I have a curious claim to fame. I have almost certainly seen more individual images of comets than any person in history. A good ballpark estimate would be around 50,000 unique images of comets, but that may be slightly on the low side. Either way, it’s a lot.
Since late 2003, I have been in charge of the NASA-funded Sungrazer Project—one of the oldest, most successful, and perhaps least-known astronomy-based citizen science projects to date. This week, we just hit a major project milestone: the discovery of our 3,000th comet!
The Sungrazer Project enables anyone in the world with an Internet connection to search for and report potential new comets in images recorded by the joint ESA/NASA Solar and Heliospheric Observatory, or SOHO, satellite.
The SOHO mission was launched in December 1995, carrying an armada of scientific instrumentation designed to study the sun, its surface, its interior, its atmosphere, and so much more. It’s no exaggeration to say that SOHO revolutionized our understanding of the sun with amazing discoveries made by all 15 instruments on board. However, I’m going to focus on just one instrument—the hero of this story—the Large Angle Spectrometric Coronagraph, or LASCO.
LASCO comprises a pair (actually three, but one died) of so-called coronagraph telescopes—specialized instruments designed to study the region of space immediately surrounding the sun by using a solid central disk to block direct, blinding sunlight. This design allows the telescopes to see not only massive solar eruptions as they emerge from the sun, but also much smaller and fainter objects such as near-sun and sungrazing comets and the occasional asteroid. It is with this camera that SOHO has found the vast majority of its 3,000 comets, and that’s because LASCO allows us to see a region of space that is otherwise completely impossible to view from Earth. With only a dozen or so exceptions, all of the comets that SOHO has discovered have been objects that get bright only when they’re ridiculously close to the sun. Normally at this point they would be rendered invisible by the blinding light from the sun, but thanks to SOHO’s LASCO telescope, they have no place to hide.
Prior to SOHO’s launch, the LASCO team of scientists was well aware of the possibility of observing the occasional comet in the images. Previous coronagraph missions such as P78-1/Solwind and the Solar Maximum Mission had discovered a few comets each, so it was known that as long as LASCO performed to specifications, they should see and discover at least a few comets.
And indeed that is exactly what happened. By December of 1996, after just eight months of somewhat routine mission operations, project scientists had already identified a whopping six new comets. Over the following two or three years, this number climbed steadily, and by the late 1990s, the mission was fast approaching its 100th discovery—a remarkable achievement at the time.
Back then, the Internet was still only emerging from its infancy. There was no social media, little blogging, and word spread much slower than today. However, around this time, amateur astronomers began to notice that the SOHO spacecraft was discovering comets and—quite pioneering for the era—was delivering its data to the Internet in something approaching real time. This is when SOHO comet hunting began to heat up.
My predecessor, Doug Biesecker, based at NASA Goddard Space Flight Center, began receiving increasing numbers of email reports from amateur astronomers of comets that mission scientists had overlooked in the first few mission years. Comet numbers quickly rose to the 200s, and word of the project spread. That led to a transformative moment: the creation of the Sungrazer Project and a corresponding Web page through which amateur astronomers could report possible comet sightings in the data. On Nov. 2, 2000, Doug posted a simple message to this new website—“Announcing a new scheme by which to report comets”—unwittingly heralding a new era in modern comet discovery.
I joined the team and took the wheel of the project in October 2003, with around 600 comets on the board. Now, 12 years later, we’ve just hit 3,000 new comet discoveries. That’s a truly extraordinary statistic!
Prior to SOHO’s launch in 1995, we had around 900 or so comets on official record, nearly all ground-based discoveries, with only a couple of dozen of those discovered by space-based telescopes. That’s 900 cataloged, measured, and recorded comets, throughout human history. Then comes SOHO, and in less than 20 years, we add 3,000 to that list! Yes, other spacecraft and sky surveys have also added a significant number in the intervening years, but none have come close to SOHO’s tally, and it may be some decades before they do.
Image by ESA/NASA/NRL
Of course, within this wealth of data lies a wealth of science. SOHO has revealed numerous secrets of the origins and fates of near-sun comets. We’ve discovered three previously unknown families of near-sun comets and added more than 2,000 new members to the so-called Kreutz family of comets, only a dozen or so of which were known prior to SOHO. We’ve seen huge comets fly near the sun and get their tails whacked by coronal mass ejections; we’ve seen moderate-sized comets fly too close to the sun and succumb completely to solar radiation. We’ve seen pairs of comets, comets with tails, comets with no tails, and a bunch of objects that probably aren’t comets at all but just act like them when they get too close to the sun.
We astronomers traditionally define comets as a big lump of rock and dust loosely bound together by lots of frozen water and gases. As these objects are exposed to sunlight, they begin to sublimate (turn directly from solid into gas), giving them their distinctive fuzzy “coma” and long flowing “tail.” Asteroids, on the other hand, are much more dense and not bound together by volatile ices, hence they don’t ever sublimate in sunlight—unless they get ridiculously close to the sun.
See where I’m going with this? It’s entirely possible that some of the “comets” that SOHO has discovered are not necessarily comets in the traditional sense, but instead may actually be overly adventurous asteroids that get so close to the sun that their rocky surfaces begins to vaporize. They’re basically just big, hot, glowing rocks! This is still somewhat speculative—a lot of study remains before we can make a definite claim here. But it is a great example of one of the very many questions that we can address as a consequence of SOHO’s huge database of discoveries.
Here’s my favorite aspect of SOHO’s milestone: It has overwhelmingly been achieved by amateurs, volunteers, and citizen scientists. We’ve had teachers, students, journalists, and engineers finding comets. We’ve had people from all over the world finding comets. We’ve even had two different 13-year-olds finding comets! An Internet connection, free time, and patience have remained the only prerequisites, though we also recommend bringing a healthy dose of dedication, as SOHO comet hunting is surprisingly competitive, and it can take quite a while to get up to speed with the regulars.
The bottom line is that the mission, its accomplishments, the results, and the professionals and amateurs involved have been simply extraordinary. It’s an honor and privilege to sit in my current position at the helm of this project, and I would not change it for the world. And it’s not over yet! SOHO continues to operate and celebrates its 20-year anniversary this coming December. Quite impressive for a satellite that was designed to operate for just two years and was lost, frozen solid in space, for two months back in 1998!
Accordingly, the Sungrazer Project rolls on too. While LASCO keeps taking images, people will keep finding comets, and we will keep cataloging them. There’s no indication that the inner solar system will ever be clear of comets, so hopefully the Sungrazer Project will continue on in some form for many years—and missions—to come.
Oh, and should someone in the future decide to attempt to steal my crown and look at more than 50,000 images of comets … well, best of luck to him or her with that!
