How to find a comet before it hits Earth

How to find a comet before it hits Earth
by Heidi Toth for NAU Review
Flagstaff AZ (SPX) Dec 20, 2024

Q: How do you find a comet that could pose a threat to Earth but hasn't passed our planet in the last 200 years or more?

A: You look for its footprint.

This is the basis of research led by Samantha Hemmelgarn, a first-year doctoral student in Northern Arizona University's Department of Astronomy and Planetary Science. In a study published in Planetary Science Journal in November, she and her co-authors, including adviser Nick Moskovitz from Lowell Observatory, used data from meteor showers - the "footprints" left by comets - to pinpoint where these comets are in the sky and determine whether they pose a threat to Earth.

"This research gets us closer to defending Earth because it gives us a model to guide searches for these potentially hazardous objects," Hemmelgarn said.

The why and how of the research

Historically, long-period comets, which have orbits of more than 200 years, have been virtually invisible to researchers until they get close to Earth and move toward the sun. The fear, of course, is that one will go undiscovered in the sky until it's too late and then hit the Earth. While the actual risk is incredibly small, Hemmelgarn said, the impact of even a small comet could be catastrophic to life on Earth, causing another Ice Age and ozone layer loss.

So, they want to be proactive in identifying these comets. The researchers used a sample of 17 meteor showers they knew had long-period comet parents and created synthetic comets, which are models that represent where the parent comets could be in space based on the paths of those meteor showers. They compared the location of the real parent comets the last time they were near the sun to where the model predicted each comet would be. In most of the tests, the model accurately predicted a comet's location and helped predict the comet's direction and speed, which will help astronomers know where to find the real one with a telescope.

This means researchers can find these comets in the sky before they get close to Earth.

"Even if the next extinction level impact is millions of years away, it's been fascinating to develop a model that traces the 'shooting stars' humans marvel at every night back to a region in space where we can discover the objects that left them behind," Hemmelgarn said.

Her journey to this discovery

The day she graduated, Hemmelgarn would never have predicted that this exciting piece of the planetary defense puzzle would one day have her name on it.

Of course, that's because she graduated with a degree in marketing and a job offer as assistant manager for Walgreens, where she did a management internship. For years, she thrived in that environment, employing her problem-solving skills to ensure her store stocked what her diverse customer base needed.

However, with the advent of online retail, she found herself without the chance to solve problems and make decisions about her store. When she met her now-wife, Hayley, in 2019, Hemmelgarn realized she wanted something new.

"When I saw the passion and joy she exhibited for her career as a genomic epidemiologist, I realized that the same feeling I once had for retail management wasn't there anymore," she said. "I always had a passing interest in astronomy, began researching how a person could make a career in that field and decided it was as good a time as any to change careers since I still have many working years ahead of me."

In 2020, she started a bachelor's program in physics and astrophysics at NAU, which she finished a year ago, and in the fall, she began a doctoral degree. This is her first publication as first author.

What comes next

In the next phase of this work, Hemmelgarn and Moskovitz plan to apply this method to 247 long-period comet meteor showers with unknown parents. They'll use data from the Rubin Observatory's upcoming Legacy Survey of Space and Time (LSST) to find the faintest objects, which Hemmelgarn hopes will include some of these missing long-period comets.