While skywatchers around the world have been raving about the appearance of Comet Tsuchinshan-ATLAS, there has been talk on social media of another spectacular comet set to appear at the end of this month.
The lineage of this other object apparently connects it with a family of cometssome of which have been among the most brilliant ever observed. For this reason, some may have already labeled it “The Great Halloween Comet”.
Unfortunately, it now looks like that will happen not happen.
We’ll get into the details in a moment, but first let’s explain why there was an immediate wave of excitement when the discovery of this new comet was announced.
Discovered on September 27 in Hawaii by the Asteroid Terrestrial-impact Last Alert System (ATLAS) project, the object was originally cataloged as “A11bP7I.” But soon enough observations came to confirm that this very faint 15th-magnitude object – almost 4,000 times brighter than the faintest star that can be perceived without optical aid – was indeed a comet and not a asteroid. And once its existence was confirmed and a trajectory for it derived, that’s when the excitement began.
Related: The dazzling comet Tsuchinshan-ATLAS appears in the night sky: How to see it
Because the newly discovered object, which we will call Comet ATLAS, is a Kreutz sings.
The sun-grazing comet family
In 1888, astronomer Heinrich Kreutz (1854-1907) noted that sun-grazing comets all follow approximately the same path. Apparently they are all fragments of a single giant comet that broke apart in the distant past. And it is quite likely that these fragments themselves have broken up repeatedly as they orbited the sunresulting in periods ranging from about 500 to 800 years. In honor of his work, this particular group of comets is named the Kreutz Sungrazers. Two of these sungrazers (in 1843 and 1882) not only developed very long tails, but also achieved the rare distinction of being clear enough to be seen in broad daylight with the naked eye.
This helps to explain the excitement surrounding Comet ATLAS. When the comet burst onto the scene last month, social media interest in seeing it increased almost exponentially overnight. Orbital calculations showed it was destined to “graze” the sun on October 28, coming within just 341,000 miles (548,000 kilometers) of our star.
Ikeya-Seki 2.0?
Back in October 1965, another Kreutz sungrazer, Comet Ikeya-Seki, became so brilliant that at its peak it was reportedly 10 times brighter than full moon and was visible even during the day, simply by blocking the sun with a hand or behind a building.
In the days following its sweep around the sun, Ikeya-Seki was a spectacular sight in the late October and early November morning sky. An incredibly brilliant, twisting tail extended from the east-southeast horizon an hour or two before sunrise, appearing as a slender searchlight beam about as long as Big Dipper.
At its maximum length, Ikeya-Seki’s tail stretched 70 million miles, ranking it as the fourth largest ever recorded. Only the large comets of 1680, 1811 and 1843 had tails that extended further into space. While Ikeya-Seki’s head faded rapidly, the tail continued to be visible well into November, even as the comet moved rapidly away from the Sun.
With the newly discovered comet ATLAS moving in a similar orbit and also set to orbit the Sun just one week later in the calendar compared to Ikeya-Seki’s 1965 appearance, many arbitrarily assumed that we are in for another spectacular comet show this year at late October to November.
But sun-grazing comets are far from rare.
Most ‘grazers’ are small, but Comet ATLAS is (relatively) large
Beginning in 1979, orbiting space observatories began detecting sun-grazing comets using instruments called coronagraphs. A coronagraph is designed to look at the Sun’s atmosphere by blocking the Sun’s bright disk. Small sun-grazing comets, which would normally be too faint and too close to the sun’s glow for us to see, can be picked up using a coronagraph.
Indeed, sunrazers are now routinely detected using the Large Angle Spectrometric Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SOHO) satellite, a joint effort of The European Space Agency and NASA. Comet Tsuchinshan-ATLAS (which is not a sungrazer) passed within the field of view of the LASCO coronagraph for a few days centered on 9 October.
Amateur astronomers have discovered thousands of comets using SOHO images on the Internet, and SOHO comet hunters come from all over the world. More than 5,000 SOHO comets have been identified as Kreutz sungrazers. Some are probably just a few meters across; none have survived their sweep around the sun.
Comet ATLAS, however, appeared to be much larger, perhaps a mile or two (2 or 3 km) across, leading some to speculate that it could be very bright. For example, the Japanese comet expert Seiichi Yoshida has suggested that it can reach magnitude -4.5 – as bright as the planet Venus.
But unfortunately, these forecasts now appear to be overly optimistic.
Low expectations for a good show
Based on the latest observations from the Comet Observation Database (COBS), Comet ATLAS has been eerily slow to brighten as it approaches the Sun. The latest estimates place it at a magnitude of only 12 or 13 – still very faint. Some observers have even suggested that it has muted a bit in recent days and that its core has even split into two pieces. That breakup was apparently confirmed on October 9 by The Astronomer’s Telegram.
Perhaps the most damning statement about the future of Comet ATLAS was recently published on International Comet Quarterly Facebook page by John E. Bortlea famous amateur astronomer who made a special study of comets after observing more than 300 in his lifetime.
He writes:
“This latest comet from the Kreutz family has no real chance of survival. About 30 years ago I did an analysis of the photometric behavior of all the then-known Kreutz group members seen from 1843 to the 1980s. In that study I determined that the large Comet of 1965 (Ikeya-Seki) was actually the intrinsically faintest member of the surviving Kreutz group family in the last 150 years.Those only slightly fainter than this essentially do not survive their closest approach to the Sun (perihelion) intact was the case with the Great Comet of 1887 and the more recent Comet Lovejoy of 2011, which survived only as tail remnants as far as Earth observers were concerned.
“Given that Comet ATLAS appears to be several orders of magnitude fainter compared to Comet Ikeya-Seki,” Bortle concluded, “I certainly expect that even under the best of circumstances this newcomer can only hope to present itself as a short-lived tail without a body. post-perihelion, if there is any kind of remnant at all.”
Shades of the Great Pumpkin
As mentioned earlier, some social media have suggested it Comet ATLAS can become “super bright” at Halloween. But based on the evidence that we at Space.com have presented here, that unfortunately does not appear to be the case. Indeed, there now appears to be a good chance that when Comet ATLAS arrives at its closest point to the Sun on October 28, our star’s immense thermal and tidal forces will cause its core to completely fragment, disintegrate, or simply dissolves, perhaps leaving its wake (as Bortle suggests) nothing more than a corporeal tail.
In a way, it goes back to the story told annually in the cartoon “Peanuts”. The Great Pumpkin. In that story, Linus believes that on Halloween night the Great Pumpkin will rise out of the pumpkin patch and deliver toys to those who believe in him. Of course, The Great Pumpkin never shows up, leaving Linus very disappointed.
So it looks like those who think they’ll get a pre-sunrise view of a “Great Halloween Comet” in 2024 will, like Linus, almost certainly be disappointed.
Expectation. . .
But when will another great and spectacular member of the Kreutz group, like Ikeya-Seki, appear? No one can say for sure. The last Kreutz Sungrazer to brighten was Comet Lovejoy in 2011. It is not possible to assess the chances of another very bright Kreutz comet arriving in the near future. But given that at least a dozen have reached naked-eye visibility over the past 200 years, another large comet from the Kreutz family will almost certainly arrive at some point.
In fact, these comets are like trains of all sizes, moving along the same railway track as they pass our station (Earth) in space.
And like an impatient commuter, we can only watch and wonder what awaits us up the lane!
Joe Rao serves as an instructor and guest lecturer at New York’s Hayden Planetarium. He writes about astronomy for Natural history magazinetea The Farmers’ Almanac and other publications. Follow us on Twitter @Spacedotcom and we Facebook.