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NEWS | Sept. 15, 2015

3000th 'Sungrazer' Comet Imaged by NRL Space Instrument LASCO

By Kyra Wiens

On September 15, 2015, Karl Battams—a computational scientist at the U.S. Naval Research Laboratory (NRL)—confirmed the discovery of the 3,000th near-sun comet using an NRL instrument. The comet was very small and only visible for a few hours before being vaporized by the sun's intense radiation, he said in a statement this morning. But despite their small size, these comets really present real science value in a multitude of ways.

The comet images come from NRL's Large Angle and Spectrometric Coronagraph Experiment (LASCO) instrument, which orbits on the Solar & Heliospheric Observatory (SOHO). We are taking images of the region of space that surrounds the sun, says Battams, and this allows us to see small objects very near the sun that would otherwise be invisible from earth. SOHO is a collaboration between NASA and the European Space Agency (ESA).

NRL's been sharing LASCO data online since 1995; as a result, volunteers and citizen scientists discover most of the LASCO comets. I could make a fulltime job out of looking for comets and I still wouldn't find a fraction of the ones that these guys have found, says Battams; so, for me, the 3000th comet is mostly their achievement. Worachate Boonplod, a science writer from Thailand, discovered the 3,000th comet in data recorded by the spacecraft on September 13 and 14.

Russ Howard, who first started looking at comets through coronagraphs in the 1970s, is the NRL Principal Investigator for LASCO. After, unexpectedly, observing the first sungrazer, We saw probably one a year for five years, he says. But now, thanks to LASCO and crowd-sourcing, We've gone from one a year to one every few days.

From a science perspective, says Battams, it's more than doubled the population of known comets on record. More than half of all known comets now carry SOHO's name. And that's changed the science.

It allows you to rethink things, how much material there is entering our world, says Howard.

The SOHO satellite hovers in force balance between the sun and our planet. SOHO is always right there, it's always looking right down the barrel of the gun, says Battams. And when the sun takes aim at earth, in the form of powerful solar eruptions, it can directly impact daily life and military operations.

The mission was looking for these big eruptions from the sun, called coronal mass ejections, or CMEs, says Howard. A major CME, like one that NRL watched just barely miss earth in 2012, could cause an estimated $2 trillion in damages and take 4-10 years for recovery. Even more normal space weather can disrupt satellite communications and radar, and blow out power transformers; so forecasting space weather is hugely important and many NRL programs are devoted to improving these capabilities.

The three-day predictions of CMEs that LASCO provides from SOHO give time for utilities to disconnect transformers from the grid, for airplanes to reroute away from the poles, and for satellites to be switched into safe mode.

Battams also studies the chemistry of the comets themselves to learn about how our planets formed. Comets are the leftover building blocks of when the solar system was formed, he says, and what we hope to do is learn about the initial conditions and early composition of the very early solar system, and from that try and piece together how everything came together to form the planets and everything we have now.

In December 2015, SOHO will mark 20 years in space. I think the longevity of it is a testament to all these people who build the spacecraft, operate the observatory, and work on the data, says Howard. There's really a dedication.

Sungrazers probe near the sun to predict space weather
In studying sungrazers, NRL has learned a lot about the sun and how its activity affects us here on earth. We can treat the comets as mini-probes of the solar wind and near sun conditions, says Battams. You can look at their behavior, how their tails are reacting to the solar environment—it's like a wind sock on an air field.

These data points help scientists understand and better forecast space weather. It's almost like dropping a rock in a pond, says Battams. So we have a model of how we think the pond's going to behave, but when we drop the rock in a pond we can compare our model to what we actually observe.

Sungrazing comets can, on rare occasion, also help us learn about the magnetic fields around the sun. In 2011, We had a big comet that went right near the sun, says Battams. For a short time, it kind of lit up the magnetic field lines near the sun. These events help scientists better understand CMEs, and how they impact space weather.

SOHO has really shown that CMEs are the cause of the major geomagnetic storms, says Howard. What happens is this huge amount of material is headed out into space. And if it hits the earth's magnetosphere, this protective envelope of magnetic fields, it causes the atmosphere to ring—to sort of move in and out.

CMEs affect us more than one might think for a sun almost one million miles away. That causes sub-storms to develop in the earth, it causes the atmosphere to heat up—and so that increases drag on spacecraft, it induces a field in the earth's crust, says Howard. And if you have a long transmission line, you get what's called a backwards [electromotive force], which can burn up transformers in power substations. It's an amazing event.

Scientists still don't fully understand what causes CMEs. The holy grail is to try to predict it, says Howard. But for now, at least, you can have a few days advance warning. Light gets here in eight minutes, but the material travels more slowly: it takes one to three days.

NRL builds coronagraphs for space so we can see our sun
NRL began working on LASCO in the mid-1980s. We built the telescopes here on the lab, says Battams. That's where we designed them, engineered them, and built them. They're completely NRL's baby.

NRL's challenge was to build an imager that would work for the sun. The coronagraph is a simple telescope, says Howard, with one peculiar property: that it can reject this very immense light coming from the sun itself, so it can look at the very faint emission. It's like an artificial eclipse, or covering over something bright with your hand so you can see the fainter light around it.

LASCO is the only coronagraph that's always between our planet and the sun. SOHO sits at a location in space that's known as the first Lagrange point, says Battams. Instead of orbiting around earth, SOHO rotates about this point, called L1, in a slightly inclined plane. It's able to see the sun 24 hours a day, 7 days a week.

Following LASCO's success, NASA launched two more satellites in 2006 with NRL coronagraphs. The idea, says Howard, was to have two coronagraphs, from two different view points—much like binoculars. The twin Solar TErrestrial RElations Observatory (STEREO) satellites traverse the same orbit as earth: one ahead, and one behind. What it meant was we could see the things coming to earth from the side, and that was a huge development, says Howard—especially for being able to update incoming CMEs on an hourly basis.

But the twin STEREOs drift: as the STEREOs get farther from earth, they don't see what's coming toward as us well; and when they're directly behind the sun, they're turned off completely. Without LASCO, we would be blind, says Battams.

NRL also had a joint experiment on SOHO, called the Extreme ultraviolet Imaging Telescope (EIT). It was looking at the sun in the UV [ultraviolet], and it made just beautiful pictures, says Howard.

Because of when SOHO was launched, in 1995, NRL was able to share the data in a novel way: online. Karl developed this website for anybody in the world to measure [sungrazers], it was really unique, says Howard. And that really sparked an interest, that you could see what was happening near the sun anytime you wanted.

So the discovery of the 3,000th comet really was a worldwide effort. Now, says Howard, people in Europe, people in Asia, wake up before we do and they download the data and search for these comets.

For Howard, especially as a father himself, I think it encourages interest in the science, he says. The first person who reports it gets credit for it, that's a big deal.

Do comets hold the keys to earth's origins?
In addition to space weather, studying the chemistry of the comets themselves may lead to a better understanding of how our delicate blue planet came to be. One of the biggest questions we have now is, where did earth get its water? says Battams. When earth was very young, it was kind of like this big molten ball—so where did all the water come from?

Collisions, before gravity helped sweep things up, used to be much more frequent. The solar system is a lot cleaner and tidier place now than it was if you go back, say, 3.5-4 billion years, he says. At that time, a lot of this debris would have impacted the primitive earth—including, possibly, water.

You have to keep going backwards in time, and at some point you reach the point of where comets were formed, says Battams. We know that comets are mostly made of frozen water and frozen gas. They also have, by the way, amino acids, complex molecules, carbon—many of the basic ingredients for life.

There's a ton of question marks about our origins, says Battams. So you study what's left over from that time and see what you can figure out from there.

Most of the comets LASCO sees, about 85 percent, are the smaller remnants of a larger comet that's broken apart. What will have happened is, several millennia ago, a big comet went near the sun and, due to the sun's gravity, it basically crumbled and formed a small family of comets, says Battams. This comet group continued to orbit the sun—crumbling further each time it came back around. After that happened a few times, we were left with this long string of comets, and that's a lot of what we're seeing with SOHO.

LASCO's revelations could tell us as much about our future as they do about our past. That gives us information about the evolution of objects in the inner solar system, and the way their orbits evolve and the way they might fall apart, says Battams.

There's something different happening with our sun; NRL gets ready
There are no immediate plans to replace LASCO, but NRL is building two new cameras for the Solar Orbiter and Solar Probe Plus missions. There's a nice balance with everything, says Battams. Solar Probe, for example, is going to fly right through the region of space we've been seeing 3,000 comets go through. We've been watching these little ice balls go through there, now we get to send our probes.

He's been studying sungrazers since he came to NRL in 2003. In some ways, my job gets boiled down to 1s and 0s, and data types and variables floating around in computer programs, he says; but it's honestly not too many steps away from looking at why are we here and what are we made of, and am I drinking a bottle of comet water?

Russ Howard—for whom the first comet ever seen from space is named, after he and two NRL colleagues discovered it in 1979—became the Principal Investigator for LASCO in 1998. He still has a lot of questions about CMEs. We still don't understand how they're formed, how they propagate, and what's the impact at earth. You look at it—here's the event, here's the response—but you don't know the physics of how it's actually happening and you can't predict.

Working with NRL colleague Dr. James Chen, Howard was able to use LASCO and STEREO data to define the structure of CMEs. We wrote several papers defining these events as something called a magnetic flux rope, he says, describing them as cylindrical tubes that are bent—kind of like a croissant. The model was called the graduated cylindrical shell—but everyone loves the term croissant, he says.

But not all CMEs fit the croissant model. Do we have the model right? says Howard. It's more complex, or it's two croissants put together. He laughs, and says, Or is it a scone—or a blueberry muffin?

Additionally, he's noticed there's something happening with our sun now that's very puzzling. We think now that the sun is undergoing a change in its behavior, [unprecedented] since the space age began, he says. There's less activity going on, the magnetic field is weaker and the CMEs are less massive.

Because it's different, this is tremendously exciting to Howard. Science is fun, I guess that's the point, he says. All the questions that are out there to answered, new data to be analyzed, new instruments to be built.

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