Is it challenging to get to Neptune, the farthest planet?
Neptune is the farthest planet in the solar system. Since its discovery, only one spacecraft
has reached this distant planet, making it the most unexplored planet of all, but why
has it only been visited once? Is it because is too far from Earth, or is there something
else preventing us from reaching Neptune?
The first approach The only spacecraft to reach Neptune was Voyager
2 in 1989. This was the first time the human race had placed a spaceship near this planet.
Although one hundred and forty-three years had passed since its discovery, we knew very
little about this planet. Neptune is the farthest of the four "giant
planets", is thirty times farther from the Sun than Earth, and takes 165 years to circle
the Sun; since its discovery, Neptune has not yet given a complete turn to the Sun.
Its diameter is about four times larger than our planet's, but it lacks a solid surface
where we can walk, just like all other gaseous planets.
With the help of observations with telescopes from Earth, it was discovered that this planet
has two moons; one of them is Triton, one of the most exciting objects in the Solar
System since, according to its light spectra, it could contain large amounts of liquid water.
Although the telescopes of the time were very powerful, Neptune is so far away from Earth
that it is impossible to observe its asteroid ring; because of this, the data collected
in a few hours by Voyager 2 gave us more information about Neptune than about a century and a half
of astronomical observations from Earth. To scientists' surprise, Voyager 2 revealed
a large dark spot on Neptune, similar to Jupiter's famous red spot. It is a gigantic hurricane
with winds that exceed one thousand kilometers per hour, being the most violent in our Solar
System. On Earth, the Sun supplies the energy the
winds produce. In the case of Neptune, the temperature at the top of the cloud cover
is minus 210 degrees Celsius, so solar energy is insufficient to give rise to the winds
observed by Voyager 2. Astronomers think that the planet follows
a process of contraction from which it formed billions of years ago; this process would
be the one that provides enough energy to generate these powerful winds. However, the
general structure of the winds on Neptune has yet to be understood by scientists to
date. Observations from Earth had provided evidence
of rings around Neptune. However, this evidence was inconclusive as more than rings appeared
to be pieces of rings, like thin arcs of matter swirling around Neptune.
Voyager 2 helped us make this more expensive once and for all, and during its approach
to Neptune in 1989, it found four complete rings, two of them thin and the other two
wide. The thin rings are located near the orbit
of two satellites thought to be responsible for their stability and are therefore called
"shepherd moons." The two most extensive rings are formed by
highly opaque material that reflects approximately one ten-thousandth of the light that falls
on them; this is why it would have been impossible to detect them from Earth. If we had not sent
the Voyager probe 45 years ago, today, we would not know of these rings of asteroids
around Neptune. The reason why Neptune's rings are so opaque
is that they contain a large amount of dust, which can only be explained if, in the vicinity
of Neptune, there is a greater abundance of meteorites than in the innermost areas of
the Solar System. For more than a century, only one moon of
Neptune, called Triton, was known. In 1949 Gerard Kuiper discovered a second satellite
named Nereid, which rotates far from the planet. As happened in the previous encounters of
the Voyager spacecraft with other planets, Neptune had more "hidden" satellites that
were not visible from Earth. Voyager 2 discovered six new moons, including Despoina and Galatea,
the two shepherd moons mentioned above. He also found Proteus, the largest of the
"new moons" discovered by Voyager, which has a surface completely covered with craters,
the largest of which is almost half the size of Proteus. Despite these findings, Neptune's
largest moon Triton, the one known for more than a century, remains the most interesting.
A difficult journey Being the farthest planet in the solar system,
it is logical that space agencies think twice before carrying out a mission to this planet.
The Voyager 2 probe took more than a decade to reach the orbit of Neptune, and this was
thanks to the fact that it had several gravitational assists with which it took the momentum and
thus shortened the travel time; without those gravitational assists, it would likely have
taken at least five more years to reach Neptune. Can you imagine that? A 15-year mission to
reach a planet brings challenges that are very difficult to overcome. Neptune is more
than four billion kilometers from Earth; even the sun's rays become scarce at this distance.
Due to the absence of light, any spacecraft sent to this planet must necessarily use a
nuclear power source since the solar panels will not capture enough light.
Mounting a nuclear battery on a spacecraft involves several engineering challenges. Still,
beyond those challenges, these batteries considerably increase the spacecraft's weight, eventually
making it more expensive. In summary, the difficulties that would arise
to reach Neptune are the same as those that arise to reach Uranus, which is much closer.
In a previous video, we explained why it is so difficult to get to Uranus. We recommend
you watch it. "At this point, add the video's thumbnail
about how difficult it is to get to Uranus." Despite all the difficulties that may arise
in reaching Neptune, this planet has exciting features that are attractive to astronomers;
thanks to this, there is currently a proposal by NASA to send a ship back to this planet.
A unique climate Neptune's meteorology is characterized by
very dynamic storm systems, with winds reaching almost 600 m/s (2200 km/h) and almost reaching
supersonic flow speeds. Although its composition is very similar,
Neptune has a much more violent atmosphere than Uranus. Voyager 2 observed weather phenomena
on Neptune during its flyby in 1989 but observed no comparable phenomena on Uranus during its
flyby in 1986. In 2007, Neptune's upper troposphere of the
south pole was found to be about 10 K warmer than the rest of the planet, which averages
about 73 K (−200 °C). The temperature difference is enough for methane, which freezes in the
troposphere elsewhere, to escape into the stratosphere near the pole.
This hotter region is due to the tilt of Neptune's axis, which has exposed the south pole to
the Sun during the last quarter of Neptune's year, equivalent to about 40 Earth years.
As Neptune slowly moves toward the opposite side of the Sun, the south pole will darken,
and the north pole will brighten, causing the methane release to shift to the north
pole. Due to seasonal changes, Neptune's southern
hemisphere cloud bands have been observed to increase in size. This trend was first
seen in 1980 and is expected to last until 2020. The long orbital period makes the seasons
on Neptune last forty years. The jewel in the crown, Triton
In addition to the exotic weather, Neptune has something that Uranus does not have, and
this is the main reason why NASA is planning a new mission to Neptune and not to Uranus,
which is much closer than Neptune. We're talking about Triton. With a diameter
of 2707 km, Triton is the largest satellite of Neptune and the seventh in the solar system,
as well as being the only large moon that has a retrograde orbit, that is, an orbit
whose direction is contrary to the rotation of the planet (something exceptional in a
body of such size). Because of this retrograde orbit and its composition,
similar to that of Pluto, astronomers consider Triton to have been an object captured from
the Kuiper belt by the gravitational pull of Neptune.
Triton is composed of a crust of nitrogen frozen on top of a mantle of ice, which is
believed to cover a solid core of rock and metal. It also has an average density of 2,061
g/cm³, and according to observations of its chemical spectrum, it is composed of approximately
15-35% water in the solid state, i.e., ice. This natural satellite is one of the few in
the solar system known to be geologically active. Due to this activity, its surface
is relatively young and reveals a complex geological history from mysterious and intricate
cryovolcánico and tectonic terrains. After Voyager 2 passed through in 1989, enigmatic
images revealed what appeared to be liquid nitrogen geysers emanating from its icy surface.
This discovery left the scientific community astonished since it completely changed the
classical concept of volcanism because, until then, it was assumed that icy bodies should
not be geologically active. Triton was the first exception to that rule;
this natural satellite showed us that there must not necessarily be a rock fluid for geological
activity. Still, it can also be nitrogen or water.
Ice volcanoes The fact that Triton has so few craters indicates
that its surface is constantly renewed due to some geological process.
Valleys and ridges are in a complex pattern all over the surface, probably resulting from
freeze-heating cycles and volcanoes. The Voyager 2 probe observed icy volcanoes (plumes) vertically
spewing liquid nitrogen, dust, or methane compounds, coming from below the surface,
in smoke reaching 8 km high. Probably, this volcanic activity is due to the ozone warming
caused by the Sun, and not like the heating of the volcanoes recorded on Io.
Hili and Mahilani are the observed Tritonian Cryovolcanoes, both named after water spirits
from African mythologies. Triton is one of the seven bodies in the solar system that
possess volcanic activity along with Earth, Io, Venus, Europa, Enceladus, and Titan.
We could continue talking for hours about this fantastic satellite, but we need another
video; if you want a video about Triton, the largest Neptune moon, let us know with a comment.
Thanks to this satellite, with enormous possibilities of hosting liquid water and perhaps even living
beings, the OPAG (Outer Planets Assessment Group) has named Neptune a priority for space
research, even above Uranus. OPAG wants to start developing a mission to
Neptune before 2024 to take advantage of the 2028-2030 launch window to send a mission
to Neptune. The probes to the ice giants must use Jupiter's
gravitational assistance to reduce the duration of the trip, but Jupiter and Neptune are in
the correct position every twelve years or so; with Jupiter's gravitational assistance,
the probe would reach Neptune in the year 2043, approximately.
However, to date, there still needs to be a clear proposal of which will be the ship
in charge of revealing the mysteries of this unexplored planet.
Will we soon see a new mission to explore Neptune? Let us know what you think in the
comments of this video.