The peoples of ancient cultures around the world long considered comets to be “harbingers of doom.” Unlike the planets, which moved in periodic and predictable orbits, comets were erratic and seemingly random. These celestial objects, trailing tails of fire in their wake, were seen as warnings from an angry God.The assassination of Julius Caesar was marked by the presence of a comet, as was the bloody battle between Pompey and Caesar. Halley’s Comet was blamed for bringing the Black Death upon the people of England, and the Incas watched a comet streak through the sky days before being conquered by Francisco Pizarro. [1]
Today we know that comets are not prophets of the apocalypse sent by a vengeful deity. But what is a comet? Astronomers often refer to comets as “dirty snowballs.” These large chunks of rock and ice begin their life cycles far out in the Oort Cloud, a spherical swarm of icy bodies that exists over 5,000 astronomical units outside our solar system (an astronomical unit is the distance between the Earth and the Sun). [2]
Over time, the gravity from a star or other large body nudges these rocky balls of ice out of their Oort Cloud orbits. These fledgling comets plummet toward the Sun, and the heat begins to melt some of the ice that makes up the comet. The melted ice becomes a vapor trail behind the comet. The faster and hotter the comet gets, the longer the tail becomes. [3]
This past Wednesday marked the first time mankind landed a probe on a comet. The European Space Agency (ESA) spacecraft Rosetta released the robotic lander Philae 20 kilometers above the surface of comet 67P. Philae was released at 8.35 GMT and began its 7 hour descent to the surface of the comet. These 7 hours were filled with suspense for the scientists and engineers at ESA – following release all they could do was watch and wait. [4]
Philae touched down on the surface of 67P at 15.33 GMT, but not everything went according to plan. The harpoons that were meant to anchor Philae to the comet’s surface failed to fire, and as a result Philae bounced 1 kilometer back up into the “air” (not really, comets have no atmosphere). After falling back to the surface, Philae bounced up once again. All this time, the comet continued to rotate and Philae moved farther and farther away from its intended landing site. [4]
On Thursday the ESA announced some bad news. Philae’s rough landing has left it in a shadowy spot, and its solar panels aren’t receiving enough light to keep operating. Philae’s battery left Earth with only a 60-hour charge, so it is likely that Philae will shutdown sometime on Friday. Faced with an imminent shutdown, ESA scientists are in a rush to collect all the data they can. Philae’s X-ray spectrometer, drill, and MUPUS hammer have all been activated. [5] Photographs from 67P have also been streaming in since the landing. Even if Philae does not survive through the night, it still represents a leap in mankind’s scientific knowledge, and should be viewed as a success.
[1] http://www.nasa.gov/mission_pages/deepimpact/media/f_ancient_prt.htm
[2] http://solarsystem.nasa.gov/planets/profile.cfm?Object=KBOs&Display=OverviewLong
[3] http://www.qrg.northwestern.edu/projects/vss/docs/space-environment/1-what-is-a-comet.html
[4] http://www.theguardian.com/science/2014/nov/13/philae-landing-rosetta-mission-good-bad-news
[5] http://www.washingtonpost.com/news/speaking-of-science/wp/2014/11/14/rosettas-missing-philae-lander-is-frantically-doing-improvised-science-even-as-its-batteries-die/