Welcome to the dark folds of one of the closest comets in years. The 1000-foot radio telescope dish at Arecibo Observatory in Puerto Rico pinged comet 209P/LINEAR with radar between May 23-27 and reconstructed images of its rugged surface from the echoes received in return. Cliffs and ridges dominate the landscape.
Recently, dust boiled off the comet birthed a brand new meteor shower called the Camelopardalids. While forecasts cautiously predicted up to 100 meteor per hour, the actual visual rate was closer to 5-10 per hour. We learned earlier this week, the comet shed much smaller dust particles than expected. Most were below the naked eye limit when they flared across the sky. But the fact that meteor experts could actually predict a never-before-seen meteor shower is worthy of high praise.
We rarely get to image comets because they rarely make such close approaches to Earth. Today 209P/LINEAR is just 5.1 million miles from the planet, making it the closest comet to fly by Earth since Comet IRAS-Aracki-Alcock buzzed past in 1983.
“Comet 209P/LINEAR has no chance of hitting Earth,” said data analyst Alessondra Springmann. “It comes no closer than 5.2 million miles (8.3 million km) to Earth, safely passing our planet.”
Arecibo radar has observed other comets including 103P/Hartley 2 in 2010, 8P/Tuttle in 2007 and 2008 and 73P/Schwassmann-Wachmann 3 in 2006. Circumstances and proximity made images of 209P/LINEAR the highest resolution of any comet ever obtained with the big dish.
In addition to the views of its topography, radar determined 209P’s diameter at 1.5 x 1.8 miles (2.4 by 3 km) with a rotation rate of 11 hours. Although the comet travels from near Jupiter’s orbit into the inner solar system every 5.1 years, there won’t be any decent radar imaging opportunities for at least the next 50 years as there are no particularly close approaches for some time. Close approaches all depend on where the Earth is in relation to the comet when it drops into the inner solar system.
I’ve been watching 209P/LINEAR for the past 10 days and can say it’s one of the most unusual comets I’ve ever seen. Most display bright heads and long tails when this close, but not this one. It’s faint, tiny and very compact. Last night 209P shone at magnitude +12.6 and looked more like a small, fuzzy star than a comet. Because it’s so near us, the comet’s moving rapidly across the sky at the rate of a degree (two moon diameters) every few hours. I was able to detect movement in just one minute when it happened to pass near a star.