Photo Michael Jäger of Stixendorf, Austria
Michael Jäger of Stixendorf, Austria, took the picture on Dec. 31, 2016, just as the comet was swinging around the sun en route to Earth. Since then 45P's icy nucleus has been heated by solar radiation, causing it to spew brightening jets of gas into the comet's green atmosphere. Why green? Because the comet's vaporizing nucleus emits diatomic carbon, C2, a gas which glows green in the near-vacuum of space.
According to the Minor Planet Center, this is the 8th closest pass of any comet in the modern era (since ~1950, when modern technology started being used to study comets). It will only be 31 times farther from Earth than the Moon. Interestingly, 45P made an even closer approach on its previous orbit (23 lunar distances), so it is also on the list as the 5th closest.
Proximity makes the comet bright despite its small size. Forecasters say 45P could be on the verge of naked eye visibility (6th magnitude) when it emerges into the pre-dawn sky later this week. The best time to look is during the dark hours before sunrise between Feb 9th and 12th. The comet will be racing through the constellation Hercules high in the eastern sky.
Is komeet 45P zijn staart verloren?At the end of December 2016, Comet 45P/Honda-Mrkos-Pajdusakova plunged toward the sun with a long tail streaming behind it. Now the comet is headiing for Earth for a close encounter on Feb. 11th. Apparently, however, it left something behind. "Comet 45P has lost its tail," reports Bill Williams of the Chiefland Astronomy Village in Florida, who photographed the approaching comet last night:
Credit Bill Williams
"The comet still sports a gorgeous green atmosphere ('coma') and is now exiting the dense Ophiuchus Milky Way starfield," says Williams. "The comet sure is moving fast!"
WIlliams isn't the only observer to notice the missing tail. Moreover, the comet is at least 3 times dimmer than forecasters expected. "It is rather faint and diffuse," notes Dr. Brian Ottum of Dark Sky New Mexico, who photographed the green fuzzball on Feb. 7th. "45P seems unlikely to reach naked eye visibility."
What happened? On Dec. 31, 2016, the comet slingshot around the sun inside the orbit of Venus. Solar heating might have vaporized so much material from the comet's icy core that there is insufficient left for a flamboyant tail. For the same reason, the comet may be dimmer than expected. Amateur astronomers with small telescopes can monitor the situation. The best time to look is during the dark hours before sunrise between Feb 9th and 12th. The comet will be racing through the constellation Hercules high in the eastern sky.