NASA has turned its top telescopes on a rare visitor from beyond our solar system, the interstellar comet 3I/ATLAS, revealing surprising details about its makeup and behavior. In recent weeks, the James Webb Space Telescope, Hubble Space Telescope, and SPHEREx mission have teamed up to study this object, which is speeding through at over 130,000 miles per hour and showing traits that puzzle experts.
This comet, first spotted in July 2025 by the ATLAS survey in Chile, marks only the third confirmed interstellar object to enter our solar system. Scientists are racing to learn more before it swings past the sun and heads back into deep space, offering a unique chance to peek at materials from another star system.
Discovery of a Cosmic Traveler
Astronomers detected 3I/ATLAS on July 3, 2025, as it barreled toward the inner solar system from the direction of the constellation Cassiopeia. Unlike typical comets born in our own solar system, this one hails from far outside, likely ejected from another star’s orbit millions of years ago.
Initial ground-based observations showed a fuzzy glow around the comet, hinting at outgassing as it warmed near the sun. But early data raised questions, with some experts noting its path and brightness did not match standard comet models.
By late July, NASA mobilized its space assets for closer looks. This quick response highlights how modern astronomy can pivot to study fleeting events, much like the rapid follow-up on the 2017 interstellar object Oumuamua.
The comet’s speed and trajectory mean it will not stick around long. It will pass closest to the sun in late September 2025, then slingshot away, never to return.
Hubble’s Close-Up View
The Hubble Space Telescope snapped the sharpest images yet of 3I/ATLAS on July 21, 2025, when it was about 277 million miles from Earth. These photos allowed experts to estimate the nucleus size at up to 5 kilometers across, larger than many expected for an interstellar wanderer.
Hubble revealed a teardrop-shaped dust cocoon around the core, suggesting active venting of material. This detail helps explain the comet’s brightness, which has fluctuated as it approaches the sun.
Astronomers note that Hubble’s visible-light images complement other data, painting a fuller picture of the comet’s surface and immediate surroundings. Such clarity is vital for spotting subtle features that ground telescopes might miss.
Webb’s Infrared Discoveries
On August 6, 2025, the James Webb Space Telescope trained its Near-Infrared Spectrograph on 3I/ATLAS, capturing data that researchers are still poring over. Early analysis points to unusual chemical signatures, including a lack of water vapor that is common in solar system comets.
Webb’s infrared view penetrates dust clouds, revealing hidden details about the comet’s composition. This capability has already sparked debates about how 3I/ATLAS formed and what its home system was like.
The observations tie into broader studies of interstellar objects, building on Webb’s past work with distant galaxies and exoplanets. Scientists expect a full report soon, which could reshape ideas about comet chemistry across the galaxy.
One key takeaway is the comet’s forward glow, which some say defies typical comet behavior. This has led to theories about its structure, from icy shards to something more exotic.
SPHEREx Mission’s Key Findings
The SPHEREx mission, launched earlier in 2025, observed 3I/ATLAS from August 7 to 15, focusing on its spectral data to map ices and gases. Results show a massive carbon dioxide coma stretching 348,000 kilometers, with the comet losing about 70 kilograms of CO2 per second.
Surprisingly, water ice is present in the nucleus, but almost no water vapor appears in the coma, with an upper limit of just 4.5 kilograms per second. This imbalance suggests 3I/ATLAS formed in a cold, distant environment where CO2 dominated over water.
SPHEREx’s all-sky survey design made it perfect for this task, providing wide-field views that track the comet’s changes over days. These findings add to the mission’s goals of studying cosmic ices and the universe’s early history.
Here are some standout details from SPHEREx data:
- Dominant gas: Carbon dioxide, forming a bright, expansive coma.
- Mass loss rate: 70 kg/second of CO2, indicating high activity.
- Water detection: Minimal in the coma, despite nucleus ice.
- Distance during observations: About 3.2 AU from the sun.
What Makes 3I/ATLAS So Unusual
Experts are buzzing over traits that set 3I/ATLAS apart from known comets. Its retrograde orbit and lack of a visible tail in some views hint at a different origin story, possibly from a shattered planet or exploded star.
Some researchers, including Harvard’s Avi Loeb, speculate it could even be artificial, though most lean toward natural explanations like unusual outgassing. The comet’s red color slope and symmetric glow add to the mystery, challenging models of cometary evolution.
To put this in perspective, compare it with past visitors:
| Feature | 3I/ATLAS (2025) | 2I/Borisov (2019) | 1I/Oumuamua (2017) |
|---|---|---|---|
| Origin | Interstellar | Interstellar | Interstellar |
| Size Estimate | Up to 5 km | 0.2-0.5 km | 0.1-0.4 km |
| Key Composition | CO2 dominant, low water | Typical comet gases | No coma detected |
| Speed | >130,000 mph | ~110,000 mph | ~59,000 mph |
| Notable Trait | Large CO2 coma | Visible tail | Cigar shape, no tail |
This table shows how 3I/ATLAS stands out in size and chemistry, offering fresh clues about diverse cosmic environments.
The findings echo recent events, like the 2024 detection of potential interstellar meteors, underscoring how our solar system interacts with the wider galaxy.
Future Studies and Broader Impact
As 3I/ATLAS nears the sun, more observations are planned, including possible ground-based telescope follow-ups. By October 2025, it will pass within 29 million kilometers of Mars, providing another viewing window before it fades from sight.
These studies boost planetary defense efforts, honing skills to track incoming objects. They also deepen understanding of how solar systems form and exchange materials over cosmic distances.
In the coming months, combined data from Webb, Hubble, and SPHEREx could reveal if 3I/ATLAS carries signs of ancient stellar processes or even organic compounds.
What do you think about this interstellar mystery? Share your thoughts in the comments and pass this article along to fellow space fans for more discussion.
