Evrim Yazgin
Cosmos science journalist
Icarus, son of inventor Daedalus, is one of Greek mythology’s most tragic characters. Imprisoned by King Minos of Crete, Icarus’ father hatched an escape plan – they would fly off the Mediterranean island on wings made of feathers stuck together with wax. Famously, Daedalus warned Icarus not to fly too close to the Sun, lest his waxen wings melt. But Icarus forgot his father’s warnings and crashed to his death.
Now, emulating Icarus’s demise, a comet has been witnessed by astronomers to similarly ignore Daedalus’s warnings and pass too close to the Sun, causing it to disintegrate from the Sun’s heat.
Using a collection of powerful telescopes, astronomers from Macau, the US, Germany, Taiwan and Canada observed the near-Sun comet named 323P/SOHO. And, for the first time, they captured the moment such a comet has been broken up in its perilous orbit.
Publishing their results in the Astronomical Journal, the researchers also believe their findings help explain the scarcity of comets with periodic orbits in such close proximity to the Sun.
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Oftentimes, objects orbiting the Sun don’t follow the roughly circular, concentric orbits we’re used to seeing in textbooks. These “extreme” or “eccentric” orbits are highly unstable and can be greatly affected by the gravitation of other bodies in the solar system.
As such, comets with eccentric trajectories often end up in near-Sun orbit. Being so close to the Sun’s bright light, they are hard to spot and even harder to study. But even taking this into account, there are far fewer of them than expected.
So, why are there so few near-Sun comets? What is happening to them before they make their final dive into the Sun?
Using Japan’s Subaru Telescope, the Canada France Hawaii Telescope (CFHT), the Gemini North telescope (also in Hawaii), Lowell’s Discovery Telescope in the US, and the Hubble Space Telescope, the astronomers tracked 323P/SOHO to get a better picture of these near-Sun objects.
First problem: the group didn’t know what the orbit of 323P/SOHO looked like, so they had no idea where to look.
They used the wide field of view of the Subaru Telescope to “cast a wide net” and get a better picture of the comet’s orbit. Using this knowledge, they knew where to direct the other telescopes.
“We couldn’t have made this discovery without observations from the telescopes on Maunakea, made possible by the University of Hawaii,” says lead author of the paper Man-To Hui, who was a University of Hawaii researcher at the time of the observations, and now an assistant professor from Macau University of Science and Technology. “The observations from the Subaru Telescope were the initiator, shrinking orbit uncertainties and making follow-up observations possible. CFHT provided the best coverage data and Gemini provided the densest data points.”
Surprisingly, the comet changed shape as it passed the Sun. At first, it looked like a dot. Soon after, it had a long tail of ejected dust. The researchers believe that the Sun’s intense radiation caused the comet to break apart. This process, known as thermal fracturing, is seen every day when you pour hot liquid over ice cubes. This could be, according to the researchers, the reason there are so few near-Sun comets left.
But the observations also raise other questions. Why did they find that 323P/SOHO is coloured unlike anything else in the solar system? Do other near-Sun comets share this colouring?
Further analyses of near-Sun comets may answer these and other questions about these Icarus-like celestial bodies.