This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Hello ancestor! The surface of a comet, with one of Philae's landing feet (Credit ESA/Rosetta/Philae/CIVA)
As the European Space Agency's Philae lander bounced and settled onto the surface of comet 67P/C-G's crumbly nucleus it wasn't just space exploration, it was time travel.
This stupendous feat of spacecraft design and operation has brought us to a place little changed from its original state, a condensation and agglomeration of one small part of the dusty nebula that collapsed under its own weight 4.57 billion years ago to make our solar system.
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Comet 67P/C-G belongs to a family of cometary bodies known as the Jupiters. These objects have orbits of around 20 years or less, and are constantly being perturbed by Jupiter's gravitational field. Because of that they can be temporary interlopers, sometimes flung into the Sun or even out of the solar system. Detailed analysis of 67P's orbital history (it was only discovered in 1969) suggests that sometime around 1840 a closer encounter with Jupiter altered its orbit so that instead of only ever coming within 4 astronomical units (AU) of the Sun, it began to come as close as 3 AU. More orbital shifts took place, and probably sometime in 1959 it was perturbed into its present orbit that brings it as close as 1.29 AU to the Sun, in a 6.45 year period.
Where do the Jupiter family comets come from? They have relatively low orbital inclinations (the orbits are little tilted with respect to the plane of the major planets) and the current best bet is that most are from the Kuiper belt, a zone just beyond the orbit of Neptune. Gravitational perturbations over billions of years result in the orbit of some of these frigid objects bringing them close enough to get snared by the influence of massive Jupiter, and corralled into the inner solar system.
67P/C-G is therefore a piece of ancient history. Formed beyond the orbits of the inner planets, it is a mix of material from the original solar nebula and the chemical and physical processing that took place in the proto-stellar, proto-planetary disk - a swirling, orbiting structure where planetary embryos carved out their turf, perhaps like the remarkable structures seen recently in the HL Tauri system by the ALMA telescope.
The HL Tauri system, a proto-planetary disk only a few million years old (Credit ALMA (ESO/NAOJ/NRAO))
This cometary nucleus contains silicate solids, from dust to fragile rocks, and a great inventory of volatiles - water, carbon dioxide, and a probable wealth of richer organics that may include the precursors to amino acids (if not the real things). Rosetta has already sniffed a heady mix boiling off the nucleus.
Although 67P/C-G has effectively remained in stasis for most of the past 4.5 giga years; billions, even trillions, of its siblings and its cousins - from drier, rockier asteroids to metal rich planetary embryos - contributed to building the surface of a young Earth, and to depositing its chemical wash. The same wash out which life seems to have emerged a few hundred million years later.
So it's not crazy to think of the picture of the surface of 67P as part of our family album. Some piece of you - atoms in your cells - came from precisely this kind of place. These elements have spent 4.5 billion years cycling through Earth's bio-geo-chemical systems. Perhaps some of them were once part of other organisms: bacteria, plants, or even a dinosaur, used and discarded a million times over billions of years. But right now they're part of you. You are a fleeting vessel for these components of a far deeper history - the history being examined by a small robotic lander that was itself constructed from precisely the same mix of ancient atoms.
