WHERE IS INTERSTELLAR COMET 3I/ATLAS?

 

WHERE IS INTERSTELLAR COMET 3I/ATLAS? Answer: In the constellation Virgo. You can find 3I/ATLAS in the morning sky (look east before sunrise) very close to the 4th magnitude star eta Virginis. The comet itself is 10th magnitude, so it is a relatively easy target for mid-sized backyard telescopes. Sky maps: Nov. 23, 24, 25, 26.

INTERSTELLAR COMET 3I/ATLAS IN COLOR: Who needs satellites and space agencies? Using a backyard telescope on Earth, amateur astronomers Michael Jäger and Gerald Rhemann have just captured the best-yet color image of interstellar visitor 3I/ATLAS. It is unmistakably a comet.

"We used a 12-inch telescope with a QHY600 cooled astronomy camera and color filters," says Jäger.

With one exception (discussed below), the photo is "classic comet." The comet's long tail streams straight away from the sun, sculpted by solar wind. Its blue color comes from carbon monoxide ions, CO+, a compound found in almost all Solar System comets. The comet's head is green because of another common molecule, diatomic carbon (C2), which is released from icy comet cores when they get close to the sun.

Now for the exception: There is a jet poking out of 3I/ATLAS's head toward the sun. It stands out in this black-and-white image taken by Michael Jäger and Gerald Rhemann on Nov. 20th:

This is unusual. Solar System comets rarely have such "anti-tails." This has prompted some (actually just one) astronomer to suggest that 3I/ATLAS might have an artificial thruster.

There is, however, a completely natural explanation. 3I/ATLAS spent a very long time in interstellar space. Billions of years of cosmic ray bombardment may have altered its surface--knocking hydrogen atoms out while heavier molecules remained behind. Now that 3I/ATLAS is in our solar system, sunlight is warming that crust and causing it to shed relatively large, heavy grains of dust. These grains are too massive to be quickly pushed around by radiation pressure or the solar wind. Instead they linger, creating a sunward-pointing jet that does not bend backward like a normal tail.

The backyard conclusion: 3I/ATLAS is a comet, and a wonderful one.

Realtime Comet Photo Gallery