How to spot comets that can impact Earth? Look at the t(r)ail, scientists suggest

Comets are common in the universe, but not a lot of them are frequent visitors to our solar system. Those that do take the trip, do so after an interval of years. Some of them even have a 200-year period of return, making it harder to detect them. They are born towards the outer edges of the solar system and are known as long-period comets (LPCs).

Such comets pose a risk to Earth and can ram into the planet without being detected beforehand. As per estimates, such comets can cause up to six per cent of all impacts on Earth.

Halley's Comet probably has the shortest cycle and visits Earth every 76 years. It last came in 1986 and will next approach us in 2061. This helps scientists prepare for it. But some comets, like the recent A3 Tsuchinshan-ATLAS, visit unannounced.

Scientists have found a way to know when such a comet might fly by Earth - Follow the trail.

Comets leave behind a breadcrumb-like trail of meteoroids. These cosmic visitors are icy bodies that when approaching the sun, heat up a bit, causing much of its ice to vapourise. The comet's rocks and dust turn into a meteoroid stream, and their path parallels the comet's.

When these meteoroid streams strike Earth, some of them rain down the atmosphere as meteor showers. Scientists say that these trails can help learn about the meteoroid's speed and direction of travel, leading to the discovery of the parent comets.

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Locating parent comets

The study authors tested the theory by looking at 17 meteor showers with known parent LPCs. Based on each shower's properties, they generated one family of synthetic LPCs for each meteoroid stream.

They then virtually placed the comet clusters at distances from where they were bright enough only for the Rubin Observatory. To know how accurate they were, they matched the locations of these synthetic comet families with the real comets' positions.

Most of the actual parent comets were found to largely lie in the same area, close to the centres of their respective artificial clusters. They also found that back-projecting the meteoroid streams made the field to check for parent comets much narrower.

They also found that locating comets that were billions of miles away and one day might potentially hit Earth gave experts years to do something about the incoming impact.

Samantha Hemmelgarn, a graduate student at Northern Arizona University and the study's first author, said that there are at least 247 orphaned meteoroid streams whose paths cross with Earth. "Hopefully with LSST, we will be able to detect comets on Earth crossing orbits much sooner than we can now," she said.