London - On 13 August, Comet 67P/Churyumov-Gerasimenko reaches the pinnacle of its epic trip around the solar system: its closest approach to the Sun.
Then, this dirty snowball from the Kuiper Belt of asteroids, comets and dwarf planets (including Pluto) will be at its most active. Under the heat of the Sun's rays, the comet's icy surface will see the and boil, producing jets of gas steaming off into space.
The cosmic interloper was discovered in 1969 by two Soviet astronomers, and is named after them. Unlike some of the more magnificent comets of recent years, Comet 67P is a regular visitor to the inner Solar System: it orbits the Sun in just 6.45 years. At its closest to our local star, it lies at roughly the distance of the Earth. A moderate telescope will be needed to see it.
However, 67P is a comet with a difference. For a start, it has a companion: in orbit about it is Europe's Rosetta space probe. Named after the Rosetta Stone, which led archaeologists to decode the Egyptian civilisation, scientists are hoping that the cosmic Rosetta will shed light on comets - which may have brought water and the raw materials of life to Earth.
Rosetta was launched on 2 March 2004. To match the speed of the comet, Rosetta had to swing past Earth three times, using our planet's gravity to let gently fly alongside 67P. The 10-year mission was a triumph for the space dynamics team. As Rosetta approached 67P, mission controllers were astonished by its shape. The 4km body looked like a black rubber duck, with a head, neck and body.
Instruments from Rosetta soon detected the stench from the comet: rotten eggs and horse manure, not to mention sulphur dioxide. But this pungent mix of chemicals was everything the scientists were hoping for: they were the very elixir of life. On 12 November last year Rosetta - now in orbit around 67P - went one further. It launched a dishwasher-sized probe, Philae, to land on the comet's surface.
The probe landed in a dark crater, under a cliff; relying on solar power, it was the worst place to be. But it sent back data for two days, revealing that, under a dusty crust, comet 67P is replete with water. Philae has been intermittently in contact over the past few months: and as 67P warms up, things can only get better.
But what about Rosetta? The mission has been extended by nine months until September 2016. And then? We asked mission project scientist Matt Taylor about the possibility of Rosetta joining Philae on 67P's surface. He enthused: “For me, this is a strong possibility, and I feel a wonderful and spectacular conclusion to this mission. But there is plenty of science to do yet!”
WHAT'S UP
Watch out for a celestial firework display on the night of 12-13 August, as the Earth runs into debris from Comet Swift-Tuttle. These specks of dust burn up in the upper atmosphere, appearing as a brilliant meteors streaking across the sky.
This annual treat is known as the Perseid meteor shower, because perspective makes the shooting stars seem to stream outwards from a point in the constellation Perseus. But don't focus on this radiant. The speeding meteors can appear anywhere in the sky.
Because the Moon's brilliant light is well out of the way, it's an exceptional year for viewing the Perseids: expect to see a meteor every minute or so. They will be most prolific after midnight, so be prepared to stay out late.
Down on the southwest horizon, you'll notice two bright “stars”: on the left is Antares, marking the heart of Scorpius (the scorpion); while the object on the right is the planet Saturn - grab a telescope to see its famous rings.
High overhead, three bright stars make up the corners of Summer Triangle. Brightest is Vega, in the constellation Lyra (the lyre). To its left is Deneb, in the tail of the celestial swan, Cygnus. And below you'll find Altair, in the constellation of Aquila (the eagle). Though they look similar in brightness, Deneb is the odd one out. Vega and Altair are near neighbours to the Sun, only about 20 light years away. But Deneb lies at a whopping 2000 light years' distance: to appear so bright, astronomers reckon it shines 100 000 times more brilliantly than the Sun!
DIARY: WHAT TO LOOK FOR
7 August 3:03am: moon at last quarter
14 August: 3:53pm new moon
22 August, 8.31 pm: moon at first quarter
29 August, 7.35 pm: Full Moon
The Independent