The Dangerous Lives of Sungrazer Comets

Great March Comet of 1843

Do comets have family histories? Some do. We’ll discover the genealogical history of a special family of comets, the so-called Kreutz sungrazers. They are hands down among the most spectacular celestial apparitions in human history. They are glorious because they are risk takers: they come close – exceedingly close – to the sun’s broiling surface and therefore release copious amounts of gas and dust after perihelion, visible in their incredibly long and beautiful tails [1]. If the earth is well situated at that moment, commentaries from awestruck humans will fill the history books.

But hazards lurk. As the centuries wear on, the risk increases that they will inch ever closer to the sun’s surface and confront the indignity of fragmentation [2]. This is so because with each hair-raising solar passage, their cometary bodies, however tightly or loosely they may be bound, will experience differential forces of the sun’s gravity, tidal forces, tending to rip them apart. Even the daredevils that survive pay a price. Volatilization from intense solar heat may shrink them like a snowball in an oven. Drag from solar gasses, the effects of their own outgassing, the perturbing effects of the giant planets, and nontidal fragmentation anywhere along their path, may alter their orbits, slightly or even significantly over time, potentially bringing them still closer to the sun during their next trip in. Being large is an advantage, but if a sungrazer gets too close to the the sun, the consequences are usually grave: it will break into fragments, some of which may or may not survive as comets, or it will vanish whole and forgotten in the sun’s cauldron.

Following the 19th century work of German astronomer Heinrich Kreutz (1854-1907), scientists have stubbornly sought to crack the mystery of these celestial showstoppers. Where did they originate? Why do they happen in groups? Will there be future sungrazers? There is still much uncertainty, but a clearer picture has recently emerged. Brian Marsden, formerly of the Harvard-Smithsonian Center for Astrophysics, a modern pioneer in this field, divided the sungrazers into two groups that he determined must have split from a truly giant, ancient progenitor comet. JPL comet specialists Zdenek Sekanina and Paul Chodas have continued that work over the last quarter-century with a virtual torrent of publications, variously revised on the basis of each new-found piece of evidence (as is the process of science), including a trove of orbital data on dwarf sungrazers detected from the Solar and Heliospheric Observatory (SOHO) coronagraphs and other solar satellites.

They accept most members of Marsden’s groups, but now Sekanina, in a recent breakthrough paper, has offered a revised theory about the Kreutz family tree, whose remaining elements “fit together as nicely as the final pair of pieces in a puzzle.” [3] It is reminiscent of the history of biology, determining the phylogeny of each species, first from basic morphology and later, with DNA analysis, sorting and shuffling things around, so that now we know that hippopotamuses are the closest living relatives to whales!

The Great September Comet of 1882 seen from South Africa

The great progenitor, Aristotle’s Comet: 372 BC

This ancient relative, the great grandfather comet, appeared in the fourth century BC. Aristotle saw it when he was 12. It must have been a colossal object. Its break-up over various perihelion passages through the centuries spawned more than a half dozen large and spectacularly famous comets and many long-gone littler ones.

What was this progenitor comet like? Imagine you are the young Aristotle. It is a “clear and frosty” winter evening of the year, 372 BC. It is during “the archonship of Asteius” around the time of the terrible “earthquake in Achaea and the tidal wave” that destroyed the city of Helike [4]. You look to the west, just after sunset. You see a “great comet” of astonishing brightness. In your Meteorlogica, composed 40 years after the event, you write, Its light stretched across the third of the sky in a great band, as it were, and so was called a path. It rose as high as Orion’s belt, and there disappeared [5].

Later writers, quoting earlier sources now lost, have given vivid descriptions of this comet. Diodorus Siculus in the first century bc wrote: [T]here was seen in the heavens during the course of many nights a great blazing torch which was named from its shape a flaming beam… This torch had such brilliancy… and its light such strength that it cast shadows on the earth similar to those cast by the moon [6].

            Marsden speculated that this great comet as the sungrazers’ progenitor; Sekanina’s new theory convincingly supports itafter some doubts, Sekanina now concurs [7]. Whatever the source, it was real, and huge.

After one orbit: the daylight comets of A.D. 363

Seven centuries pass, and 734.9 years after the maiden appearance of Aristotle’s comet, another exceedingly brilliant comet – actually two or more comets, it seems – appear in A.D. 363. This is the return of Aristotle’s comet, but now it had seemingly fragmented, like the aging Roman Empire would soon be. Roman historian Ammianus Marcellinus records that “in broad daylight comets were seen.” Sekanina emphasizes Ammianus’s used the plural of ‘comets’ in his account, suggesting that Aristotle’s Comet did split before it reappeared. These two largest fragments of the progenitor likely arrived at perihelion only days apart from each other, near or after the end of October.

Why would it come apart? Sekanina proposes that the big object was likely a contact-binary comet whose lobes parted somewhere along its journey to its 4th century perihelion. There’s been “gradually accumulating evidence based on spaceborne close-up imaging of cometary nuclei and Kuiper Belt objects,” Sekanina says, that “the contact binary is a fairly common figure among these objects.” Two prominent examples are comet 67P/Churyumov-Gerasimenko) and 486958 Arrokoth, a trans-Neptunian object located in the Kuiper belt [8]. Thus, the theory goes, the comet split near its aphelion into its two lobes (with perhaps a small connecting neck) that were first witnessed as separate objects within a few days of the 363 perihelion. Sekanina calls these lobes of this comet, Lobe I and II and which we’ll for simplicity also refer to as Lobe I and Lobe II, as a kind of family name, even though technically after separation they are no longer ‘lobes.’ Under current theory, this is the first great division of the Kreutz family tree which gave rise to all the later offspring.

After two orbits: The Great Comet of 1106

After the A.D. 363 apparition, we wait for the next full revolution of the comet. After 742.2 years have elapsed, we are in the early 12th century, the so-called High Middle Ages, and just after the First Crusade to Jerusalem involving knights, peasants, and serfs. It is late January 1106, and a truly remarkable comet lights up the sky around the world. It is the return of Lobe I. By all contemporary accounts it was a mighty one to behold. It was first seen from Belgium in broad daylight. Observers in Japan estimated its tail to be 100° in length and white in color. The Welsh ‘Chronicle of the Princes’ for 1106 reported this:  In that year there was seen a star wonderful to behold, throwing out behind it a beam of light of the thickness of a pillar in size and of exceeding brightness, foreboding what would come to pass in the future.

A Muslim chronicle said: a star appeared in the heavens with locks of hair like a rainbow. It went from the West to the middle of the heavens and it was seen close to the Sun before its appearance during the night. It continued appearing a number of nights, then disappeared.” [9] A Chinese manuscript described it as appearing “like a broken-up star.”

There does not seem to be a record of Lobe II’s arrival, but it’s possible that it was poorly placed for observation. We will get to that in a minute, but let’s continue to follow the family’s so-called Population I descendants of Lobe I.

After three orbits: The Great March Comet of 1843, and kin

Lobe I also breaks into fragments far from the sun; the biggest part of it arrives 737.1 years after its 1106 visit. The world is now quite different. Spring, 1843; England’s Victorian Age is dawning; Napoleon III will soon make himself Emperor of the French. Up in the sky, after an insanely tight loop around the sun, the greatest fragment of Lobe I blossoms into one of the most splendid comets ever seen, the finest of the century. Its tail is 8° to 10° in broad daylight. By mid-March it’s almost 50°; a German astronomer on the 21st traces it for 64°.

The Great March comet of 1843

The other fragments of the Lobe I family are destined to return in their time. They become superstar comets with these names:[10]

(a)   The Great March Comet of 1843 (C/1843 D1), just noted, spectacular by every account, the largest fragment of Lobe I, lead member of its subgroup, the first or second brightest comet in history [11].

(b)   The Great Southern Comet of 1880 (C/1880 C1).

(c)   The Great Southern Comet of 1887 (C/1887 B1), the “headless wonder”.

(d)   Comet Pereyra of 1963 (C/1963 R1 (Pereyra) [12].

These objects from Lobe I of Aristotle’s Comet were identified by Marsden as belonging to a family of its own, which he called Subgroup I, and which Sekanina has called Population I. But why should these comets, and no other roughly contemporaneous ones, for example, be grouped together? What makes a family? It’s a matter of genes, of course (metaphorically speaking, of course).

Population genetics (of comets)

What are the markers in the genetics of cometary orbits that allow comparison of one comet’s orbit with another, either to group them into families as Marsden and Sekanina have done, or to find out if they are one and the same comet, as Edmond Halley did? There are not many: the approximate time of perihelion, T; the perihelion distance, q (in au), and three angular coordinates: the longitude of the ascending node, Ω; longitude of the perihelion ω; and angle of inclination i. [13]

From similarities in the orbital elements of earlier-seen comets, Halley, for example, was able to conclude that the comets of 1531, 1607, and 1682 were one and the same comet whose return in 1758 he famously predicted [14]. Dr. Marsden originally used the same Halley look-back method to match the markers for each group of the Kreutz comets. Here’s the data for the comets of Marsden’s Subgroup I/Sekanina’s Population I: 

You can see how similar their numbers are. Notice the hazardously tight q for C/1887: this daredevil ventured too close to the sun (only 27,000 km above the solar surface) and literally lost its head, remembered now as the “headless” comet [15].

The fate of Lobe II of Aristotle’s Comet

Lobe II is the missing sibling of X/1106 C1. It passed perihelion as the ‘Chinese Comet’ of 1138, 32 years after Lobe I did, according to Sekanina [16]. It fathered two brilliant Population II offspring: C/1882 R1 and C/1965 S1 [17]. Other fragments of Lobe II became C/1970 K1 (first generation split) and C/2011 W3 (second generation split), the latter known to us as Comet Lovejoy [18]. This comet appeared a year after Marsden died, so his analysis didn’t include it [19]. The pieces from Lobe II became spectacular 19th through 21st century showpieces with these names:

(e)   The Great September Comet of 1882 (C/1882 R1 A). This comet, which some say was the brightest of all the sungrazers in the last 200 years, was the main residual mass of Lobe II. [20]

(f)    Comet Ikeya-Seki (C/1965 S1-B), perhaps the greatest comet of the 20th century.

(g)   Comet White-Ortiz-Bolelli (C/1970 K1) [21].

(h)   Comet Lovejoy (C/2011 W3), a breathtaking recent comet.

Here is the updated table of the key orbital elements of the comet populations descended directly or secondarily from Lobe II of the ancient progenitor:

These numbers are also of a kind, with a few variants justifying only slightly different population assignments. The huge and brilliant Great September Comet C/1882 R1-A broke into four fragments at perihelion. Lovejoy was a blaze of glory in 2011 that had all of the sungrazer attributes, but its numbers didn’t mesh neatly with the two original subgroups, thus warranting a subgroup/population designation of its own [22]. It had the lowest q of the group, passing a scorching 135,000 kilometers over the sun’s surface.

Comet Ikeya-Seki

In all, C/1843 D1 and C/1882 R1, the first members of each table, were the largest surviving masses of Lobe I and Lobe II of Aristotle’s Comet. We can therefore trace the lineage of those two ruling patriarchs after Aristotle’s Comet broke up into two lobes, from 363 to1106 to 1843 (Population I); and 363 to 1138 to 1882 (Population II). Lobe II was more susceptible to fragmentation than Lobe I at large heliocentric distances. The nearly 40-year wide separation between their perihelion times was “the outcome of the initial rate of separation of their precursors, magnified by the orbital evolution over the lifetime of the Kreutz system.” [23].

Game Changers

            If you read through Sekanina and Chodas’s papers you will see the evolution of their theory since Brian Marsden’s pioneering work, shaped by empirical evidence and better mathematical techniques as the years went by. These events in particular were game changers in the study of the Kreutz sungrazers:

(1)   The discovery from spacecraft that many comets are contact binaries, suggesting the possibility, or even likelihood, that the progenitor comet was a contact binary and its superfragments were its original lobes.

(2)   The delayed post-perihelion fragmentation of Comet Lovejoy. The comet underwent severe morphological changes several days after perihelion, including loss of its nuclear condensation (a euphemism for ‘its head’) [24]. Intensive study of this comet yielded evidence – adding to the emerging view – that sungrazing comets can and do fragment non-tidally anywhere in their orbits [25], and clusters of tidally fragmented comets appear to arrive within 80 to 90 years of each other [26].

(3)   The realization that cometary fragmentation is normal and consistent with the historical record with C/1882 [27] and with the disintegrations of Comet Shoemaker-Levy 9 (C/1993 F2) in 1993 and Comet Schwassmann-Wachmann (C/73P) in 2006 (both of which I witnessed telescopically), in which “cascading fragmentation” can create ghostly “strings of pearls” as the fragments pass across the sky [28]. Quite recently, too, Comet West (C/1976 V1) broke into four parts a month after perihelion.

(4)   New analysis of the great population of dwarf sungrazers detected by spacecraft, most especially the SOHO spacecraft, revealing up to nine separate groups of sungrazers, many not seen from Earth – including and enlarging upon the already known representatives of Populations I, II, IIa, and III – further bolstering the case of continuous and ongoing fragmentation of these objects, and the likely return of future sungrazers in the near and far future [29].  

(5)   From these studies, it’s plain that there are more astonishing sungrazing comets to come, as evidenced for example by the recent arrival of C/2024 S1 (Atlas). This Population II sungrazer, arriving only 13 years after Lovejoy, may be a fragment of the parent comet of the Great September Comet of 1882 and Comet Ikeya-Seki [30].

Comet Lovejoy

Simulation

Below is a computer simulation of the innermost orbits of three great Kreutz comets at perihelion, Great March Comet C/1843 D1 (bright red), Ikeya-Seki C/1965 S1-B (dull red), and Lovejoy C/2011 W3 (brown). I created it with Maple mathematical software using NASA/JPL Solar System Dynamics (SSD) database orbital elements [31]:

Appendix

 Chart of Notable Sungrazing Comets

(From JPL Small-body Database)

ACKNOWLEDGEMENT I wish to acknowledge and warmly thank Dr. Zednek Sekanina, Senior Research Scientist at Jet Propulsion Laboratory/CalTech, for his review of this article, his many constructive insights on the history of his work, and his welcome edits to the above account.

REFERENCES

Marsden, B.G. “The Sungrazing Comet Group. II.” Astron J.  98, no. 6 (Dec. 1989): 2306-2321.

___________. “The Sungrazing Comet Group.” Astron J.  72, no. 9 (November 1967): 1170-1183.

Sargent, David. 2009. The Greatest Comets in History: Broom Stars and Celestial Scimitars. New York: Springer.

Sekanina, Zdenek. “Comet ATLAS (C/2024 S1) — Second Ground-Based Discovery of a Kreutz Sungrazer in Thirteen Years.” arXiv:2411.12941 [astro-ph.EP]. (November 2024). https://doi.org/10.48550/arXiv.2411.12941.

__________. “New Model for the Kreutz Sungrazer System: Contact-Binary Parent and Upgraded Classification of Discrete Fragment Populations.” arXiv:2109.01297 [astro-ph.EP]. (September 2021). https://doi.org/10.48550/arXiv.2109.01297.

__________. “Statistical Investigation and Modeling of Sungrazing Comets Discovered with the Solar and Heliospheric Observatory.” Astrophysical Journal, no. 566 (February 2002): 577-598. https://doi.org/10.1086/324335.

Sekanina, Zdenek, and Paul W. Chodas. “Comet C/2011 W3 (Lovejoy): Orbit determination, outbursts, disintegration of nucleus, dust-tail morphology, and relationship to new cluster of bright sungrazers.” arXiv:1205.5839v1 [astro-ph.EP]. (May 2012). https://doi.org/10.48550/arXiv.1205.5839.

_________. “Fragmentation hierarchy of bright sungrazing comets and the birth and orbital evolution of the Kreutz system. II. The case for cascading fragmentation.” Astrophysical Journal 607, no. 1 (July 2007): 663-657. https://doi.org/10.1086/517490.

_________. “Fragmentation hierarchy of bright sungrazing comets and the birth and orbital evolution of the Kreutz system. I. Two-superfragment model.” Astrophysical Journal 607, no. 1 (May 2004): 620-639. https://doi.org/10.1086/383466.

_________. “Fragmentation Origin of Major Sungrazing Comets C/1970 K1, C/1880 C1, and C/1843 D1.” Astrophysical Journal no. 581 (December 2002): 1389-1398.

Sekanina, Zdenek, and Rainer Kracht. “The Great Comet of 1106, A Chinese Comet Of 1138, and Daylight Comets in Late 363 as Key Objects in Computer Simulated History of Kreutz Sungrazer System.” arXiv:2206.10827v2 [astro-ph.EP]. (July 2022). https://doi.org/10.48550/arXiv.2206.10827.  NOTES

[1] Kreutz sungrazers travel on similar orbits with typical periods of about seven to ten centuries. They are usually seen between August and April, and best observed from the southern hemisphere. Those appearing between May and July approach from behind the sun from our vantage point and may arrive and sail off unseen.

[2] Marsden (1989) 2313. “[R]epeated fragmentation of the members of the Kreutz group as they keep returning to perihelion at random times results in… a tendency for q generally to decrease, suggesting that all members will eventually hit the Sun." The letter q is the standard symbol for an object’s perihelion distance expressed in astronomical units. A perihelion distance q of .004638 au is about one solar radius.

[3] Sekanina (2021), 14.

[4] According to the Greek geographer Pausanias, a great earthquake in 373 BC destroyed the Achaean city of Helike. The quake caused the city to subside, and a massive tsunami then killed all its inhabitants.

[5] Quoted from Seargent, 67.

[6] Ibid.

[7] Sekanina (2021), 14-15.

[8] Sekanina (2021), 6.

[9] The accounts in this paragraph were taken from Sargent, 91-94.

[10] According to Sekanina: Lobe I split into C/1843 D1 and a fragment … that subsequently split again into C/1963 R1 and another fragment… the parent to C/1880 C1 and C/1887 B1. The debris of comet C/1843 D1 is detected as SOHO dwarf comets of Population I, whereas the debris of C/1963 R1 ended up … [as] a side branch to Population I. Sekanina (2021), 10.

[11] It is somewhat controversial whether C/1106 was part of Lobe I or II. Originally thought to be in Lobe II, Sekanina’s new modeling points to it as in Lobe I, and hence the father of the Population I comets in our story. Sekanina (2021), 10-12.

[12] The parentage of Pereyra was a for a time questionable, and has been called a “maverick comet” by Sekanina, but is part of the Population I family. Sekanina and Chodas early on realized that comets can alter their originally given elements by the forces induced during the fragmentation process. Their new modeling then assigned Comet Pereyra to Group II. They put it this way: “A major result of Paper I [Sekanina & Chodas (2004)] was the finding that a sungrazer can easily transit from one subgroup to the other because of the extra momentum it acquires during fragmentation events experienced in the course of a single revolution about the Sun.” Sekanina & Chodas (2007), 657. Now, however, Pereyra seems to have been welcomed back into the Population I family as a “side branch” under more recent theory. See Sekanina (2021), 3. Its exact parentage path off of Lobe I, however, is still being worked on. See Sekanina & Kracht (2022), 31,

[13] There are a few things to remember when orienting the orbit of the comet in space relative to our solar system. The plane of a comet’s orbit intersects the ecliptic plane along a line, the endpoints of which are called the nodes. Where the comet is ascending at that point, the node is called the ascending node. The number of degrees along the ecliptic plane from the vernal equinox ϒ (the standard reference point in the solar system) to the ascending node is called the longitude of the ascending node and is denoted by Ω. Now, the number of degrees from the ascending node (now measured counterclockwise for along the plane of comet’s orbit) to the comet’s perihelion point is called the longitude of the perihelion, denoted by ω. The tilt of the comet's orbital plane and ecliptic plane is called the comet’s inclination, denoted by i. The shape of an orbit is determined by its eccentricity, denoted by e. All of the sungrazers have near-parabolic or parabolic orbits, so eccentricity isn’t particularly useful measure for comparison among them.

[14] Edmond Halley first inquired if comets appearing at different times in history are in fact the same comet orbiting the sun. His work on the subject appeared in 1705 under the title, A Synopsis of the Astronomy of Comets.

[15] C/1887’s admission to this group was uncertain for Marsden but confirmed by Sekanina. Sekanina (2002), 585, and citations within. C/1963 R1 (Pereyra) is technically a “side branch” of Population I according to Sekanina. Sekanina (2021), 3.

[16] Sekanina & Kracht (2022).

[17] See generally Sekanina & Kracht (2022).

[18] Sekanina (2021), 10. The hierarchy is simplified here but is fully elaborated in Sekanina's paper and 'Pedigree Chart.'

[19] Marsden tentatively included Comet du Toit (C/1945 X1) on his Subgroup II list, but it was only briefly seen, and with its uncertain orbit is described now as “rather problematic to assign to either list.” Sekanina (2021), 2, n.2.

[20] Sekanina & Chodas (2007), 660. Sekanina & Chodas (2004), 662.

[21] This comet defined Marsden’s Group IIA, not neatly fitting his Groups I or II. See Marsden (1989). Marsden found that some sungrazing comets discovered from the spaceborne SOLWIND and solar Maximum Missions (SMM) coronographs also seemed to be sortable into Group I or II. See the NASA/JPL Solar System Dynamics (SSD) database, Small-Body Database Lookup. See also https://cometography.com/lcomets/1970k1.html for some notes on its discovery.

[22] Sekanina and Chodas argue that the orbits of a small swarm of the SOHO sungrazer comets seem to fit well with Lovejoy’s orbit, suggesting that they and it belong to an entirely separate group, perhaps a new Group III. They do find that C/2011 W3 is indirectly related to X/1106 C1 and C/1843 D1, and in the coming years and decades it may be followed by more equally bright or brighter sungrazing comets in similar orbits. For the full discussion, see Sekanina & Chodas (2012).

[23] Sekanina (2021), 1, 5 & 15.

[24] Sekanina & Chodas (2012). The comet survived perihelion but began to fragment 2 days later.

[25] According to Sekanina, when a cometary nucleus splits into two parts, either fragment leaves the point of breakup with an orbital momentum that differs from the parent’s orbital momentum. This difference is manifested by a separation velocity that determines the fragment’s heliocentric orbit that deviates from the parent’s orbit. Sekanina (2021), 5.

[26] Sekanina and Chodas (2004), 657. “[T]he course of evolution of the Kreutz system at the upper end of the mass spectrum may be better ascertained from the distribution of the sungrazers’ arrival times than from the sources of subgroups. If so, the fragment hierarchy should be determined primarily by the cascading nature of the fragmentation process,” according to Sekanina and Chodas (2004). Hence the updated tables reveal clusters showing relatively similar times of arrival, consistent with the trailing nature of the fragmentation process depicted by those authors.

[27] Sekanina & Chodas (2007), 660 et seq. “Because of the alignment of the fragment condensations in a train embedded in an elongated sheath of diffuse material, they were sometimes likened by the observers — just as the condensations of D/Shoemaker-Levy 9 more than 100 years later. . . — to a ‘‘string of pearls’’ or ‘‘beads on a thread of worsted.’’ Ibid.

[28] Sekanina & Chodas (2007), 658-657. Sekanina has reorganized his thinking to accommodate the fact that there are many more sungrazers than were originally known. New discoveries have reshaped his thinking in a way best summarized by this quote from the paper of his a few years ago: “Given the thousands of members known nowadays, I deem it more appropriate to call their total the Kreutz system and to divide the ensemble into fragment populations. Accordingly… I consistently replace the term used by Marsden with the new one, even when I refer to his own work: his Subgroups I and II are now Populations I and II, respectively.” Sekanina (2021), 2.

[29] Sekanina (2021), 4. The dramatic plot of 193 dwarf Kreutz sungrazers on this page is well worth examining. It is the centerpiece of the paper.

[30] Sekanina says, “The new sungrazer might be closely related to comet du Toit (C/1945 X1), but most exciting is the possibility that it is a fragment of the parent comet of the Great September Comet of 1882 (C/1882 R1) and comet Ikeya-Seki (C/1965 S1).” Sekanina (2024), 1 & 7.

[31] The image is approximately to scale and accounts for comet positions drawn from their orbital elements as of their perihelion dates, ignoring the solar system barycenter offset. The solar system barycenter is the point about which the sun, planets, asteroids, and comets actually revolve. The position of perihelion relative to the sun itself is continually offset by where the planets are, but is influenced mainly by the position of Jupiter and to a lesser extent Saturn at any given time. The effect is slight (it still lies within the sphere of the sun). Marsden did account for this and had both sets of data in his papers.