A recent Gemini Observatory image of comet 3I/ATLAS (background) overlaid with the new Two-meter Twin Telescope image of the comet's jet (inset). (Image credit: Comet photograph: International Gemini Observatory/NOIRLab/NSF/AURA/Shadow the ScientistImage Processing: J. Miller & M. Rodriguez (International Gemini Observatory/NSF NOIRLab), T.A. Rector (University of Alaska Anchorage/NSF NOIRLab), M. Zamani (NSF NOIRLab); Inset: Teide Observatory, M. Serra-Ricart, Light Bridges)
Welcome, dear readers of FreeAstroScience. Here’s a question worth your coffee: why is interstellar comet 3I/ATLAS seemingly firing a giant jet toward the Sun—and is that weird? In this article, written by FreeAstroScience only for you, we’ll unpack the new images, the physics of comet jets, and what makes this object a special guest from deep time. Stick with us to the end for a clean mental model—and a few “aha” moments you can share tonight.
What did the new images actually show?
Fresh telescope images reveal a sunward-pointing jet shooting from 3I/ATLAS’ nucleus. The snapshot—built from 159 exposures of 50 seconds each—was taken with the Two-meter Twin Telescope (TTT) at Teide Observatory on Aug. 2, then shared via The Astronomer’s Telegram on Oct. 15. The jet appears fan-shaped, aligned roughly toward the Sun, while the comet’s classic tail points away. That geometry is textbook comet behavior, not a red flag.
A few standout facts:
- Size: ~5–11 km across (3–7 miles), making 3I/ATLAS the largest interstellar object seen so far.
- Jet length (estimate): ~10,000 km. Likely dust plus CO₂, matching a large gassy plume the James Webb Space Telescope saw in August.
- Context: It’s only the third interstellar object ever detected in our neighborhood—and possibly older than the Sun.
Here’s a quick “at a glance” table to ground the details:
| Property | Value / Status | Notes |
|---|---|---|
| Nucleus size | ~5–11 km | Largest interstellar object observed to date |
| Jet direction | Sunward (fan-shaped) | Tail remains anti-solar, as expected |
| Estimated jet length | ~10,000 km | Likely dust + CO₂ |
| Key dates | Mars flyby Oct 3; Perihelion Oct 29; Reappears mid-Nov | Currently behind the Sun |
| Imaging details | TTT, 159 × 50 s frames (Aug 2) | Shared Oct 15 via Astronomer’s Telegram |
(All details as reported in the Live Science summary of the observations.)
Why can a comet point a jet toward the Sun?
Because sublimation isn’t uniform. As the comet rotates and warms, weak spots on the sunlit side vent gas and dust. That vent becomes a geyser, often fanning out as the nucleus spins. Meanwhile, sunlight and the solar wind sweep other material into the anti-solar tail—so you can see a sunward jet and an anti-solar tail at the same time. A similar fan-like jet was seen from Comet NEOWISE after its 2020 solar flyby.
A pocket-size physics model
- Energy in (sunlight) vs. energy out (thermal radiation + sublimation) sets surface temperature.
- Volatile ices (like CO₂) sublimate at lower temperatures than water ice, so they can dominate early activity.
- Rotation sculpts the jet into a fan.
Below is a compact energy-balance relation for a sunlit patch:
Where (A) is albedo, (S_0) the solar constant at 1 AU, (r) the heliocentric distance in AU, (\varepsilon) emissivity, (\sigma) the Stefan–Boltzmann constant, and (\eta) a beaming term.
Sublimation mass flux (J) from a vent can be sketched by the Hertz–Knudsen relation:
Here (P(T)) is the vapor pressure at temperature (T), (m) the molecular mass, and (k) Boltzmann’s constant. Hot spot → high (P(T)) → strong jet. That’s the entire story in one line.
So… is this unusual for 3I/ATLAS—or just normal comet drama?
It’s normal comet physics. The twist is the interstellar origin. 3I/ATLAS isn’t from our Oort Cloud; it’s a wanderer from another star system. That raises stakes: by sampling its chemistry and activity, we glimpse how other planetary nurseries work. The object also seems highly active, with JWST reporting a substantial gas plume in August and earlier observations noting unusual vigor.
Could radiation pressure make a sunward jet look strange?
Light pushes dust. Gravity pulls it. The ratio of those forces for a grain is the classic (\beta) parameter. When (\beta) is high (tiny grains), radiation pressure can rapidly turn ejected material anti-solar, feeding the tail. Larger grains (low (\beta)) linger near the source and keep the jet well defined.
| Effect | Scales with | Outcome |
|---|---|---|
| Solar gravity | Grain mass | Pulls inward |
| Radiation pressure | Cross-section & reflectivity | Pushes outward, anti-solar |
| Gas drag (near vent) | Local sublimation flux | Launches & shapes the jet |
Bottom line: a sunward jet is expected, and a long anti-solar tail can grow simultaneously. That’s exactly what observers report.
How do astronomers turn pixels into kilometers?
The team combined many short exposures to boost signal, then mapped angles to distances using geometry and the comet’s range. If the jet spans an angular separation (\theta) (in radians) at a comet–observer distance (\Delta), the projected length (L) is:
Using the reported ~10,000 km scale gives a practical feel for the feature’s size—even if the exact value will sharpen with follow-up analysis.
What’s the timeline—what should we expect next?
3I/ATLAS passed Mars on Oct. 3, heads to perihelion on Oct. 29, and remains on the far side of the Sun. It should reappear for Earth-based observing in mid-November. That window matters: researchers want to see how the jet and tail evolve after the heat of perihelion.
| Date (2025) | Event | Why it matters |
|---|---|---|
| Oct 3 | Passes Mars | Best “nearby” vantage before solar conjunction |
| Oct 29 | Perihelion | Peak heating—activity can ramp up |
| Mid-Nov | Reemerges from behind the Sun | Fresh look at post-perihelion changes |
All dates and visibility notes summarized from the latest reporting.
Is it alien tech in disguise?
A few voices floated the idea—because interstellar objects are rare and mysterious. But the overwhelming consensus is that 3I/ATLAS behaves like a comet. The sunward jet + anti-solar tail pattern is routine, and these new images reinforce a natural origin. Also, the Astronomer’s Telegram post with the jet image is a community alert, not a peer-reviewed paper—a reminder to stay curious, but cautious.
Our take: The alien-probe angle makes headlines; the physics makes sense. And when the physics is enough, that’s an “aha.”
How bright could it get—and could we see it?
Reports suggest increasing activity as it nears the Sun, and some images hint the comet “could” turn greenish—a common C₂ emission signature in comae. Still, brightness predictions are tricky. For now, the practical advice is simple:
- Wait for mid-November reappearance for updated observing guidance.
- Use binoculars or a small telescope and watch official circulars for coordinates.
- Expect change: jets can rotate, flare, or fade from night to night.
All current status notes trace back to the same observing reports summarized above.
Why does 3I/ATLAS matter for planetary science?
Because every interstellar comet is a free sample from another protoplanetary disk. Its volatile blend, dust sizes, and activity patterns help:
- Benchmark models of planet formation in other systems.
- Test how early chemistry differs beyond the Sun’s nursery.
- Constrain how often such objects wander through—and what they carry.
3I/ATLAS, being large and old, could be a time capsule from before the Sun existed. That’s goosebump stuff.
Quick reference: the core concepts
- Sunward jet ≠ suspicious. It’s how vents behave on a rotating, sunlit comet.
- Tail points away from the Sun due to radiation pressure and solar wind.
- 3I/ATLAS is big (5–11 km) and hyper-interesting because it’s interstellar.
- Key dates: Oct 3 (Mars), Oct 29 (perihelion), mid-Nov (reappearance).
Conclusion: What should we carry forward?
We’ve seen how a sunward jet from an interstellar comet fits our best physics—and why 3I/ATLAS is a scientific gift. It reminds us that the universe delivers surprises that are still explainable, if we look closely enough. As it swings through perihelion and reemerges, we’ll learn whether its activity surges, its color shifts, or its tail blossoms into something spectacular. Either way, we’re watching a messenger from elsewhere write a bright, temporary line in our sky. And that’s worth your curiosity.
This post was written for you by FreeAstroScience.com, where we explain complex science simply to spark wonder—and to remember that the sleep of reason breeds monsters. Come back soon; the sky keeps telling new stories. /
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