Sungrazer at 15: How Crowdsourcing Changed Comet Hunting

By Sara Francis


Dr. Karl Battams started his career at the U.S. Naval Research Laboratory (NRL) 15 years ago, he was an astrophysics graduate, eager to do almost anything in his field. Inheriting a languishing citizen science project certainly qualified as “anything.” After more than 15 years, that project has now produced some of the most scientifically exciting discoveries of Battams’ career.

Named for a type of comet that passes extremely close to the sun, the Sungrazer project enables the identification of previously unknown comets with the help of anyone willing to look through a library of images from two NRL space-based imaging telescopes: the Large Angle and Spectrometric Coronagraph (LASCO) telescopes on the joint European Space Agency/NASA and Heliospheric Observatory (SOHO), and the Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) instrument suite on the Solar Terrestrial Relations Observatory (STEREO).

The multidecades-volume of data from these satellites are publicly available online for anyone who would like to join the comet hunt.

“All someone really needs to find comets is an internet connection and lots of patience,” Battams said.

Originally started at NASA in 2001, the Sungrazer project fell dormant in early 2003 after its original researcher and student assistant left. Late that same year, however, NRL’s Solar and Heliospheric Physics Branch took on the administration role, and the program resumed with renewed interest by amateur astronomers and continued funding by NASA. Since then, participants for Sungrazer have made more than 3,600 discoveries of previously unknown near-sun comets.

The youngest Sungrazer participants to find comets have been around 13 years old, according to Battams. (Some of those same teenagers who found comets for the project are now adults finishing their PhDs.) Although the list of names of active participants is constantly changing, the core number stays relatively stable. Generally, Battams said, it’s a group of about 100 primaries from around the world who have generated most of the findings.

Well over half of all cataloged comets in recorded history were discovered through this project, but despite more than 23 years of SOHO data Battams doesn’t recommend looking through old images to find overlooked objects. He estimates 95 to 98 percent of every object to have passed through the telescope fields of view have already been “discovered” by someone. Almost all discoveries are made in the latest real-time data downlinked continuously from their parent missions.

With all the attention this past year focused on NASA’s Parker Solar Probe, Battams is eager to emphasize the contributions that the Sungrazer program has also made to our understanding of the sun. The project has produced several unique discoveries that shed light on heliospheric interactions with comets.

“Comets entering the very near-sun environment are like natural solar probes,” Battams said. “By cataloging them and studying their interaction with the solar wind and sun’s magnetic field, we can learn things about the sun that just wouldn’t be possible without launching lots of very expensive missions. Comets are imperfect probes, of course, but also free and plentiful.”

In 2007, the comet C/2007 P1 (McNaught) put on a stunning show when it passed through the first light imagery of NRL’s SECCHI cameras, resulting in what Battams considers “one of the most spectacular image sequences of any comet in history.”

“Our Solar and Heliospheric Physics group at NRL are the principal investigators of the SECCHI imaging system on STEREO, and it was the day that we opened the telescope doors for first light,” Battams said. “We received our very first images and immediately visible were big bright streaks that we were not expecting. We were wondering,

‘What is that? Did something go wrong? Is this stray light?’ Thankfully, we quickly figured out that the spacecraft [STEREO] was rotated, and our mysterious streak was in fact comet McNaught. It was really fortuitous that we captured it in the very first images.”

Another major comet event, this time in 2011, was the flight of C/2011 W3 (Lovejoy) through the sun’s million-degree outer atmosphere. Battams and several other scientists from around the world coordinated more than 10 instruments on various satellites including Hubble, STEREO, and SOHO, to watch it plunge through the solar corona.

At perihelion, as the comet was closest to the sun, observations revealed large volumes of cometary material being stripped from the comet nucleus and vaporizing— with the comet’s atomized material subsequently clinging to the sun’s magnetic field lines, illuminating them for a few minutes. Despite seemingly surviving this journey, Lovejoy ultimately succumbed to its losses after passing the sun and heading out into space, where it completely broke apart and faded away.

In 2007, the comet C/2007 P1 (McNaught) passed through the first light imagery of NRL’s Sun-Earth Connection Coronal and Heliospheric Investigation (SECCHI) cameras on the NASA Solar Terrestrial Relations Observatory spacecraft, producing bright streaks and spectacular image sequences that initially confounded Battams and his fellow researchers. Photo by NASA/NRL

“While we are interested in the comet itself, some of the most unique science here is what it tells us about the environment it’s in,” Battams said. “For example, studying the tail can give you information much like that of a wind sock—so solar wind speed, strength, direction; [the tail] adds unique data points.”

In 2012, comet C/2012 S1 (ISON) was discovered as part of a routine sky survey by the International Scientific Optical Network (ISON), when it was about a billion kilometers from the Earth. Traveling from the Oort Cloud far outside of our solar system, ISON followed a sungrazing orbit that would take it extremely close to the sun on Thanksgiving Day 2013.

With widespread speculation that its brightness could rival that of the full moon, the comet created a lot of interest among the press, with some even saying it could become the “comet of the century.”

“We knew it was going to go very close to the sun and had the potential to get very bright,” Battams said. “But we always thought that ‘comet of the century’ was almost certainly going a little too far.”

Today, after 15 years with the Sungrazer project, Battams has developed an enduring fascination with one particular family of comets that seem to have no discernible historical source.

Sometimes, larger comets that are only near-sun or sun-skirting orbiters are pulled apart by the sun’s gravity into a cloud of smaller comets and become a “family,” with the new smaller comets often remaining on a similar orbital path as the original comet, their “parent.” The Sungrazer project has identified three previously unknown comet families, all but one of which have been traced back to parent objects somewhere in the nearly 8,000 years of recorded sightings.

The family of comets that continues to intrigue Battams is known as the Meyer group, named for amateur comet hunter Maik Meyer who first identified the family connection. The Meyer group has no identifiable parent, and new comets keep showing up—more than 200 to date. Meyer group comets are all tiny, and all look the same, but because of their high-inclination, near-sun orbit, no satellite or ground-based observer has been able to follow them long enough to determine whether they are on a closed orbit, or what their return date might be.

What Battams does know is that they are not following a short period path, but one that is more likely on the order of at least decades; it could be centuries. Beyond that, he only has a lot of questions.

“We know literally nothing about them; we don’t where they came from, where they are going to, their orbital trajectory, or their size. We’re not even certain they’re actually comets [versus asteroids],” Battams said. “They are an absolute mystery and I would dearly love to know what their deal is. Of all the Sungrazer project discoveries, these are the ones that intrigue me the most.”

In 2018, Battams was honored to learn that main-belt asteroid 2001 FF18 had been renamed in his honor in recognition of his 15-year stewardship of the Sungrazer project. Accompanying the announcement of the asteroid’s renaming to Asteroid 29598 (Battams) was the following citation:

“Karl Battams . . . is an astrophysicist and computational scientist at the U.S. Naval Research Laboratory in Washington, D.C. He has been in charge of the Sungrazer Project since 2003, overseeing most of the project’s [more than 3,400] sungrazing comet discoveries, and has contributed to the study of numerous near-sun comets.”

While delighted to receive the recognition, Battams continues to ponder whether NASA will ever attempt to probe his asteroid.

About the author:
Sara Francis is a writer with the U.S. Naval Research Laboratory.

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