidden simply because of where they travel. The Sun, which makes life on Earth possible, also blinds us to parts of the cosmic neighbourhood we would rather keep an eye on.
For astronomers, the message is clear: the sky is not fully mapped yet – especially not at its brightest edges.
And for everyone else, it is a humbling reminder that space still has the occasional surprise, even when we think we know it well
