Even though it was more than 3 million miles away from Earth when it zipped past us back in March, 252P/LINEAR made one of the closest encounters of any comet in recorded history. And it has the distinction of being the closest celestial object – other than the moon – ever observed by the Hubble Space Telescope.
These images were taken on April 4 (around two weeks after 252P/LINEAR made its closest sweep past our planet) when the comet was about 8.7 million miles away. The comet, which is 750 feet across, actually has a “twin” that flew about a million miles closer to the Earth a few days behind it. But at half 252P/LINEAR’s size, the little sibling wasn’t large or bright enough for a good close-up.
The time-lapse above uses frames taken between 30 and 50 minutes apart. The bright light – rotating like the beam of a lighthouse – is a jet of dust being emitted as the comet is warmed by the sun. Comets are made up of a core called a “nucleus” made of dust, ice, and dirt – basically a dirty snowball – that sublimates into a fuzzy aura called a “coma” under the warmth of the sun. What we’re seeing is the resulting jet of material, shooting out in a narrow streak and illuminated by sunlight.
Scientists believe that the comet’s nucleus is spinning in the time-lapse, causing the jet to sweep around like a beacon. Unfortunately, the comet was too small for the Hubble to resolve the nucleus itself.
Comet 252P/LINEAR is now more than 25 million miles away from Earth. Its orbit will return it to the inner solar system in just five years, but it won’t come anywhere near as close as it did this time around.