Indeed, as we search for life on other planets, we've used the Earth as our standard reference. Practically speaking, it's the only model we've got — and it appears to be a pretty damned good one; Earth has been teeming with life for billions of years and, quite importantly, it's even spawned a radio-capable, space-faring civilization.
That being said, what makes us so sure it's the best model for habitability? Could other planets or moons be even more suitable for life? A pair of astrobiologists say yes. To find a habitable and ultimately an inhabited world, they argue we should adopt a biocentric approach rather than a geo- or anthropocentric one.
What causes the structure in Comet Lovejoy's tail? Comet C/2014 Q2 (Lovejoy), which is currently at naked-eye brightness and near its brightest, has been showing an exquisitely detailed ion tail. As the name implies, the ion tail is made of ionized gas -- gas energized by ultraviolet light from the Sun and pushed outward by the solar wind. The solar wind is quite structured and sculpted by the Sun's complex and ever changing magnetic field. The effect of the variable solar wind combined with different gas jets venting from the comet's nucleus accounts for the tail's complex structure. Following the wind, structure in Comet Lovejoy's tail can be seen to move outward from the Sun even alter its wavy appearance over time. The blue color of the ion tail is dominated by recombining carbon monoxide molecules, while the green color of the coma surrounding the head of the comet is created mostly by a slight amount of recombiningdiatomic carbon molecules.
This does NOT mean that anything ever actually lived there. But it is the first time that the ingredients for the evolution of microbial life, and the correct conditions to support it, have been directly observed beyond Earth. Mars still has water frozen at its poles, and once had quite a bit of water above and below the surface.