Observations by the spacecraft revealed that Comet 3I/ATLAS is rapidly increasing in brightness as it wobbles behind the Sun.
The comet is flying around the sun, obscuring it from Earth’s view, to reach perihelion (the closest point to our star) on Thursday (October 29).
But while much of the world waits for its reappearance, some researchers and amateur astronomers are using probes to track its path.
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On October 18, amateur astronomer and veteran comet spotter Worakate Boonplod discovered the comet in images from the National Oceanic and Atmospheric Administration’s GOES-19 weather satellite. The GOES-19 weather satellite uses an instrument called CCOR-1 to observe the Sun as part of its regular space weather monitoring. Boonprod noted that comet 3I/ATLAS is easily detectable and is set to remain visible to the spacecraft until October 24th.
“Its brightness is comparable to nearby stars of magnitude around 11,” Boonprod wrote in the Comets Mailing List group, part of the group email service Groups.io. (In astronomy, higher magnitudes correspond to brighter objects; objects above magnitude 6 are usually too faint to be seen with the naked eye.) “The comet is moving from left to right (with respect to both the field of view and the background stars) and should exit the CCOR-1 field of view on October 24.”
The GOES-19 satellite was not the only satellite to capture comet 3I/ATLAS. It also tracks NASA and the European Space Agency’s Solar and Heliospheric Observatory (SOHO), as well as NASA’s Coronal Heliosphere Unified Polarimeter (PUNCH) mission, which includes four small satellites aiming for the Sun, Universe Today reported. SOHO orbits the Sun at a distance of about 1 million miles (1.5 million kilometers) from Earth, and its Large Angle Spectroscopic Coronagraph (LASCO C3) instrument is tracking comet 3I/ATLAS until October 26. A coronagraph, similar to those used on SOHO and GOES-19, is a device that intentionally blocks the sun in an image to study the surrounding atmosphere, or corona.
On Wednesday (October 28), two researchers posted their findings on the preprint server arXiv, reporting that Comet 3I/ATLAS brightened rapidly prior to perihelion. The researchers estimate that at perihelion, the comet will brighten to around magnitude 9. It’s still too faint to see with the naked eye, but if it’s visible from Earth, it’s bright enough to be seen with a high-powered backyard telescope.
The study relies on space-based solar observing instruments such as GOES-19 and SOHO, and the study found that the comet is significantly bluer than the Sun, consistent with outgassing contributing significantly to the comet’s increased brightness near its perihelion, according to the study authors. This is expected for comets, as they heat up as they approach the Sun, and surface ice sublimates to gas, which wraps around the body of the comet and contributes to its tail. Solar radiation ionizes the gas, making it even brighter.
Since its discovery in July, scientists have used a variety of telescopes to learn everything they can about Comet 3I/ATLAS. The comet is only the third interstellar comet ever recorded, and previous discoveries show it passing through the solar system in an unusually flat and straight orbit at speeds in excess of 130,000 miles (210,000 km) per hour.
Despite some rather enthusiastic speculation that comet 3I/ATLAS could be an alien spacecraft, most astronomers are convinced that this interstellar visitor is a space rock from a distant, unknown star system.
NASA said in a statement that the comet’s speed is the fastest ever recorded for a solar system object and suggests it has been traveling for billions of years, gaining momentum from the slingshot effect of gravity as it soars past stars and nebulae.
In fact, 3I/ATLAS may be the oldest comet ever observed, with one study suggesting it is about 3 billion years older than our 4.6 billion year old solar system. The comet is likely the largest interstellar object ever observed, but researchers are still figuring out its exact size. According to data from the Hubble Space Telescope, 3I/ATLAS has a maximum width of about 3.5 miles (5.6 km).
The comet will be visible again to Earth-based telescopes by early December, and could be visible to spacecraft orbiting Jupiter as it approaches the gas giant in March 2026, NASA said.
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