Once upon a time...
A year had passed since Rosetta had arrived at her new home,
Comet 67P/Churyumov-Gerasimenko.
It had been a busy time for Rosetta...
and for her lander Philae,
who had been sent to the surface of the comet.
The landing didn't go exactly as planned,
but Philae still managed to make his first measurements
of the comet’s surface
before his battery ran out
and he fell into a long, deep sleep...
Rosetta continued studying the comet,
learning new and wonderful things
as she followed it on its journey through the Solar System.
It measured 4 km across,
and from the gravitational pull that Rosetta felt,
she could calculate the mass of the comet:
ten billion tonnes!
Although the comet looked like a giant rock,
it was made of something much lighter
– so much so that it would float on water!
As the comet got closer to the hot Sun
Rosetta saw its activity increase.
She collected samples of the gas and dust that streamed into space
in order to learn more about what the comet was made of
and where in the Solar System it was born.
One of the most important questions scientists back home wanted to answer
was where Earth's water came from.
Could it have come from comets and asteroids billions of years ago?
Rosetta was surprised to discover
that the water vapour flowing away from her comet
had a different flavour to Earth's oceans.
The scientists wondered what it would mean for their theories
of how the Solar System evolved.
There were many other types of gases too,
and it smelt like a weird mixture of rotten eggs,
horse stables and marzipan!
Rosetta also collected thousands and thousands of dust grains,
small and large.
Some of them seemed very fluffy,
like the head of a dandelion.
As the days and weeks passed,
the comet looked more and more spectacular.
Rosetta flew close by to get a better look.
But there she found herself surrounded by a lot of dust.
Although it wasn’t as dangerous
as when grandfather Giotto flew past Comet Halley
at high speed many years ago,
Rosetta still became disoriented
and almost lost her way,
so decided to continue her work from a safer distance.
Rosetta began to see the surface of the comet changing
as they got nearer to the Sun.
She saw jets of dust coming out of pits
and patches of ice being revealed.
Even though the comet was becoming more active,
it was still quite cold on the surface:
Rosetta measured temperatures around minus one hundred degrees celsius,
and it was even colder underneath!
Thinking about the cold,
she worried about Philae,
who had been asleep for several months.
She didn't even know exactly where he had finally landed,
and wondered whether there was enough sunlight there
to recharge his batteries.
Then, one Saturday in June,
she received a phone call:
it was Philae! He was awake!
She quickly told everyone on Earth...
Rosetta wanted to tell Philae all that had happened
while he had been asleep
and the many exciting things she had learned about the comet,
but the connection wasn't very good.
It was very frustrating
and Rosetta had to move to different locations
to try to find the best spot
for a better connection.
Philae hoped he would soon be able to do more experiments
on the comet surface
while Rosetta studied it from afar.
As the comet reached its closest point to the Sun,
Rosetta and Philae were very excited
to witness this once-in-a-lifetime event...
...and they looked forward to seeing
what would happen to the comet over the next year
as they headed back towards the outer Solar System...
To be continued...