March 2005 Sky from the Keeble Observatory
Life, at least as we know it here on Earth, depends on the presence of water; usually
liquid, usually at moderate temperatures, but definitely a requirement. One of the
primary mission objectives for the current fleet of Mars probes and rovers is to
seek evidence for the presence of water, either in the distant past or in some form
in the present.
We have surmised since the 1970s that Mars was once a much warmer, wetter world
than we see today. Currently, the atmosphere is too thin to allow liquid water –
it would boil away into gas. It’s also too cold, even if the atmosphere would allow
liquid, the temperature for most of the planet during most of its year stays below
freezing. But it was not always so! Extensive now-empty flow channels are reminiscent
of river systems. The landing site for the Pathfinder/Sojourner probe was clearly
a massive flood plain, tumbling and fracturing rocks, but the floods were long ago,
perhaps billions of years in the past.
Chemical, visible, and geological (areological?) evidence collected by the Spirit
and Opportunity rovers tell us that both landing sites were once wet. The Opportunity
site was once a salty lake bed, with ripples from shallow water preserved in the
rock layers. But those sites were wet long, long ago.
Recent data from the European Space Agency’s Mars Express give a tantalizing hint
that a lake the size of the North Sea was present on Mars as recently as 5 million
years ago ... practically yesterday to a planetary astronomer’s eye. Images of large,
flat, fractured plates on a young region known as Elysium Planitia bear startling
resemblance to pack ice floating on the sea. Researchers conjecture that this 500
by 560 mile region flooded and then rapidly froze two to five million years ago,
possibly due to a catastrophic flood from a fissure to the northeast known as Cerberus
Fossae. It’s even possible that some of the ice itself is preserved beneath the
As with all science, the final verdict will await further data. The landscape does
resemble some fractured lava flows found in Iceland – we’ll probably have to wait
for a lander to give us a closer look.
(Image courtesy European Space Agency)
Lunar phases for March: Last Quarter on the 3rd, at 12:37 pm; New Moon at 4:11 am,
on the 10th; First Quarter on the 17th, at 2:19 pm; Full Moon on the 25th, at 3:58
Evening planet watchers will have their best view of Mercury in the early parts
of March. I will be almost twenty degrees above the setting Sun by midmonth, before
rapidly diving back into the Sun’s glare by the end of the month. Saturn, high above
the eastern horizon at sunset, is still close to Castor and Pollux. It will match
them in brightness, but will show less “twinkle” since it actually presents a disk
rather than a point source. Saturn sets at about 4:00 am. Jupiter will rise around
9:00 pm early in March, at sunset by month’s end.
The morning sky finds Jupiter low to the west southwest at sunrise on the 1st, setting
before sunrise later in the month. Mars rises at about 4:00 am, and can be found
low in the southeast at dawn. Venus is hidden by the Sun’s glare, but returns to
the evening sky next month.
An overhead view about 3 hours after sunset at mid-month finds Saturn, Castor, and
Pollux almost at zenith. Below Gemini, towards the southwest horizon we can see
the familiar shape of Orion. Above and to the right lies Taurus and the familiar
asterism of the Pleiades. That brilliant blue star to the left of Orion is Sirius,
in the constellation Canis Major. To the northeast the sky is largely vacant, with
only a few bright stars. The familiar shape of Ursa Major is easily seen high above
the horizon, with the “dipper” standing on its handle. Follow the two stars at the
end of the “dipper” towards Polaris, the pole star. With binoculars, you may still
find Comet Machholz, which will be just above and to the left of Polaris on the
1st, moving slowly to the east so that it is above and to the right by the 31st.
For your own monthly star chart, you can direct your web browser to
http://www.skymaps.com. You will find extensive descriptions of what's worth
looking for, and you can download and print a single copy for your personal use.