* Astronomy

Comet Lovejoy flies into Sun to reveal solar secrets

A comet's close encounter with the Sun has given scientists a look at a solar region that has never been visited by spacecraft.
In 2011, comet Lovejoy hurtled deep into the Sun's violent atmosphere - an area called the solar corona.
Telescope images have revealed how the comet's tail was pulled about by an intense magnetic field, allowing scientists to characterise this force for the first time. 
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Title: Comet C/2011 W3 (Lovejoy): Orbit Determination, Outbursts, Disintegration of Nucleus, Dust-Tail Morphology, and Relationship to New Cluster of Bright Sungrazers
Authors: Zdenek Sekanina, Paul W. Chodas

We describe the physical and orbital properties of C/2011 W3. After surviving perihelion, the comet underwent major changes (permanent loss of nuclear condensation, formation of spine tail). The process of disintegration culminated with an outburst on December 17.6 (T+1.6 d) and this delayed response is inconsistent with the rubble pile model. Probable cause was thermal stress from the heat pulse into the nucleus after perihelion, which could also produce fragmentation of sungrazers far from the Sun. The spine tail was a synchronic feature, made up of dust released at <30 m/s. Since the nucleus would have been located on the synchrone, we computed the astrometric positions of the missing nucleus as the coordinates of the points of intersection of the spine tail's axis with lines of forced orbital-period variation, derived from orbital solutions based on preperihelion astrometry from the ground. The resulting osculating orbital period was 698±2 years, which proves that C/2011 W3 is the first major member of the predicted new, 21st-century cluster of bright Kreutz-system sungrazers. The spine tail's tip contained dust 1-2 mm in diameter. The bizarre appearance of the dust tail in images taken hours after perihelion with coronagraphs on SOHO and STEREO is readily understood. The disconnection of the comet's head from the preperihelion tail and the apparent activity attenuation near perihelion are both caused by sublimation of all dust at heliocentric distances smaller than ~1.8 solar radii. The tail's brightness is strongly affected by forward scattering of sunlight by dust. The longest-imaged grains had a radiation-pressure parameter beta ~ 0.6, probably submicron-sized silicate grains. The place of C/2011 W3 within the hierarchy of the Kreutz system and its genealogy via a 14th century parent suggest that it is indirectly related to the celebrated sungrazer X/1106 C1.

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Sungrazing comets aren't a new thing. In fact, the orbiting Solar and Heliospheric Observatory (SOHO) watches one fall toward the sun and evaporate every few days. These frequent kamikaze comets, known as "Kreutz sungrazers," are thought to be splinters of a giant comet that broke apart hundreds of years ago.  Typically they measure about 10 meters across, small, fragile, and easily vaporised by solar heat.
Based on its orbit, Comet Lovejoy was surely a member of the same family - except it was 200 meters wide instead of the usual 10.  Astronomers were eager to see such a whopper disintegrate.  Even with its extra girth, there was little doubt that it would be destroyed.
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Orbital elements:
    C/2011 W3 (Lovejoy)
Epoch 2011 Dec. 25.0 TT = JDT 2455920.5
T 2011 Dec. 16.01211 TT                                 MPC
q   0.0055561            (2000.0)            P               Q
z  +0.0129748      Peri.   53.62275     +0.18408854     -0.90052085
 +/-0.0000477      Node   326.53456     -0.96007510     -0.07885569
e   0.9999279      Incl.  134.40945     +0.21063526     +0.42760259
From 96 observations 2011 Nov. 27-Dec. 24

MPEC 2011 - Y23