Most telescopes stare deep into the dark night.
This one pointed towards sunset, and something unexpected streaked across the frame.
In late September 2025, astronomers scanning the sky near the Sun’s blinding glare picked up a massive, unusually fast asteroid looping inside the orbit of Venus. The object, now catalogued as 2025 SC79, had slipped past traditional surveys for years, raising fresh questions about what else might be hiding in this bright, hard‑to-watch corner of space.
A rare catch in the Sun’s blinding “twilight zone”
The find belongs to Scott S. Sheppard of the Carnegie Institution for Science, a specialist in tracking elusive Solar System objects. He was using the powerful Dark Energy Camera (DECam) mounted on the National Science Foundation’s 4‑metre Blanco telescope in Chile.
Instead of pointing DECam at a dark, high patch of sky, Sheppard targeted the so‑called twilight zone, the region close to the Sun where the sky glows and camera sensors struggle. In that glow, on 27 September 2025, two back‑to‑back images showed a faint point of light shifting position: asteroid 2025 SC79.
Hidden in the Sun’s glare, 2025 SC79 had been effectively invisible to most ground-based surveys until a narrow twilight window revealed it.
Follow‑up observations from the Gemini telescope and the Magellan telescopes confirmed the object’s reality and pinned down its orbit. Such cross‑checks matter, because the bright background and distorted optics near the Sun can easily fake signals that look like moving objects.
The episode highlights a long‑recognised blind spot. Most asteroid searches avoid the sky close to the Sun. It is too bright, too risky for sensitive instruments, and less comfortable for observers. That choice leaves a wedge of space — potentially full of near‑Earth objects — poorly monitored.
A 700‑metre rock running inside Venus’s orbit
Early calculations suggest 2025 SC79 is about 700 metres across, a genuine heavyweight by near‑Earth asteroid standards. Its orbit is even more striking.
The asteroid belongs to a rare group called Atira asteroids, whose orbits lie entirely inside Earth’s path around the Sun. Within that select club, 2025 SC79 goes one step further: its entire orbit sits inside the orbit of Venus, making it only the second object of its kind ever identified.
It loops around the Sun in just 128 days. That orbital period makes it one of the fastest known asteroids, second only to 2021 PH27, which circles the Sun in 113 days. For comparison, Mercury, the innermost planet, completes an orbit in 88 days.
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Whipping around the Sun in 128 days, 2025 SC79 experiences temperatures above 400°C and intense solar radiation on each close pass.
The path of 2025 SC79 also crosses Mercury’s orbit, meaning the asteroid experiences repeated gravitational nudges. Over thousands or millions of years, those subtle pulls can reshape its orbit, potentially altering how close it comes to other planets.
Why Atira asteroids fascinate scientists
Only a few dozen Atira asteroids are known. Their orbits are squeezed deep inside the inner Solar System, where solar heat, radiation, and planetary gravity all combine in a complex environment.
- They help test models of how rocky bodies migrate inward from the main asteroid belt.
- They reveal how extreme heat and solar wind slowly strip and alter asteroid surfaces.
- They probe a region where future spacecraft could, in theory, sample primitive material under harsh conditions.
Studying 2025 SC79, especially its exact orbit and spin, offers a natural laboratory for these processes. It may also challenge existing theories on how long such objects can survive so close to the Sun before breaking up or being flung elsewhere.
Could 2025 SC79 ever hit Earth?
First, the reassuring part: current calculations show that 2025 SC79 does not pose an immediate threat to Earth. Its present orbit keeps it confined well inside our planet’s path.
Yet its size means it cannot be ignored. An object 700 metres across carries enormous kinetic energy. If a similar body hit Earth, the result would be a continent‑scale catastrophe.
A 700m impactor could flatten a region the size of a country and trigger serious climate disruption, even without wiping out life worldwide.
For comparison, the asteroid that ended the age of the dinosaurs was around 10 kilometres wide, far larger than 2025 SC79. Still, impact simulations show that a 700‑metre rock striking land could create a crater more than 10 kilometres across, inject dust and aerosols into the atmosphere, and cause long‑lasting damage to agriculture and infrastructure over a wide area.
Planetary defence experts classify such bodies in the “city killer” to “small country killer” range. That places them firmly on the list of objects that agencies like NASA aim to track well in advance.
Planetary defence and the Sun-side blind spot
The late detection of 2025 SC79 underlines a persistent problem: some of the most dangerous asteroids may hide in regions that current surveys rarely see.
Most near‑Earth asteroid searches use night‑time, wide‑field telescopes that scan away from the Sun. They have catalogued thousands of objects, yet they struggle with asteroids that spend most of their time on the Sun‑facing side of Earth’s orbit.
| Region of sky | Ease of observation | Asteroid coverage |
|---|---|---|
| Night side (opposite the Sun) | Favourable: dark and stable | High, many surveys ongoing |
| Near-sun twilight zone | Challenging: glare and short windows | Patchy, few dedicated campaigns |
| Directly toward the Sun | Extremely difficult from Earth | Almost no ground-based coverage |
The Dark Energy Camera project that found 2025 SC79 is partially funded as part of NASA’s effort to identify so‑called “planet killers” — large asteroids that could trigger global or near‑global disasters. Yet the programme only samples the twilight zone during limited windows at dawn and dusk.
Space‑based observatories sitting between Earth and the Sun, or flying in Venus‑like orbits, could eventually close this gap. Missions on the drawing board aim to look outward from inside Earth’s orbit, watching for inward‑moving rocks that ground‑based telescopes simply miss.
What we still do not know about 2025 SC79
Right now, scientists know the rough size and orbit of 2025 SC79. Almost everything else remains up for grabs.
Key unknowns include:
- Composition: Is it mainly rock, metal, or a mixture? That affects both its strength and how it heats up.
- Density: A solid, metal-rich body behaves very differently from a “rubble pile” of loosely bound fragments.
- Surface properties: Its colour and reflectivity (what astronomers call albedo) reveal how space weathering has reshaped it.
- Rotation: The spin rate influences how sunlight slowly changes its orbit (through the Yarkovsky effect).
Answering these questions needs repeated observations when the asteroid swings back into view from Earth, away from the worst of the Sun’s glare. Spectroscopic measurements — splitting its light into colours — will give clues about minerals on its surface.
How 2025 SC79 survives intense heat, radiation and tidal forces may reshape ideas about which asteroids can exist close to the Sun.
Researchers suspect that bodies like 2025 SC79 may have started life in the main asteroid belt between Mars and Jupiter. Over millions of years, gravitational kicks from giant planets and subtle thermal forces could have nudged them into progressively tighter orbits, eventually trapping them inside Venus’s path.
What an impact of this size would actually look like
Asteroid impact assessments often get boiled down to scary headlines, but scientists run detailed simulations based on size, speed, angle and composition. For an object in the 700‑metre range, the likely scenarios include:
- Ocean strike: A massive tsunami spreading across nearby coasts, plus water vapour injection into the upper atmosphere.
- Land strike: Fireball, intense heat flash, supersonic shockwave and a deep crater, with devastation over hundreds of kilometres.
- Global effects: Regional climate cooling, disrupted rainfall patterns and failures in food production for several seasons.
Those simulations feed into civil defence planning, evacuation strategies and long‑term efforts to build impact‑deflection technology. Missions like NASA’s DART test, which nudged a small asteroid in 2022, were designed to show that even a modest spacecraft can slightly alter an object’s orbit if spotted early enough.
Jargon check: near-Earth objects, Atiras and “planet killers”
Asteroid discussions come with plenty of technical terms. A few are worth unpacking:
- Near-Earth Object (NEO): Any asteroid or comet that comes within 1.3 times the Earth–Sun distance.
- Atira asteroid: An asteroid whose entire orbit lies inside Earth’s orbit, like 2025 SC79.
- Planet killer: Informal label for objects roughly 1 kilometre across or larger, capable of causing global or near‑global catastrophe.
- Twilight survey: A search that targets the sky just after sunset or just before sunrise, when Sun‑hugging objects are briefly visible.
2025 SC79 sits just below the classic “planet killer” size, yet comfortably above the threshold where impacts become civilisation‑scale events. Its sudden appearance from the Sun’s glare acts as a reminder that even with sophisticated telescopes and sky surveys, some large asteroids are still being found late and in unexpected places.
As new facilities come online — including planned space‑based infrared telescopes dedicated to asteroid hunting — astronomers expect many more such sunward objects to emerge from hiding. Each new orbit charted not only sharpens planetary defence strategies but also fills out the dynamic, still‑evolving story of how rocks move and change in the inner Solar System.
Originally posted 2026-03-03 14:44:55.