Comet Lovejoy Is Falling Apart

Where’s my head? Comet Lovejoy on April 22 is basically all tail. Compare to below. Credit: Gianluca Masi and Michael Schwartz

Oh, it’s still there, but not like it used to be. In early April, Comet C/2017 E4 Lovejoy was the ticket — bright, dense head and streak of a tail almost at the naked eye limit of visibility. Certainly it was an easy if small binocular object with a bright future, provided it held together in one piece while approaching the sun. But something happened about April 10. Instead of getting brighter, Lovejoy started to fade.

In its heyday on April 7, Lovejoy’s bright and big head glowed a pale aqua-green. The unusual, flattened shape of the coma led many to predict that the comet might be ripe for breakup. Credit: Damian Peach

As coma shrank and dimmed, it was clear that the comet was disintegrating. A week and a half after observers first noticed the fade, Lovejoy literally lost its head. Now it’s just a streak in the sky galloping from Andromeda into Triangulum like some cosmic headless horseman. Because it’s faded to around magnitude +9.5-10, you’ll need an 8-inch scope to spot it. Your viewing window will be very short with the comet only about 8° high in the northeastern sky at the start of dawn.  Lovejoy’s glory days appear to be over.

Comet breakups aren’t uncommon. NASA used the Hubble Space Telescope to photograph Comet 332P/Ikeya-Murakami disintegrating as it approached the sun in Jan. 2016. The comet debris consists of a cluster of building-size chunks near the center of the image. They form a 3,000-mile-long trail, larger than the width of the continental U.S. The fragments are drifting away from the comet roughly the walking speed of an adult. The main nucleus of Comet 332P is the bright object at lower left. It measures 1,600 feet across, about the length of five football fields. The comet shards brighten and dim as icy patches on their surfaces rotate into and out of sunlight. Credit: NASA/ESA

Despite their solid appearance, as seen in the many closeup photos taken by the Rosetta Mission of comet 67P/C-G, comets are fragile things. When you see photos of comets, they look big and impressive, but it’s a tiny object that makes the big object. Most comet nuclei, composed of dust and ice, are quite small, on the order of a kilometer or two across. Every time they go around the sun, they loose mass, some as much as hundreds of tons a second, as solar heating vaporizes the comet’s ice.

On April 23 at perihelion (closest approach to the sun) we see a tiny, remnant comet head returning to view. The feature had disappeared in photos taken on April 25. Some of the fresh ice exposed from the breakup, vaporizes and brightens the lower part of the tail just above the head. Credit: Gianluca Masi and Michael Schwartz

If a comet happens to pass near Jupiter — and many do — the planet’s powerful gravity can weaken the object or even break it apart. If Jupiter doesn’t get it, the gravity and heat of the sun can work over the object and cause it to crumble right before our eyes.  Geysers of dust and gas, often released from just below the surface, apply pressure to the icy nucleus and carve out hollows that further weaken icy dustball. More recently, astronomers have discovered that avalanches also play an important part in the comet’s breakdown. All this activity ramps up whenever a comet leaves the refrigerated depths of deep space at one end of its orbit and ventures closer to the sun.

Comet Lovejoy made its closest approach to the sun on April 23, but the breakup began earlier. The question is when. Was it two weeks prior when the comet began to fade or even earlier? At discovery on March 9 by Australian amateur Terry Lovejoy, the comet was rather faint until around the 28th when it quickly became much brighter. A sudden, unexpected leap in brightness is called an outburst. Could huge avalanches coupled with jetting geysers have begun the breakup? They would have provided lots of fresh material for the sun to boil off and increased the comet’s brightness many times over.

Comet Lovejoy slides from Andromeda into Triangulum the Triangle low in the northeastern sky at dawn.  Created with Stellarium

There may still be a shred of Lovejoy left. In the most recent photos there’s a tiny bright spot at the position of the comet’s nucleus. How long it may continue to “feed” the tail is unknown, but I suspect this comet is not long for our skies and will likely never return.

After a lifetime of observing them, one learns never to count too much on comets.