Download August05 - Holt Planetarium

FRIENDS OF THE PLANETARIUM NEWSLETTER – AUGUST 2005
There has been plenty of activity on the astronomy and space frontier so let’s get right to it. In
July, the NASA probe Deep Impact released an impactor which went on to collide with comet
Temple 1 at 10 km./sec. The fireball of vaporized impactor and comet material shot skyward,
expanding rapidly above the impact site at approximately 5 km./sec. Scientists are still
analysing the data to determine the exact size of the crater but it appears to be at the large end
of the original expectations, which was from 50 to 250 metres.
The image depicts the first moments after Deep Impact's probe
interfaced with comet Tempel 1.
The major surprise was the opacity of the plume the
impactor created and the light it gave off. This suggests that
the dust excavated from the comet’s surface was extremely
fine, more like talcum powder than beach sand. The surface
is definitely not what most people think of when they think
of comets – an ice cube. How can a comet hurtling through
our solar system be made of a substance with less strength
than snow or even talcum powder? You have to think of it
in the context of its environment. This city-sized object is
floating around in a vacuum. The only time it gets bothered
is when the sun cooks it a little or when someone slams a 370 kg. wakeup call at it at 37,000
km. per hour!
In other solar system news, a planet larger than Pluto has been discovered in the outlying
regions of the solar system. The planet is a typical member of the Kuiper belt but its sheer size
in relation to the nine known planets means that its classification will be very tricky. It may
end up being called a minor planet, a planetoid, an asteroid or a planet. Where that leaves
Pluto is another story. Currently about 97 times further from the sun than the Earth, the
“planet” is the farthest known object in our solar system and the third brightest of the Kuiper
belt objects.
Meanwhile, the Cassini probe continues to send back intriguing information from the Saturn
system. Saturn’s tiny moon Enceladus, which ought to be cold and dead, instead displays
evidence for active ice volcanism. The NASA spacecraft has found a huge cloud of water
vapour over the moon’s south pole, and warm fractures where evaporating ice probably
supplies the vapour cloud. Enceladus is the smallest body so far found that seems to have
active volcanism. Saturn’s auroras are also causing quite a stir. Once thought to be a cross
between Earth’s and Jupiter’s auroras, Saturn’s auroras are proving to be very different and
somewhat of an enigma.
NASA's latest Mars mission, Mars Reconnaissance Orbiter (MRO) was successfully launched
on Friday the 12th. At 2,180 kilograms, MRO is twice the mass of other recent Mars missions.
The orbiter carries six scientific instruments for examining the surface, atmosphere and
subsurface of Mars in unprecedented detail from low orbit. For example, its high-resolution
camera will reveal surface features as small as a dishwasher.
Finally, our hats are off to NASA for the success of the return to flight mission of the space
shuttle Discovery. After some worrying moments, Discovery touched down at Edwards Air
Force base in California. Docked to the International Space Station, the two made a brilliant
pass over Napier on Friday the 5th. You can see the ISS pass overhead again on August 20th at
7:02 pm. and on the 22nd at 6:19 pm. Get out there and enjoy the spectacle.