Interstellar visitor reappears from sun’s shadow with baffling glow

A mysterious interstellar visitor has emerged from behind the sun, now glowing in a way that has left scientists stunned.

The comet is not visible from terrestrial telescopes, having passed through solar conjunction relative to Earth on October 21.

Harvard professor Avi Loeb, who has been studying the object for months, said: ‘This unfavorable geometry, a possible hint of design, placed the comet within the fields of view of several space-based solar coronagraphs and heliospheric imagers, allowing continuous observation during its final approach to perihelion.’

The object, named as 3I/ATLAS, made its closest approach to the sun on Wednesday, observed by three NASA spacecraft.

Data showed that 3I/ATLAS brightened at a rate about seven times faster than typical comets as it reached perihelion on October 29.

In other words, its light was increasing at an unusually rapid pace as it neared the sun, and researchers who captured the observations noted: ‘The reason for 3I/ATLAS’s rapid brightening, which far exceeds the brightening rate of most Oort cloud comets at similar distances from the sun, remains unclear.’

Even more puzzling, the comet now appears distinctly bluer, a reversal from its previously reddish hue.

Scientists speculate that the blue glow likely comes from gas emissions, including carbon molecules (C2) and other compounds, rather than just sunlight reflecting off dust.

The study, conducted by researchers from the Lowell Observatory in Arizona and the US Naval Research Laboratory in Washington DC, pulled data from the STEREO‑A (Solar TErrestrial RElations Observatory) and SOHO (Solar and Heliospheric Observatory).

They also used the GOES‑19, a weather satellite carrying the CCOR‑1 coronagraph, which helped capture the comet’s brightness and color while it was hidden behind the Sun from Earth-based telescopes.

CCOR‑1 detected a glowing plume extending nearly 186,000 miles around the object, comparable to the carbon dioxide halo observed months earlier.

The GOES‑19 satellite revealed that 3I/ATLAS is enveloped in a huge, fuzzy coma, roughly half as wide as the full moon. 

Ground-based telescopes had trouble observing 3I/ATLAS. At the same time, it was very close to the sun, but radio observations were able to detect emissions from the comet, showing it was producing huge amounts of water-related molecules. 

The production rate of these molecules increased sharply as the comet approached the Sun, following a pattern similar to the rapid brightening observed in optical images. 

The comet is expected to return to visibility in twilight and night skies during November and December, allowing ground-based telescopes to study it in much greater detail. 

Early analysis suggests 3I/ATLAS will emerge considerably brighter than before.

Scientists still do not fully understand why it brightened so fast, but it may be related to unusual activity from gases like carbon dioxide (CO2) and water (H2O), or unique properties of the comet’s nucleus, such as its composition, shape, or structure. 

Observations from spacecraft also show that 3I/ATLAS has a large, fuzzy coma about half the size of the full moon, and its light is distinctly bluer than the sun, likely due to gas emissions from molecules like C2 and Amino groups, rather than just reflected sunlight from dust.

 Its brightness increased much faster than typical comets, with a measured rate far exceeding the standard for Oort cloud comets, and the post-perihelion behavior remains uncertain; it could continue brightening, level off, or fade quickly.