Why is Mercury the most difficult planet to visit despite being close to earth?
Even though Mercury is the second closest planet to Earth, this is also the most challenging
planet to visit, but why? Is it because it is too close to the sun?
Because of its high temperatures? Or will the composition of the planet have something
to do with it? The answer will surprise you!
The closest planet to Earth is Venus; yes, you heard right, Venus; although it is popularly
said that the planet more like Earth is Mars, the closest is Venus because it is only 25
million miles (40 million km) from the Earth at its closest point.
Does that mean that the second closest to Earth if it is Mars? No! The second closest
planet to Earth is Mercury since the shortest distance between Earth and Mercury is 48 million
miles (77.2 million km). The average distance between Earth and Mars is about 55 million
miles (88.5 million km). During Perihelion, the distance between Earth
and Mars is drastically reduced to just 36 million miles (59 million km), yet this only
happens once every 26 months. So most of the time, Mars is far from Earth than Mercury.
When humanity began exploring the solar system's planets with spacecraft, the first planet
to be visited was Venus in 1962, followed by Mars in 1965 and Jupiter in 1973.
We had to wait until 1974 for the Mariner 10 space probe to visit the planet Mercury
for the first time. Subsequently, in the following years, several
space exploration probes were sent to study the farthest planets of the solar system in
1974, 1979, 1992, 1995, 2000, and recently in 2007. Several missions have been launched
to explore Mars and the outer planets and even study asteroids and far-away comets.
But Mercury did not receive a single mission for 30 years. Was it because the Mariner 10
exploration probe gave us all the information we needed from Mercury, and there was nothing
more to discover? No, the Mariner probe only managed to fly over Mercury 3 times, and during
those three flybys, it only managed to map 40% of the planet's surface.
Scientists were very interested in continuing to study this planet since it was fascinating
for scientific research and the reason why they had not sent more exploration probes
to study this planet is that it was the most challenging of all but ... Why is Mercury
the most difficult planet to visit? THE MOST CHALLENGING PLANET
The reasons why it is so difficult to visit Mercury can be divided into 2, temperature
and speed; let's start with temperature. It is no secret that Mercury is the closest
planet to the Sun; because of this, the temperature on its surface usually reaches 806 ºF (430
ºC). These temperatures are very high for the circuits and components of any space exploration
probe, so the ships sent to the planets closest to the Sun must be equipped with protective
panels that protect the equipment from the scorching sun temperatures.
These panels are usually placed on only one side of the ship, and with the help of the
communication antennas, these are always kept pointing at the sun to protect the ship's
instruments. Secondly, we have the most crucial reason
it is so difficult to send ships to Mercury, the proximity to the Sun.
As you know, all bodies with mass exert a force of gravitational attraction that attracts
other smaller objects towards them; the Sun is the most massive object in the entire solar
system; this means that as the ships approach the Sun, you are accelerating more and more
until there comes the point where they become difficult to control.
This is one of the problems that have most caused the loss of space probes in the vicinity
of the Sun; maneuvering such an accelerated ship only with rockets is a challenging task
to achieve since, usually, space exploration probes do not carry as much fuel, because
they are much smaller than a human-crewed ship.
MINIMIZE WEIGHT AS MUCH AS POSSIBLE When it comes to spacecraft, engineers will
always try to keep everything as light as possible because the heavier a ship weighs,
the more fuel it will take to get it off the ground, and the more fuel you need, the more
expensive the mission will be, which is not at all attractive if you have a shoestring
budget. The more fuel is placed in a space exploration
probe, the less space there will be to place scientific instruments, which in the end,
are the most important; however, for 30 long years, scientists and engineers did not find
any way in which a probe with little fuel could accelerate so fast as to reach Mercury.
But that changed in 1985 when scientist Chen-wan Yen, an MIT graduate in Nuclear Physics, proposed
a way to reach the planet Mercury with the technology available at the time.
A RISKY ROUTE To reach Mercury with the technology available
at the time, Chen-wan Yen used his knowledge in orbital mechanics and developed a very
particular route in which a spacecraft could travel an enormous distance passing through
several planets, which would slow it down enough to be captured by Mercury's gravity
using very little fuel. Instead of sending a spacecraft directly to
Mercury, Chen-wan Yen's new route charted a much longer path in which the spacecraft
would have to circle the sun about 15 times before reaching Mercury's orbit.
The probe in charge of carrying out this complicated mission would be the Messenger space probe,
and to achieve this feat, the spacecraft would use the gravitational assistance of Earth,
Venus, and Mercury. Passing through the earth once, Venus twice, and Mercury 3 times.
With each flyby, the average speed of MESSENGER relative to the sun would gradually increase,
but the speed of the spacecraft relative to Mercury would decrease.
How is this? Imagine you want to get on a train from a
moving car. The train travels 60 miles per hour (96.5 km/h) along the tracks parallel
to Main Street and will pass through the general store precisely at 1 p.m.
You're geared up for action parked along Main Street in your car. At 12:59:30, you start
accelerating down the street to intercept the train. Your car's starting point is closer
to the general store than where the train is now, but the train is going faster (60
mph), and both are going in the same direction. As you accelerate up to 10 mph relative to
your starting point, you're going to 50 mph relative to the train. When you increase your
speed relative to your starting point (the store), your speed relative to the train decreases.
You're getting closer! You calculate your acceleration to pass the
store at precisely 60 mph while the train passes. You will go to zero mph about the
train and 60 mph about the store. Similarly, the Messenger exploration probe
used the gravitational assistance of the planets to accelerate relative to the sun, but getting
closer and closer to the speed of Mercury. Once MESSENGER approached Mercury at the right
speed, it could fire its main engine enough to be captured by the planet's gravity and
begin orbiting it. MESSENGER SCAN PROBE
Messenger was a relatively small exploration probe, launched on August 3, 2004, measuring
just 1.3 meters wide and weighing just over a ton. The probe had a propellant thruster
to help it maneuver and control its direction. This heat shield protected equipment from
high temperatures and two solar panels that, unexpectedly, scientists used as solar sails
that helped slow down the spacecraft's speed a bit due to the solar wind.
The sun emits solar radiation that spreads throughout the solar system; this radiation
falls on the spacecraft and pushes them very slightly, though the thrust of the solar wind
is tiny and typically does not influence the trajectories of the spacecraft. Because the
journey of the Messenger probe was going to be so long and last so many years, it was
a great help to slow down, and so the scientists tried to keep the solar panels pointing at
the sun at all times so the probe saved a lot of fuel, which helped it extend its useful
life. Messenger made all its orbits correctly and
without many complications, passing through the earth, Venus, and finally approaching
Mercury 3 times until it managed to be captured by its gravity on March 11, 2011.
Messenger's entire route covered approximately 4.9 billion miles (7.885 million km) and took
approximately seven years to complete the entire journey.
Once Messenger reached Mercury's orbit, it began to perform eccentric orbits, alternating
its distance between 125 miles (200 km) and 9,320 miles (15,000 km) of Mercury; this was
done because Mercury's surface acts as a giant solar mirror that radiates a lot of heat into
space, if a spacecraft stays too long close to Mercury, even with a heat shield, it could
damage some equipment or in the worst case cause ship failures.
The sun has a brightness seven times more intense on Mercury than on the earth, which
is why it was decided that the probe would perform eccentric orbits that would allow
it to approach and move away from Mercury periodically to cool off from the high temperatures
reflected by the planet. During the next four years, the Messenger
probe would be responsible for sending thousands of photographs of the surface of Mercury,
providing essential information that would help us understand the planet's chemical composition,
the geography of its surface, and its internal structure.
Finally, on April 30, 2015, the fuel of the Messenger probe ran out, and the scientists
in charge of the mission decided to crash the ship into Mercury, thus ending one of
the most important missions in history. Thanks to the Messenger mission, a significant
discovery was achieved. In the images sent by the probe, indications have been observed
that could demonstrate the existence of frozen water at the poles of Mercury.
Currently, the European Space Agency (ESA) and the Japanese Space Agency (JAXA) have
launched a new mission that will be responsible for revealing once and for all if Mercury
can have water or not, this is the Bepi-Colombo mission, and it is estimated that it will
reach the orbit of Mercury in 2025. Would you like us to make a video where we
talk in-depth about this new mission? Let us know in the comments.