This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Over the coming month the European Space Agency's (ESA) Rosetta mission will fire its main engines no less than eight times to tweak its interplanetary intercept course with Comet Churyumov–Gerasimenko; eventually sidling up to the 4 kilometer wide cometary nucleus at about 7.9 meters per second in early August. At that point, with some gentler rocket burns, the roughly 3,000 lb spacecraft will try to insert itself into an orbit around this lumpy body. A couple of months later, after the surface of the nucleus has been mapped, Rosetta will release Philae - a 200 lb lander that will drift down to the body and attach itself with harpoons and drills.
The current best guess at what Comet Churyumov-Gerasimenko looks like up close (NASA, ESA and Philippe Lamy (Laboratoire d'Astronomie Spatiale))
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Together, mother and daughter spacecraft will ride the comet as it plunges sunward. The closest pass to the Sun, or perihelion, will take place August 13th 2015 - although it's not particularly extreme - this is no sungrazer. The closest approach is actually 25% further from the Sun than Earth's orbit. But for a potentially volatile and fragile cometary nucleus this could certainly be close enough to cause some icy fireworks.
By that time it's unclear that Philae will still be active, its nominal mission lifetime is only a week after landing, but it could last much longer. With a suite of no less than 10 instruments, Philae is a potent little probe. It has imaging systems, sample analysis tools, environmental monitors, and together with its mothership Rosetta it can help probe the interior structure of the nucleus via radio tomography (basically how well radio waves propagate through the body at different sight-lines).
Rosetta is also jammed with gear, from cameras to mass spectrometers and spectrographs, as well as dust collectors that can be scrutinized by an atomic force microscope.
It's an incredible mission, with the potential for incredible scientific discovery. The one real wildcard though is Churyumov–Gerasimenko itself. Back in May 2014 it started producing a classic cometary halo of ejected dust as the nucleus started warming up, but by early June this had seemingly dissipated - it was just a temporary outburst. Despite this reduction in the halo, the nucleus is still releasing water as it warms up - or 'sweats' - as described in this ESA infographic:
And that's the thing with comets, they're fickle beasts - a characteristic well demonstrated by the now somewhat infamous ISON in 2013. We'll have to wait and see what this one does as its little passengers hang on through the cometary summer.
