Hi guys, and welcome back! In this article I’m going to continue our voyage through space, which we have begun with my last post.
Remember? I said that in the remotest areas of our Solar System a spherical area, called Oort cloud, probably exists; it is the starting point from which comets begin their periodical journey to the inside regions of our Solar System.
But what is a comet? In this post we will deal more in depth with this interesting topic.
A comet is a relatively small icy celestial body, whose orbit extends beyond that of Pluto; comets can be considered as a sort of “heavenly messengers”, that regularly or occasionally approach the Sun and undergo a superficial heating that leads to the sublimation of their outer layers; it is in this way that the coma (the bright “hair” that surrounds the nucleus of a comet) and the tail form.
If comets pass close to the Earth, they are very bright and they can be observed with the naked eye. Some of the most famous comets are Halley’s comet and the comet Hale-Bopp.
Halley’s comet is undoubtedly the most known of all comets; its revolution period is of 76 years, and it was sighted for the first time in 1531.
Its last passage near the Earth was in 1986, and it will be observable again in 2062. After its passage in 1910, the European space probe Giotto was built, in anticipation of its future passage in 1986. Giotto’s images showed an irregular cometary nucleus, covered by a carbonaceous crust, rotating on itself in 53 hours.
The comet of Hale-Bopp (so-called from its discoverers Alan Hale and Thomas Bopp) was visible from the Earth during the Spring of 1997 for a total period of 569 days: this was a record, that got over the previous, belonging to the Great Comet of 1811, that had been observable for about 270 days.
It is interesting to know that the revolution period of the comet Hale-Bopp is of about 2537 years! This means that it will return to be visible in about a million years. It is too much time for us, my friends!
Other famous comets are: the comet Encke, a periodic comet discovered by Pierre Méchain but whose name is taken from Johann Franz Encke, who studied its orbit, foreseeing its return in 1822. It is one of the comets with the shortest revolution period (about 3 years and 4 months); the comet Hyakutake, discovered in January 1996 by the Japanese astronomer Yuji Hyakutake. This comet passed near the Earth that year in March, and was one of the nearest cometary approaches to our planet in the last 200 years. It was nicknamed the Great Comet of 1996 for this reason; finally, the comet Linear, that crossed our sky in July 2000.
Until a short time ago, it was impossible for men to reach a comet: instead this has happened, guys! In fact a space mission developed by the ESA (European Space Agency) called “Rosetta” was launched in 2004. Its objective was to study the comet 67P/Churyumov-Gerasimenko.
The mission relies on two elements: the space probe Rosetta and the lander Philae, which landed on the surface of the comet on 12thNovember 2014. The probe was baptized with the name Rosetta to remember the Rosetta stone, an ancient artifact on which the same text was written in three different languages, including Egyptian hieroglyphs, which enabled the archaeologist Champollion to translate the ancient Egyptian language, until then incomprehensible. Similarly, the probe Rosetta will serve as a link between meteorites, that scientists can study on the Earth, and the Solar System, that men can not visit yet but which comets cross continuously.
But what are the main steps that characterize this mission? I’ll try to summarize them briefly.
Rosetta started its voyage through the Solar System about 10 years ago, in 2004; after all this time, on 20th January this year Rosetta successfully completed the awakening from its hibernation phase and sent a signal to Earth, received by the NASA (National Aeronautics and Space Administration) and confirmed by the ESA operative centre (European Space Agency) in Darmstadt (Germany), at a distance of more than 500 million kilometers. On 6th August 2014 Rosetta reached a distance of 100 km from the comet 67P and prepared itself to choose the place of landing, that was confirmed on 15thSeptember; on 12th November Philae was finally launched toward the comet, reaching it after 7 hours of voyage.
But when it landed, the harpoons did not activate and the lander failed to stabilize itself in the place that had been chosen: so Philae was forced to land away from the planned landing site. Unfortunately, in this place the photovoltaic panels of Philae can receive only 90 minutes of sunlight in 12 hours. As a result, on 14th and 15th November the batteries of the lander exhausted, soon after the first perforation of the comet; the new “home” for Philae is much less hit by sunlight compared to the needs of the batteries, and for this reason ESA decided to hibernate the little robot again and wait for the spring 2015, when the comet 67P will be closer to the Sun and the photovoltaic panels will receive the amount of light necessary to reactivate Philae to complete its mission.
However, a few hours after landing on the comet 67P, Philae was able to “sniff” some organic molecules made of carbon, which ESA is currently studying. To discover whether comets can carry the basic elements of life is the main aim of the Rosetta mission, in addition to the success of landing for the first time on a comet that is traveling through space at a very high speed.
Just so, guys! Maybe comets brought life also to other areas of space, and this means that.. we could not be alone, my friends! The presence of these microscopic clues of life was confirmed on 18th November.
Now Philae “is sleeping”, but we will talk again about this interesting topic in spring! While we wait you can have a look at… Rosetta blog ! 😉
I hope you liked this article! 🙂 See you soon!