Comet Double-Whammy: A Lesson in Planetary Defense?


The Discovery Channel Telescope at Lowell Observatory in Arizona played a key role in identifying the true nature of Comet P/2016 BA14, which will be the third closest comet flyby to occur in recorded history on Tuesday morning. To find out more, Discovery News reached out to Lowell Observatory astronomer and near-Earth object expert Nick Moskovitz.

On Monday morning, Comet 252P/LINEAR buzzed Earth at a distance of 3.3 million miles (14 times the Earth-moon distance), the start of an unprecedented cometary event that will be followed by the flyby of Comet P/2016 BA14 on Tuesday (March 22) at 7:30 a.m. PDT (10:30 a.m. EDT). BA14 will come even closer to Earth, at a distance of only 2.2 million miles (9 times the Earth-moon distance).

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Though never a threat to Earth and small by comet standards, these two objects are noteworthy for several reasons, but primarily they highlight the need for surveys to detect them and the followup studies by more powerful observatories to characterize what they actually are.

“Most newly discovered objects are being found by surveys that scan the sky with relatively small (1-2 meter) telescopes,” astronomer Nick Moskovitz, of Lowell Observatory, told Discovery News. “When you take a much larger telescope like the DCT (Discovery Channel Telescope) and point it to some of these new discoveries you can see much fainter which enables us to detect subtle indications of cometary activity like a tail or coma.”

The Discovery Channel Telescope at Lowell Observatory specializes in the study of small solar system bodies such as comets and asteroids, playing a key role in revealing BA14′s true nature. Discovered by the University of Hawaii’s PanSTARRS telescope on Maui in January, Comet P/2016 BA14 was initially identified as an asteroid. But its strikingly similar orbit to Comet 252P/LINEAR prompted DCT astronomers to take a closer look.

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252P/LINEAR is a well known 250 meter-wide comet with a known orbit. It was discovered by MIT’s Lincoln Near Earth Asteroid Research (LINEAR) survey in 2000 and tracked since then. To find a second object traveling along a similar trajectory seemed to be more than a coincidence. So when the DCT was used to zoom in on BA14, the detection of a faint cometary tail proved that it was also a small comet.

“Most of these newly discovered objects do not show cometary activity, they are asteroids, but we don’t really know how many comets are hiding out there waiting to be discovered,” added Moskovitz.

As the DCT has such a wide aperture (so more like from the faintest of objects can be captured) and large single CCD (charge-coupled device), astronomers are able to image extremely diffuse features, such as the thin gaseous emissions from small comets. The DCT is also ideally located in a dark sky site in the Coconino National Forest near Happy Jack, Ariz., at an elevation of 2,360 meters (7,740 ft).

According to Moskovitz, telescopes like the DCT provide a critical role in planetary protection operations. While powerful optical telescopes are not used for sky surveys, the DCT has a very specific role to play.

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“The DCT is not well suited to large scale discovery efforts, but is one of the best facilities in the world for characterizing physical properties,” he said. Although Moskovitz wasn’t directly involved in the study of BA14, his main research interests focus on the characterization of NEOs using the DCT, an effort that identifies comets and asteroids that could be a potential danger in the future.

Moskovitz points out that planetary protection involves two steps: “The first is to discover every object that could pose a hazard to the Earth. The second is to characterize the properties of any potential impactors. We use the DCT to refine orbits, measure compositions, determine sizes and shapes, and the rotations of near-Earth asteroids, all of which are essential to better understanding the impact hazard and the viability of various impact mitigation strategies.”

Further observations of comets 252P/LINEAR and P/2016 BA14 by other telescopes, such as the Hubble Space Telescope and NASA’s Infrared Telescope Facility, will be carried out to study their compositions to see if they really did originate from the same body as their synchronized Earthly encounters suggest. At some point in their history, they may have belonged to the same comet but broke into two (or more) chunks. As comets and asteroids orbit the sun, solar radiation can cause these interplanetary travelers to spin (known as the Yarkovsky–O’Keefe–Radzievskii–Paddack, or “YORP”, effect); eventually, these fragile structures can rip themselves apart. This mechanism may be responsible for the coincidence of the double-comet event.

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“I generally view observations of NEOs as being important for three reasons,” said Moskovitz. “First, these objects can and do occasionally impact the Earth. We want to understand them from the perspective of impact hazard assessment.

“Second, some NEOs are easier to reach by spacecraft than the Moon and thus are ideal candidates for future robotic and human exploration. However, such exploration requires that we can intelligently select targets based on ground-based telescopic studies.

“Thirdly, NEOs come to us from many different regions of the solar system and are some of the most primordial bodies in the inner solar system. Thus by studying these objects we can gain a deeper understanding of formative and evolutionary processes in the solar system.”

Though cometary close encounters can be a frightening reminder about how many NEOs there are buzzing Earth, this encounter will be an incredibly valuable scientific opportunity for us to learn more about the early evolution of the solar system.

Correction: An earlier version of this article was titled "Comet Double-Whammy: A Lesson in Planetary Protection?" -- This was an incorrect use of definitions. "Planetary protection" is a field of study dedicated to the protection of Earth from potentially harmful hypothetical extraterrestrial organisms and the protection of other planets from potentially harmful terrestrial microbes hitching a ride on spacecraft. The detection of NEOs and impact mitigation strategies is known as "planetary defense." The title has been edited to reflect this change.

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