Australian Sky & Telescope — July 2017

24 AUSTRALIAN SKY & TELESCOPE July 2017

And what an arrival it was! As Rosetta approached its

target, images first showed an unresolved dot of light, then a

roundish blur, then a larger and distinctly not roundish blur.

Soon it became obvious that the nucleus looks nothing like

a lumpy potato, as Hubble Space Telescope light curves had

hinted. Instead, this comet has two distinct lobes, earning it

a descriptive nickname of the Rubber Ducky — with a ‘head’

(the small lobe) and ‘body’ (the large lobe) connected by a

narrow ‘neck’.

Somehow we needed to find a place to land Philae on this

duck in a very short time. We feverishly mapped and analysed

the nucleus before it became too active as it neared the Sun.

Following some scientific arm-wrestling, the team deployed

the lander on November 12, 2014.

But Philae failed to ‘stick the landing’ — a faulty valve

prevented its hold-down thruster from working, and harpoons

meant to secure it to the surface didn’t fire. Instead the lander

bounced a few times over the course of a couple of hours and

drifted more than a kilometre to an unknown location that

unfortunately proved too shadowed to let its batteries recharge.

However, Philae was able to run many of its primary

science activities and transmit results to the mother ship

during the 57-hour lifetime of its onboard battery. What was

frustrating was that the lander's true location was unknown

and remained that way until the last few weeks of the mission,

when it was located during a close flyover by Rosetta. Getting

the exact location was important for determining the accuracy

of Philae’s radio-wavelength probing of the comet’s interior

and also to know the context for other Philae measurements.

Rosetta itself continued to orbit and study the comet with

20 cm

Rosetta: Living With a Comet

June 28, 2014

First resolved image of nucleus

March 21, 2014

First view of the comet after wake-up

September 30, 2016

End of mission

March 2016

Comet still active

August 13, 2015

Comet at perihelion

Orbit of Comet

67P/Churyumov-Gerasimenko

Jupiter

Mars

ROSETTA RESULTS