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Mercury -
planet of extremes
Most of you may be aware that Sri Lanka
is caught in a bit of a heat wave since the Earth is moving closer to
the Sun than before, during this period. But, Earth is the third planet
from the Sun, and obviously, we know that the other two planets might be
having a worse experience than us, because they are closer to the Sun.
Just imagine how it might be to live on the planet closest to the
Sun. Therefore, let's focus today on Mercury which is the planet closest
to the Sun, and the smallest planet of the solar system.
Mercury is a terrestrial planet. Do you know what a terrestrial
planet is. It is a planet that has a rocky body.
There are four terrestrial planets in the solar system; Mercury, Venus,
Mars, and of course our dear Earth. The other planets of the solar
system are made up of gases.
This tiny planet is not properly visible like some of the planets. It
can be seen to a certain extent during early mornings or evenings. Apart
from that, there is the possibility of seeing it during a total solar
eclipse.
The surface of Mercury is very similar to that of the Moon. It is
filled with plains and craters which show that it has been geologically
inactive over the past years. Since it is a small planet, its
gravitational pull is not enough to hold a stable atmosphere. It has a
weak atmosphere consisting of hydrogen, helium, oxygen, sodium, calcium
and potassium.
But, Mercury has a strong magnetic field although not as much as the
Earth. Surface temperatures on Mercury range from about 180oC (degrees
Celsius) to 430oC(degrees Celsius).It has been known for centuries that
Mercury revolves around the Sun once every 88 days, and for a long time,
it was thought that the length of a day was the same. Scientists bounced
a radar beam off the planet and found the true period to be 58.6 days,
exactly two-thirds the orbital period.
This strange relationship between the orbit and the spin means that
on Mercury, a single day lasts twice as long as a year!
Missions related to Mercury
Mariner 10
The Mariner 10, which was launched in 1974, is the only spacecraft
that has reached Mercury and done experiments so far. It has done a
wonderful service by mapping about 45 per cent of the planet's surface
and providing a lot of important information about Mercury.
The first close-up shots taken from Mariner revealed the rocky nature
of the planet and many other geological features. The Mariner has come
close to Mercury three times to experiment on the planet. In the first
approach, it detected the magnetic field of Mercury.
The second approach was for taking images of the planet's surface.
The third approach gave a lot of magnetic
data. Unfortunately, after this third close 'encounter', the Mariner ran
out of fuel and the controllers of the Mariner had to shut it down.
However, it is believed that it is still orbiting the Sun.
MESSENGER
This is NASA's second mission regarding Mercury, and MESSENGER stands
for MErcury Surface, Space ENvironment, GEochemistry, and Ranging. This
was launched on August 3, 2004.
It is really interesting how the spacecraft will come close to
planets to adjust its path in order to start orbiting around Mercury.
So, it made a close approach to the Earth in February 2005, and to Venus
in October 2006. It will approach Venus again in 2007, followed by three
close approaches to Mercury in 2008 and 2009. Finally, it will start
orbiting around the planet in March 2011.
After orbiting Mercury starts, it will be testing on Mercury's high
density, its geological history, the nature of its magnetic field, the
structure of its core, whether it has ice at its poles, and how its weak
atmosphere is formed.
 However,
the MESSENGER is still on its way to Mercury and it will provide a lot
of important information in the future.
BepiColombo
This is actually a joint mission by Japan and the European Space
Agency. This name has been given to the mission in order to respect
Giuseppe BepiColombo who was an important person when it came to
experiments and new findings about Mercury.
He was also a partner in designing the Mariner spacecraft. The
BepiColombo mission consists of two probes which will be orbiting
Mercury. One probe will be mapping the planet since a complete mapping
could not be done by the Mariner 10.
The other probe will be studying about the magnetosphere of Mercury.
The rocket carrying the probes is expected to be launched in 2013, and
the probes will start orbiting Mercury in 2019.
Compiled by Aravinda Dassanayake |
